On behalf of the Organizing Committee, I would like to welcome you to the 46th US Rock Mechanics/Geomechanics Symposium. We have one of the most successful Symposia to date, with more than 350 papers, five Keynote Speakers, 44 Technical Sessions, two Poster Sessions, two Short Courses, two Worskhops, 15 Exhibitors, three Technical Tours and a large number of exciting Special Activities.

The Symposium focuses on new and exciting advances in rock mechanics and geomechanics and encompasses all aspects of rock mechanics, rock engineering and geomechanics. This annual meeting has turned out to be the focal event for the Rock Mechanics and Geomechanics community, bringing together professionals and students from geophysics, civil, geological, mining and petroleum engineering.

The Symposium has become truly multidisciplinary providing diverse views for problems that cut across disciplines. Multiple examples can be found in many of the sessions where one topic is of interest to different industries. The Symposium has also become, following a growing trend from past events, multinational, with just over 50% of the papers from countries outside the US.

A great Symposium must take place at a great city. Chicago, also called "Paris on the Prairie," is one of the great cities of the world. It is located on the shores of Lake Michigan in the heart of the Midwestern United States. It is home to the world renown Chicago Symphony Orchestra, the Lyric Opera, the unparalleled Art Institute of Chicago museum, major national sports teams, internationally acclaimed jazz and blues festivals, breathtaking architecture, home of the greatest collection of Frank Lloyd Wright creations, award-winning theater, and much more.

The Symposium could not have happened without the effort and dedication of many people who worked tirelessly throughout the year. I want to acknowledge the contributions of the Organizing Committee, and also of Kathryn Greco, Hill Montague, Wayne Gibson, and Peter Smeallie. I am very grateful for their assistance and commitment.

Thank you for participating in the Symposium, arguably one of the best to date. Let’s enjoy the Conference, learn as much as we can, meet old friends, make new ones, and take advantage of the many things that Chicago has to offer.

Antonio Bobet Chair of the 46th US Rock Mechanics/Geomechanics Symposium Professor of Civil Engineering Purdue University

2 46th US Rock Mechanics/Geomechanics Symposium ACKNOE WL DGEMENTS

O rganizing Committee Antonio Bobet Russ Ewy Laura Pyrak-Nolte Symposium Chair Symposium Technical Chair Symposium Technical Chair Purdue University Chevron Energy Technology Co. Purdue University Luc Beauchamp Murali Gadde Marisela Sanchez-Nagel CARMA Liaison Symposium Technical Chair Symposium Poster Awards Mines and Aggregates Safety Peabody Energy Committee Chair and Health Administration Itasca Houston Giovanni Grasselli Steve Brandon University of Toronto Peter Smeallie Lachel & Associates American Rock Mechanics Bezalel Haimson Association Bill Dershowitz University of Wisconsin Ex-officio member Azra Tutuncu Haiying Huang Golder Associates Symposium Technical Chair Symposium Paper Awards Colorado School of Mines Chuck Dowding Committee Chair Technical Tours Chair Georgia Institute of Technology Erik Westman Northwestern University Symposium Technical Chair Joe Labuz Virginia Tech Symposium Technical Chair University of Minnesota

Session Chairs/Developers Tony Addis Ali Fakhimi Mary MacLaughlin Anil Ray Anita Ai Erling Fjaer Ali Mese Jean Claude Roegiers Jose Andrade Sergio Fontoura Doug Milne Marisela Sanchez David Beck Murali Gadde Brijes Mishra Doug Schmitt Doug Blankenship Ahmed Ghassemi Sonia Mogilevskaya Sam Spearing Ronaldo Borja Steve Glaser Dan Moos Sergey Stanchits Tom Bratton Giovanni Grasselli Joe Morris Doug Stead Alvin Chan Marte Gutierrez Seiji Nakagawa Roberto Suarez-Rivera Alexander Chudnovsky James Hambleton Maria Nikolinakou Azra Tutuncu John Cook Gang Han Gildardo Osorio Ted Urbancic Brian Crawford Mike Hardy Rimas Pakalnis Jianlin Wang Bill Dershowitz Haiying Huang Euripides Papamichos Shugang Wang Mark Diederichs Takatoshi Ito Greg Pepin Norm Warpinski Tom Doe John Kemeny Lee Petersen Erik Westman Chuck Dowding Paul La Pointe Will Pettitt Sarah Wilson John Dudley Gang Li David Potyondy David Yale Herbert Einstein Yueming Liang Andrey Pyatigorets Hide Yasuhara Derek Elsworth Marc Loken Laura Pyrak-Nolte Wen-lu Zhu Essie Esterhuizen Loren Lorig Mileva Radonjic Mark Zoback

P oster Sessions Coordinator Teri Nichols ConocoPhillips

3 46th US Rock Mechanics/Geomechanics Symposium ACKNOE WL DGEMENTS cont.

P aper Awards Committee Haiying Huang John McLennan Marisela Sanchez-Nagel Chair University of Utah Itasca Houston Georgia Institute of Technology

P oster Awards Committee Alvin W . Chan Maria-Katerina Nikolinakou Marisela Sanchez-Nagel Shell University of Texas Chair Itasca Houston Brian Crawford Azadeh Riahi ExxonMobil Itasca David J . Scarpato Haley & Aldrich Inc. Teri Nichols Lance A . Roberts ConocoPhillips RESPEC Consulting & Services Karim Zaki Chevron ETC

AM R A Board of Directors President Don Banks Mark D . Zoback Vicksburg, MS Stanford University John Curran Vice President Rocscience Antonio Bobet Russell T . Ewy Purdue University Chevron Energy Technology Co. Immediate Past President Michael Hardy Azra N . Tutuncu Agapito Associates, Inc. Colorado School of Mines Mary MacLaughlin Treasurer Montana Tech Bill Dershowitz Golder Associates, Inc. John McLennan University of Utah Secretary Anthony Iannacchione Gangerico Ramos University of Pittsburgh ConocoPhillips Erik Westman Virginia Tech

Symposium Staff Peter Smeallie Jim Roberts Executive Director, ARMA Registrar Staff Katy Greco Katharine Smeallie Registrar Registrar Staff Hill Montague, Sr . Symposium Communications

4 46th US Rock Mechanics/Geomechanics Symposium S PonSORS

The 46th U.S. Rock Mechanics/Geomechanics Symposium is sponsored by the American Rock Mechanics Association, a professional society that serves as the direct link in the United States to the professionals, firms, teachers, and students in the fields of rock mechanics and rock engineering.

The following companies have generously provided support for the 46h symposium:

Agapito Associates, Inc. Sponsor of the 25 June Symposium Luncheon and Keynote Address

Chevron, Sponsor of Student Scholarships for Discounted Symposium Registration

ConocoPhillips, Sponsor of the 25-26 June Poster Presentations

Golder Associates, Inc., Sponsor of the 25-27 Morning Coffee Breaks and the Symposium Program Document

Haley & Aldrich, Inc., Sponsor of the 25 June Afternoon Coffee Break

Itasca International Inc., Sponsor of the Symposium Delegate Bag

MTS Systems Corp., Sponsor of the 24 June MTS Lecture, and Opening Reception

MWH Global, Sponsor for Planning and Organizing Two Technical Tours

TerraTek TerraTek--A Schlumberger Company, Salt Lake City, Utah Sponsor of the 25 June Future Leaders Luncheon Salt Lake City, Utah

Special thanks to Derek Elsworth and Sidney Green for support of the ARMA Fellows activities at the symposium.

5 46th US Rock Mechanics/Geomechanics Symposium EXHIBITORS

E xhibition Schedule Sunday, 24 June 7:00 pm – 9:00 pm Monday, 25 June 9:30 am – 4:00 pm Tuesday, 26 June 9:30 am – 4:00 pm Wednesday, 27 June 9:30 am – 2:00 pm

Booth 1 AE G: Association of Environmental and Engineering Geologists PO Box 460518 Denver, CO 80246 www.aegweb.org AEG is the acknowledged international leader in environmental and engineering geology, and is greatly respected for its stewardship of the profession. AEG offers information on environmental and engineering geology useful to practitioners, scientists, students, and the public. Stop by for information on our Annual Meeting in Salt Lake City, 15-21 September 2012.

6 46th US Rock Mechanics/Geomechanics Symposium Booth 2 E ngineering Seismology Group 20 Hyperion Court Kingston, Ontario K7K 7G3 Canada www.esg.ca ESG Solutions is a leader in microseismic monitoring solutions for the mining, geotechnical and petroleum industries. Our integrated solutions provide far-field observations of mine seismicity utilized to increase mine safety, improve ground support design and calibrate numerical models to optimize mine design and efficiency. Booth 3 A DAM Technology Suite 3 41 Belmont Avenue Belmont, WA, 6104 Australia www.adamtech.com.au ADAM 3DM Analyst software has been used for open-pit surveying and geotechnical mapping. With the addition of autonomous Unmanned Aerial Vehicles to ADAM’s product range, low-cost and quick- turnaround aerial mapping is now a reality, and 3DM Analyst Underground Mapping Field Kit extends the functionality of the software to underground applications as well. Booths 5 & 6 I tasca Consulting Group 111 Third Avenue South Minneapolis, MN 55401 www.itasca.com Itasca International Inc. is an international engineering consulting and engineering software development firm that specializes in solving hydogeology, geomechanical, and seismological problems in the mining, civil, petroleum, waste isolation, and defense industries. Itasca works directly with mining companies, industrial companies, government agencies, and as a specialist consultant to other consulting firms. The dynamic interchange between consulting and software, complemented with hands-on field experience, forms the core of Itasca’s unique, expert services to its customers. Booth 7 M TS Systems Corp. 14000 Technology Drive Eden Prairie, MN 55344 www.mts.com Engineers worldwide rely on MTS for the testing technology and expertise needed to accurately and efficiently determine the characteristics of rock and concrete materials, components and structures for research and industrial applications. The MTS offering integrates high-performance servohydraulic load frames, precision uniaxial and triaxial accessories, and leading-edge controls and software.

7 46th US Rock Mechanics/Geomechanics Symposium Booth 8 Geo- Institute of ASCE 1801 Alexander Bell Drive Reston, VA 20191-4400 www.geoinstitute.org The Geo-Institute (G-I), founded in 1996, is a membership organization and one of eight specialty institutes of the American Society of Civil Engineers. The G-I represents over 11,000 individual members and 60+ Organizational Members who work to advance the geo-professional community. Geo-Strata, is the official bi-monthly magazine of the G-I. www.ASCE/geo. Rob Schweinfurth, Director at 703.296.6015 or [email protected]. Booth 9 MetaRock Laboratories, Inc. 6723F Stella Link Road Houston, TX 70005 www.metarocklab.com MetaRock Laboratories, Inc. is a unique and diversely skilled Geo-Mechanics and special core analysis laboratory. We are able to provide high quality testing and consulting services (i.e., Triaxial, Uniaxial, UCS, SCAL, etc.) on rock samples. We have extensive experience in designing and developing testing apparatus/vessels and pumps. Additionally, we have experience and capabilities related to elevated temperature testing and equipment, custom software and integration, and acoustic velocity and anisotropy measurements as a function of stress. Booth 10 M Ala GeoScience USA, Inc. 465 Deanna Lane Charleston, SC 29492 www.malags.com MALA GeoScience USA, Inc. is the North American representative for Reutech Mining’s Movement and Surveying Radar (MSR) systems. The MSR systems provide highly accurate, real-time, all weather surveying and slope movement measurements in open pit mines using state-of-the-art radar and surveying technology. Booths 12, 13, 14 T erraTek / A Schlumberger Company Reservoir Characterization Group 1935 S.Fremont Drive TerraTek Salt Lake City, UT 84104 Salt Lake City, Utah www.slb.com/terratek TerraTek -- A Schlumberger Company Schlumberger Innovation Center Research Partnership to Secure Energy for America / TerraTek Leaders in the understanding that Rocks Matter™ for energy recovery, mining applications, and civil engineering problem solving, particularly for Tight Shales Gas and Oil recovery.

8 46th US Rock Mechanics/Geomechanics Symposium Booth 15 Weatherford Laboratories 8845 Fallbrook Drive Houston, TX 77064 www.weatherfordlabs.com Weatherford Laboratories provides a single source with the industry’s most comprehensive, integrated rock and fluid analysis worldwide. Booth 16 Rocscience Inc. 31 Balsam Avenue Toronto, Ontario M4E 3B5

Canada software tools for rock and soil www.rocscience.com Rocscience develops geotechnical software used worldwide by over 5,000 users in over 100 countries. Our suite of programs includes slope stability, settlement and consolidation, and stress analysis, support design and underground modeling. Created by experienced engineer-developers, our high-quality programs enable users to save time and money when designing solutions in both soil and rock. Booth 17 Golder Associates, Inc. 18300 NE Union Hill Road Redmond, WA 98052 www.golder.com Golder Associates, Inc. is a leading international geo-engineering consulting firm, offering geomechanics, hydrodynamics, geologic, and geophysical service including site characterization, planning and permitting, engineering, and development. Golder Associates provides services to the oil and gas, mining, transportation, and environmental industries. Golder Associates’ FracMan Technology Group is a recognized leader in analysis and engineering of fractured reservoirs, rock slopes, underground mines, tunnels, geothermal, and Carbon Capture and Storage (CCS). Booth 18 G CTS Testing Systems 6103 S. Maple Avenue, #1 Tempe, AZ 85283 www.gcts.com GCTS provides a full line of computer servo-controlled testing systems for rocks, soils, pavements, and construction materials. Advanced systems for Triaxial, Direct Shear, Point Load, Indirect Tension, Hydraulic Fracture, Poly-Axial, Hollow Cylinder, Ultrasonic, and other specialized equipment including high-pressure/high temperature triaxial cells. For more information about our testing equipment, please visit our web site at www.gcts.com.

9 46th US Rock Mechanics/Geomechanics Symposium HOTEL MEETING ROOMS T he Westin Michigan Avenue Chicago 909 North Michigan Avenue, Chicago, Illinois 60611 Phone (312) 943-7200

10 46th US Rock Mechanics/Geomechanics Symposium 11 46th US Rock Mechanics/Geomechanics Symposium G LEneRA INFORMATION Maps Local maps are available from the hotel. T ransportation and Parking The hotel, located on busy Michigan Avenue, is served by nearby subway (called ‘L’ as in “elevated”) stations, bus routes and taxis. Bus route and subway maps are available from the hotel. Parking is available for a fee within the hotel and in neighboring garages. Registration and Speaker Ready Room On-site registration is available on the second floor pre-function lobby during the following hours:

• Friday, 22 June 8:00 am - 10:00 am • Saturday, 23 June 7:30 am - 10:00 am • Sunday, 24 June 7:30 am - 9:00 pm • Monday, 25 June 7:00 am – 6:45 pm • Tuesday, 26 June 7:00 am – 6:30 pm • Wednesday, 27 June 7:00 am – 4:00 pm

The speaker ready room is located in the registration area. A laptop and LCD will be available. The speaker ready room will be available during the same hours as the registration desk from Sunday through Wednesday. Please see the registration desk for access. Speakers Breakfast Podium speakers and session chairs are required to attend the speaker’s breakfast from 7:00 am – 7:50 am in the Great Lakes Ballroom on the day of their presentation. Tables will be identified by session, and speakers will load their presentations via a portable USB storage device to the session laptop. Presentations must be in PowerPoint (.ppt or .pptx) format only and must be capable of running on a Windows XP or later machine. In addition to uploading the presentation, speakers will be able to meet their session chair(s). It will be helpful if speakers bring along 2 or 3 written sentences about yourself so that the session chair can prepare an introduction.

If you wish to review your presentation prior to loading it onto the session laptop, you will be able to do so in the speaker ready room.

12 46th US Rock Mechanics/Geomechanics Symposium S Pecial EVENTS

Friday, 22 June 8:30 am - 5:00 pm Workshop 1: Geomechanics Solutions for Environmental and Technical Challenges in Unconventional Resources Ontario

Saturday, 23 June 8:00 am - 5:00 pm Workshop 2: ISRM-ARMA Workshop on Petroleum Geomechanics Testing Lincoln Park 8:30 am - 4:00 pm Technical Tour 1: Urban Underground Limestone Mine Lobby

Sunday, 24 June 9:00 am - 4:00 pm Short Course 1: Floor Stability in Underground Coal Mines: The Illinois Basin Experience Garfield arkP 8:30 am - 4:00 pm Short Course 2: Monitoring and Modelling Seismic Rock Mass Response to Mining Marquette Park 8:30 am - 12:00 pm Technical Tour 2: Fermilab Lobby 9:00 am - 4:00 pm ARMA Board Meeting Parks Boardroom 9:30 am - 12:30 pm House of Blues Gospel Brunch Lobby 1:30 pm - 4:00 pm Architectural River Boat Cruise Lobby 7:00 pm – 9:00 pm Opening Reception and Exhibits Great Lakes Ballroom

Monday, 25 June 12:30 pm – 1:45 pm Sponsored Lunch Great Lakes Ballroom 12:30 pm – 1:45 pm Lunch Meeting of the ARMA Publications Committee Erie 1:00 pm - 5:00 pm Chicago Grand Tour Lobby 6:15 pm – 9:45 pm Chicago Cubs vs. New York Mets, Wrigley Field Lobby 7:00 pm – 9:45 pm ARMA Fellows Dinner and Meeting Signature Room Tuesday, 26 June 12:30 pm - 2:00 pm Lunch Meeting of the ARMA Future Leaders Erie 7:00 pm – 9:30 pm Awards Banquet Great Lakes Ballroom

Wednesday, 27 June 9:00 am - 1:00 pm Museum of Science and Industry Lobby 12:30 pm – 1:15 pm Meeting of the CSM Student Chapter Huron 12:30 pm - 2:00 pm Lunch Meeting of the Organizing Committee for San Francisco 2013 Erie 6:00 pm - 10:00 pm Dinner Cruise Aboard The Spirit of Chicago Lobby Thursday, 28 June 9:30 am - 4:00 pm Technical Tour 3: Chicago's Tunnel and Reservoir Project (TARP) Lobby

13 46th US Rock Mechanics/Geomechanics Symposium Technical Tours Technical Tour 1: Urban Underground Limestone Mine Date: Saturday, 23 June 2012; 8:30 am – 4:00 pm Cost: $75 - Price includes transportation and box lunch. Limited to 35 participants This field trip will include a motorized tour of an underground limestone mine near Bolingbrook, Illinois, owned by Vulcan Materials Corp. This facility is located beneath a mined-out surface mine that is producing aggregate in the Galena Platteville formation. It is one of a half a dozen such quarries in the Chicago metropolitan area, which have been developed underground to maintain a sustainable and reasonably-priced supply of aggregate despite urban growth and encroachment. The tour will consist of an above-ground orientation and a below-ground motorized tour. Orientation will include discussion of urban mine economics, sustainability, as well as rock mechanics, pillar stability and blasting considerations.

Technical Tour 2: Fermilab Technical Tour Date: Sunday, 24 June 2012; 8:30 am – 12:00 noon Cost: $75 - Price includes transportation The NuMI (Neutrinos at the Main Injector) Project is located at Fermi National Accelerator Laboratory (Fermilab) in Batavia, Illinois, and is an addition to the existing high‑energy physics program on the Fermilab site. The NuMI Project consists of various experimental physics laboratory facilities that are housed in an underground complex extending over 1,200 m (4,000 ft) in length and at a depth of 15 to 110 m (50 to 350 ft) below ground. The system of tunnels and halls is excavated through soft ground, mixed-face, dolomitic limestones, siltstones, and shales. Construction cost for the civil contract was more than $30.5 million. Some of the major project components include: • Two 6.7 m (22 ft) diameter access shafts; • Soft ground and mixed-face tunnels; • Drill & blast tunnels; • 1000 m (3,300 ft) of 6.7 m (22 ft) diameter TBM tunnel; and Two large experiment halls, each 67 m (225 ft) long, 8.2 m (27 ft) wide, and 9 to 18 m (30 to 60 ft) high, one excavated under low rock cover and the other excavated in shales at 100 m (350 ft) below grade. Special consideration had to be paid to low rock cover and ground inflow conditions.

The tour will include an overview and description of the NuMI Project and the background and purpose of the experiment facilities will also be described. Visitors to the project will have an opportunity to see the experiment halls and learn about some of the technical challenges facing design and construction of large openings in shale.

14 46th US Rock Mechanics/Geomechanics Symposium Technical Tour 3: Chicago's Tunnel and Reservoir Project (TARP) Date: Thursday, 28 June 2012; 9:30 am – 4:00 pm Cost: $75 - Price includes transportation and box lunch The Tunnel and Reservoir Project (TARP, also commonly known as the Deep Tunnel Project or the Chi- cago Deep Tunnel) is one of the largest civil works projects ever constructed. It serves the 375-sq-mile Greater Chicago Metropolitan region and aims to reduce flooding from storm events and to reduce the harmful effects of untreated floodwater and sewage flowing uncontrolled into the Chicago River and Lake Michigan. Commissioned in the mid-1970s, completion of the system is not anticipated until 2029 but substantial portions of the system have already opened and are currently operational.

This tour will include an overview and description of the TARP system, its history, design and construction milestones and challenges, with a focus on technical aspects and details of interest to ARMA symposium participants. We will visit two of the quarry sites, McCook and Thornton, which are to be used as storage reservoirs. At each of these, we will observe and discuss rock slope stability issues and stabilization measures, construction of the tunnels connecting to pump stations and large diameter conveyance system, and in situ stress issues that have posed design and construction challenges. Two of the TARP pump-station caverns are located at McCook. Principal features of the project include: • Ov er 120 miles of 24- to 35-ft diameter excavated tunnels, bored in carbonate rock by TBMs up to 350-ft below ground; • H undreds of vertical drop shafts and connecting tunnels to divert storm flows into the main tunnel system from existing combined sewer overflow outlets; • F our underground pumping stations, with capacities of 710, 320, 240, and 150 million gallons per day (MGD), to lift the collected wet-weather flows to existing sewage treatment plants and/or to storage reservoirs; and • Three quarried reservoirs with storage capacities of 83,000, 40,000, and 27,000 acre-ft and one underground mined storage reservoir with a 2,000-acre-ft capacity.

S Pecial ACTIVITIES House of Blues Gospel Brunch Date: Sunday, 24 June 2012; 9:30 am – 12:30 pm Cost: $89 - Price includes roundtrip transportation, brunch, and music. House of Blues Chicago opened in 1996 and is located in the historic Marina City complex on the Chicago River. Modeled after the spectacular "Estavovski" Opera House in Prague, the spectacular views from the exclusive Opera Boxes are a unique and unforgettable experience. From legendary acts such as The Who and Al Green to contemporary artists such as Pearl Jam and Jurassic 5, House of Blues Chicago has been host to some of the world’s most renowned musicians. In keeping with tradition, the House of Blues Chicago displays the "Crazy Quilt" and keeps a metal box of mud from the Delta Mississippi underneath its stage. House of Blues hosts the world famous Sunday morning Gospel Brunches featuring inspiring gospel performances and an amazing buffet.

15 46th US Rock Mechanics/Geomechanics Symposium Architectural River Boat Cruise Date: Sunday, 24 June, 2012; 1:30 pm - 4:00 pm Cost: $55 - Includes roundtrip transportation from the Westin hotel. River cruise on the Chicago River providing a fantastic view of Chicago’s skyline on Chicago's most comprehensive boat tour. This signature tour of Lake Michigan and the Chicago River includes live narration featuring an overview of architecture and history.

Chicago Grand Tour Date: Monday, 25 June 2012; 1:00 pm – 5:00 pm Cost: $39 Professional guided tour of all that Chicago has to offer on Chicago’s finest overall sightseeing tour. You will see the best of Chicago–magnificent outdoor art by world renowned twentieth century sculptors, the Water Tower and its elegant relative Water Tower Place, Lake Shore Drive, and the Magnificent Mile. Drive past three of the five tallest buildings in the western hemisphere as well as Soldier Field, the Art Institute of Chicago, Marina City, State Street and the “Loop”, Gold Coast high rises, and the Museum Campus. Your group will visit spectacular Millennium Park, featuring the Frank Gehry-designed Jay Pritzker Pavilion and and Anish Kapoor's hugely popular Cloud Gate sculpture.

Major League Baseball: Chicago Cubs vs. New York Mets Date: Monday, 25 June 2012: 6:15 pm – 9:45 pm Cost $85 - Price includes roundtrip transportation and one terrace-reserved seat at the ballpark. Limited to first 35 registrants. Two storied franchises do baseball battle at the fabled “friendly confines” of Wrigley Field. Wrigley Field was built in 1914 and has hosted the Chicago Cubs for 95 years. It was the site of the one of baseball’s most historic moments: Babe Ruth's "called shot," when Ruth allegedly pointed to a bleacher location during Game 3 of the 1932 World Series; Ruth then hit Charlie Root's next pitch for a homer.

16 46th US Rock Mechanics/Geomechanics Symposium The Museum of Science and Industry (MSI) Date: Wednesday, 27 June 2012; 9:00 am – 1:00 pm Cost: $52

Walk through a human heart, feel as though you are flying the original Apollo aircraft, or play private eye and track down a suspected murderer with the most modern computer imaging equipment. At Chicago’s famous Museum of Science and Industry, there is something for every- one. Along with time to freely roam the museum, guests will be split into two groups, each experiencing both the Smart Home Exhibit and the VIP Highlights Tour. Throughout the Highlights Tour, take a whirl- wind trip around the Museum and see the Burlington Zephyr, Chick Hatchery, Boeing 727 and much more. Guests will receive audio players along with a group docent to ensure a memorable experience. The Smart Home exhibit leads guests through a three-story modular and sustainable “green” home in the Museum’s backyard. This outing includes the Coal Mine Tour which has been a permanent exhibit since 1933. Step on the hoist and take a narrated ride to the bottom of a mine shaft. You’ll examine the evolution of technology used in mining coal, and experience first-hand the work environment of the U.S. mining industry. Upon entering the mine shaft, you’ll see coal that has been mined and loaded into coal mine trains, where the coal is weighed. From the trains, coal is emptied into a large hopper, called a “skip,” which brings the coal to the surface. Next, see a demonstration of a sump pump that collects water seepage from the mine and removes it to the surface. The tour continues in the safety room. Here you’ll receive a demonstration of methane gas testing methods used in a coal mine.Then, board a work train to view a demonstration of roof bolting before you disembark in various work rooms of the mine, which show both historic and modern mechanical methods of mining coal. Various “miners” operate machinery such as a room and pillar-type undercutting machine, a twin extension face drilling machine, and an automated coal loading machine. From here you’ll travel through a geology crosscut where you’ll be able to examine fossils imbedded in the shale above a coal seam. Next, take a journey into the longwall mining room for a demonstration on modern mining techniques. The final stop on the tour is in the mine control room, located above ground, where you’ll observe and learn how modern mines are controlled with modern equipment, closed circuit television monitors and computers.

Dinner Cruise Aboard The Spirit of Chicago Date: Wednesday, 27 June 2012; 6:00 pm – 10:00 pm Cost: $137 - Price includes buffet dinner, exclusive roundtrip transportation, transportation staff, 3 hour cruise aboard The Spirit of Chicago, cash bar, all taxes and gratuities. Get ready for the time of your life. Step aboard the Spirit of Chicago and enjoy an exciting evening of vibrant fun. This engaging lakefront excursion turns every occasion into a festive celebration of dining and dancing. And marvel at the most spectacular skyline views in the city. Spirit’s Classic Dining Cruises feature outstanding buffets prepared fresh onboard; the Executive Chef cruises with every group to ensure everything will be perfect.

17 46th US Rock Mechanics/Geomechanics Symposium SO YMP SIUM PROGRAM Assemble in Hotel Lobby Assemble in Hotel Lobby Assemble in Hotel Lobby Superior East Great Lakes Ballroom Parks Boardroom Garfield Park Assemble in Hotel Lobby Marquette Park Superior East Superior East Great Lakes Ballroom Great Lakes Ballroom Ontario (Lunch: Huron) Lincoln Park (Lunch: Millenium Park) Sponsored by MWH Global Registration-- Registration-- Friday, 22 June 2012 Friday, Short Course 1-- Sunday, 24 June 2012 Sunday, Short Course 2-- Saturday, 23 June 2012 Saturday, Workshop 1-- Workshop Exhibit Set Up-- Opening Session-- ARMA Board Meeting-- ARMA Sponsored by MTS Systems Corporation MTS Lecture: Jay Melosh, Purdue University Workshop 2-- Workshop Technical Tour 2: Fermilab-- Tour Technical Registration and Speakers Ready Room-- Opening Reception and Exhibits-- ISRM-ARMA Workshop on Petroleum Geomechanics Testing Workshop ISRM-ARMA

Monitoring and Modelling Seismic Rock Mass Response to Mining "Dynamic Fragmentation, Asteroid Impacts and Meteorites from Mars" "Dynamic Fragmentation, Floor Stability in Underground Coal Mines: The Illinois Basin Experience Technical Tour 1: Urban Underground Limestone Mine-- Tour Technical Special Morning Activity: House of Blues Gospel Brunch-- Special Morning Special Afternoon Activity: Architectural River Boat Cruise-- Geomechanics Solutions for Environmental and Technical Challenges in Unconventional Resources Geomechanics Solutions for Environmental and Technical 8:30 am - 5:00 pm 8:00 am - 5:00 pm 8:30 am - 4:00 pm 7:30 am - 9:00 pm 8:30 am - 4:00 pm 9:00 am - 4:00 pm 1:30 pm - 4:00 1:00 pm - 4:00 6:00 pm - 6:20 6:20 pm - 7:00 7:00 pm - 9:00 9:00 am - 4:00 pm 8:00 am - 10:00 7:30 am - 10:00 9:30 am - 12:30 pm 8:30 am - 12:00 noon

18 46th US Rock Mechanics/Geomechanics Symposium Millenium Park Millenium Park Millenium Park Millenium Park 16--Rock Mass Characterization dependent Behavior 12--Acoustic Emission 8--Time and Environment- 8--Time 4--Novel Testing Techniques 4--Novel Testing Assemble in Hotel Lobby Erie Superior East Rock Assemble in Hotel Lobby Ontario Ontario Ontario Ontario Huron and Damage Sponsored by Haley & Aldrich, Inc. Sponsored by Haley & Sponsored by Agapito Associates, Inc. 3--Geothermal & 11--Challenges in 11--Challenges Physical Properties Numerical Modeling 7--Influence of CO2 on 15--Modeling Anisotropy Hydrothermal Processes in Great Lakes Ballroom Sponsored by ConocoPhillips Great Lakes Ballroom Great Lakes Ballroom Huron, Sponsored by Golder Associates' Mining Rock Mechanics Services Sponsored by Golder Great Lakes Ballroom, Monday, 25 June 2012 Monday, Great Lakes Ballroom, Set-up First Poster Session-- Exhibits Open-- Plenary Address-- Mining - I Behavior - I Lincoln Park Lincoln Park Lincoln Park Lincoln Park Speaker's Breakfast-- 6--Support and and Deformation 2--Coal Mine Strata 14--Drilling Mechanics Registration and Speakers Ready Room-- Lunch Meeting of the ARMA Publications Committee-- ARMA Lunch Meeting of the 10--Rock Mass Excavation First Poster Session-- Reinforcement in Hard Rock Luis D. Alfaro, Panama Canal Authority, "The Panama Canal Expansion" Authority, Alfaro, Panama Canal Luis D. Special Afternoon Activity: Chicago Grand Tour-- Afternoon Special Great Lakes Ballroom, Coffee Break and Exhibits-- Paul Young, University of Toronto, "Rock Fracture Dynamics and Induced Seismicity" University of Toronto, Young, Paul Lunch and Plenary Address-- Lunch and Plenary Reservoirs ARMA Fellows Dinner--Meet in Hotel Lobby; Dinner at the Signature Room at the 95th (875 N Mich Ave) Ave) Fellows Dinner--Meet in Hotel Lobby; Dinner at the Signature Room 95th (875 N Mich ARMA Special Evening Activity: MLB, Chicago Cubs vs New York Mets, Wrigley Field-- Mets, Wrigley York Activity: MLB, Chicago Cubs vs New Special Evening Coffee Break-- and Perforations Michigan Ballroom Michigan Ballroom Michigan Ballroom Michigan Ballroom 1--Geomechanics of of Hydraulic Fracturing in Reservoirs and Caprocks 9--Shale, Sand and Chalk 13--Numerical Modeling of Behavior Around Wellbores Fractured Shale Reservoirs 5--Geomechanics Modeling Fractures in Unconventional Sessions 1 - 4 Sessions 5 - 8 Sessions 9 - 12 (Details on p 22) (Details on p 23) (Details on p 25) (Details on p 24) Sessions 13 - 16 7:00 am - 7:50 8:00 am - 9:30 7:00 am - 6:45 pm 9:30 am - 4:00 pm 1:00 pm - 5:00 2:00 pm - 3:30 3:30 pm - 4:00 4:00 pm - 5:30 5:30 pm - 6:30 6:15 pm - 9:45 7:00 pm - 9:45 9:30 am - 10:00 9:30 am - 10:00 12:30 pm - 1:45 12:30 pm - 1:45 10:00 am - 10:50 am - 12:30 pm 11:00

19 46th US Rock Mechanics/Geomechanics Symposium Lincoln Park Lincoln Park Lincoln Park Lincoln Park Response of Rocks 32--Static & Dynamic 20--Failure Response 28--Mapping and Imaging 24--Heterogeneity in Rocks Superior East Huron 27--Rock Fall Millenium Park Millenium Park Millenium Park Millenium Park 19--Fluid Flow, 19--Fluid Flow, Fractured Media in Geomechanics and Slope Analysis Geomechanics and on the Reservoir Scale Great Lakes Ballroom 31--Discrete Simulations 23--Carbon Sequestration Sponsored by ConocoPhillips Geophysics of Cracked and Sponsored by TerraTek, a Schlumberger Company Sponsored by TerraTek, Great Lakes Ballroom Great Lakes Ballroom Great Lakes Ballroom Great Lakes Ballroom Erie, Huron, Lunch on your own Sponsored by Golder Associates' Oil & Gas Geomechanics Services Sponsored by Golder Tuesday, 26 June 2012 Tuesday, Exhibits Open-- Ontario Ontario Ontario Ontario Set-up Second Poster Session-- Plenary Address-- Banquet-- Awards ARMA President's Address, Mark Zobak President's ARMA Mining - II Behavior - II Speaker's Breakfast-- 22--Support and Coffee Break and Exhibits-- 18--Coal Mine Strata Stress Determination Caverns and Tunnels 30--Advances in In Situ Registration and Speakers Ready Room-- 26--Stability and Support of Reinforcement in Hard Rock Second Poster Session-- Great Lakes Ballroom, Face Lunch Meeting of the ARMA Future Leaders-- ARMA Lunch Meeting of the Reservoirs Formations Coffee Break-- 21--Production Hydraulic Fracture Michigan Ballroom Michigan Ballroom Michigan Ballroom Michigan Ballroom Naturally Fractured 17--Unconventional Characterization in Shale Fracture Interactions in John Rudnicki, Northwestern University, "Formation and Extension of Localized Compaction in Porous Sandstones" John Rudnicki, Northwestern University, Monitoring into Natural and Reservoir Geomechanics 29--Modeling of Hydraulic Geomechanics at the Sand 25--Integration of Microseismic (Details on p 26) (Details on p 27) (Details on p 28) (Details on p 29) Sessions 17 - 20 Sessions 21 - 24 Sessions 25 - 28 Sessions 29 - 32 7:00 am - 7:50 8:00 am - 9:30 7:00 am - 6:45 pm 9:30 am - 4:00 pm 2:00 pm - 3:30 3:30 pm - 4:00 4:00 pm - 5:30 5:30 pm - 6:30 7:15 pm - 9:30 9:30 am - 10:00 9:30 am - 10:00 12:30 pm - 1:45 12:30 pm - 1:45 10:00 am - 10:50 am - 12:30 pm 11:00

20 46th US Rock Mechanics/Geomechanics Symposium Ontario Ontario Ontario Properties Interfaces and Faults Stabilization and 40--Fluid-induced Fractures and Along Processes in Natural Micro- and Macro-scale Porous Media: Connecting 44--Transport and Coupled 44--Transport Destabilization of Fractures --Erie 36--Fluid Flow & Deformation in Assemble in Hotel Lobby Assemble in Hotel Lobby Assemble in Hotel Lobby --Huron Superior East and Testing Crack Growth Millenium Park Millenium Park Millenium Park 43--Applications of Numerical Modeling 35--Fracture Processes 39--Numerical Modeling of Great Lakes Ballroom Great Lakes Ballroom Great Lakes Ballroom Great Lakes Ballroom Great Lakes Ballroom Lunch on your own Sponsored by Golder Associates' FracMan Technology Group Associates' FracMan Technology Sponsored by Golder Sponsored by MWH Global Thursday, 28 June 2012 Thursday, Wednesday, 27 June 2012 Wednesday, Exhibits Open-- Closing Session-- Plenary Address-- Exhibit Take Down-- Exhibit Take Lincoln Park Lincoln Park Lincoln Park Speaker's Breakfast-- 38--Behavior of 34--Surface Mine Pit Slope Stability 42--Case Studies Meeting of the CSM ARMA Student Chapter ARMA Meeting of the CSM in Hard Rock Mining High Porosity Materials Registration and Speakers Ready Room-- Great Lakes Ballroom, Lunch Meeting of the Organizing Committee for San Francisco 2013 Special Morning Activity: The Museum of Science and Industry-- Special Morning Technical Tour 3: Chicago's Tunnel and Reservoir Project (TARP)-- 3: Chicago's Tunnel Tour Technical Special Evening Activity: Dinner Cruise Aboard The Spirit of Chicago-- Activity: Dinner Cruise Special Evening Paul La Pointe, Golder Associates, "It’s the Cracks that Matter: DFN Modeling of Everything Rock" Associates, "It’s Paul La Pointe, Golder Volume Coffee Break-- Reservoirs Michigan Ballroom Michigan Ballroom Michigan Ballroom 33--Classic and Novel Stimulated Reservoir 41--Interaction of Natural Wellbore Stability Evaluation Wellbore and Induced Fractures 37--Monitoring of Hydraulic Fracturing in Unconventional (Details on p 30) Sessions 33 - 36 9:30 am- 4:00 pm (Details on p 31) (Details on p 32) Sessions 37 - 40 Sessions 41 - 44 7:00 am - 7:50 8:00 am - 9:30 7:00 am - 4:00 pm 9:00 am - 1:00 pm 9:30 am - 2:00 pm 2:00 pm - 3:00 2:00 pm - 3:30 3:45 pm - 4:00 9:30 am - 10:00 12:30 pm - 2:00 12:30 pm - 1:15 12:30 pm - 2:00 6:00 pm - 10:00 10:00 am - 10:50 am - 12:30 pm 11:00

21 46th US Rock Mechanics/Geomechanics Symposium m onday technical program Ontario (pp 49-51) Session 4 Permeability Measurement with Novel Testing Techniques Novel Testing Unequal Stresses Development and Use Ultra-High Fluid Pressure and layered rock under Brazilian test on the development of failure 161 - Forward and inverse modeling in 561 - Intermediate stress effect 650 - Split-platen Compression Test: 492 - Numerical simulation for 656 - 204 - Impact of coal microstructure in porous rocks process of laboratory tests on CO2 injection reverse: strength anisotropy (pp 46-48) Session 3 Millenium Park Processes in Rock Thermo- Hydro-Mechanical Geothermal & Hydrothermal Candidate for Nuclear Waste Candidate for Nuclear Waste Geomaterial Properties of Newberry Welded Tuff Properties of Newberry Welded Properties of Lindsay Limestone: A A Properties of Lindsay Limestone: Dependent Healing 472 - Thermo-Hydro-Mechanical Stiffness and Deformation of 316 - Stiffness 329 - 415 - Deformation and Failure on Temperature of 427 - Effect Rocks 605 - Residual Conductivity of a Damage and Temperature- Influence of Self-Propping, Time, and Time, Influence of Self-Propping, Salt Rock Subject to Anisotropic Salt Rock Subject to Behavior of Carbonate Yielding Bauxite-Propped Geothermal System- Behavior of a Low Permeability Closure Stress Repository in Canada (pp 43-45) Session 2 Lincoln Park Monday, 25 June 2012 Monday, Assessment of Subsidence Coal Mine Strata Behavior - I Applications of PC-Strand for Mining and Civil Subsidence in an Area with a Major Subsidence in an Australia 320 - 167 - Calibration of FLAC3D to Mechanics Transfer 184 - Increased Assessment of Mine 220 - 137 - Horizontal stress related failure Critical Pipeline and Utility Corridors field observations and numerical Fully Grouted Rock Bolts Pillar Crushing Event – Newcastle, Risk for Mine Mitigation Beneath in bedded mine roofs—insight from Simulate the Shear Resistance of models (pp 40-42) Session 1 Geomechanics of Michigan Ballroom Trajectory Optimization for Trajectory An Explanation for Anomalous An Explanation for Reservoirs and Caprocks hydrocarbon reservoirs overlain by Geomechanics and Reservoir Producing Oil Sands Reservoirs Time Dependent Subsidence Time by Coupled Modeling of rock salt caprocks 669 - Overburden Stability under 145 - Modeling stress development 139 - Evaluation of Caprock Stability 198 - Production-Induced Compaction 518 - 327 - Geomechanical Evaluation for Reservoirs Prediction of Casing Failure Due to Varying Pressure Loading Varying and fault slip in producing Short Term Gas Storage in Depleted Term Short Offshore Wells and Numerical Wells Offshore Simulation under Steam Injection for Time 9:00-9:15am 8:15-8:30am 8:30-8:45am 8:45-9:00am 9:15-9:30am 8:00-8:15am

22 46th US Rock Mechanics/Geomechanics Symposium Ontario Behavior (pp 60-62) Session 8 Impression relaxation test, a new Time-dependent behavior of Time-dependent The inference of physico- of material scalping The effect Laboratory Testing of Waste of Waste Testing Laboratory Instrument for Measurements of ------Time and Environment-dependent Time strength of Questa Mine materials Materials and the evaluation of the effect of and the evaluation of effect relaxation method to determine the Isolation Pilot Plant Surrogate Waste Isolation Pilot Plant Surrogate Waste rock Linear Thermal Expansion Coefficient Thermal Expansion Coefficient Linear 162 385 391 510 639 256 mechanical properties from needle time dependent characteristics of salt of Rocks granite and constitutive equation and water content on the shear mechanical properties of soft rocks penetration tests water content and weathering on their (pp 57-59) Session 7 Millenium Park Influence of CO2 on Physical Properties Comparison of mechanical Constraining Elastic Rock Chemo-mechanical Permeability evolution in dual of CO2's varying phase Effect An integrated experimental and ------media cement as well cement at different cement as well at different Recovery Reservoir Using Sonic Log on static and dynamic moduli of a modeling approach to determine the conditions, rock properties, and behaviors of geopolymer and class G Properties in A CO2 Enhanced Oil A Properties in permeability evolution in wellbore- curing temperatures for geological Data interplay between deformation development of clay smears 232 234 407 426 568 582 sequestration of carbon dioxide cement fractures exposed to carbon- permeability dual stiffness sorbing permeability dual stiffness fully saturated dolostone dioxide-rich brines (pp 54-56) Session 6 Monday, 25 June 2012 Monday, Lincoln Park Hard Rock Mining - I Numerical Modeling of Rock Discussion on Rebar and Advances in Methods of Ground Support Strategies for Laboratory and in situ - - - - - Support and Reinforcement in Turquoise Ridge Joint Venture, Ridge Joint Venture, Turquoise Empirical Stope Design Shotcrete Composite Backfill investigations on the corrosivity of Bolts Subject to Dynamic Loading Failures 158 259 288 299 439 support systems Barricades with Focus on Past Weak Ground Masses at the Weak Nevada Session 5 Michigan Ballroom Stimulated Reservoir Volume Stimulated Reservoir Volume 3D Modeling of Natural Modeling Fractures with Geomechanical Modeling of Fluid Driven Rock Deformation Acoustic emission studies of - Geomechanics Modeling of Shale Reservoirs (pp 51-54) - - - - - Hydraulic Fracturing in Fractured different fluid viscosities different Fractured Shale Gas Reservoirs Numerical Application to Stimulation Numerical Methodology Hydraulic Fracture Initiation and hydraulic fracture evolution using via the Combined FEM/DEM Continuum Damage and Its Weakening Weakening 196 275 516 468 403 597 Discontinuity Method with Slip Propagation in a Mechanically Poroelastic Displacement by Hydraulic Fracturing in Naturally Fracture Stimulation Using a Stratified Geologic System Estimates Time 11:00-11:15am 11:15-11:30am 11:30-11:45am 11:45-12:00pm 12:00-12:15pm 12:15-12:30pm

23 46th US Rock Mechanics/Geomechanics Symposium Ontario (pp 71-73) Session 12 Acoustic Emission Time-lapse Passive Seismic Time-lapse Acoustic Emission and properties of Hydraulic Fracture Propagation in Unjacketed Tests on Sandstone Tests Unjacketed Characterization from Logging and Saturated Sandstone in Triaxial Triaxial Saturated Sandstone in 644 - Orthotropic Horizontal Stress Heterogeneous Rock Samples 589 - 527 - AE from Undrained and 581 - 399 - Relating acoustic wave 228 - Crack Initiation Stress for Core Derived Acoustic Anisotropies Coal Mines: A Comparison of A Coal Mines: Compression Ultrasonic Transmission Monitoring Ultrasonic Transmission of Longwall Tomography Velocity velocities to formation mechanical Methods (pp 68-70) Session 11 Challenges in Millenium Park Numerical Modeling DEM/Pore Network Modeling of numerical models Mechanical Properties: Dealing with Layered Rock Masses with Different Layered Rock Masses with Different Approach for Elastic Rock NURBS for curve interfaces appropriate input parameters for Heterogeneity 621 - Effective stress coefficient for stress coefficient 302 - Effective A Numerical Local Upscaling A 654 - Finite Element Analysis of 608 - Finite Element A mortar method based on A 313 - 304 - Challenges in selecting uniaxial strain condition Fluid Injection into Granular Media Stresses Induced by Gravity in Elastic Moduli (pp 66-68) Session 10 Lincoln Park Monday, 25 June 2012 Monday, and Deformation Rock Mass Excavation A hydraulic specific energy A arch effect around a tunnel in soft arch effect from Nepal Himalaya mechanisms and dynamic pressure rock 285 - Probabilistic approach in discussion based on tunnel projects Indentation Test for the Test 270 - Indentation 674 - Progressive failure 435 - Rock Squeezing Prediction by 300 - Tube Turbodrilling Turbodrilling Tube assessing tunnel squeezing – a a Support Vector Machine Classifier a Support Vector Measurement of Rock Brittleness performance indicator for Coiled Session 9 Michigan Ballroom Around Wellbores and Around Wellbores Perforations (pp 63-65) Investigation of Three Modes of Investigation of Analysis of Horizontal Wellbore Analysis of Horizontal Wellbore Shale, Sand and Chalk Behavior Shales Condition Chemo-Hydraulic Parameters of Fine-grained Rocks Borehole/TWC Failure by Application Borehole/TWC Failure by Production in Realistic Downhole Stability in Clay Shale Shear Strength Anisotropy in 290 - Shear Strength 479 - Solids production in chalk A Predictive Model for Sand A 314 - 284 - One-Dimensional Closed-Form 545 - 559 - of the Modified Cam-Clay Material Solutions for Estimation of Thermo- Solutions for Estimation of Model Time 2:00-2:15pm 3:15-3:30pm 3:00-3:15pm 2:45-3:00pm 2:30-2:45pm 2:15-2:30pm

24 46th US Rock Mechanics/Geomechanics Symposium Ontario (pp 81-84) Rock Mass Session 16 Characterization - Comparison of Deformability Methods Analysis A critical look at geotechnical A 563 - Mining Techniques Numerical Validation and 512 - Numerical Validation Stiffness Characterization of 203 - Stiffness 115 120 - Models for Geomechanical Effect of Deformation Rate on 140 - Effect Materials estimation Formations at DUSEL Using Data Formations at DUSEL Modulus Estimation for Tunnel Tunnel Modulus Estimation for classification for rock strength Refinement of Empirical Rock Mass Shear Strength of Questa Rock Pile Karst Rock Mass Characterization of the Rock Mass Rock Mass by Direct and Indirect (pp 79-81) Session 15 and Damage Millenium Park Modeling Anisotropy - Influence of direction argillaceous rock (Opalinus Clay) at to tensile principal stress under damage model (Failure) Criteria in Rock Mechanics principal elastic axis and contact area Behavior of Fractured Rock Masses the laboratory-scale diametrical compression methodology for evaluating the 663 - Modeling of the strength and 113 Scale Effects on the Elastic 124 - Scale Effects 125 - Modeling brittle rock material Yield 640 - Some Considerations on Extension of Maxwell’s 446 - Extension of Maxwell’s effective properties of rock effective deformation anisotropy of an by using a coupled elasto-plastic (pp 76-78) Session 14 Lincoln Park Monday, 25 June 2012 Monday, Drilling Mechanics The Role of Natural Vibrations The Role of Natural Vibrations Accurate Bottomhole Pressure Drilling Fluid Pressure Program - Part Confining Pressure in Penetration Mechanism of a Single Versus Depth of Cut Versus for Fracture Gradient Prediction and Single Cutter-Rock Interaction under Simulation of Core Disking 569 - Issues with Numerical 622 - Mechanical Specific Energy PDC Cutter Analytical Modeling of PDC 341 - 235 - 142 - Interpretation of Single Cutter 402 - Tests for Rock Mechanical Properties Tests I (pp 74-76) Session 13 Michigan Ballroom Hydraulic fracture initiation from The role of pre-existing in Unconventional Reservoirs Numerical Modeling of Fractures treatments Analysis Trajectories and Fracturing Pressure Trajectories Propagation in Low Permeability borehole: Numerical and an open-hole: wellbore size, fracturing in enhanced reservoir 633 - Factors Influencing Fracture 224 - Modeling Hydraulic Fracture 601 - 480 - Simulating Hydraulic Fracturing 555 - Fracture development from a 647 - Reservoirs Data in a Horizontal Completion pressurization rate and fluid-solid experimental investigations with Discontinuous Deformation coupling effects Time 5:15-5:30pm 5:00-5:15pm 4:15-4:30pm 4:45-5:00pm 4:30-4:45pm 4:00-4:15pm

25 46th US Rock Mechanics/Geomechanics Symposium T UESday technical program Ontario (pp 116-118) Session 20 Failure Response Multi-scale investigations on the Formalized approaches to Relationship between shear Compactant features observed of bridge length and The effects Stress-Dependent Brittle-to------curves of rocks subjected to direct material on surface crack growth and mechanisms affecting the strength and mechanisms affecting varying in texture shear tests the elastic modulus of a marble 367 566 448 615 306 624 rock: Granite and Limestone Geothermal Wells Geothermal Wells stress and shear strain at post-peak under true triaxial states of stress compression defining damage thresholds in brittle Ductile Deformation of Tuff in Tuff Ductile Deformation of coalescence under uniaxial Session 19 Millenium Park Numerical Studies on Coupled Experimental Study on Permeability Estimation from Effective Staged Differential Seismic Detection of Flow Topology analysis method for Topology Geophysics of Cracked and ------Fractured Media (pp 113-115) Fluid Flow, Geomechanics and Fluid Flow, Multiple Porosity Model for Naturally Aperture and Rock-Water Dissolution Aperture and Rock-Water Reservoirs Flow and Geomechanics with the Relationship between Hydraulic Paths in a Air-Filled Fracture under Paths in a Seismic Velocity based on Crack and Seismic Velocity Fractured Tight and Shale Gas Tight Fractured 296 469 481 553 565 676 networks Grain Models Acoustic Velocity in Carbonates Acoustic Velocity Stress water flows in 2D discrete fracture Medium (SDEM) Models for the of Granite (pp 110-112) Session 18 Lincoln Park Tuesday, 26 June 2012 26 June Tuesday, Evaluation of roadway in- Optimization of coal measure Review of fundamental The Coal and Gas Co- Effect of Mesoscale Fracture Effect Estimating Mining Recovery ------Coal Mine Strata Behavior - II anisotropy in underground coal efficiency of the degassing process: efficiency Commercial Scale Underground Coal software stability in the presence of stress rocks stress relief to increase the geotechnical mechanisms of valley during the Uniaxial Compression Factor and Cavity Stability of CT Scanning Method- An Scanning Method- CT numerical modeling using FLAC Gasification Plants 211 242 308 324 370 471 closure subsidence effects Process of Coal Containing Gas with Experimental Approach extraction Technology in China Technology extraction mines Session 17 (pp 107-109) Geomechanics Michigan Ballroom Creep Behavior of Barnett, Geomechanical evolution of Proppant Embedment and The Role of Mechanical and Drainage of Poroelastic Microcrack nucleation in porous Unconventional Reservoir ------Characterization and Field Shales production compressive stress states with Haynesville, and Marcellus Shale solids under predominantly Fractures and Its Implications on the Development in North American Development in North Reservoirs Reservoirs applications to shale gas exploration 664 562 194 330 321 291 Performance of Naturally Fractured Fractured Unconventional Shale Acoustic Anisotropies on Reservoir Acoustic Conductivity of Hydraulic Fractures in fractured reservoirs during gas Time 8:00-8:15am 8:15-8:30am 8:30-8:45pm 8:45-9:00am 9:00-9:15am 9:15-9:30pm

26 46th US Rock Mechanics/Geomechanics Symposium Ontario Session 24 (pp 127-129) Heterogeneity in Rocks Structural Integrity of Oil Scaling Problem in Rock Heterogeneity from Anisotropy and of Effect Shale Rock Properties: Peak The Influence of Fieldscale ------Quasistatic Processes: Shock- Induced Surface Deformation Heterogeneity upon Dynamic and Heterogeneity on the Bending of Storage Caverns at a Strategic Geologic Structures 189 444 509 577 611 649 Rock Fabric Scanning Technique Petroleum Reserve Site with Highly Strength, Acoustic Anisotropy and Thermal Profiles using an Optical Heterogeneous Rock Fracture Induced Damage and Injection Heterogeneous Salt and Caprock Session 23 (pp 124-127) Millenium Park Carbon Sequestration on the Reservoir Scale Influences of Anticline Passive Seismic Imaging for The Effects of The Effects Shared Earth Models Give Evaluation of leakage potential Probabilistic analysis of a ------Application at a Shallow Carbon considering fractures in the caprock Model Consistency in Simulations; geological media Sequestration/Water Floods on Sequestration/Water for sequestration of CO2 in 579 319 459 522 544 653 CO2 injection Verification, Verification, and Accounting Pressures Associated with CO2 Pressures Exterior Stress Fields Reservoir Geometry on Critical Pore faulted hydrocarbon reservoir during Carbon Sequestration Monitoring, dioxide Sequestration Site Sequestration Session 22 (pp 122-124) Lincoln Park Tuesday, 26 June 2012 26 June Tuesday, Hard Rock Mining - II Revisiting the design challenge Methodology to Determine Reliability based support Ten Months of Ground Imaging Ten Stress heterogeneity and - - - - - Support and Reinforcement in Reflector Tracing Ahead of TBM Using Seismic Ahead of Peak Particle Velocity in Peak Particle Velocity 150 298 412 476 532 rock Underground Drift Developments of permanent bolts and shear above large caverns complexity: implications for mining design for an excavation in brittle reinforcement in laminated ground (pp 119-121) Session 21 at the Sand Face Michigan Ballroom Scale effect in volumetric sand Scale effect The Effect of FracPacks on The Effect Effect of Mechanical and Effect Sand prediction by different Sand production model based of stress anisotropy The effect Production Geomechanics ------Failure Cavity Development — on episodic functions on sanding: An experimental study on sanding: production Sand Stability during Depletion Experimental and Numerical Studies 266 489 482 671 126 374 hollow cylinder test criteria and validation through a Physical Properties of Rocks on Post- Time 11:00-11:15am 11:15-11:30am 11:30-11:45am 11:45-12:00pm 12:00-12:15pm 12:15-12:30pm

27 46th US Rock Mechanics/Geomechanics Symposium Ontario Session 28 (pp 139-141) Mapping and Imaging Characterization of Damage in Uncertainty of Volumetric as a new On Site Visualization Numerical modeling of strain Comparison of Standard of a 3-D LiDAR point Verification ------Explosions Measurements Mitigation Project, Metaline Falls, Structural Mapping Results to 3-D applications Boundary Transformer Banks Rockfall Transformer Boundary 531 494 456 368 552 186 management for rock engineering Photogrammetric Model Results: discontinuity orientations Washington Washington sensor installed inside a grouted visual scheme for risk and safety Anisotropic Rock Due to Buried cloud viewer for measuring transfer from rock mass to a fibre optic Fraction Estimates Using 2-D borehole Session 27 (pp 136-138) Millenium Park Comparison of 2D and 3D DDA Comparison of 2D and 3D DDA Modeling and Remedial Perforation of rockfall of Rockfall Shape on Effect Rigid body dynamics for rock - A case study of slope stability A ------Rock Fall and Slope Analysis Rock Fall and Slope Rockfalls Problems along Werka Rockfalls Problems along Werka impact Measures of Rock Slope Stability and fall trajectory simulation 493 631 484 267 122 237 site of Tapovan-Vishnugad site of Tapovan-Vishnugad India Normal Coefficient of Restitution Normal Coefficient evaluation of cut-slopes switchyard in rockfall analysis Hydropower Project, Uttarakhand, protection barriers by normal block Descent Road West of Saudi Arabia of Saudi Descent Road West Session 26 (pp 133-136) Lincoln Park Tuesday, 26 June 2012 26 June Tuesday, Caverns and Tunnels Stability and Support of Rock mechanical Ground Conditions Characteristics of Rock for Measuring Technology New Subway Project in Istanbul, of Initial Geostress on Effects ------Powerhouse Caverns No.3 Intake, Nevada the Displacement of Underground Starter Tunnel for the Lake Mead Tunnel Starter disposal in clay rock considerations associated with the Deformation and Fractures in an 123 135 343 497 677 378 System Installed in the Realigned Bolts construction of a deep nuclear waste Underground Powerhouse Caverns the In Situ Performance of Rock Turkey Turkey Encountered and the Support (pp 130-133) Session 25 Michigan Ballroom Understanding Hydraulic for Microseismic and 3D VSP Fracture Network Engineering: Induced hydraulic fractures or Microseismic Responses from Integrating Microseismic with ------into Natural and Hydraulic Fracture Characterization in Shale Reservoirs Integration of Microseismic Monitoring Modeling the response of natural Cooper Basin, Australia to Characterize Induced Fractures in Geomechanical Integration of treatments Strategies of One Horizontal Well in Strategies of One Horizontal Well reactivated natural fractures? Fracture Variability Through Fracture Variability fracture networks to stimulation infill evaluation in Greater Tindilpie, Tindilpie, infill evaluation in Greater Surface Microdeformation Monitoring Two Hydraulic Fracture Stimulation Two 276 201 594 618 554 667 a North American Shale a North Hydrofracture Numerical Simulations Combining Microseismic Imaging and Characterization Microseismic and Seismic Reservoir the Immature Eagle Ford Shale Time 2:00-2:15pm 2:15-2:30pm 2:30-2:45pm 2:45-3:00pm 3:00-3:15pm 3:15-3:30pm

28 46th US Rock Mechanics/Geomechanics Symposium Ontario of Rocks (pp 150-152) Session 32 Interface Waves along Interface Waves When to use static or dynamic Combining static and dynamic Static vs. Dynamic Behavior of A Numerical Investigation of the A of Shear Specific Stiffness - Static & Dynamic Response - - - - - elastic dispersion Fractures and Fracture Intersections moduli in geomechanical models Fractures in Anisotropic Media Fractures in 610 294 307 523 537 542 Scaling of Fracture Stiffness measurements for evaluation of Shale Session 31 (pp 148-150) Geomechanics Millenium Park Discrete Simulations in Distinct Element Model Modeling direct shear tests with Mechanical, Failure and Flow A Flat-Jointed Bonded-Particle A Simulation of carbonate rocks Direct shear tests to model the ------computed tomography images based Discontinuities discontinuity shear strength scale elastic properties using 3D X-Ray on Discrete Element Method and Analysis of Unstable Failure Rock effect as an emergent characteristic effect 501 212 416 457 651 632 PFC2D Finite Element Method mechanical Models Material for Hard Rock FEM/DEM: Investigation of shear behavior of rock joints by Properties of Sands: Micro- Session 30 (pp 145-147) Lincoln Park Determination Tuesday, 26 June 2012 26 June Tuesday, Review of borehole in situ of residual Study on effect Borehole breakout formation of the Laboratory Verification Wireline hydraulic fracturing Stress changes at the crest of Advances in In Situ Stress ------situ stress measurement by hydraulic unconsolidated deepwater sediments South McMurdo Sound Drill Hole considerations Diametrical Core Deformation and stress estimation in aperture and system compliance in in- situ Stress Measurements 168 461 169 254 447 588 various ground conditions and Analysis (DCDA) Developed for In- dipping structures stress measurement techniques for stress determinations in the ANDRILL ANDRILL stress determinations in the numerical stress estimation fracturing method Session 29 Michigan Ballroom Static & Dynamic Data Shale Gas Resources: Energy How important is the Numerical Modeling of Formations (pp 142-144) A Microscopic Numerical A Montney Shale Geomechanical ------Modeling of Hydraulic Fracture Interactions in Naturally Fractured Reservoir Numerical Simulations of a Layered Characteristics Hydraulic Fractures Interaction in Material Fracturing in Compression Challenges for Coupled Hydraulic Fracturing 668 209 657 441 292 238 Formations design on tight shales? Complex Naturally Fractured between Natural Fractures and Characterisation of a Fractured Gas Challenges: 2D and 3D FEM/DEM Potential and Associated Exploitation Potential and Geomechanics and Transport Geomechanics and Transport poroelastic effect to completion poroelastic effect Integration for Improved System for Modeling Interaction Time 4:00-4:15pm 4:15-4:30pm 4:30-4:45pm 4:45-5:00pm 5:15-5:30pm 5:00pm-5:15pm

29 46th US Rock Mechanics/Geomechanics Symposium WE EDN Sday technical program Ontario Session 36 Effect of grain scale geometric Effect Multiscale Modeling of 3D Cracking and Theory, Network Pore-scale deformation in high- Two-scale characterization and Two-scale High Resolution Dual Modality scale Properties (pp 185-187) ------Fluid Flow & Deformation in Porous Media: Connecting Micro- and Macro- discrete mechanics Realistic Microstructure modeling of porous continua from porosity rocks heterogeneity on tensile stress (Neutron and X-ray) Imaging of compression Numerical Simulation Based on 175 253 268 322 465 670 generation in rock loaded Partially Saturated Sand and Direct Homogenization Frictional Sliding Granular Systems by Computational and Testing Session 35 (pp 182-184) Millenium Park Fracture Processes Fracture initiation and The Strength and Crack Size of process zone in fracture Role of Microstructure Size in Fracture Characterization in Fracturing Behavior of Inclined ------Bending Stresses Using Acoustic Bending Stresses Using under High Strain Rate of Marble Analog Rock and Granite Under propagation in the Quintner Fracture Process Zone Development Emission 401 258 421 156 628 338 Limestone Loading Cracks under Static and Cyclic testing of rock Behavior of the Rock-like Gypsum Session 34 (pp 179-181) Surface Mine Lincoln Park Pit Slope Stability Wednesday, 27 June 2012 Wednesday, Heterogeneous Distribution of Simulation of Three- Forensic Evaluation of Pit Evaluation of Structurally- Modelling rock bridge failure a methodology for Towards ------Analysis Distribution for Slope-Stability characterizing intact rock bridges in and brittle fracturing in large open pit 133 248 251 360 452 466 rock slopes large open pits Quarrying Operations the Coefficient of Permeability and an the Coefficient Slope Instabilities Controlled Failures in Large Dimensional Pore-Pressure Equivalent Homogeneous Approach Session 33 (pp 176-179) Stability Evaluation Michigan Ballroom Potassium Efficacy versus Potassium Efficacy The challenge of drilling the A coupled model for A Determination of Safe Salinity Drilling in Fracture Shales: Stability Integrated Wellbore Classic and Novel Wellbore Classic and Novel Wellbore ------prediction and stress analysis during Ecopetrol's first well, in the Cupiagua Analysis for Well Trajectory Trajectory Analysis for Well Window in Drilling Shale Formation Osmosis and a Biological Analog to Osmosis and a Biological 317 417 445 453 463 533 Problem Shale-Fluid Interactions Optimization and Field Development wellbore/reservoir temperature Another Look at the Mud Weight Another Look at the Mud Weight field. A Geomechanics point of view A field. fluid circulation in the West Kazakhstan Field in the West Time 8:00-8:15am 8:15-8:30am 8:30-8:45pm 8:45-9:00pm 9:00-9:15am 9:15-9:30pm

30 46th US Rock Mechanics/Geomechanics Symposium Ontario Session 40 Faults (pp 196-199) Evolution of Induced Seismicity Long-term Evolution of Rock Experimental study on stress Bubble nucleation in Modeling and Numerical - - Coupled Continuum Modeling - - - - Fluid-induced Stabilization and Destabilization of Fractures and Thermal, Hydraulic, Mechanical and Geomechanics in Composite Gas of Fracture Reactivation and Induced Reservoirs Due to Interactions between Permeability in Sandstone and Geothermal Operations wave interaction with rock fractures Temperature-controlled Conditions Temperature-controlled Hydrate Deposits 603 151 154 170 297 400 Mudstone under Pressure- and stimulation: A laboratory study A stimulation: groundwater triggered by seismic Simulation for Coupled Flow and Chemical Processes in EGS Seismicity during Enhanced Growth Session 39 (pp 193-196) Millenium Park Modeling mixed-mode fracture Study of stress and strain fields Three-dimensional Boundary A multi-modal approach to 3D A 2D Frictional crack initiation - A Finite-Element Method for A ------Numerical Modeling of Crack Gravity Load numerical manifold method Discrete-Fracture Propagation using propagation in 3D the Finite Element Method 450 179 213 593 339 190 using Impulse-Based Dynamics and Element Modeling of Fractures under Fracture and Fragmentation of Rock around a flaw tip in rock Modeling Fluid-Pressure Induced and propagation analysis using the Random Meshes Behavior of Session 38 (pp 191-193) Lincoln Park Wednesday, 27 June 2012 Wednesday, High Porosity Materials Soil model for rock properties stress Influence of effective Modeling the onset of Experimental Study and True Triaxial Compression Triaxial True Heterogeneity within ------chalk Triaxial Compression Stress Paths Triaxial Behavior of a Weakly Consolidated Behavior of a Weakly Sandstone and the Effect of the Sandstone and the Effect coefficient on mechanical failure of coefficient Modeling of the Hydromechanical deformation bands in sandstone 143 182 286 335 430 347 reservoirs rocks Strength and Fault Angle Strength and Fault bifurcation in porous sedimentary prediction in exploration settings Tests on a Medium-High Porosity Tests Sandstone under Proportional Intermediate Principal Stress on Session 37 (pp 188-190) Michigan Ballroom Emergence and Propagation of Direct measurement of contact Application of the distinct- A Numerical Evaluation of the A Simulation of Hydraulic Initiation and Propagation of ------in Unconventional Reservoirs Monitoring of Hydraulic Fracturing Casing- Cement Interface sliding interface Natural Fractures Delamination Cracks along the Geomechanical Interactions Between element method to investigate the area and seismic stress along a a Natural Fracture System 287 449 331 223 252 538 a Hydraulic Fracture Stimulation and influence of natural fractures and in- Poroelastic Media propagation Secondary Cracks in Thermo- Secondary Cracks in situ stresses on hydrofrac Fractures and their Interactions with Time 11:00-11:15am 11:15-11:30am 11:30-11:45am 11:45-12:00pm 12:00-12:15pm 12:15-12:30pm

31 46th US Rock Mechanics/Geomechanics Symposium Ontario Session 44 Interfaces (pp 207-210) Experimental Study of Portland Particle Swarms in Confining Coupled stress and flow along Geochemical controls on fracture Simultaneous anhydrite Monitoring slip initiation and Natural Fractures and Along Natural Fractures and ------Wellbore Stability for Carbon Capture Wellbore interfaces in the wellbore environment with seismic wave transmission Transport and Coupled Processes in Transport 206 227 350 437 549 619 a closed swelling rock system Cement/Rock Interface in Relation to propagation along frictional interfaces evolution in carbon sequestration dissolution and gypsum precipitation in Fractures and Storage (CCS) in relation to CO2 sequestration (pp 204-207) Session 43 Applications of Millenium Park Numerical Modeling Impact of post-failure rock of micro-parameters on Effect Continuum representation of Applied back-analysis methods Generic Stope Model for A On Using Spatial Methods for ------Analysis mi for intact rock using particle flow response for tunneling using numerical brittle rock failure bulking-induced Heterogeneous Slope Stability mass behavior on excavation modeling 262 272 541 672 176 432 modeling displacements around tunnels Mechanisms in Deep Gold Mines Investigation of Fracturing the Hoek-Brown strength parameter Session 42 (pp 202-204) Lincoln Park Case Studies in Hard Rock Mining Wednesday, 27 June 2012 Wednesday, Rock support design in burst- Mining Remnant Underground Excavation in hard rock under Numerical analysis of room How can an intensive - - - - - implemented at mass mining potash mine Mine Pillars with Large Open Pit prone ground utilizing an interactive preconditioning concept be closure rate in an underground - Key Elements of Slope Stability 174 524 599 679 681 design tool Norway Development in a Jointed Rock Mass panel caving project Analysis Using Three-Dimensional high in-situ stress at Rana Gruber, high in-situ stress at Rana Gruber, method? Application to Cadia East method? Numerical Modeling Methods Session 41 Michigan Ballroom Experiments on Permeability Simulation of fracture clusters Radial cracking of a borehole Natural Fractures Numerical modelling of thermo- Gas Production Induced Stress Fractures and Stimulated ------Reservoir Volume (pp 199-201) Reservoir Volume Interaction of Natural and Induced fully coupled thermo-hydro- Shale based thermal fluid flow and EOR by pressure and thermal shock and Permeability Variations in and Permeability Variations Evolution with Temperature of Oil Temperature Evolution with in unconventional reservoir using hydro-mechanics involving AMR- Characterization in a Carbonate geomechanics: application to thermal 386 436 530 642 425 433 Coalbed Methane Reservoirs Heavy Oil Fiel mechanical FEM analysis Time 2:00-2:15pm 2:15-2:30pm 2:30-2:45pm 2:45-3:00pm 3:00-3:15pm 3:15-3:30pm

32 46th US Rock Mechanics/Geomechanics Symposium P lenary Presentations

Sunday, 24 June, 6:20 pm – 7:00 pm MTS Lecture - Dynamic Fragmentation, Asteroid Impacts and Meteorites from Mars

Jay Melosh, Purdue University, West Lafayette, Indiana, USA Meteorites from Mars and the Moon were first recognized in the 1980’s. We now know that these rocks were blasted off their parent planets by high-speed impacts of asteroids. When an asteroid slams down onto the rocky surface of a planet at speeds exceeding the speed of sound, shock waves spread out from the impact site. Rock directly underneath the impact site is raised to pressures and temperatures that melt or vaporize it, but rocks adjacent to the surface rebound in tension as they are accelerated up and away from the impact site. Some of this material falls back onto the surface of the planet, creating long lines of secondary craters radiating away from the impact, but other fragments are accelerated to more than escape velocity and may eventually land on Earth or even be ejected into interstellar space. The mechanics of this process is now becoming clearer, and the consequences are far-reaching. Rocks ejected from close to the surface escape strong heating, and it is possible that living organisms—microbes—could travel between planets in such rocky “spaceships.” Ejecta from Mars may be present in the soil of its tiny moon Phobos, waiting to be picked up by future sample return efforts like last year’s ill-fated Russian Phobos-Grunt mission. A current challenge is estimation of the size of planetary ejecta fragments as a function of the size and speed of the impacting asteroid. A mystery presently focuses on Mercury’s craters, whose secondary craters are ten times larger, for their parent crater size, than those on Mars or the Moon. Is the Mercurian crust so much stronger? Do the higher speed impacts on Mercury paradoxically produce larger fragments than the slower impacts on Mars or the Moon? There is still ample room for fundamental discoveries about how rocks break under high strain rates and at planetary size scales.

H. J. Melosh is a Distinguished Professor of Earth and Atmospheric Science at Purdue University in West Lafayette, IN. He received an AB degree in Physics from Princeton University in 1969 and a PhD in Physics and Geology from Caltech in 1973. His principal research interests are impact cratering, planetary tectonics, and the physics of earthquakes and landslides. His recent research includes studies of the giant impact origin of the moon, the K/T impact that extinguished the dinosaurs, the ejection of rocks from their parent bodies and the origin and transfer of life between the planets. He is a science team member of NASA’s Deep Impact mission that successfully cratered comet Tempel 1 on July 4, 2005 and flew by comet Hartley 2 on November 9, 2010.

Professor Melosh is a Fellow of the Meteoritical Society, the Geological Society of America, the American Geophysical Union and American Association for the Advancement of Science. He was awarded the Barringer Medal of the Meteoritical Society in 1999, the Gilbert prize of the Geological Society of America in 2001 and the Hess Medal of the American Geophysical Union in 2008. He was a Guggenheim Fellow in 1996-1997 and a Humboldt Fellow at the Bavarian Geological Institute in Bayreuth, Germany, in 2005-2006. Asteroid #8216 was named “Melosh” in his honor. He was elected to the U.S. National Academy of Sciences in 2003 and the American Academy of Arts and Sciences in 2011. He has published approximately 180 technical papers, edited two books and is the author of a major monograph, Impact Cratering: A Geologic Process and a text “Planetary Surface Processes” with Cambridge University Press.

33 46th US Rock Mechanics/Geomechanics Symposium Monday, 25 June, 10:00 am – 10:50 am Rock Fracture Dynamics and Induced Seismicity

Paul Young, University of Toronto, Toronto, Ontario, Canada Understanding rock deformation and fracture is important at all scales in nature. Such processes vary from intergranular microcracking, leading to preferential alignment of microcracks in laboratory rock samples and in situ rock masses, to massive earthquakes due to rupture along key lithospheric plate boundaries. Thus, fracturing contributes directly to seismic behavior, mechanical properties, rock fluid interactions, and engineering applications. The research described in this talk utilizes unique experimental rock deformation and geophysical imaging instrumentation at the University of Toronto to simulate in the laboratory true 3D stress, thermal and fluid conditions in the Earth to study dynamic rock fracture and induced seismicity. Laboratory experiments and micromechanical modeling techniques have been used to carry out investigations into the physics of rock fracture with relevance to induced seismicity, fault mechanics and fluid transport in rocks. Laboratory true-triaxial experiments will be described that show the influence of sigma 2 on induced seismicity and 3D permeability of rock. In addition, in situ experiments will be described which show the application of induced seismicity and micromechanical modeling and provide insight into hydro-thermal-mechanical processes associated with full-scale experiments for the deep geological disposal of radioactive waste and enhanced oil recovery processes using hydraulic fracturing.

Professor R. Paul Young has a Ph.D. in Geophysics, M.Sc. in Rock Mechanics and a B.Sc. in Geological Sci- ences. He is currently Vice-President (Research) at the University of Toronto. In the last ten years, he has held the Keck Chair in Seismology and Rock Mechanics at the University of Toronto, the Chair of Earth Science at the University of Liverpool and has been President of the British Geophysical Association. He has been awarded many honors for his research and innovation, notably, Fellow of the Royal Society of Canada, the Willet G Miller Gold Medal of the Royal Society of Canada for his research in earth sciences and the John A. Franklin Award for Rock Mechanics by the Canadian Geotechnical Society. He is also a Fellow of the American Association for the Advancement of Science and is a Chartered Engineer. Over the past 30 years, Professor Young has pioneered techniques used today in monitoring and interpreting induced seismicity in the mining, petroleum and nuclear waste disposal industries. Through his research groups at Queen's University and the University of Toronto, Canada, Keele University and Liverpool University, UK, as well as through spin off companies such as the Engineering Seismology Group, Canada and Applied Seismology Consultants, UK, significant scientific advances have been made in seismology and rock mechanics. He has published over 220 scientific papers in refereed journals and conference proceedings, supervised over 40 Ph.D. students and post- doctoral research fellows and developed innovative instrumentation systems for induced seismicity/acoustic emission monitoring. Professor Young’s research is focused on rock fracture dynamics and induced seismicity with application to natural geologic hazards such as earthquakes and volcanic activity and engineering applications such as mining, hydrocarbon recovery, hydraulic fracturing and deep underground storage for nuclear waste isolation and CO2 sequestration.

34 46th US Rock Mechanics/Geomechanics Symposium Monday, 25 June, 1:00 pm – 1:45 pm The Panama Canal Expansion

Luis D. Alfaro, Panama Canal Authority, Panama This presentation gives a description of the main structures of the Panama Canal, the drivers for expanding the Canal, details on the various components of the Canal Expansion Program, and the status of the work performed to date. The presentation also highlights how developments in rock mechanics have had a significant impact on this major undertaking.

Luis Alfaro began working in the Panama Canal in 1983 as a Geotechnical Engineer. In 1991 he was promoted to Manager of the Geotechnical Branch in the Engineering Division. During this period he undertook the widening of the Canal’s Gaillard Cut. In 1997 Dr. Alfaro was promoted to Manager of the Engineering Division, and as of 2007 he is the Canal’s Vice-president of Engineering. In this position he oversees the work of the specialized groups working in the fields of Civil, Structural, Hydraulics, Geotechnical, Mechanical-Electrical, Specifications, Estimating and Geomatics. He holds a Bachelor’s degree in Civil Engineering from the University of Panama. In 1997 he obtained a Master of Science degree in Geotechnical Engineering from Purdue University and in 1980 a Ph.D. from Purdue University.

Tuesday, 26 June, 10:00 am – 10:50 am Formation and Extension of Localized Compaction in Porous Sandstones

John Rudnicki, Northwestern University, Evanston, Illinois, USA Narrow, roughly planar zones of localized porosity loss have been observed in porous sandstones both in the field and in the laboratory. In the laboratory the bands form perpendicular to the maximum compressive stress and are inferred to do so in the field. Although this mode of localization has been recognized only recently in porous rocks, it is common in a variety of other porous materials, e.g., cellular solids and metal foams. The significance of these compaction bands in sandstones is that both laboratory and field studies have shown that bands reduce the permeability by one to several orders of magnitude, and they form barriers to fluid flow. Consequently, their presence in subsurface formations would affect applications involving fluid injection or withdrawal, including sequestration of CO2 to mitigate adverse effects on the climate.

This talk will summarize laboratory and field observations of compaction bands and discuss theoretical results for their formation and extension. Theoretical results for band formation based on localization theory are roughly in accord with laboratory observations although detailed quantitative comparison is limited by the simplicity of the models and available data. Field data indicate that the midpoint width of the band scales as the square root of the band half-length L. This dependence is consistent with that of a very thin elliptical inclusion subjected to uniform compactive displacement w over the central portion of the band. If it is assumed that propagation of the band requires a critical value of energy released per unit area of advance, then w is proportional to the square root of L. The decrease of energy release rate (proportional to the square

35 46th US Rock Mechanics/Geomechanics Symposium of the stress intensity factor at the tip of the band) with band length in this model suggests that the bands form with an energy release rate above the critical value and then grow unstably (dynamically) until the energy release rate falls to the critical value.

Micro-computed tomography images of a sandstone core from the field have unprecedented views of three- dimensional microstructural features. Upscaling methods indicate that a permeability reduction of an order of magnitude, less than suggested previously.

John Rudnicki earned his Bachelor’s (1973), Master’s (1974) and PhD (1977) degrees at Brown University. Following a Research Fellowship in Geophysics at Caltech, he was Assistant Professor in the Department of Theoretical and Applied Mechanics at the University of Illinois at Urbana-Champaign. In 1981, joined the faculty at Northwestern University where he is now Professor in the Department of Civil and Environmental Engineering and the Department of Mechanical Engineering. His research has been in the general area of inelastic behavior and failure of solids, particularly, geomaterials. He has been especially interested in the development of localized deformation and in the effects of coupling between deformation and fluid diffusion in connection with applications to the mechanics of earthquakes, energy storage and recovery, disposal of toxic wastes and geological sequestration of CO2.

He is a Fellow of the American Society of Mechanical Engineers (ASME) and in 2008, he was awarded the Brown Engineering Alumni Medal. In 2006, he received the Maurice A. Biot Medal from Engineering Mechan- ics Division of the American Society of Civil Engineers "for his fundamental contributions to the mechanics of porous media and its applications to rock mechanics and geophysics" and in 2011, the Daniel C. Drucker Award from the ASME “For providing a new fundamental understanding of deformation instabilities in brittle rocks and granular media, including their interactions with pore fluids, with applications to fault instability, quantification of energy radiation from earthquakes and environment- and resource-related Geomechan- ics.” He has a held a variety of editorial and committee assignments, including Chairman of the Geosciences Council for the Dept. of Energy Basic Energy Sciences, a member of the Advisory Council of the Southern California Earthquake Center, and is currently a member of Editorial Advisory Board of the International Jour- nal for Numerical and Analytical Methods in Geomechanics. He teaches courses at both the undergraduate and graduate levels. He recently developed and teaches a popular undergraduate course on the Mechanics of Sports. He was undergraduate Advisor of the Year in the McCormick School of Engineering and Applied Sci- ence in 2009 and on the Associated Student Government Honor Roll for Faculty and Administrators in 2010.

36 46th US Rock Mechanics/Geomechanics Symposium Wednesday, 27 June, 10:00 am – 10:50 am It’s the Cracks that Matter: DFN Modeling of Everything Rock

Paul La Pointe, Golder Associates, Inc., Redmond, Washington, USA Understanding fractures is understanding rock. From the network of natural fractures, we learn about the intact rock strength and deformability, the in-situ stress, rock connectivity, kinematics, and comminution. Natural fractures play key roles in groundwater flow and transport, oil and gas production, mining, tunneling, dams, rock slopes, and the environment. This talk illustrates how rock is characterized from its fractures, and how rock mass behavior is controlled by its fractures. We will explore the wide range of applications of discrete fracture network (DFN) approaches, and will address the future of rock mechanics with ever more realistic synthetic rock mass models and better empirical methods.

Paul La Pointe received his doctorate in Mining Engineering with a specialization in rock mechanics from the University of Wisconsin in 1980, where he began a long fascination with the characterization and engineering of fractured rock masses. After graduation, he worked for the ARCO Coal Company to carry out geomechanical modeling and field characterization of fractured rock in support of in-situ coal gasification field experiments, followed by work on fracture-related blasting, highwall and portal stability issues for Anaconda Minerals subsequent to moving into development of fractured reservoirs for the ARCO Oil & Gas Company. In 1992, Paul joined Golder Associates in Seattle, Washington as part of the FracMan Technology Group, helping to develop software, technology and consulting services in fractured rock for the petroleum, mining and nuclear waste industries, working on a wide variety of projects throughout the world. Dr. La Pointe is currently a Principal of Golder Associates and the Senior Practice Leader for Upstream Consulting in the Oil & Gas industry. He has co-authored or edited four books on the mathematical characterization and modeling of fractured rock and other complex heterogeneous rock systems, as well as having published more than one hundred papers and abstracts related to the characterization and engineering of fractured rock. He has served on the editorial board of the Interna- tional Journal of Rock Mechanics and Mining Sciences since 1983, and is a former member of the Board of Directors for ARMA. He has taught courses on the mathematical and statistical characterization of complex system for AAPG, ARMA, SPE, OGCI, GSA, CSEG and the University of Washington, and been a member of several Peer Review and Expert panels for the Yucca Mountain and WIPP projects.

37 46th US Rock Mechanics/Geomechanics Symposium ab stract table of contents

Session 1: Geomechanics of Reservoirs and Caprocks ...... 40 Session 2: Coal Mine Strata Behavior - I ...... 43 Session 3: Geothermal & Hydrothermal Processes in Rock ...... 46 Session 4: Novel Testing Techniques ...... 49 Session 5: Geomechanics Modeling of Hydraulic Fracturing in Fractured Shale Reservoirs ...... 51 Session 6: Support and Reinforcement in Hard Rock Mining - I ...... 54 Session 7: Influence of CO2 on Physical Properties ...... 57 Session 8: Time and Environment-dependent Behavior ...... 60 Session 9: Shale, Sand and Chalk Behavior Around Wellbores and Perforations ...... 63 Session 10: Rock Mass Excavation and Deformation ...... 66 Session 11: Challenges in Numerical Modeling ...... 68 Session 12: Acoustic Emission ...... 71 Session 13: Numerical Modeling of Fractures in Unconventional Reservoirs . . . 74 Session 14: Drilling Mechanics ...... 76 Session 15: Modeling Anisotropy and Damage ...... 79 Session 16: Rock Mass Characterization ...... 81 Posters - Carbon Sequestration ...... 84 Posters - Drilling and Wellbore / Reservoir Geomechanics ...... 88 Posters - Stability and Support of Underground Openings ...... 96 Posters - Rock Properties and Rock Mass Characterization ...... 101 Session 17: Unconventional Reservoir Geomechanics ...... 107 Session 18: Coal Mine Strata Behavior - II...... 110 Session 19: Fluid Flow, Geomechanics and Geophysics of Cracked and Fractured Media ...... 113 Session 20: Failure Response ...... 116 Session 21: Production Geomechanics at the Sand Face ...... 119 Session 22: Support and Reinforcement in Hard Rock Mining - II ...... 122 Session 23: Carbon Sequestration on the Reservoir Scale ...... 124 Session 24: Heterogeneity in Rocks ...... 127 Session 25: Integration of Microseismic Monitoring into Natural and Hydraulic Fracture Characterization in Shale Reservoirs ...... 130

38 46th US Rock Mechanics/Geomechanics Symposium Session 26: Stability and Support of Caverns and Tunnels ...... 133 Session 27: Rock Fall and Slope Analysis ...... 136 Session 28: Mapping and Imaging ...... 139 Session 29: Modeling of Hydraulic Fracture Interactions in Naturally Fractured Formations ...... 142 Session 30: Advances in In Situ Stress Determination ...... 145 Session 31: Discrete Simulations in Geomechanics ...... 148 Session 32: Static & Dynamic Response of Rocks ...... 150 Posters - Formation Characterization and Mechanical Earth Modeling ...... 153 Posters - Numerical, Analytical and Constitutive Modeling ...... 157 Posters - Slope Stability and Open Pit Mining ...... 163 Posters - Fracture Mechanics and Fracture Flow ...... 168 Posters - In Situ Stresses ...... 173 Session 33: Classic and Novel Wellbore Stability Evaluation ...... 176 Session 34: Surface Mine Pit Slope Stability ...... 179 Session 35: Fracture Processes and Testing ...... 182 Session 36: Fluid Flow & Deformation in Porous Media: Connecting Micro- and Macro- scale Properties ...... 185 Session 37: Monitor ing of Hydraulic Fracturing in Unconventional Reservoirs ...... 188 Session 38: Behavior of High Porosity Materials ...... 191 Session 39: Numerical Modeling of Crack Growth ...... 193 Session 40: Fluid-induced Stabilization and Destabilization of Fractures and Faults ...... 196 Session 41: Inter action of Natural and Induced Fractures and Stimulated Reservoir Volume ...... 199 Session 42: Case Studies in Hard Rock Mining ...... 202 Session 43: Applications of Numerical Modeling ...... 204 Session 44: Transport and Coupled Processes in Natural Fractures and Along Interfaces ...... 207

39 46th US Rock Mechanics/Geomechanics Symposium Ses s ion 1: Geomechanics of Reservoirs and Caprocks Monday, 25 June, 8:00 am – 9:30 am Chairs: Alvin Chan, Maria Nikolinakou

ARMA 12-327 Geomechanical Evaluation for Short Term Gas Storage in Depleted Reservoirs Khaksar, A., White, A., Rahman, K. and Burgdorff, K. Baker Hughes Inc., Perth, Western Australia, Australia Ollarves, R. Santos Ltd, Brisbane, Queensland, Australia Dunmore, S. MD Energy Pty Ltd, Perth, Western Australia, Australia ABSTRACT: Depleted hydrocarbon reservoirs are attractive targets for short term gas storage with frequent injection and production cycles. Optimum well completion and injection-storage-production design in depleted reservoirs would require understanding of important rock mechanics issues. These include drilling and completion challenges of new wells in low pressure reservoirs accounting for potential rock fatigue due to cyclic injection/depletion and loading and unloading, determination of maximum sustainable storage pressures that would avoid fracturing and fault reactivation. This paper describes a case study from a coal seam gas project considered for a liquefied natural gas plant in Australia and demonstrates a systematic approach for geomechanical risk assessments for short term gas storage in depleted sandstone reservoirs. Geomechanical analyses show that despite a low fracture gradient in depleted reservoirs and the presence of non-depleted overburden rocks, new high angled wells can be drilled safely with a relatively low mud weight in the non-depleted sections and with air in the reservoir section. Fracturing and faulting assessments confirm that the critical pressures for fault reactivation and fracturing of intact rocks are beyond the planned storage pressures and a maximum pressure of 200-300 psi beyond the initial reservoir pressures may be possible from fracturing or fault reactivation aspects. Sand production prediction evaluations indicate that new injection-production wells can be completed with no downhole sand control due to a very low risk of sanding even after considering rock weakening associated with cyclic loading.

ARMA 12-145 Modeling stress development and fault slip in producing hydrocarbon reservoirs overlain by rock salt caprocks Orlic, B. and Wassing, B.B.T. TNO, Earth, Environmental and Life Sciences, Utrecht, The Netherlands ABSTRACT: Geomechanical simulations were conducted to study the effects of depletion-induced stresses on fault stability in gas reservoirs overlain by elastic and viscoelastic salt caprocks. We used a synthetic disk-shaped faulted reservoir model which resembles the structure of a gas field in the Northern Netherlands that experienced induced seismicity during gas production. Simulations indicate that the fault area most sensitive to fault reactivation is located at juxtaposition of reservoir blocks across the fault where the degree of overlap between the blocks is less than 50%. Location of the reactivated zone predicted by numerical modeling is in accordance with the seismological localization of epicenters of past production- related seismic events. Initial isotropic state of stress in salt caprock before depletion, and viscoelastic salt relaxation processes during and after reservoir depletion, affect initial stress state and evolution of depletion-induced stresses around the reservoir. High horizontal stresses in salt caprock in combination

40 46th US Rock Mechanics/Geomechanics Symposium

Client: Gibson Group – Wayne Gibson Size 5.5 x 8.5h NO bleed Proof # 4 Date: JUNE 14, 2012 Colours: Black/0 Approved: File: 5268 GIBSON ARMA2012 Program GUTS Line Screen: 150 Fonts: Bliss, Helvetica Neue with lower stresses in the reservoir beneath it promote opening of reservoir-bounding faults and easy reactivation during depletion. Fault zones along the interface between the reservoir and salt caprock may already be critically stressed before depletion and are likely to be reactivated in early stages of production.

ARMA 12-139 Evaluation of Caprock Stability by Coupled Modeling of Geomechanics and Reservoir Simulation under Steam Injection for Producing Oil Sands Reservoirs Chin, L.Y. ConocoPhillips Company, Houston, Texas, USA Tomberlin, T.A. ConocoPhillips Canada, Calgary, Alberta, Canada Ramos, G.G. ConocoPhillips Company, Bartlesville, Oklahoma, USA Chalaturnyk, R.J. University of Alberta, Edmonton, Alberta, Canada ABSTRACT: Producing bitumen from oil sands reservoirs by steam injection will increase reservoir pressure that can change stress states and induce deformations in the reservoir and its surrounding formations, in particular the caprock overlying the reservoir. Caprock failure may lead to steam release to the overlying aquifers or to surface, that can cause significant economical, environmental, and safety impacts on field production operations. We developed a coupled model for evaluating caprock stability in the SAGD process by integrating a geomechanical model and a thermal reservoir simulator. The developed model was validated by predicting surface heave data measured from interferometric synthetic aperture radar (InSAR) images. The validated model was employed to evaluate caprock stability over a wide range of geological and geometric descriptions and steam injection conditions for SAGD field productions. For cases evaluated, safety factors were calculated to quantify the potential caprock instability induced by tensile or shear failure mechanism during steam injection. The possible ranges of safety factors are predicted by the model under various steam injection conditions.

ARMA 12-198 Trajectory Optimization for Offshore Wells and Numerical Prediction of Casing Failure Due to Production-Induced Compaction Shen, X., Bai, M., Standifird, W., Mitchell, R. Halliburton, Houston, Texas, USA

ABSTRACT: In the past, trajectory optimization of a wellbore referred to the design of a well path, including a preferred geostress direction and fault structure, to maximize the penetration rate. This paper considers additional parameters during the trajectory optimization process: pore pressure depletion history, creep property of rocks, and interaction between rock and casing during petroleum production. After considering these additional parameters, a wellbore trajectory can be designed that will be easier to drill and will ensure the longevity of casing utility. A numerical example of casing and wellbore trajectory design in the Ekofisk petroleum field was performed to evaluate the suitability of this trajectory design technique. Seabed subsidence was simulated at the global level with a full field perspective, and casing failure was calculated at a secondary submodel level at the reservoir scale. Inelastic-visco deformation of

41 46th US Rock Mechanics/Geomechanics Symposium

Proof # 4 Approved: the reservoir and fluid flow in porous media was calculated. Three sets of numerical results were analyzed to select the optimal wellbore trajectory. The primary submodel and secondary submodel were balanced during the optimization process such that a fine mesh can be adopted for casing failure prediction within the background of the field scale phenomenon.

ARMA 12-669 Overburden Stability under Varying Pressure Loading Zhang, Z., Wang, J., and Yale., D.P. ExxonMobil Upstream Research Company, Houston, TX, USA ABSTRACT: This study employs analytical and numerical methods to investigate overburden stability (and in particular caprock integrity) for fields with repeated five-spot injector-producer pattern during an injection/production petroleum recovery process in a shallow reservoir environment (<400m depth). Both simplified “pancake” model and more complicated model with real geological variation are studied. First, key parameters influencing cap rock integrity are identified, and their reasonable representative range of variation obtained. Finite element models are carried out to study bending and shearing stresses developed in the rock as pressure between injector and producer varies. Weak spots in overburden are identified, and various strength criteria are employed, including tensile and shear failure criteria, to ensure safety margin. An extensive parametric study is carried out to evaluate practical range of overburden thickness and mechanical property for safe field operation of injection and production processes in shallow reservoirs.

ARMA 12-518 An Explanation for Anomalous Time Dependent Subsidence Mossop, A. Shell / NAM, 9400 HH Assen, The Netherlands ABSTRACT: The onset of surface subsidence in response to fluid extraction from subsurface reservoirs, often exhibits an apparent delay, with lag times on the order of years. More recently, geodetic monitoring above reservoirs from which fluid production has ceased appears to show subsidence continuing for a number of years afterwards. Such a time lagged response is consistent with problems of the non-equilibrium/ diffusive class. Specifically, the reservoir appears to follow a time decay volume strain behaviour. These observations are not consistent with simple reservoir pore pressure diffusion. This presentation describes a novel explanation for the anomalous time dependent subsidence phenomenon. It is based on the realisation that the generally applied nucleus of strain concept which assumes correspondence between poroelasticity and thermoelasticity is not strictly true and that a bulk stiffness formulation is more appropriate. This means that the mean volume strain of the reservoir is far more sensitive to details of the pore pressure distribution (cf. Hashin-Shtrikman theory) than is typically modeled. Such details would have little impact on subsidence for cases where reservoir permeability is uniform, which is the assumption for the standard derivation of the pressure diffusion equation. However, permeability in real rock is typically observed to have a heavy-tailed distribution (e.g. log-normal, Lévy, etc.) and global equilibrium proceeds much more slowly than uniform diffusivity measures would predict.

42 46th US Rock Mechanics/Geomechanics Symposium Ses s ion 2: C oal Mine Strata Behavior - I Monday, 25 June, 8:00 am – 9:30 am Chairs: Sam Spearing

ARMA 12-137 Horizontal stress related failure in bedded mine roofs—insight from field observations and numerical models Esterhuizen, G.S. Bajpayee, T.S. Office of Mine Safety and Health Research, National Institute for Occupational Safety and Health Pittsburgh, Pennsylvania, United States of America ABSTRACT: As part of a project to develop improved roof support strategies, numerical model analyses were conducted to better understand horizontal stress related failure of bedded roof rocks. Detailed numerical models were used to simulate the bedded roof rocks, failure initiation in individual beds, and the progression of failure under increasing horizontal stress. The studies showed that classical beam theory is useful for understanding the general response and potential failure of bedded rock. The initial curvature of the rock laminations and the relatively stiff end-loading conditions in a mine roof appear to limit the potential for sudden catastrophic buckling of roof beds in the situations modeled. “Cutter” type roof failure near the excavation corners was more likely to occur in the models when the lamination interfaces were weaker and less stiff. A ground response curve developed from numerical model results indicated that support pressures would have to be impractically high to prevent horizontal stress related failure of the roof rocks from taking place in a laminated roof.

ARMA 12-167 Calibration of FLAC3D to Simulate the Shear Resistance of Fully Grouted Rock Bolts Tulu, I.B. West Virginia University (WVU) Mining Engineering Department, Morgantown, WV, USA Esterhuizen, G.S. National Institute for Occupational Safety and Health (NIOSH), Pittsburgh, PA, USA Heasley, K.A. West Virginia University (WVU) Mining Engineering Department, Morgantown, WV, USA ABSTRACT: The resistance to lateral shearing is an important yet poorly understood component of the reinforcement provided by fully grouted rock bolts. Numerical models such as the FLAC3D finite difference code can be used to investigate the effect of shear resistance on roof stability. However, calibrating a numerical model to realistically simulate the complex processes that occur at the shearing interface can be challenging. This paper outlines recent work in which a systematic procedure was developed to match numerical model results to the measured shear response of fully grouted rock bolts. In this paper, results of the shear tests of reinforced rock joints published by Haas [1] and McHugh and Signer [2] were modeled with FLAC3D to identify and calibrate the critical parameters of the rock bolt model both in tension and in shear. In particular, the model response to changes of the bolt/joint angle and the surrounding rock type were calibrated and compared with the published tests results. It was found that the structural pile element in FLAC3D can be used to accurately represent grouted bolt shear and tensile behavior. The best ap-

43 46th US Rock Mechanics/Geomechanics Symposium proach to calibrate the FLAC3D structural pile element model was found to be: 1) select the structural element segment size less than half of the active length, 2) calibrate the shear spring cohesion and stiffness based on pull test results, and 3) calibrate the normal spring cohesion and stiffness based on shear test results. Using this method, the calibrated model results fit the test results very well.

ARMA 12-184 Increased Transfer Mechanics of PC-Strand for Mining and Civil Applications Tadolini, S.C. Minova International, Bowerston, OH, USA Defossez, S. NV Bekaert SA, Belgium ABSTRACT: PC-Strand tendons or Prestressed Concrete (PC) strands, commonly referred to as cable bolts, have become a major rock reinforcement device for underground mining and civil applications. The most common configuration is a 1+6 strand designates a center king-wire, with 6 outer wires wound around it to form a 15 mm (0.6 in) diameter cable. The capacity of which approaches 30 tons but the performance is largely dependent on the anchorage medium and the ability of the system to transfer stresses back into the rock mass while reinforcing and suspending the immediate roof. Recent developments to improve the transfer mechanisms of the PC-strand via the anchorage medium by imprinting the individual wires with uniquely designed deformations. These deformations have resulted in improved anchorage and subsequent cable bolt performance. This paper will describe the numerical modeling simulations that were undertaken to refine and optimize the designs that were evaluated in a series of laboratory and field experiments. The indented PC-strand is being introduced to underground coal mines for several different ground control applications.

ARMA 12-Paper 220 Assessment of Mine Subsidence in an Area with a Major Pillar Crushing Event – Newcastle, Australia Knott, D. L., PE, Associate Geotechnical Engineer Coffey Geotechnics Pty Ltd, Warabrook, NSW, Australia Baker, S. Geotechnical Engineer Coffey Geotechnics Pty Ltd, Warabrook, NSW, Australia Ditton, S., Principal Geotechnical Engineer Ditton Geotechnical Services, Charlestown, NSW, Australia Love, A., Senior Principal Coffey Geotechnics Pty Ltd, Warabrook, NSW, Australia ABSTRACT: This paper demonstrates the use of historical and ‘new’ information to develop a model for pillar strength and subsidence analyses using empirical and numerical methods. The subsidence assessment was for a 4ha (10 ac) multi-storey redevelopment site along Newcastle Harbour. The 6m (20.3ft) thick Borehole Coal Seam was mined using the room and pillar method in the 1880’s and 1890’s, approximately 70m (230ft) beneath the harbour. The mined height was approximately 5m (16ft) and the pillars were approximately 5.5m (18ft) wide; thus, resulting in marginally stable pillars. Soon after mining was completed in one area in 1896, pillar failure occurred. It probably failed due to the fall of the 1.2m (4ft) thick roof coal layer, which had been left inplace, further increasing the height of the pillars. An approximately 25ha (60 ac) crushed area with up to 1.2m (4ft) of trough subsidence resulted. The workings were not flooded and the colliery closed in 1905 and allowed to flood. The investigation targeted pillars with boreholes to assess their condition and coal thickness. A downhole geophysical survey was also performed to confirm the coal thickness. The amount of crushing was

44 46th US Rock Mechanics/Geomechanics Symposium determined by comparing the coal thickness in a borehole in a pillar with the thickness of coal in a borehole in an unmined location. The site is within a Mine Subsidence Board (MSB) district and the MSB is the referral authority for any improvement. In order to gain approval for development, it is necessary to; Demonstrate the risk of subsidence in the future is acceptable; and / or should subsidence occur, the resulting damage is acceptable and safe, serviceable and repairable; or Reduce the risk of subsidence by stabilization. The stability of pillars was assessed using numerical modelling with LaModel. The model was calibrated and predicted that when the unmined roof coal falls, the pillars fail, fitting the historical records. Subsidence was estimated with the Surface Deformation Prediction System (SDPS) program. The subsidence associated with the crush was modelled and a model was developed assuming future crushing in areas with uncrushed or partially crushed pillars. Potential future subsidence was determined by subtracting the subsidence associated with the crush from the worst case crushing. To mitigate potential subsidence impacts, grouting is planned to strengthen the pillars by providing confinement and reducing their effective height.

ARMA 12-320 Assessment of Subsidence Risk for Mine Mitigation Beneath Critical Pipeline and Utility Corridors Hanna, K., Hodges, S., and Pfeiffer, J. Zapata Incorporated, Golden, CO, USA Heasley, K. West Virginia University, Morgantown, WV, USA ABSTRACT: A multi-phase geotechnical and geophysical mine subsidence investigation was conducted at an abandoned coal mine site in the western U.S.A. The mine lies at depths ranging from 15 to 27.4 m (50 to 90 ft), and it is overlain by critical pipeline/utility corridors containing high pressure water, fiber optic, gas, and petroleum lines. Any future subsidence/sinkhole occurring beneath or adjacent to the corridors could pose a significant threat to the structural integrity of the pipelines leading to the nearby power plant. This paper describes the investigation with a variety of techniques, including: 1) surface seismic multi-channel analysis of surface waves (MASW) and seismic reflection techniques identifying mine working anomalies; 2) exploratory drilling confirmation and rock/coal sampling; 3) downhole laser and video camera void mapping; 4) geotechnical evaluation for determining subsurface ground/mine workings conditions, degree of failure/failure modes, and relative subsidence risk levels; and 5) LaModel numerical modeling analysis for determining potential subsidence/sinkhole areas. A summary of significant results with emphasis on high risk zones identification and mitigation strategy is presented.

45 46th US Rock Mechanics/Geomechanics Symposium Ses s ion 3: Geothermal & Hydrothermal Processes in Rock Monday, 25 June, 8:00 am – 9:30 am Chairs: Wen-lu Zhu, Herbert Einstein

ARMA 12-316 Stiffness and Deformation of Salt Rock Subject to Anisotropic Damage and Temperature-Dependent Healing Xu, H. and Arson, C. Texas A&M Center for Tectonophysics Zachry Department of Civil Engineering, Texas A&M University, College Station, Texas, USA. Chester, F. M. Texas A&M Center for Tectonophysics Department of Geology & Geophysics, Texas A&M University, College Station, Texas, USA. ABSTRACT: This research is motivated by the increasing need for geostorage facilities, mainly: nuclear waste disposals, high-pressure gas reservoirs and carbon dioxide sequestration systems. A new constitutive model is formulated to account for anisotropic damage due to tensile cracks and healing due to Diffusive Mass Transfer (DMT). The damage variable is the difference between the second-order crack density tensor and a scalar viscoplastic healing variable. The viscoplastic healing variable is needed to model the effects of DMT on the reduction of damage-induced deformation. Contrary to the damage and healing models proposed previously for salt rock, the proposed framework accounts for crack-induced anisotropy, and anisotropy is treated in both damage and healing evolution laws. Compression, extension and compression loading and unloading cycles have been simulated with Theta-Stock Finite Element code. The results illustrate well the influence of anisotropic damage on stiffness degradation and residual strain development. An algorithm has also been written to study the trends of the coupled damage and healing model for a stress path comprising an isotropic compression, and axial compression, a healing period and an unloading phase. The results match the theoretical expectations, and show that the proposed model can predict anisotropic damage and healing.

ARMA 12-329 Thermo- Hydro-Mechanical Properties of Lindsay Limestone: A Candidate for Nuclear Waste Repository in Canada Nasseri, M.H.B Department of Civil Engineering, University of Toronto, Toronto, Ontario, Canada Goodfellow, S. Department of Civil Engineering, University of Toronto, Toronto, Ontario, Canada Wanne, T. Nuclear Waste Management Organization, Toronto, Ontario, Canada Young, R.P. Department of Civil Engineering, University of Toronto, Toronto, Ontario, Canada ABSTRACT: The results of the coupled THM experiments obtained within a triaxial geophysical imaging cell on Lindsay limestone, a candidate for a deep geological repository site, suggest that the specimens tested at higher temperatures are characterized with the higher strength and deformational properties and heating does not cause strength weakening. The evolution of seismic wave velocities with temperature under hydrostatic and deviatoric stress increments reflects the effect of thermal pressurization during heating stages and at the time of axial microcracks formation prior to failure strength of the tested specimens at 50, 100 and 150 oC. Lindsay

46 46th US Rock Mechanics/Geomechanics Symposium limestone shows a constant thermal pressurization rate of ~0.21 MPa/oC and a linear thermal dilatational coefficientα = 3 to 3.5 × 10-5) during THM experiments heated up to 100 and 150 oC. All specimens show a systematic decrease of permeability (k) as a function of heating and deviatoric stress increments followed by an increase in k values responding to fracture initiation and propagation parallel to σ1 direction prior to failure. This study shows that there exists a self-consistent behaviour among the evolution of seismic wave velocities with heating, deviatoric stress increments, deformational pattern and transport properties of the tested specimens at various stages of THM experiments.

ARMA 12-415 Deformation and Failure Properties of Newberry Welded Tuff Wang, J., Jung, W., Ghassemi, A. Texas A&M University, College Station, Texas, USA ABSTRACT: In this paper we present the results of a testing program to characterize the rock mechanical properties of welded tuff from Newberry Volcano. The rock samples are from drill core obtained from the well GEO-N1 on the western flank of Newberry Volcano taken from a depth of 4013 ft depth from the surface. As part of the rock characterization process, petrographic thin sections of welded tuff were prepared and used to describe rock texture and mineralogy. High resolution X-ray CT scanner was also used to provide 3D images of the rock pore structure. Rock permeability and porosity were measured using a pulse permeameter. Furthermore, triaxial compression tests were performed to determine Young’s modulus, Poisson’s ratio, and the failure envelop for the rock samples. The relationship between petrophysical, mechanical, and failure properties are discussed.

ARMA 12-427 Effect of Temperature on Yielding Behavior of Carbonate Rocks Lisabeth, H. P. University of Maryland, College Park, Maryland, USA Watter, K.E. and Zhu, W. University of Maryland, College Park, Maryland, USA ABSTRACT: Knowledge of temporal and spatial variations in fluid flow, which is of critical importance to resource recovery, requires better understanding of the changes and the rates of changes of permeability and porosity at reservoir conditions. Permeability and porosity are dynamic physical properties that are sensitive to mechanical and thermal loads. With increasing pressure and temperature, rocks undergo a transition in failure mode from localized brittle failure to non-localized plastic flow. However, the mechanisms (i.e., microcracking, crystal plasticity, pressure solution etc.) that control the brittle-ductile transition and their dependence on temperature are not well-understood. In this study, we deformed porous Indiana limestone samples with initial porosity of ~16% at temperatures of 298, 323 and 348 K under effective pressures ranging from 10 to 50 MPa. In each deformation test, pore fluid (distilled water) pressure and strain rate were kept constant at 10 MPa and 1x10-5/s. We use strain gauges and a pore pressure intensifier to track volumetric strain and the pore volume change during deformation. Simultaneous changes in permeability and sonic velocity were measured in a subset of samples. In comparison to dry samples, our data show lower yield strength and enhanced compaction in water-saturated samples, and these effects are exacerbated at elevated temperature. The initial yield envelopes (in the differential versus effective mean stress domain) indicate a strong temperature-dependence of yield strength. Furthermore, the shape of a yield envelope changes considerably with increasing temperature, indicating a transition in dominant deformation mechanisms. Initial microstructural analysis shows that both dilatant microcracking and mechanical twinning play important roles in deformation. We suggest that the increased water-weakening at elevated temperatures results from the interplay among microcracking, crystal plasticity, and likely solution transfer.

47 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-472 Thermo-Hydro-Mechanical Behavior of a Low Permeability Geomaterial Najari, M. Graduate Student, Department of Civil Engineering and Applied Mechanics, Montreal, QC., Canada Selvadurai, A.P.S. William Scott Professor and James McGill Professor, Department of Civil Engineering and Applied Mechanics, Montreal, QC., Canada ABSTRACT: In this paper coupled thermo-hydro-mechanical behaviour of a cylindrical sample of Stanstead Granite containing a fluid inclusion is studied. The sample was immersed in a hot water bath and the time-dependent temperature change and pore pressure change within the cavity were measured. The experiment was repeated by subjecting the surface of the cylindrical sample to cooling, which resulted in the development of negative cavity pressure. This test was repeated for six cycles and hysteresis behaviour of the cavity pressure generation was examined under the described THM test procedure. The finite element code COMSOL MultiphysicsTM was used to model the interaction of temperature change, porous skeleton deformation and pore pressure change in the conducted experiments. The model includes the compressibilities of the porous skeleton, the solid grains and the fluid.

ARMA 12-605 Residual Conductivity of a Bauxite-Propped Geothermal System- Influence of Self-Propping, Time, and Closure Stress Stoddard, Trevor Dept. of Chemical Engineering, University of Utah, Salt Lake City, Utah, USA McLennan, J.D. Dept. of Chemical Engineering, and Energy and Geoscience Institute, University of Utah, Salt Lake City, Utah, USA Moore, Joseph Energy and Geoscience Institute, University of Utah, Salt Lake City, Utah, USA ABSTRACT: Enhanced Geothermal Systems (EGS) are geothermal resources that are developed through hydraulic stimulation. Inadequate permeability and production from natural fractures and pores can be overcome via injection of cold water below fracturing pressure, by conventional hydraulic fracturing, or by some cyclic combination of these processes. At low injection rates or where thermal fracturing is being exploited, shearing of pre-existing weaknesses and potentially developing virgin fractures is envisioned to provide permeable, self-propped pathways. Alternatively, injection at pressures substantially above the minimum principal stress can also hydraulically connect, reopen, or create fractures and also possibly induce shearing (as known from microseismic monitoring). The heat from this artificially fractured reservoir is subsequently transferred to the injected fluid and extracted through a production well. Conventional steam turbines or binary cycle power plant can be employed for electric generation. The technical challenges in developing EGS reservoirs are substantial and include controlling fracture direction and morphology, establishing an adequate heat transfer surface area, and maintaining conductivity. The latter was the focal point of investigation. It is commonly assumed that that the induced fractures will fail by shear and be self-propping. If tensile fractures are generated, they need to be explicitly held open by proppant (and it needs to be ensured that the proppant is not produced back into the wellbore). The conductivity of bauxite propped fractures over extended periods of time and at elevated temperatures were measured in laboratory tests in order to assess the temporal and thermal dependency of conductivity in a typical surrogate fracture.

48 46th US Rock Mechanics/Geomechanics Symposium Ses s ion 4: N ovel Testing Techniques Monday, 25 June, 8:00 am – 9:30 am Chairs: Euripides Papamichos, Marte Gutierrez

ARMA 12-161

Forward and inverse modeling of laboratory tests on CO2 injection in porous rocks Chen, T., Katsuki, D. and Gutierrez, M. Colorado School of Mines, Golden, CO 880401, USA ABSTRACT: This paper discusses applications of forward and inverse modeling techniques to immiscible two-phase fluid flow in porous medium observed in a laboratory test in which supercritical CO2is injected into rock core sample initially saturated with saline water. The relative permeability curves of rock sample are assumed to be describable by polynomial functions of CO2 saturation. The Brooks-Corey capillary pressure model is used to represent the capillary pressure curve of rock sample. A good agreement between estimated and experimental curves indicates that inverse analysis using second-derivative method can estimate a parameter value set providing appropriate relative permeability curves.

ARMA 12-561 Intermediate stress effect in reverse: strength anisotropy Meyer, J.P. and Labuz, J.F. Department of Civil Engineering, University of Minnesota, Minneapolis, MN, U.S.A. Lin, Q. Department of Energy and Resources Engineering, College of Engineering, Peking University, Beijing, P.R. China ABSTRACT: Because rock is typically sampled in the form of a right circular cylinder, it is convenient from a laboratory testing perspective to produce failure by the application of an axi-symmetric state of stress called triaxial compression, where the major principal stress σI= σa the axial stress, and the intermediate and minor principal stresses σ I >σ II = σ r the radial stress. For isotropic rock, compression testing σ I >σ II = σ III leads to a conservative estimate of strength parameters, as opposed to triaxial extension, where σ I >σ II = σ III. However, it is shown that even though a rock may exhibit only slight (< 10%) elastic anisotropy, anomalous behavior can occur in strength testing such that a “reverse” intermediate stress effect appears.

ARMA 12-650 Split-platen Compression Test: Development and Use Fry, M. F. Colorado School of Mines, Golden, CO, USA* Hustrulid, W. A. Veradale, WA, USA ABSTRACT: A method of experimental measurements for post-yielding behavior is to measure the distribution of boundary stresses in materials under compression. To date, there is one type of testing method used to measure boundary stress distributions for homogeneous and isotropic materials. This testing method is referred to as the split-platen compression test. The method used for this test involves placing a cylindrical sample of material between a set of eight concentric steel rings and the solid platen of a compression testing

49 46th US Rock Mechanics/Geomechanics Symposium machine. Strain gauges are bonded to the outer surface of the rings, and strain measurements are taken while the sample is loaded by the testing machine. The readings are then reduced into axial stresses at the interface between the rings and the sample. Careful investigation of the axial stresses calculated from the split-platen measurements show that they are inaccurate by a significant amount. It is demonstrated with a finite element analysis that the rings of the split- platen are bending during the experiment because of the friction at the ring-sample interface. This bending of the rings influences the strain measurements, resulting in the inaccurate calculation of axial stresses. Based on this hypothesis, a new split-platen apparatus is developed to compensate for bending, allowing for a better calculation of the axial stresses and the additional calculation of the shear stresses at the ring-sample interface. New split-platen compression tests are conducted on samples of concrete material to validate the method used to reduce the strain measurements into stresses at the ring-sample interface. This method involves the development of ring stress equations based on results from a finite element analysis performed on each ring of the new split-platen apparatus. For the experiments with the concrete samples, the calculation of stresses from the measured strain readings demonstrates excellent results showing nonuniform distributions of axial and shear stresses as a function of axial shortenin.

ARMA 12-492 Numerical simulation for layered rock under Brazilian test Liu, W. C. and Tien, Y. M. Department of Civil Engineering, National Central University, Taiwan No. 300, Jungda Rd., Chunli City, Taoyuan County 320, Taiwan Juang, C. H. Department of Civil Engineering, Clemson University, Lowry Hall, Box 340911, Clemson SC 29634, USA ABSTRACT: This paper presents the results of the numerical simulation of the failure process, failure modes and tensile strength of layered rock. This paper employs 2-D Particle Flow Code (PFC2D) to simulate layered rock models for different inclination angles that varies between 0° to 90° under Brazilian test. Based on the numerical simulation results, the effect of inclination angle plays an important role in the tensile strength and failure mode of layered rock. The tensile strength of layered rock decreases with the increase of the inclination angle. The failure of simulated layered rock with varied inclination angles under Brazilian test is classified into three modes: (a) split across layer when the inclination angle is 0° to 45°, (2) split along layer when the inclination angle is 60° and 90°, and(3) mixed mode could be observed for  = 75 °. Besides, the numerical simulation results agree well with the experimental data from other investigators, in terms of failure modes.

ARMA 12-656 Permeability Measurement with Ultra-High Fluid Pressure and Unequal Stresses Ewy, R.T., Bovberg, C.A., Hagin, P.N. and Shalz M.L. Chevron Energy Technology Co., San Ramon, CA and Richmond, CA, USA ABSTRACT: Permeability is commonly assumed to be a function of effective stress, which considers only the difference between stress and fluid pressure. This approach allows permeability to be measured with very low values of fluid pressure in the laboratory. However, it is likely that permeability at high stress and high fluid pressure will be different than permeability at low stress and low fluid pressure, even for the same effective stress (stress minus fluid pressure). This is because pore pressure may influence permeability differently than confining stress. To test this, we developed a system to measure permeability along the axis of a rock sample, for which axial stress, confining stress, and fluid pressure can all be varied independently, and with fluid pressures approaching 138 MPa (20,000 psi). The highest stress is orthogonal to flow, to duplicate conditions that are

50 46th US Rock Mechanics/Geomechanics Symposium important for reservoir production. We present results from several consolidated reservoir sandstones, showing that the effective stress coefficient for permeability is less than or equal to one over a large range of stress and pressure conditions, but that it can exceed one when pore pressure is high and effective stress is low.

ARMA 12-204 Impact of coal microstructure on the development of failure process Zhao, Y.X. and Jiang, Y.D. State Key Lab of Coal Resources and Safe Mining, China University of Mining and Technology, Beijing, China State Key Laboratory for Geomechanics and Deep Underground Engineering, China University of Mining and Technology, Beijing, China Han, J.L. and Xu, D. School of Mechanics and Civil Engineering, China University of Mining and Technology, Beijing, China ABSTRACT: This paper presents a numerical study on the failure process of coal sample under uniaxial loading condition. Our approach combines X-ray micro-computed tomography (microCT) imaging with micro- finite difference analysis (micro FDA). The three-dimensional images of a coal sample before compression were acquired by microCT scanner to create finite difference model. Finally, the FLAC3D software was employed to calculate the deformation features. The model was used to examine the effects of microstructures in coal on compressive failure process by studying the stress distributions and material deformation. Results indicate that the nature of internal material distribution in coal sample affect failure features greatly.

Ses s ion 5: Geomechanics Modeling of Hydraulic Fracturing in Fractured Shale Reservoirs Monday, 25 June, 11:00 am – 12:30 pm Chairs: Tom Bratton, Dan Moos

ARMA 12-196 Modeling Fractures with Continuum Damage and Its Numerical Application to Stimulation Estimates Shen, X. Halliburton, Beijing China ABSTRACT: In rock mechanics, the mechanical damage variable is interpreted as an index of material continuity, which varies from 0 for intact rock to 1 for completely separated broken rock. The volumetric density of cracks created by injection fluid can be represented by a scalar damage variable. A coupled calculation of hydromechanical problems with a 3D finite element method (FEM) is performed in this paper. This model was used to estimate stimulation measures of a horizontal well in a tight sand field. The parameter calibration of the proposed continuum damage model was performed with measured microseismic data of a fracture propagation under injection stimulation obtained from existing nearby well. A 3D damage evolution was calculated for a given injection fluid flow rate value. With the calibration of parameters, the numerically calculated distribution of the continuum damage variable within the formation, which represents both natural and induced fractures around the horizontal injection well for a specific injection pressure, closely correlates with the data measured by seismic monitoring. This calibrated continuum damage model was used to predict the fracture propagation

51 46th US Rock Mechanics/Geomechanics Symposium resulting from an injection stimulation of a horizontal well in a tight sand formation. The numerical results for the distribution of mechanical variables, including continuum damage, pore pressure, and principal stress components, are analyzed and shown.

ARMA 12-275 Geomechanical Modeling of Hydraulic Fracture Initiation and Propagation in a Mechanically Stratified Geologic System Smart, K.J., Ofoegbu, G.I., Das, K. and Basu, D. Southwest Research Institute®, San Antonio, Texas, USA ABSTRACT: Fluid flow through rock is the fundamental process in several energy related areas including hydrocarbon exploration/production and enhanced geothermal energy production. Creating new fractures or reactivating pre-existing fractures through hydraulic fracturing is key to increasing reservoir productivity when the natural reservoir permeability is insufficient for economic fluid movement. This paper focuses on predicting the fracture potential of different lithologic layers in a mechanically stratified rock sequence by simulating the interplay between inelastic rock deformation and the stress state that results from a change in pore or fracture fluid pressure. The initiation and growth of inelastic deformation in a continuum model is used to simulate the initiation and propagation of hydraulic fractures, and distinguish between tensile and shear failure. Rock mechanical behavior is modeled with an elastic-plastic material model that uses a combination of continuum damage mechanics and classical plasticity theories to capture both the elastic and inelastic deformation and progressive degradation of elastic stiffness. Model results suggest that: (i) for our material properties and stress states, tensile failure predominates over shear failure; (ii) in the absence of near wellbore mechanical layering, higher stress anisotropy favors more discrete zones of inelastic strain than conditions of lower stress anisotropy; and (iii) weak, low permeability intervals close to the wellbore can substantially retard the growth of hydraulic fractures.

ARMA 12-516 Fluid Driven Rock Deformation via the Combined FEM/DEM Methodology Rougier, E., Knight E.E. Geophysics Team, Los Alamos National Laboratory, Los Alamos, NM, USA Munjiza, A. School of Engineering and Material Sciences, University of London, London, UK ABSTRACT: The combined finite-discrete element method (FEM/DEM or FDEM) has become a tool of choice for a whole range of problems involving fracturing and fragmenting solids. The key advantage of the FDEM is the introduction of finite displacements, finite strain based deformability models combined with a suitable material law; these are then merged with objective discrete crack initiation and crack propagation solutions that have a great deal of fidelity in reproducing complex fracture patterns and eventual fragmentation. So far, these are mostly limited to dry crack networks. Work is currently in progress at Los Alamos National Laboratory to incorporate fluid driven fracture processes into the FDEM. In this paper a novel ISF (Integrated Solid-Fluid) solver for fluid flow over crack manifolds has been developed as an integral part of this ongoing research effort. The future aim is to integrate this solver with FDEM fracture geometry with a view of modeling fluid driven fracture.

52 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-468 Stimulated Reservoir Volume by Hydraulic Fracturing in Naturally Fractured Shale Gas Reservoirs Ge, J. Energy and Environmental Research Center, University of North Dakota, Grand Forks, North Dakota, USA Harold Vance Department of Petroleum Engineering, Texas A&M University, College Station, Texas, USA Ghassemi, A. Harold Vance Department of Petroleum Engineering, Texas A&M University, College Station, Texas, USA ABSTRACT: The stimulated reservoir volume and permeability enhancement of tight sand and shale gas reservoirs after stimulation by hydraulic fracturing is of major interest to the petroleum and geothermal reservoirs. In this work, we build a 3D fracture model for a hydraulically induced fracture in an infinite reservoir, and investigate the response of the reservoir rock in the vicinity of the main fracture with reference to rock failure and permeability variation. In this model, the 3-dimensional fracture-induced stresses and pore pressure around the hydraulic fracture are estimated using an analytical approach. The response of the rock mass to the variations of pore pressure and in situ stress is calculated by considering the joint orientations and frictional properties, as well as a rock mass failure criterion. By considering the minimum required effective treating pressure and the pore pressure distribution due to stimulation by hydraulic fracturing, we estimate the extent of the slip zones around the main fracture. The stimulated reservoir volume can thus be calculated based on the predicted failure geometry around the injection zone. This is of interest in interpretation of micro-seismicity in hydraulic fracturing and in assessing permeability variation around a stimulation zone. The model can also be used to optimize the treating pressure for stimulation, as well as to assess the accuracy of more complex numerical models.

ARMA 12-403 3D Modeling of Natural Fracture Stimulation Using a Poroelastic Displacement Discontinuity Method with Slip Weakening Safari, M. R. Harold Vance Department of Petroleum Engineering, Texas A&M University, College Station, TX, USA Ghassemi, A. Harold Vance Department of Petroleum Engineering, Texas A&M University, College Station, TX, USA ABSTRACT: This paper presents the development and an application of a 3D poroelastic model for hydraulic stimulation of natural fractures while considering shear slip and dilation on preexisting fractures using a slip-weakening approach to fracture deformation. The model uses a coupled finite element/boundary element method to solve for stress, fracture displacements, fluid pressure and leak off to the matrix. Fractures are simulated by considering the nonlinearity of deformation in shear directions and linear behavior in normal direction. The linear slip weakening model is used to simulate the loss of frictional resistance to shear and the residual strength of the pre-existing fractures. Pressure-dependent leak-off is considered to help assess the rock response to injection. After theoretical descriptions and presentation of some aspects of model development, examples are presented to highlight the role of fracture deformation during injection with reference to induced micro-seismicity. Simulation of injection into a large fracture show that shear slip induced permeability enhancement and downhole pressure variations. However, there is lag time between the slip event and permeability change. On the other example effect of shear failure of natural fracture on hydraulic fracture studied and showed that how hydraulic stimulation can end up with shear failure on natural fracture.

53 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-597 Acoustic emission studies of hydraulic fracture evolution using different fluid viscosities Chitrala, Y., Sondergeld, C.H. and Rai, C.R. University of Oklahoma, Norman, Oklahoma, USA ABSTRACT: ABSTRACT: In the past decade, with the widespread commercialization of the shale plays, there is an increasing demand on the fracturing industry. Thus, it becomes important to understand and optimize the amount of horsepower and the fracturing fluids necessary for a fracturing job. We present, laboratory hydraulic fracturing experiments on Indiana limestone and Lyons sandstone using two different viscosity fluids (60 cP and 1000 cP oil). A uniaxial horizontal stress of 1000 psi was applied to control the fracture direction. The main objective is to understand the effect of fluid viscosities on hydraulic fracture propagation. We used the two techniques: microseismicity, to monitor the fracture propagation and scanning electron microscopy (SEM), to understand the fracture morphology. Spatial and temporal propagation of the fracture is observed along the maximum stress direction. Shear type fracture mechanisms are found to dominate. Lower pressurization rates and higher breakdown pressures are noted when 1000 cP oil is used. A fracture trace is visible on the plugs recovered in the fractured zone defined by the microseismic event locations. Thicker cracks are evident corresponding to increase in cumulative number of events recorded. SEM observations confirm the wider aperture at the injection point and the frequent occurrence of the terminations and bifurcations farther along the fracture front.

Ses s ion 6: Suppo rt and Reinforcement in Hard Rock Mining - I Monday, 25 June, 11:00 am – 12:30 pm Chairs: Rimas Pakalnis, Doug Milne

ARMA 12-158 Numerical Modeling of Rock Bolts Subject to Dynamic Loading Chen, L. -B. and Chen, G. and Sheng, G. University of Alaska Fairbanks, Fairbanks, AK, USA ABSTRACT: In this paper, the impact dynamics of rock bolts with passive friction control is modeled and analyzed. Numerical investigations are performed for the rock bolts with a frictional energy absorber, exemplified by the Roofex bolt of Atlas Copco, under various dynamic loadings. The results are compared with those from fully grouted rigid bolts. A general three-degree-offreedom lumped parameter dynamic model is developed for rock bolts with passive friction control. The studies indicate that without the frictional energy absorber, the bolts are highly susceptible to failure under dynamic impact loads, while the bolts with the frictional energy absorber significantly reduce this risk. The studies reveal that the frictional energy absorber of the rock bolt starts to slide under impact forces. However, the sliding behavior varies with impact speed and impact frequency. The investigation also discovers that detachment of rock bolt head from rock surface may occur under certain impact load, even though the loading on the surrounding rock is still within its elastic strength limit. The findings suggest that appropriate design of the frictional energy absorber is of importance for the optimal performance of the rock bolts subject to dynamic loading in a given rock formation.

54 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-259 Advances in Methods of Empirical Stope Design Milne, D. University of Saskatchewan, Saskatoon, Saskatchewan, Canada Pakalnis, R University of British Columbia, Vancouver, British Columbia, Canada ABSTRACT: Empirical methods in rock mechanics for stope design have evolved since they began to be widely applied in the early 1980s. This paper uses case studies to illustrate the effects of changes in graphical design techniques based on the Stability Graph and Span Graph, as well as changes to numerical design techniques based on the empirical m and s failure criteria. The Stability Graph and Span design techniques have evolved, primarily through changes to the design lines used to predict opening stability and dilution based on hundreds of case histories. The m and s based design methods have primarily changed based on changing the link between rock mass characterization and the m and s values used to calculate the factor of safety. A back analysis approach is often applied to numerical design methods using the m and s failure criteria. This makes it challenging to compare data from different case histories. Due to the difficulty in comparing case histories, changes to the m and s failure criteria have been based on the expertise and experience of a limited number of rock mechanics practitioners.

ARMA 12-288 Ground Support Strategies for Weak Ground Masses at the Turquoise Ridge Joint Venture, Nevada. *Sandbak, L. A., *Rai, A. R., *Howell, R. S., and *Bain, N. G. *Barrick Gold Corporation, Turquoise Ridge Joint Venture, Golconda, NV, USA ABSTRACT: The high grade Carlin-type gold ore at the Turquoise Ridge Joint Venture underground mine (TRJV) consists of disseminated gold in very weak and altered limestones, mudstones, and carbon rich clays. These sediments are typically highly faulted and sheared, and are often bordered by highly altered dacite dikes. The highest grade ore is typically the weakest, and ranges from the Very Poor to Poor rock category, as defined by the rock mass rating (RMR) of Bieniawski (1976). The combination of a low dipping ore body geometry, complex geology, and weak rock requires the undercut drift and fill mining method including the use of cemented rock fill (CRF). An important design criterion is to keep openings in weak rock as small as possible to prevent unraveling and minimize supplementary support and to insure a high strength and quality controlled CRF.

Typical ground support consists of friction bolts and wire mesh in both ore and waste, covered by shotcrete in long term mine openings. When these support elements are not adequate, support strategies may incorporate shotcrete and groutable spiling in ore topcuts. Additional support strategies for development drifts include cable bolting and shotcrete arches for rehabilitation, and crf “arches” as a replacement of weak rock masses around long term mine openings. Movement monitoring using cross drift and multiple position extensometers are used to monitor drift movement in problem areas, and are needed to quantify and validate computer modeling.

55 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-299 Laboratory and in situ investigations on the corrosivity of support systems Hadjigeorgiou, J. Lassonde Institute of Mining, University of Toronto, Ontario, Canada Dorion, J.F. Niobec Inc., St-Honoré, Québec, Canada Ghali, E. Université Laval, Québec City, Québec, Canada ABSTRACT: This paper presents the results from a 5 year laboratory and in situ investigation into the cause of corrosivity of rock support systems in underground hard rock mines. Long term in situ monitoring of corrosion was complemented by controlled investigations in corrosion chambers. During site visits, samples of corroded support units were collected from several mines and subsequently analyzed using S.E.M. and photomicrography. A series of controlled experiments in the corrosion chambers qualified and quantified the influence of minerals and rock deposits on the corrosion rate of steel and rock support.

ARMA 12-439 Discussion on Rebar and Shotcrete Composite Backfill Barricades with Focus on Past Failures Hughes, P. B. University of British Columbia, Vancouver, British Columbia, Canada Pakalnis, R. University of British Columbia, Vancouver, British Columbia, Canada Christman, P. Wolverine Mine, Yukon Zinc Corporation, Yukon, Canada ABSTRACT: The advantage of rebar and shotcrete composite backfill fences are the ease in construction, high strength and limited footprint within the mine. This paper discusses the critical aspects of design, the strength of the fence and the imposed load of the backfill. Construction of these fences is typically done by embedment and grouting of rebar within the walls, the construction of a rebar lattice, placement of adhering surface, and the spraying of the shotcrete to the desired thickness. The effect of each of these steps to the behavior of the fence is discussed from practical examples. The effect of the placement of backfill from the point of imposed loads on the barricades is investigated. The effect of fill rate, backfill pulp density and fill heights are discussed. The thickness of shotcrete and the depth of embedment of rebar within are discussed.

56 46th US Rock Mechanics/Geomechanics Symposium Ses s ion 7: I nfluence of CO2 on Physical Properties Monday, 25 June, 11:00 am – 12:30 pm Chairs: Derek Elsworth

ARMA 12-232 Comparison of mechanical behaviors of geopolymer and class G cement as well cement at different curing temperatures for geological sequestration of carbon dioxide Nasvi, M.C.M. Monash University, Melbourne, VIC, Australia Ranjith, P.G. Monash Uniersity, Melbourne, VIC, Australia. Sanjayan, J. Swinburne University of technology, Melbourne, VIC, Australia.

ABSTRACT: Carbon dioxide (CO2) sequestration into deep underground reservoirs such as saline aquifers, oil reservoirs and coal seams have found out to be one of the best practical solutions to reduce significant amount of greenhouse gases from the environment. The success of any large scale CO2 sequestration project depends on many factors, and two of the important factors are (a) the stability of injection well and (b) well cement. To date, OPC based cement has been used as well cement, and it has been found that it is unstable in CO2 environments as it undergoes degradation, strength reduction, and shrinkage. Therefore, a comprehensive experimental study has been undertaken to investigate the suitability of geopolymer as well cement and the mechanical behavior of geopolymer and class G cement was compared under different down-hole temperatures. When the uniaxial compressive strength (UCS) of geopolymer and G cement was compared, it was found that geopolymer possess higher UCS values at elevated temperatures (above 50 .C) and G cement possesses the highest values at ambient conditions. The peak strength of both geopolymer and class G cement was observed at curing temperatures of 50-60 .C. In addition, acoustic emission (AE) test data revealed that the crack propagation stress thresholds of class G cement are higher at ambient conditions, whereas geopolymer possesses highest values at elevated temperatures. The photogrammetric results of strain measurement show that geopolymer undergoes shear failure at lower curing temperatures, whereas the failure was splitting at elevated temperatures. In addition, the type of failure of class G cement was shear failure for all the curing temperatures and the ultimate failure strain did not vary much with the curing temperature.

ARMA 12-234

Constraining Elastic Rock Properties in A CO2 Enhanced Oil Recovery Reservoir Using Sonic Log Data Guan, S. and Tutuncu, A.N. Colorado School of Mines, Golden, CO, USA ABSTRACT: The main objective of this paper is to investigate the geomechanical property changes taking place with CO2 injection in Delhi Field. Sonic velocity has been cross plotted with clay content and density logs, and the correlation has been used to create synthetic sonic logs based on neural network that provides an alternative way to extrapolate the rock property changes to any well location in the field where sonic log data is not available. Nevertheless, neural network cannot be applied to predict the sonic log after the CO2 injection as the sonic data is not yet available after CO2 injection. Hence, the Eberhart- Phillips correlation was utilized to calculate the velocity changes caused by pore pressure changes that the

57 46th US Rock Mechanics/Geomechanics Symposium pressure data from several wells in the field is available. While Eberhart-Phillips correlation doesn’t take into account the CO2 saturation effect on the compressional velocity, the Gassmann equation has been applied to calculate the effects of CO2 saturation, and the result can be utilized to linearly input into the

Eberhart-Phillips correlation to couple the effects of CO2 saturation and effective stress. And then the 3D Young’s modulus cube, Poisson’s ratio cube, unconfined compressive strength(UCS) in various effective stress scenarios have been evaluated to predict the geomechanical risk with the associated changes.

ARMA 12-407 An integrated experimental and modeling approach to determine the interplay between deformation conditions, rock properties, and development of clay smears TerHeege, J.H., Wassing, B.B.T., Orlic B., TNO, Geological Survey of the Netherlands, Utrecht, the Netherlands Giger, S.B. NAGRA,Wettingen, Switzerland Ciftci, N.B., and Clennell M.B. CSIRO Earth Science and Resource Engineering, Perth, Australia ABSTRACT: Analysis of the sealing capacity of faults is of key importance in predicting presence of hydrocarbons in structural traps. In this study, an integrated experimental and modeling approach is used to determine the interplay of deformation conditions, rock properties, and clay smear development. Large-scale direct shear experiments on samples consisting of a layered sandstone-claystone-sandstone sequence are simulated using two-dimensional discrete element numerical models to study the development of clay smears for different claystone types and stress conditions that are representative for faults trapping hydrocarbon accumulations. The direct shear experiments are reproduced as closely as possible using the models with similar stress conditions and clay types with similar mechanical behavior as in the experiments. The combination of numerical models and laboratory experiments allows direct validation of models by comparison with the experiments and study of the sensitivity of fault and clay smear structures to claystone properties and stress conditions. The model results are used to determine the geometry of clay smears in terms of dominant microphysical processes leading to smears and qualitatively assess the implications for smear formation and seal breach in nature.

ARMA 12-426 Chemo-mechanical permeability evolution in wellbore-cement fractures exposed to carbon-dioxide-rich brines. Walsh, S. D. C., Du Frane, W. L., Sholokhova, Y., Settgast, R., Johnson, S. M. and Carroll, S.A. Lawrence Livermore National Laboratory, 7000 East Av., Livermore, CA, USA ABSTRACT: Fractures in wellbore cement and at the cement-host rock interface are potential leakage pathways for long-term carbon sequestration sites. Portland cement exposed to carbon-dioxide-rich brine undergoes a series of diffusion-limited reactions that form distinctive reaction fronts adjacent to the cement surface. This paper outlines a joint experimental and numerical modeling effort investigating the formation of these reaction fronts and their impact on fracture transmissivity. Prepared by LLNL under Contract DE-AC52-07NA27344.

58 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-568 Permeability evolution in dual permeability dual stiffness sorbing media Wang, S. Department of Energy and Mineral Engineering and G3 Center, Pennsylvania State University, University Park, PA, USA Elsworth, D. Department of Energy and Mineral Engineering and G3 Center, Pennsylvania State University, University Park, PA, USA Liu, J. School of Mechanical Engineering, The University of Western Australia, WA, Australia ABSTRACT: We develop a mechanistic model to represent the evolution of permeability in dual permeability dual stiffness sorbing media such as coal beds and shales. This model accommodates key competing processes of poromechanical dilation and sorption-induced swelling. Permeability evolution is cast in terms of series and parallel models with the series model better replicating observational data. The model may be cast in terms of nondimensional parameters representing sorptive and poromechanical effects and modulated by the sensitivity of the fracture network to dilation or compaction of the fractures. This latter parameter encapsulates the effects of fracture spacing and initial permeability and scales changes in permeability driven by either sorption or poromechanical effects. For a system following a Langmuir type sorption isotherm and where both poromechanical and swelling effects are individually large, a turnaround in net permeability from decreasing at low (sorbing) gas pressures to increasing at large gas pressures is expected. This new mechanistic model is capable of representing key aspects of these changes in the transport parameters of fractured sorbing media to changes in stress and pore pressure. This model is applied to well-controlled observational data for different ranks of coals, and different types of gases, and satisfactory agreement is obtained.

ARMA 12-582

Effect of CO2’s varying phase on static and dynamic moduli of a fully saturated dolostone Njiekak, G. Department of Physics, Institute for Geophysical Research, Univ. of Alberta, Edmonton, AB, Canada Yam, H., Kofman, R.S. and Schmitt, D.R. Department of Physics, Institute for Geophysical Research, Univ. of Alberta, Edmonton, AB, Canada ABSTRACT: Laboratory measurements of ultrasonic P- and S- waves velocities and strain have been performed on a dolostone under dry and CO2 saturated conditions at different stress levels. The current work attempts to assess the effects of the CO2’s varying phase state on the static and dynamic bulk moduli. Experiments were conducted under a constant differential pressure of 15 MPa (difference between the confining and the pore pressure), so the seismic effects recorded would be reflective of changes in the pore fluid properties. Results show that P- and S- waves are sensitive to changes in the pore space and CO2 phase changes (gas to liquid and gas to supercritical fluid) are evident from signal variations. Stress-strain curves of the CO2 saturated sample indicate an increase of the strain with pore pressure. This is likely attributed to the closure of isolated pores (that means pore not connected to the inter-crystalline pore space available for fluid flow) with increasing confining stress. The static bulk modulus of the saturated sample decreases with pore pressure. The dynamic bulk modulus also decreases with pore pressure but recovers when CO2 turns from gas to liquid or to supercritical fluid in the rock pore spaces.

59 46th US Rock Mechanics/Geomechanics Symposium Ses s ion 8: T ime and Environment-dependent Behavior Monday, 25 June, 11:00 am – 12:30 pm Chairs: Will Pettitt, Marc Loken

ARMA 12-162 Time-dependent behavior of granite and constitutive equation Hashiba, K., Fukui, K. and Okubo, S. The University of Tokyo, Tokyo, Japan ABSTRACT: Research on time-dependent behavior of rock is essential for long-term maintenance and stability assessment of underground structures such as tunnels, storage and waste repositories. Granite is one of the candidate rocks for a high-level radioactive waste repository, which is the important issue under consideration in the world. However, time-dependency of granite is so small that high- accuracy testing results are insufficient and there is room for further research into a constitutive equation and a simulation method. This paper demonstrated some testing results concerning the time-dependency of granite, and the variablecompliance- type constitutive equation proposed in previous research was examined if it can be applicable to granite. Consequently, the equation can simulate a stress-strain curve, loading-rate dependency and a creep strain curve with a single set of constants. The one-dimensional equation was extended to the two-dimensional one and implemented in the commercial finite element analysis program. Numerical simulation with a simple circler or elliptical tunnel model provided the sensible result that the tunnel lifetime became shorter with the increase of rock stress or the ratio of a semi-major to a semi-minor axis.

ARMA 12-385 Impression relaxation test, a new relaxation method to determine the time dependent characteristics of salt rock Mehranpour, M.H. and Rassouli, F.S. Graduate student of School of Mining Engineering, University of Tehran, Tehran, Iran Moosavi, M. Associate professor of School of Mining Engineering, University of Tehran, Tehran, Iran ABSTRACT: Relaxation impression technique is a novel relaxation test in which a cylindrical flat ended indenter penetrates into a small region of sample and after keeping the displacement at a certain point, the decrease in the stress level will be recorded. Conventional relaxation test is a time consuming and expensive technique when a number of samples are needed to be tested. In contrast, impression relaxation test requires only a small amount of sample which makes this method cheaper. In this study, the impression relaxation test will be carried out on salt rock using an apparatus, which is designed and fabricated for impression relaxation test, and the results will be compared to the results of conventional compression relaxation test.

60 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-391 Laboratory Testing of Waste Isolation Pilot Plant Surrogate Waste Materials Broome, S.T., Bronowski, D.R., Kuthakun, S.J., and Pfeifle, T.W. Geomechanics Department, Sandia National Laboratory, Albuquerque, NM, USA Herrick, C.G. Performance Assessment and Decision Analysis Department, Sandia National Laboratories, Carlsbad, NM, USA ABSTRACT: The present study results are focused on laboratory testing of surrogate waste materials. The surrogate wastes correspond to a conservative estimate of the degraded containers and TRU waste materials emplaced at the WIPP after the 10,000 year regulatory period. Testing consists of hydrostatic, triaxial, and uniaxial strain tests performed on surrogate waste recipes that were previously developed by Hansen et al. (1997) [1]. These recipes can be divided into materials that simulate 50% and 100% degraded waste by weight. The percent degradation indicates the anticipated amount of iron corrosion, as well as the decomposition of cellulosics, plastics, and rubbers (CPR). Axial, lateral, and volumetric strain and axial and lateral stress measurements were made. Two unique testing techniques were developed during the course of the experimental program. The first involves the use of dilatometry to measure sample volumetric strain under a hydrostatic condition. Bulk moduli of the samples measured using this technique were consistent with those measured using more conventional methods. The second technique involved performing triaxial tests under lateral strain control. By limiting the lateral strain to zero by controlling the applied confining pressure while loading the specimen axially in compression, one can maintain a right-circular cylindrical geometry even under large deformations. This technique is preferred over standard triaxial testing methods which result in inhomogeneous deformation or “barreling”. Manifestations of the inhomogeneous deformation included non-uniform stress states, as well as unrealistic Poisson’s ratios (> 0.5), or those that vary significantly along the length of the specimen. Zero lateral strain controlled tests yield a more uniform stress state, and admissible and uniform values of Poisson’s ratio.

ARMA 12-510 Instrument for Measurements of Linear Thermal Expansion Coefficient of Rocks Popov Y., Parshin A., Miklashevskiy D., and Abashkin V. Schlumberger Research Center, Moscow, Russia ABSTRACT: The instrument and methodology for measurements of coefficient of linear thermal expansion (CLTE) of rock samples at atmospheric pressure is described. The instrument provides the CLTE measurements on (1) core plugs (30 mm in diameter and 30 mm in length) used in petrophysical measurements and (2) on cubes (30x30x30 mm) to measure CLTE anisotropy excluding rock inhomogeneity influence on measurement results. The instrument characteristics and measurement procedure follows to basic requirements of ASTM standards. According to testing the instrument using a representative set of certified CLTE references total relative accuracy and precision (at a confidence probability of 0.95) for every 20 0C intervals was established to be less than ±4%. Theoretical modeling of heat transfer within the rock sample under studying was performed to validate necessary thermal regime of the rock sample heating and cooling according to recommendations of the ASTM standards. The new technique presents radically new possibilities for research and industrial goals. The new instrument was used to measure coefficient of linear thermal expansion on 55 rock samples (quartz and quartz-feldspar sandstones and carbonaceous rocks). Relevant temperature variations during reservoir heating were accounted for.

61 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-639 The inference of physico-mechanical properties of soft rocks and the evaluation of the effect of water content and weathering on their mechanical properties from needle penetration tests Aydan, Ö Tokai University, Ocean Research Institute, Shizuoka, Japan ABSTRACT: Needle penetration tests are used for inferring the uniaxial compressive strength (UCS) of soft rocks particularly in tunnelling through squeezing rocks in Japan. The device can measure the applied load and the penetration depth of the needle of the device. The ratio of applied load to penetration depth is called needle penetration index (NPI). In this study, this device has been used to infer the physico- mechanical properties of soft rocks from Japan, Turkey and Egypt. Various equations are developed to infer the physico-mechanical properties in terms of needle penetration index (NPI) and compared with experimental results. Some additional equations are presented to consider the effect of water content and cycle numbers of freezing-thawing.

ARMA 12-256 The effect of material scalping and water content on the shear strength of Questa Mine materials Fakhimi, A. Department of Mineral Engineering, New Mexico Institute of Mining and Technology, Socorro, NM 87801, USA, and Department of Civil and Environmental Engineering, Tarbiat Modares University, Tehran, Iran Nunoo, S. Department of Mineral Engineering, New Mexico Institute of Mining and Technology, Socorro, NM 87801, USA, and School of Engineering, University of British Columbia, Kelowna, B.C., Canada Van Zyl, D. Department of Mining Engineering, University of British Colombia, Vancouver, BC, V6T 1Z4, Canada McLemore, V.T. New Mexico Bureau of Geology and Mineral Resources, New Mexico Institute of Mining and Technology, Socorro, NM 87801, USA ABSTRACT: Direct shear tests of 50-mm, 60-mm and 300-mm samples were conducted on materials collected from Questa rock piles and their natural analogs to investigate the role of material scalping and water content on the shear strength of these materials. Normal stresses in the range of 50 to 700 kPa were used for the shear tests. The results of the laboratory tests presented in this paper suggest that scalping of the rock pile material causes reduction in friction angle. The effect of water content was studied as well. Air- dried, moist and saturated samples were tested using direct shear tests. It is shown that the friction angle of Questa rock pile material decreases with increasing water content. Therefore, for unsaturated conditions similar to that of the Questa mine region with a semi-arid environment, shear test results on saturated samples can cause underestimation of the frictional strength of the material.

62 46th US Rock Mechanics/Geomechanics Symposium Ses s ion 9: Shale, Sand and Chalk Behavior Around Wellbores and Perforations Monday, 25 June, 2:00 pm – 3:30 pm Chairs: Tony Addis, Peng Ray

ARMA 12-290 Shear Strength Anisotropy in Fine-grained Rocks Crawford, B.R. ExxonMobil Upstream Research Company, Houston, TX, USA DeDontney, N.L. and Alramahi, B. ExxonMobil Upstream Research Company, Houston, TX, USA Ottesen, S. ExxonMobil Development Company, Houston, TX, USA ABSTRACT: Significant strength anisotropy associated with weak bedding laminations can lead to wellbore instability issues when drilling inclined wells through shale formations. We have compiled a database of ≈400 orientated triaxial compression tests in 14 lithologies (mainly argillaceous shales and calcareous marls) to quantify the magnitude of strength anisotropy likely to be encountered in situ. All data is analyzed using both discontinuous single plane of weakness and continuously variable strength models. Anisotropy is primarily found to result from a systematic dependency of cohesive strength on orientation angle compared with the more random variation of internal friction which is most likely due to material inhomogeneity. Cohesive strength reduction (shearing through versus shearing along weak laminations) ranges from ≈20–80% depending on lithology. From our database analyses we observe systematically higher reduction (hence greater anisotropy) in the weaker fine-grained rocks.

ARMA 12-559 Analysis of Horizontal Wellbore Stability in Clay Shale Akl, S. A.1 Shell Exploration & Production Company – Projects and Technologies, Houston, Texas, USA Whittle, A. J. Massachusetts Institute of Technology – Department of Civil and Environmental Engineering, Cambridge, Massachusetts, USA ABSTRACT: This paper examines how the predicted mechanisms of horizontal wellbore stability are related to the constitutive model describing the mechanical behavior of the geologic formation around the wellbores. Two critical state soil models are used: Modified Cam Clay [1] and MIT-E3 [2]. The horizontal wellbores are modeled by a 2D plane strain model with horizontal and vertical axes of symmetry using nonlinear finite elements. The paper considers wellbores drilled in cross-anisotropic saturated porous formation of unlithified hard clay/soft shale. Short-term wellbore instability during drilling in low permeability formations is analyzed assuming undrained conditions. The paper compares the MCC and MIT-E3 predictions of critical mud pressures at which failure occurs; and deformations and shear strains around the wellbore at a reference mud pressure. For the horizontal wellbore, the MIT-E3 model predicts failure due to a local increase in inward deformations at the cavity wall and higher critical mud pressure than the underbalanced drilling limit. The MIT-E3 model predicts lower magnitudes of shear strains around the wellbore but higher critical mud pressure at failure than that predicted by the MCC model. The more sophisticated MIT-E3 with an asymmetric yield surface gives a more accurate prediction of failure in horizontal wellbores.

63 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-545 Investigation of Three Modes of Borehole/TWC Failure by Application of the Modified Cam-Clay Material Model Dunayevsky, V.A. Shell International E&P, Houston, Texas, USA Myers, M.T. Shell International E&P, Houston, Texas, USA Bennett, M.B. Shell International E&P, Houston, Texas, USA ABSTRACT: In this paper we discuss the use of the Modified Cam-Clay material model applied to the problem of borehole stability. We consider the case of a thick walled cylinder (TWC), which is easily extended to a borehole by allowing the outer radius to go to large values. Three mechanisms of failure will be discussed: “Runaway Instability” (RAI) when the strains at the borehole wall start growing uncontrollably, “Negative Rate of Work” (NRW) when the rate of work of plastic strains becomes negative, and catastrophic failure when equilibrium conditions cannot be met (Considere instability). The first two of these criteria were discussed in earlier papers related to depleting reservoirs and fault activation/reactivation.

Remote horizontal stresses and vertical stresses are initially given. Axisymmetric conditions are assumed. The calculation proceeds by assuming the existence of a plastic zone surrounding the interior wall. As the radius of the plastic zone is increased, the equilibrium interior boundary pressure is calculated. Three mechanism of failure are encountered. The mode of failure depends on the values of remote and vertical stress, material properties, and thickness of the cylinder wall.

ARMA 12-284 One-Dimensional Closed-Form Solutions for Estimation of Thermo-Chemo-Hydraulic Parameters of Shales Araujo, E.M.P.* Pontifícia Universidade Católica do Rio de Janeiro, Rio de Janeiro, RJ, Brazil Fontoura, S.A.B. Pontifícia Universidade Católica do Rio de Janeiro, Rio de Janeiro, RJ, Brazil ABSTRACT: This paper presents some closed-form solutions of the coupled thermo-chemo- hydraulic problem of pressure diffusion through shales. The solution is based on the Biot’s poroelasticity theory that has been extended to incorporate temperature and solute diffusion and chemical osmosis into the constitutive equations. Explicit equations in the time domain were derived for appropriate boundary conditions of specialized laboratory equipment that allows one-dimensional diffusion of temperature, salt ions and water throughout a shale sample. The results showed that the proposed closed-form solution can represent fairly well the laboratory results and it can be used as a tool for quality control assurance of tests to determine the input parameters for advanced coupled modeling of shale behavior under pressure, thermal and chemical gradients like the drilling of oil and gas wells in high pressure and high temperature environments.

64 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-314 A Predictive Model for Sand Production in Realistic Downhole Condition Kim, A.S. Halliburton, Houston, TX, USA Sharma, M.M. University of Texas, Austin, TX, USA ABSTRACT: This paper presents a model describing the process of sand production to predict the stability of wellbores and perforation tunnels as well as mass of sand produced. The sand production model incorporates formation failure and flow-driven sand erosion mechanisms. It is shown that rock failure, near wellbore damage, and fluid flow are important in the sand production process. The model has a small number of required input parameters that can be directly measured in the lab and does not require the use of empirical correlations for determining sand erosion. In addition, the effect of two-phase flow was incorporated in the model to understand a change in sanding pattern when there is water breakthrough. Two sand production tests are presented in the paper. The first test involved a thick-walled cylinder testing with single-phase flow, which served as a baseline test to validate the model. Water production was simulated by applying a two-phase model. The second test was conducted on a perforated Castlegate sample. It represented a true downhole condition where the perforation damage has impacts on the sanding and must be accounted for. Both tests were simulated using the proposed numerical model and the results successfully demonstrated the model’s capability to predict sand production under different conditions.

ARMA 12-479 Solids production in chalk Papamichos, E. Aristotle Univ of Thessaloniki, Greece and SINTEF Petroleum Research, Trondheim, Norway Berntsen, A.N., Cerasi P. SINTEF Petroleum Research, Trondheim, Norway Vandycke, S., Baele, J.-M. Mons University, Belgium Fuh, G.-F. ConocoPhillips, Houston, USA Han, G. Hess, Houston, USA Kristiansen, T.G. BP Norway, Stavanger, Norway ABSTRACT: Open hole or perforated completions in chalk fields are studied experimentally and are simulated theoretically to obtain an insight on the mechanisms involved in their stability. Hollow cylinder experiments with flow on Lixhe chalk have identified two mechanisms of chalk production: (a) Breakout failure through shear band development and pore collapse, (b) Tensile failure and destabilization due to high drawdown. Solids production results for chalk are presented where solids production by tensile failure is more often observed in water-flooded areas. Depending on the conditions it can be a rather violent phenomenon. The analysis presents the critical drawdown and depletion conditions for the two failure modes and demonstrates the influence of brine sensitivity on the results.

65 46th US Rock Mechanics/Geomechanics Symposium Ses s ion 10: Rocks Mas Excavation and Deformation Monday, 25 June, 2:00 pm – 3:30 pm Chair: Mike Hardy

ARMA 12-285 Probabilistic approach in assessing tunnel squeezing – a discussion based on tunnel projects from Nepal Himalaya Panthi, K. K. Norwegian University of Science and Technology (NTNU), Trondheim, Norway. ABSTRACT: Tunnel squeezing is a common phenomenon in the Himalayan rock mass with high degree of schistocity. Weak rocks like mudstone, shale, slate, phyllite, schist, highly schistose gneiss and the rock mass of the tectonic fault zones are incapable of sustaining high stresses. A reliable prediction on the extent of squeezing is therefore essential to make strategy regarding stabilizing measures and optimization of tunnel rock support well in advance (during planning and design). Failing to do so will result to the construction delay, cost overruns and unnecessary disputes between the client and the contractors involved in the execution of tunneling projects. In the paper, probabilistic approach of uncertainty analysis is used in assessing tunnel squeezing for the two tunnel cases from Nepal Himalaya. The main focus is given to look on the applicability of squeezing analysis using Hoek and Marinos [4] approach in combination with the equation proposed by Panthi [1] for the estimation of rock mass strength for highly schistose rocks of the Himalaya. Measured tunnel convergence (squeezing) and lab tested mechanical properties of the rocks from headrace tunnels of Kaligandaki and Middle Marsyangdi hydropower projects from Nepal Himalaya are used to verify the applicability of the proposed methods and also the uncertainty analysis approach on squeezing introduced by Panthi [1].

ARMA 12-300 A hydraulic specific energy performance indicator for Coiled Tube Turbodrilling Mokaramian, A. Department of Petroleum Engineering, Curtin University, and Deep Exploration Technologies Cooperative Research Centre (DET CRC), Perth, Australia Rasouli, V. Department of Petroleum Engineering, Curtin University, and Deep Exploration Technologies Cooperative Research Centre (DET CRC), Perth, Australia Cavanough, G. CSCSIRO, Queensland Centre for Advanced Technologies (QCAT)), and Deep Exploration Technologies Cooperative Research Centre (DET CRC), Queensland, Australia ABSTRACT: Efficient drilling of hard rocks in mineral exploration requires a comprehensive knowledge of the energy spent at the bit. The use of mechanical specific energy (MSE) proposed in the past for drilling performance studies does not consider the impact of fluid hydraulics and therefore the concept of Drilling Specific Energy (DSE) was later developed to apply the hydraulics parameters into the drilling performance optimization. With respect to the purpose of mineral exploration, coiled tube (CT) Turbodrilling has been proposed recently for deep hard rocks mineral exploration applications, with several advantages over conventional drilling methods. Coiled tube (CT) is a continuous pipe and consequently a downhole motor is needed to provide rotation and mechanical power to the bit. If DSE is to bee used as a drilling performance indicator when downhole motors are part of the bottom hole assembly (BBHA) it should be modified

66 46th US Rock Mechanics/Geomechanics Symposium in such a way that it includes motor specifications in the calculations. In this paper, a methodology is presented for performance optimization in CT Turbodrilling with respect to specific energy performance models. As a result, a hydraulic specific energy performance indicator is defined for CT Turbodrilling in hard rocks mineral exploration.

ARMA 12-435 Rock Squeezing Prediction by a Support Vector Machine Classifier Shafiei, A. Department of Earth and Environmental Sciences, University of Waterloo, Waterloo, Ontario, Canada Parsaei, H. Department of Systems Design Engineering, University of Waterloo, Waterloo, ON, Canada Dusseault, M.B. Department of Earth & Environmental Sciences, University of Waterloo, Waterloo, Ontario, Canada ABSTRACT: Redistribution of in situ stresses so they exceed rock strength leads to yielding of the intact rock material around a tunnel after excavation, causing large plastic deformations often referred to as ground squeezing. This tunneling problem typically occurs during deep tunneling in weak rock such as shales and weak schists where volumetric dilatancy accompanies the process of rock yield and deterioration. In this article, a decision support system to assist a tunnel engineer in making a decision on tunnel route design, selection of excavation technique or mitigation measures is presented. A support vector machine- based supervised classifier is proposed which employs the Q tunneling index and depth of the tunnel to predict risk of rock squeezing. Performance analysis using extensive field data obtained from several tunnels around the world indicated that the developed system is more accurate than heuristic systems currently in use. The proposed system provides a posterior probability as a support for the decision being made that can be used to assess the acceptability level of the prediction.

ARMA 12-674 Progressive failure mechanisms and dynamic pressure arch effect around a tunnel in soft rock Zhu, H. Key Laboratory of Geotechnical and Underground Engineering of Ministry of Education, Department of Geotechnical Engineering, College of Civil Engineering, Tongji University, Shanghai 200092, China Wang, C., Wang, H. Research Institute of Highway Ministry of Transport, Beijing 100191, China ABSTRACT: Tunnel collapse is one of the frequently occurring disasters in tunnel construction. It is a great threat to tunnel construction safety and may cause an initial negative influence on the tunnel structure during maintenance. In this paper, progressive failure mechanisms of the surrounding rocks of road tunnels are investigated by statistical analysis, model tests and numerical simulations. And finally a concept of dynamic pressure arch of the surrounding rock based on the progressive failure is proposed, which will be helpful to judge the tunnel stability, accurately determine the loosed load and economically design rock bolts for the practical projects.

67 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-270 Indentation Test for the Measurement of Rock Brittleness Yagiz, S. Pamukkale University, Faculty of Engineering, Geological Engineering, Denizli Turkey Rostami, J. Penn State University, Department of Energy and Mineral Engineering, University Park, 16802-5000, PA, USA ABSTRACT: Rock brittleness is an important rock characteristic, pertinent to predicting rock fragmentation behavior, energy consumption in rock cutting, and selection of proper cutting geometry. While brittleness is typically well understood as a concept, there is no universally accepted measure for this rock characteristic and often a combination of rock properties are used to define brittleness rather than single test to make a direct measurement. Typically, rock brittleness is defined indirectly as a function of uniaxial compressive strength (UCS) and Brazilian tensile strength (BTS) of rock through empirical formulas. This could be a simple ratio of UCS to BTS or any combination of these two measured physical properties along with fracture properties of the given rock type. This shows the need for alternative testing methods that can be used for measuring brittleness in a more or less direct method. One of the tests that could be considered for measurement of brittleness is indentation test. This test has been used for evaluation of rock hardness and drillability and can be considered for measuring the rock brittleness. In this study, the results of a series of indentation (or punch) tests are used to compute rock brittleness. A brittleness index is introduced from the analysis of the results of indentation test on a variety of rock types and a classification for rock brittleness is suggested for application in rock excavation.

Ses s ion 11: C hallenges in Numerical Modeling Monday, 25 June, 2:00 pm – 3:30 pm Chairs: Ronaldo Borja, Sonia Mogilevskaya

ARMA 12-621 DEM/Pore Network Modeling of Fluid Injection into Granular Media Zhang, F., and Huang, H. Georgia Institute of Technology, Atlanta, Georgia, USA Damjanac, B., Itasca Consulting Group, Inc., Minneapolis, Minnesota, USA ABSTRACT: The process of fluid injection into dense granular media is analyzed using the DEM code PFC2D® coupled with a pore network scheme. A simple approach to calibrate the microscale parameters to match the permeability of a particle assembly, predicted from the Kozeny-Carman correlation, is first established. The effect of the injection rate on the grain displacement and fluid flow mechanisms is examined. The numerical results illustrate that, as the injection rate increases, the granular medium behaviors change from that of a rigid porous medium to localized failure that leads to development of fluid channels. Existence of the fluid channels is also reflected in the fluid flow patterns. The numerical results are consistent with previous experimental observations of the injection experiments performed in a Hele-Shaw cell.

68 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-304 Challenges in selecting appropriate input parameters for numerical models Harrison, J.P. Lassonde Institute of Mining, University of Toronto, Toronto, Ontario, Canada Hadjigeorgiou, J. Lassonde Institute of Mining, University of Toronto, Toronto, Ontario, Canada ABSTRACT: The challenge of obtaining appropriate input parameters remains and may even be growing due to the increased sophistication of the numerical techniques. Indeed, this growing challenge means that increased sophistication is likely to lead to mounting errors of omission and convenience, with the result that modelling confidence and certainty reduces. This paper provides a framework to address these limitations.

ARMA 12-313 A mortar method based on NURBS for curve interfaces Florez, H. A. The University of Texas, Austin, Texas, USA Wheeler, M. F. The Center for Subsurface Modeling, Austin, Texas, USA Rodriguez, A. The ConocoPhillips Company, Houston, Texas, USA ABSTRACT: In order to tackle general sub-domains problems in geomechanics, a MFEM scheme on curve interfaces based on NURBS curves is presented in this paper. The goal is having a more robust geometrical representation for mortar spaces, which allows gluing non-conforming interfaces on realistic geometries. The resulting mortar saddle-point problem is decoupled by means of standard Domain Decomposition techniques such as Dirichlet-Neumann and Neumann-Neumann, in order to exploit current parallel machine architectures. Examples ranging from near-wellbore applications to field level subsidence computations show that the proposed scheme can handle problems of practical interest. Extensions to three-dimensional problems are also discussed.

ARMA 12-608 Finite Element Analysis of Stresses Induced by Gravity in Layered Rock Masses with Different Elastic Moduli Hoeink, T. and van der Zee, W. Baker Hughes, Houston, Texas, USA Moos, D. Baker Hughes, Palo Alto, California, USA ABSTRACT: A common practice in the oil and gas industry is to calculate horizontal stress magnitudes based on elastic properties derived from acoustic logs or seismic velocities. The derived stress variations are then used, among other things, for sweet spot identification, hydraulic fracture modeling and packer placement decisions in horizontal wells. However, the validity of the models depends on the applicability of the underlying assumptions, which include that the earth is a one-dimensional, horizontally layered elastic medium subject to constant lateral strain with properties that do not change with time.

69 46th US Rock Mechanics/Geomechanics Symposium In this paper we use finite element analysis to quantify the stresses that develop for perfectly elastic time- invariant layered materials under gravitational loading with zero lateral strain, and investigate the effect on the calculated stresses of laterally varying mechanical properties and of tilted layers. We find that the predictions of the simple model are significantly influenced both by layer tilt and lateral elastic properties variations. Titled layers have smoother vertical stress profiles compared to the profiles of perfectly flat layers. Layers with laterally varying mechanical properties also have laterally varying stresses, but the simple model over-predicts these variations and in some cases lateral variations in the ratios of least to greatest stress trend opposite to estimates based on elastic properties alone. Because even the smallest departure from the underlying assumptions results in errors in predictions, we conclude that in most cases it is risky to quantify in-situ stress magnitudes based on elastic properties.

ARMA 12-654 A Numerical Local Upscaling Approach for Elastic Rock Mechanical Properties: Dealing with Heterogeneity Khajeh, M. M. University of Alberta, Edmonton, Alberta, Canada Chalaturnyk, R.J. and Boisvert, J.B. University of Alberta, Edmonton, Alberta, Canada ABSTRACT: Upscaling elastic geomechanical properties is important for reducing the computational requirements of geomechanical simulation while honoring local heterogeneities in rock properties. During simulation elastic properties are often considered homogeneous; however, there is increasing interest in understanding the effect of heterogeneity on geomechanical simulation. Upscaling allows for the generation of realistically sized numerical models that can be simulated in a reasonable timeframe and also account for small scale heterogeneities. A novel local numerical upscaling technique is proposed to describe the macroscopic elastic behavior of complex heterogeneous media. This technique is compared to conventional analytical techniques and is shown to produce superior results when assessing the upscaling error of a synthetic facies model. The geomechanical response, volumetric strain in this study, of the coarse upscaled models are compared to the geomechanical response of the fine scale models with the proposed numerical technique producing results most similar to the fine scale model.

ARMA 12-302 Effective stress coefficient for uniaxial strain condition Alam, M. M. and Fabricius, I.L. Technical University of Denmark, Lyngby, Denmark ABSTRACT: The effective stress coefficient, introduced by Biot, is used for predicting effective stress or pore pressure in the subsurface. It is not a constant value. It is different for different types of sediment and it is stress dependent. We used a model, based on contact between the grains to describe the reason for change in effective stress coefficient under stress. Our model suggests that change in effective stress coefficient will be higher at uniaxial stress condition than at hydrostatic condition. We derived equations from the original definition of Biot to estimate effective stress coefficient from one dimensional rock mechanical deformation. We further investigated the effect of boundary condition on the stress dependency of effective stress coefficient and discussed its application in reservoir study. As stress field in the reservoirs are most unlikely to be hydrostatic, effective stress determined under uniaxial strain condition will be more relevant in reservoir studies.

70 46th US Rock Mechanics/Geomechanics Symposium Ses s ion 12: A coustic Emission Monday, 25 June, 2:00 pm – 3:30 pm Chair: Sergey Stanchits

ARMA 12-228 Crack Initiation Stress for Saturated Sandstone in Triaxial Compression Wasantha, P. L. P., Ranjith, P. G., Viete, D. R., Haque, A. and Bouazza, A. Monash University, Melbourne, Victoria, Australia ABSTRACT: Triaxial experiments were carried out on cylindrical samples to investigate the influence of confining pressure on the deviatoric axial stress at which crack initiation occurs in saturated sandstone. Samples were subjected to different confining pressures (2, 5, 8, 10 and 12 MPa) and a constant pore water pressure of 1 MPa during testing to failure. Acoustic Emission (AE) detection techniques were employed during all experiments, to identify the stress threshold values for crack initiation. The results from the testing were found to be similar, though not entirely consistent, with those from similar testing reported for dry rock of different types (granite, sandstone and marble) in the literature. Plots of cumulative AE counts against applied stress revealed that crack initiation occurs at lower deviatoric axial stress values (relative to peak deviatoric axial stress) for tests performed at higher confining pressures. This is consistent with failure occurring more suddenly following the onset of damage (i.e. a more brittle failure response) for the lower confining stress tests. Thus, increasing confinement was observed to cause progressively less brittle failure response for the tests carried out on the saturated sandstone.

ARMA 12-399 Relating acoustic wave velocities to formation mechanical properties Brandås, L.T. NTNU, Department of Petroleum Technology and Applied Geophysics, Trondheim, Norway. Weatherford Petroleum Consultants, Trondheim, Norway. Fjær, E. SINTEF Petroleum Research, Trondheim, Norway. NTNU, Department of Petroleum Technology and Applied Geophysics, Trondheim, Norway. Tokle, K. Weatherford Laboratories, Trondheim, Norway. Tronvoll, J. Weatherford Petroleum Consultants, Trondheim, Norway. ABSTRACT: Proper correlations between formation mechanical properties and acoustic data is essential for field rock mechanical analysis, and it has thereby a great significance to field operations such as hydraulic fracturing, wellbore stability during drilling, sand production risk evaluation, compaction studies, etc. This paper presents results from a correlation study between formation mechanical properties and acoustic wave velocities from wells in the North Sea. Correlations between formation compressive strength, elastic stiffness and Poisson’s number and compressional and shear transit times have been established. The data for this study was collected from triaxial compression tests performed on core plugs at various confining pressures. The results confirm that the stress level and stress configuration affects the acoustic velocities, and this should be accounted for when using generalized empirical correlations to estimate formation strength from acoustic logs in field studies. The results are found to match reasonably well with other published relations.

71 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-527 Acoustic Emission and Ultrasonic Transmission Monitoring of Hydraulic Fracture Propagation in Heterogeneous Rock Samples Stanchits, S. Schlumberger Innovation Center, 1935 Fremont Drive, Salt Lake City, UT 84104, USA Surdi, A. TerraTek, A Schlumberger Company, 1935 Fremont Drive, Salt Lake City, UT 84104, USA Edelman, E. and Suarez-Rivera, R. Schlumberger Innovation Center, 1935 Fremont Drive, Salt Lake City, UT 84104, USA ABSTRACT: The effect of preexisting discontinuities on hydraulic fracture propagation in low permeability sandstone blocks was studied by means of Acoustic Emission (AE) and Ultrasonic Transmission (UT) techniques. The blocks were loaded in a polyaxial test frame to representative effective in-situ stress conditions. We used rock samples with saw cut discontinuities oriented orthogonally to the expected direction of fracture propagation. Hydraulic fracturing was initiated by injection of silicon oil or glycerin into a borehole drilled offset from the center of the block. Detailed analysis of combined AE localizations and UT results allowed identification of various stages of hydraulic fracturing, including initiation, interaction with the preexisting interface, propagation away from the interface, and closure of the fracture. It has been found that the onset of borehole pressure breakdown closely correlates to the time when the hydraulic fracture crosses interface, and not with the fracture initiation. Injection of high-viscosity fluid results in wider fractures and higher breakdown pressures, while injection of low-viscosity fluid results in narrower width of fractures developed at lower injection pressure. These results also give a reference for understanding and interpretation of microseismic monitoring data recorded in the field.

ARMA 12-581 AE from Undrained and Unjacketed Tests on Sandstone Makhnenko, R.Y., Ge, C. and Labuz, J.F. University of Minnesota, Minneapolis, MN, USA ABSTRACT: Saturated specimens of Berea sandstone were subjected to confining pressure p and compressed axially under a plane strain condition; the biaxial deformation state is convenient for measuring axial and lateral displacements. Undrained testing involved development of pore water pressure u during application of deviatoric stress, and unjacketed tests maintained the condition of u = p. In addition, the specimens were instrumented with eight acoustic emission (AE) sensors for monitoring the microseismic activity during the tests. AE events were recorded and post-processed for rate and location analyses. A significant difference was observed between unjacketed and undrained compression in terms of AE rate change with loading. For an unjacketed test, where the pore pressure inside the rock was equilibrated with the confining pressure, the number of AE events per load step remarkably increased when the axial stress reached approximately 70% of the peak, similar to the behavior of dry specimens. However, in an undrained test, where the fluid was not allowed to leave the specimen, only a few microseismic events were recorded prior to failure of the specimen. The abrupt change in the slope of the AE rate happened only when the pore pressure in the rock decreased. This effect could be explained by the delayed tendency of the rock to dilate under an undrained condition.

72 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-589 Time-lapse Passive Seismic Velocity Tomography of Longwall Coal Mines: A Comparison of Methods Westman, E.C., Luxbacher, K.D., and Schafrik S.J. Mining and Mineral Engineering Department, Virginia Tech, Blacksburg, VA, USA Swanson, P.I. Spokane Research Laboratory, NIOSH, Spokane, WA, USA Zhang, H. University of Science and Technology of China, Hefei, Anhui, P.R. China ABSTRACT: Bumps in underground coal mines are violent events that result from a buildup of stress, usually in mines underlain and overlain by massive strata. Seismic velocity tomography can be implemented to infer stress distribution at mines and determine when a dangerous situation is developing. Three different methods were employed to compare time-lapse passive seismic tomograms at a longwall coal mine. The dataset is well sampled with a dense receiver array. Parameterization and results were compared using GeoTom, TomoDD, and SIMULPS. TomoDD and SIMULPS both allow for variable gridding and relocation of microseismic events while GeoTOM does not. All three methods produced consistent results for the data set showing clear high velocity zones in areas where abutment stress is expected and low velocity zones corresponding with gob. TomoDD proved to be the most suitable method for generating tomograms from mining-induced microseismic events because it resulted in the most consistent images and the calculated velocity distribution matched prior stress distribution measurements at the site.

ARMA 12-644 Orthotropic Horizontal Stress Characterization from Logging and Core Derived Acoustic Anisotropies Franquet, J.A. and Rodriguez, E.F. Baker Hughes, Houston, TX, USA ABSTRACT: This study provides the analytical solution of the two horizontal principal stresses for orthotropic rocks with horizontal laminations or thin beds and vertical natural fractures in term of six elastic properties; three Young’s modulus and three Poisson’s ratios. An analytical workflow is introduced for combining and complementing both borehole acoustic anistropies (azimuthal and transverse shear wave anistropies) with ultrasonic core measurements to fully characterize the stiffness tensor of an orthotropic formation. The discrepancies between divers anistotropic rock models are discussed and presented with case stories from US unconventional shale plays. The resulting horizontal stresses will require tectonic strain calibration from minifracs, straddle packer microfrac testing and/or borehole failure evidences such as breakouts or induced fractures observed on image logs.

73 46th US Rock Mechanics/Geomechanics Symposium Ses s ion 13: N umerical Modeling of Fractures in Unconventional Reservoirs Monday, 25 June, 4:00 pm – 5:30 pm Chairs: Jean Claude Roegiers, Paul La Pointe

ARMA 12-647 The role of pre-existing fracturing in enhanced reservoir treatments Zhao, X.P., Reyes-Montes, J.M. Applied Seismology Consultants Ltd., Shrewsbury, UK. Young, R.P. University of Toronto, Canada ABSTRACT: Hydraulic fracturing methods for reservoir treatment are applied to increasingly complex environments including naturally or previously fractured reservoirs. The potential interaction with the in- situ fracture network or with fracturing induced in previous treatments plays a crucial role in the outcome of the stimulation, controlling the extent and geometry of the paths of enhanced fluid migration. Passive microseismic (MS) monitoring can provide an imaging of the effect of hydraulic treatments and an indication of the relative role of pre-existing fractures in the development of the fracture network. Further insights into the mechanisms of the induced fracturing is provided by the use of Synthetic Rock Mass (SRM) numerical models that reproduce the nature of the rock and the stress conditions imposed by the engineering. The rock mass is reproduced by an assembly of bonded particles with an embedded Discrete Fracture Network (DFN) to represent joints, faults or other pre-existing fractures. This study presents the analysis of the microseismicity induced during the treatment of a pre-fractured reservoir. The observations are compared with the results from tests on SRM samples that are subjected to the same fluid disturbance applied in the field, with a suite of DFN to reproduce potential in-situ fracturing scenarios. The combination of microseismic observations with the suite of SRM models will allow an interpretation of the fracture mechanism and its relation with the reservoir pre-existing fracturing. This combined approach provides field engineers with a unique tool for the design, monitoring and optimization of reservoir treatments.

ARMA 12-601 Hydraulic fracture initiation from an open-hole: wellbore size, pressurization rate and fluid-solid coupling effects Lecampion, B. Schlumberger-Doll Research, Cambridge, MA, USA ABSTRACT: We present a model for the initiation, breakdown, and the early stages of hydraulic fracture propagation in an impermeable rock from an originally defect-free wellbore under plane-strain conditions. The model accounts for the strong fluid-solid coupling between the fluid flow within the crack and the elastic deformation due to both the wellbore stress concentration and fracture opening. The fracture process is modeled using a Dugdale cohesive zone model. The effect of the pressurization rate of the wellbore is also taken into account. The solution is obtained numerically by an iterative scheme based on boundary elements for the fracture deformation and a finite difference scheme for fluid flow. The different effects associated with the wellbore size, pressurization rate and fluid viscosity on the magnitude of the breakdown pressure observed on numerous laboratory experiments are reproduced. Quantitative comparisons of the predictions with experimental results available in the literature are discussed in details.

74 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-555 Fracture development from a borehole: Numerical and experimental investigations Alassi, H.T. SINTEF Petroleum, Trondheim, Norway Pradhan, S. and Stenebråten, J. SINTEF Petroleum, Trondheim, Norway ABSTRACT: Investigations of how tensile fractures might be developed from a pressurized borehole using both experimental and numerical tools are studied in this paper. The case study is made simple to avoid any numerical or experimental complications. The focus of this paper will be on the numerical part. An approach based on discrete element method is used to perform the numerical test which mimics a real lab test on a sandstone sample. The result shows similar fractures pattern like that obtained from the lab test, where three fractures were developed from the borehole. The results encourage us to investigate the factors that could affect such result specially that we have a match between the numerical and the experimental results. Two main factors are studied in this work: model heterogeneity and the solution scheme.

ARMA 12-480 Simulating Hydraulic Fracturing with Discontinuous Deformation Analysis Ben, Y., Xue, J., Miao Q., Wang, Y. and Shi G.-H. Engineering Computation Center, Graduate University of Chinese Academy of Science, ShiJiangShan District, Beijing, China ABSTRACT: Hydraulic fracture modeling in naturally fractured reservoirs is an emerging field. Methods to study this problem include Discrete Fracture Network Model, Discrete Element Method and Extended Finite Element Method. Each method has received some success and has its merits and drawbacks. In this paper, we target this problem with Discontinuous Deformation Analysis (DDA). Based on the original DDA code developed by Dr. Gen-hua Shi, we add a fluid network model. With the new code, we can simulate how hydraulic fractures initiate and propagate with the fluid injection.

ARMA 12-224 Modeling Hydraulic Fracture Propagation in Low Permeability Reservoirs Bhide, R.J., Zhao, N., McLennan, J.D. and Deo, M.D. 50 South Central Campus Drive, Department of Chemical Engineering, University of Utah, Salt Lake City, Utah, USA 84112. ABSTRACT: Truly comprehending the interconnectivity and conductivity of natural and hydraulically- induced fractures requires an integrated inference of fracture networks with simulations capable of inflating multiple fracture systems during injection. For example, a representative fracture network in a low permeability, naturally fractured reservoir can be inferred from outcrop studies, seismic surveys, logging and well testing data. This geometric information (complex fracture network) is imported into a weakly coupled geomechanical simulator and hydraulic fracturing is simulated. The simulator used is Itasca Corporation’s 3DEC. The impermeable nature of the matrix blocks has been a limiting feature – it is well known that relatively minor percentages of stimulation fluid are recovered when a fractured well is put on production. This suggests imbibition is certainly a possibility in the matrix as well as the fractures. Numerical calculations

75 46th US Rock Mechanics/Geomechanics Symposium have been performed to approximate fluid loss during stimulation using this commercial simulator and to assess the influence of fluid loss on the extent of fluid penetration and recovery in the natural fractures. Other parameters being considered in these simulations include the relative geometry, stress field and the injection parameters. The production component (single and multiphase) is determined by weak coupling with an in-house simulator modified for coupled poro-mechanical processes. Special attention is paid to wettability considerations and gas blockage.

ARMA 12-633 Factors Influencing Fracture Trajectories and Fracturing Pressure Data in a Horizontal Completion Manchanda, R. The University of Texas at Austin, Austin, Texas, U.S.A. Roussel, N.P. ConocoPhillips, Houston, Texas, U.S.A. Sharma, M.M. The University of Texas at Austin, Austin, Texas, U.S.A ABSTRACT: Horizontal completions are extremely important for effective drainage of shale gas reservoirs. The decisions taken to improve production performance in such environments are not always guided by engineering processes that tie production performance to completion designs. In this paper, we offer insight on the impact of fracture spacing on the propagation direction of the subsequent fractures in a sequential fracturing scenario. We use the principle of stress interference caused by open fractures to guide the propagation direction of subsequent fractures. We perform a sensitivity analysis on the factors that affect stress shadow effect. These factors include both formation properties as well as treatment variables. We apply our three-dimensional geomechanical model to observe the behavior of three typical shale gas reservoirs: Bakken, Barnett and Eagle Ford. We provide optimum spacing values for the three cases that allow fractures to follow trajectories that are transverse and orthogonal to the wellbore. We also provide an understanding of the variables that an operator can control to have an efficient drainage of the reservoir and avoid intersecting fractures. We provide a relation between the efficiency of the fracture treatment and the net closure pressure response observed in the field and explain how the net closure pressure values from the fracture treatments can be used a diagnostic tool for generating more efficient completion design.

Ses s ion 14: Drilling Mechanics Monday, 25 June, 4:00 pm – 5:30 pm Chairs: Haiying Huang, Anita Ai

ARMA 12-142 Interpretation of Single Cutter Tests for Rock Mechanical Properties Pei, J. Baker Hughes, Houston, TX, USA ABSTRACT: Single cutter tests are performed to reveal the mechanism of rock cutting. The information obtained from such tests is essential to understand the drilling behavior of an entire bit, and to optimize the drill bit design. The focus of this paper, however, is to obtain rock mechanical properties from single cutter tests. It is emphasized that rock cutting is a contact problem. One must separate the effects of

76 46th US Rock Mechanics/Geomechanics Symposium cutting geometry in order to obtain “intrinsic” rock properties. Following the theoretical framework used in the metal machining industry, a simple rock cutting model is proposed to describe the effects of both the cutting geometry and the intrinsic rock properties. The proposed model is validated by single cutter test results on Carthage limestone specimens under 13.8MPa confining pressure. It is then used to study the variation of mechanical specific energy with cutting geometry. It is shown that the proposed model produces results that qualitatively agree with experimental observations.

ARMA 12-235 Accurate Bottomhole Pressure for Fracture Gradient Prediction and Drilling Fluid Pressure Program - Part I Mokhtari M., Ermila M. and Tutuncu A.N. Colorado School of Mines, Golden, Colorado, USA ABSTRACT: Deepwater casing and cementing operations require more precise prediction of bottomhole pressure in order to avoid kicks, wellbore collapse and induced lost circulation incidents since the pore pressure/fracture gradient window is narrow in deepwater environments. To obtain more accurate bottomhole pressure, one should consider not only the hydrostatic pressure, but also the annular flow of fluids under realistic downhole conditions. In this study, we applied Yield Power Law model in the equations of motion within the annulus to represent the rheological properties of drilling fluids and cements more realistically. In addition, we have investigated the effect of eccentricity on both the pressure losses and velocity profiles. In the part II of this research, we consider more effective downhole parameters such as pipe rotation and the size of annulus. Finally, by incorporating all these effects, we will be able to analyze induced lost circulation incidents with better precision for obtaining and calibrating the fracture gradient.

ARMA 12-341 Analytical Modeling of PDC Single Cutter-Rock Interaction under Confining Pressure Rahmani, R., Smith, J.R., and Dahi Taleghani, A. Louisiana State University, Baton Rouge, LA, USA ABSTRACT: Slow penetration rate is a major factor in the high cost of deep drilling operations worldwide. A contributing factor is the excessive energy required to create and transport rock cuttings under high confining pressure. This work describes a new analytical single cutter model of cutting rock under confining pressure that was adapted from a model of machining metal. The original model quantifies an increase in shear plane area resulting from an increase in friction on the cutter face and/ or in back rake angle based on the principle of minimum energy. An adaptation of the model accounts for the effects of the confined shear strength of the rock and confining pressure-induced friction on the shear plane. Additional model terms were developed to account for the effect of specific dysfunctions, i.e. cutter balling and severe “global” balling. The model predicts distinctive characteristics of each condition: no dysfunction, cutter balling, and global balling in addition to unique changes in these characteristics as a function of confining pressure. The relevance of model predictions is supported by comparison to single cutter test results on shales.

77 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-402 The Role of Natural Vibrations in Penetration Mechanism of a Single PDC Cutter Khorshidian, H., Mozaffari, M. & Butt, S. D. Memorial University of Newfoundland, St. John’s, NL, Canada ABSTRACT: Drilling operation with Polycrystalline Diamond Compact (PDC) bit constitutes vertical oscillations which can both negatively and positively influence the efficiency of the penetration. In order to study the effect of bit vertical vibration in performance of PDC bits, a single PDC cutter-rock interaction, using distinct element methodology, was simulated. It has been observed that the inertia of the cutter play a significant role in vertical oscillations of the cutter. In addition, it has been found that the horizontal speed of the cutter increases the mechanical specific energy of penetration. But interaction between the cutter horizontal speed and vertical vibrations, due to imposing energized impacts on the rock-cutter interface, improves the value of MSE. However, there is an optimum level for cutter vertical vibrations to achieve an appropriate condition of penetration.

ARMA 12-596 Issues with Numerical Simulation of Core Disking Wilk, S.T., C. Fairhurst, and J.F. Labuz Department of Civil Engineering, University of Minnesota, Minneapolis, MN, USA ABSTRACT: A challenge in rock mechanics is the determination of in-situ stresses in regions of high magnitude stress. In certain situations, core extraction results in damage in the form of core disking and researchers have attempted to relate the disk thickness to the in-situ stress state. This paper investigates the core disking phenomenon using FLAC, and it is shown that an appropriate constitutive relation must promote tensile failure in order to replicate the disking process for a wide range of stresses. Various issues that arise during the simulation are also addressed.

ARMA 12-622 Mechanical Specific Energy Versus Depth of Cut Zhou, Y. 2, Zhang, W1, Gamwo, I.K.1, Lin, J. S.1,2* , Eastman, H. 1,3, Gill, M. 1,3,4, and Whipple, G. 1,3 1 National Energy Technology Laboratory, Morgantown, WV, USA 2 University of Pittsburgh, Pittsburgh, PA , USA 3 URS Corporation, National Energy Technology Laboratory, Morgantown, WV, USA 4 West Virginia University, Morgantown, WV, USA ABSTRACT: The relationship between Mechanical Specific Energy (MSE) and the rate of penetration (ROP), or the depth of cut per revolution, provides an important measure for strategizing a desirable drilling operation. The ROP of drilling can be related to the depth of cut for a single cutter. This study attempts to explore the mechanics of how MSE evolves with depth of cut. It represents a concerted effort that encompassed both the computational and experimental approaches. Lagrangian FEM was used to model the circular cutting of a single Polycrystalline Diamond Compact (PDC) cutter. The MSE of circular cutting was first obtained by using the volume traced by the cutter through its path in the rock, and then computed based upon the actual volume of rock being cut. It was found the former MSE decreased then leveled, while the latter was more or less constant. The relationship between these two trends was discussed in terms of the sharp cutter modeled. A parallel but more elaborated circular cutting experiment in Ultra-deep Drilling Simulator of the National Energy Technology Lab gave different trends that were characteristics of a blunt cutter. Interpretation was then extended to results from full drilling bit experiments.

78 46th US Rock Mechanics/Geomechanics Symposium Ses s ion 15: M odeling Anisotropy and Damage Monday, 25 June, 4:00 pm – 5:30 pm Chairs: Andrey Pyatigorets, David Potyondy

ARMA 12-446 Extension of Maxwell’s methodology for evaluating the effective properties of rock Mogilevskaya, S. G. University of Minnesota, Minneapolis, MN, U.S.A. Labuz, J.F. and Crouch, S.L. University of Minnesota, Minneapolis, MN, U.S.A. ABSTRACT: A novel method is presented for evaluating the effective (isotropic) elastic properties of heterogeneous, microporous or microcracked materials with random structure. The approach can be viewed as an extension of the classical Maxwell methodology. It is based on the idea that the effective properties of the material can be deduced from the effects that a cluster of inhomogeneities embedded in an infinite medium has on the far-fields; the inhomogeneities, pores or cracks, can be of arbitrary shapes, sizes, and properties.

ARMA 12-125 Modeling brittle rock material by using a coupled elasto-plastic damage model Ma, J., Zhao, G. and Khalili, N. Centre for Infrastructure Engineering and Safety, School of Civil and Environmental Engineering, The University of New South Wales, Sydney NSW, Australia ABSTRACT: A unified constitutive model for describing the stress–strain behavior of brittle rock is proposed. The elastic-plastic response of stress and strain is formulated by a bounding surface plasticity within a critical state framework. The concept of critical state is exploited in the model to separate brittle and ductile deformation regions. The critical state represents the residual state of porous rock which is approached at large shear deformation at constant deviatoric stress. The continuum damage evolution model is established in the framework of a general irrecoverable thermodynamics. The damage evolution law takes into account for confining pressure, plastic flow and brittle fracture. The fracture effect is accomplished by the applied critical damage value, beyond which fracture occurs and failure happens in the sample. The coupling effect of plastic flow and damage evolution is accomplished by combining the evolution laws of plasticity and damage. Special attention is paid to brittle fracture, brittle-ductile transition, plastic hardening/softening under damage, brittle rupture and grain crushing. This model is applied to Bentheim sandstone under a wide range of confining pressure from literature. The characteristic features of elastic-plastic damage in brittle rock are captured appropriately in all cases considered.

79 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-640 Some Considerations on Yield (Failure) Criteria in Rock Mechanics Aydan, Ö. Tokai University, Ocean Research Institute, Shizuoka, Japan Tokashiki, N. Ryukyu University, Dept. of Civil Eng., Nishihara, Okinawa, Japan Genis¸, M. Bülent Ecevit University, Dept. of Mining Eng., Zonguldak, Turkey ABSTRACT: Every material in nature starts to yield after a certain stress or strain level, and rock or rock mass is a no exception. The terms of elasticity or visco-elasticity are replaced by the terms of elasto- plasticity or elasto-visco-plasticity once material behaviour deviates from linearity. The relation between total stress and strain or strain rate tensors can no longer be used and every relation must be written in incremental form. As a result, the constitutive laws are derived using some assumptions, which include yield functions. Therefore, several yield criteria are proposed for rocks. In this article, the authors compare and discuss the applicability of various criteria used in Rock Mechanics and point out their features and shortcomings in view of experimental results. It is shown that Hoek-Brown’s criterion as one of best criteria is quite questionable in view of experimental results.

ARMA 12-124 Scale Effects on the Elastic Behavior of Fractured Rock Masses Youn, D. and Gutierrez, M. Colorado School of Mines, Golden, CO, USA ABSTRACT: Rock masses invariably contain fractures of various lengths. Due to their geometry and mechanical weakness, the mechanical characteristics of the fractured rock masses are controlled by the fractures. However, the quantification of the mechanical behavior of fractured rock masses is very complicated, because fracture geometry and mechanical behavior are length scale dependent. However, this scale dependency has not been not fully analyzed. The main objective of this research is to perform a comprehensive parametric study on the effects of fracture geometry and length in the equivalent continuum elastic compliance behavior of fractured rock masses over a wide range of length scales. The study used a combination of Oda’s elastic compliance tensor, Monte Carlo Simulation (MCS), and different Probability Distribution Functions (PDFs). Fracture geometry parameters are based on field data obtained from different sources on studies of fracturing from varied geological sites. A key concept in the equivalent continuum method is a Representative Element Volume (REV). Using the combined analysis techniques, the validity of the REV assumption is extensively investigated, and a guideline is proposed on how to define a proper REV in terms of the equivalent continuum elastic compliance of fractured rock masses.

ARMA 12-663 Modeling of the strength and deformation anisotropy of an argillaceous rock (Opalinus Clay) at the laboratory-scale Lisjak, A. Department of Civil Engineering, University of Toronto, Toronto, Ontario, Canada Tatone, B.S.A. and Grasselli, G. Department of Civil Engineering, University of Toronto, Toronto, Ontario, Canada Vietor, T. National Cooperative for the Disposal of Radioactive Waste (NAGRA), Wettingen, Switzerland

80 46th US Rock Mechanics/Geomechanics Symposium ABSTRACT: Opalinus Clay is an indurated over-consolidated argillaceous rock. The preferential orientation of clay platelets results in a strong anisotropy of its deformational and strength characteristics. The purpose of this study is two-fold: (i) to illustrate the new developments that have been introduced into the combined finite-discrete element method (FEM/DEM) to model layered materials and (ii) to show the effectiveness of this new modelling approach for simulating the short-term mechanical response of Opalinus Clay. A transversely isotropic elastic constitutive law is implemented to account for different elastic properties in a parallel and perpendicular direction to the layering, while a procedure to incorporate a distribution of preferably oriented defects is devised in order to capture the anisotropy of strength. Laboratory results of indirect tensile tests and uniaxial compression tests are used to quantitatively calibrate the numerical model. Emergent strength and deformation properties, together with the simulated damage mechanisms, are shown to be in strong agreement with experimental observations. Subsequently, the calibrated model is successfully validated by simulating the influence of the loading angle with respect to the specimen anisotropy. Finally, possible applications of the proposed approach to the design of a deep geological repository for nuclear waste are briefly discussed.

ARMA 12-113 Influence of direction of principal elastic axis and contact area to tensile principal stress under diametrical compression Tsutsumi, T. Kagoshima National College of Technology, Kirishima, Kagoshima, Japan ABSTRACT: The distributions of the principal tensile stress in orthotropic Brazilian Disk were shown under a pair of concentrated forces and compared with those by Claesson in previous author’s work. It was observed that the stress distributions are influenced by the angle of the disk’s orientation and the ratio of the elastic moduli. In this paper, the distributions of the principal tensile stress that is generated in the Brazilian disk are shown for several contact areas between the specimen and loading plates under the diametrical compression test. In this study, the load on the specimen is assumed as uniform distributed stress. The distributions of principal tensile stresses are obtained by calculation using Lekhnitskii’s theoretical solution and the equation that was added by authors. Calculations to obtain the principal tensile stresses are carried out under severalorientations of disk. Graphical representations show that the tensile stress that is generated near the loading plates decreases as the contact area between the specimen and loading plates increases. On the other hand, the tensile stress generated at the center of disk decreases by only a small amount as the contact area increases.

Ses s ion 16: Rocks Mas Characterization Monday, 25 June, 4:00 pm – 5:30 pm Chairs: Chuck Dowding, Mary MacLaughlin

ARMA 12-140 Effect of Deformation Rate on Shear Strength of Questa Rock Pile Materials Anim, K. Department of Mineral Engineering, New Mexico Tech, Socorro, NM, 87801 Fakhimi, A. Department of Mineral Engineering, New Mexico Tech, Socorro, NM, 87801, and Department of Civil and Environmental Engineering, University of Tarbiat Modares, Tehran, Iran

81 46th US Rock Mechanics/Geomechanics Symposium ABSTRACT: Understanding creep behavior of rock pile materials under both dry and moist conditions can help to evaluate long-term stability of rock piles. To this end, the effect of deformation rate on shear strength of dry and moist Spring Gulch rock pile materials from Questa mine, New Mexico, was investigated using direct shear tests with four different deformation rates of 0.5 mm/min, 0.05 mm/min, 0.0275 mm/ min, and 0.005 mm/min. Normal stresses of 160 kPa, 480 kPa and 750 kPa were used. For both the dry and moist rock pile materials, the shear strain rates used in this study show no major effect on the shear strength of the material, even though the friction angle and cohesion intercept were affected by the deformation rate. The measured internal friction angles versus rate of shear deformation were plotted in a semi-logarithmic format and the data show a fairly consistent linear trend. On the other hand, no general relationship between cohesion intercept and the rate of shear deformation was found. Direct shear tests results suggest strength degradation of the rock pile materials when water is added to the samples. The friction angles of the moist samples show greater dependency on the deformation rate compared to the situation for air-dried samples.

ARMA 12-203 Stiffness Characterization of Karst Rock Mass Marcic, D., Kovacevic, M.S. and Arapov I. University of Zagreb, Faculty of Civil Engineering, Zagreb, Croatia ABSTRACT: The paper describes determination of the deformation moduli of carbonate rocks in Croatian karst in order to predict deformation of geotechnical structures in a more reliable manner. Intensive measurements taken during geotechnical works conducted in carbonate rocks in Croatian karst have shown that measured deformations are significantly greater than that obtained in calculations that use deformability parameters in existing relations involving rock mass classifications. Furthermore, measured deformation shapes when compared to depth were evidently significantly different from deformations calculated or anticipated in the project. Research has shown that parameters affecting deformability of carbonate rocks in karst found in Croatia include the geological strength index (GSI), velocity of longitudinal waves (Vp) and the rock mass deformability index (IDm). The expression for determining rock mass stiffness is applicable in designing geotechnical structures that are built on karst found in Croatia. It can also be used for design work in other karst regions and other types of rock mass under the condition that it be adapted to the geological engineering features of such rock masses and that the geotechnical measurements on the carried out works be verified.

ARMA 12-115 Comparison of Deformability of Rock Mass by Direct and Indirect Methods Rajbal, S. Central Soil and Materials Research Station, New Delhi, India ABSTRACT: This paper deals with the comparison of modulus of deformation of rock mass between direct and indirect methods. The modulus of deformation in direct method was determined in-situ by using plate jacking test with borehole deformation measurement and it was evaluated by rock mass classification of Q-system by indirect method. It is seen from this comparison that the modulus of deformation evaluated by using mean Q value is more than two times the modulus value determined by in-situ testing. It is finally concluded that Q-system for determination of modulus of deformation needs to be updated for Himalayan rock mass. The modification has been presented in this paper. The modulus values evaluated by indirect methods should be used cautiously and it must be confirmed by in-situ testing.

82 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-512 Numerical Validation and Refinement of Empirical Rock Mass Modulus Estimation for Tunnel Analysis Hume, C. D. Mine Design Engineering, Kingston, Ontario, Canada Diederichs, M.S. GeoEngineering Centre, Queen’s-RMC, Kingston, Ontario, Canada ABSTRACT: The rock mass deformation modulus is an important parameter used for Finite Element Method (FEM) numerical analysis when evaluating tunnel closure over the life of an excavated tunnel. Challenges associated with the determination of this parameter are further exasperated when dealing with tunnels in weaker, softer rock masses where errors in stiffness estimation have a profound impact on closure predictions. In competent rock masses as potential candidates for sensitive structures, the correct modulus assessment is vital for prediction of thermal response during tunnel service life. The empirical relationship by Hoek & Diederichs (2006) based on the Geological Strength Index (GSI) has been determined for a wide range of rock. Within the range of applicability there is a large variation in measured values compared to the predicted relationship and predictive uncertainty at low GSI’s. In this paper, a practical range of rock mass quality are analyzed using FEM numerical models with an explicit representation of joints to focus on tunnel response. Tunnel closure in these simulations is used to compare to predictions based on representative deformation modulus estimates. The proposed refinement to the Generalized Hoek-Diederichs relationship is made on the basis of these simulations for tunnelling applications.

ARMA 12-563 A critical look at geotechnical classification for rock strength estimation Day, J. J., Hutchinson, D. J. and Diederichs, M. S. Geological Sciences and Geological Engineering, Queen’s University, Kingston, Ontario, Canada ABSTRACT: Rockmass characterization is an essential process for geotechnical engineering design, and most characterization programs are conducted entirely through the lens of classification systems like RQD, RMR, Q, and GSI. As underground excavations go deeper and as they encounter less routine geohazards, or as mining methods such as caving are adapted for unconventional orebody geologies, these classification systems tend to become less relevant. The authors believe that a more effective characterization approach should consider structures like joints, bedding, and foliations in a rockmass separately in order to both more accurately represent the strength of the rockmass and to better predict the behaviour and failure modes in an excavation. If structures like joints, bedding, and foliations are considered to be “interblock” structures, micro-defects within these blocks like veins, veinlets, and stockworks can be regarded as “intrablock” structures. These intrablock structures should also be considered in characterization since they can have a significant influence on rockmass strength. The effects of intrablock structures on rockmass strength are discussed using two examples from different geological settings. The first example applies RMR to a section of sedimentary rocks in Ottawa, Canada, while the second example uses GSI to discuss the influence of intrablock structures formed by hydrothermal alteration in a genetic model of porphyry copper deposits on rockmass strength.

83 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-120 Models for Geomechanical Characterization of the Rock Mass Formations at DUSEL Using Data Mining Techniques Sousa, L.R. State Key Laboratory for Geomechanics and Deep Underground Engineering, Beijing, China & University of Porto, Portugal Miranda, T. University of Minho, Guimarães, Portugal Roggenthen, W. South Dakota School of Mines and Technology, Rapid City, SD, USA Sousa, R.L. Massachusetts Institute of Technology, Cambridge, MA, USA ABSTRACT: The former Homestake gold mine in Lead, South Dakota, was selected as the site for DUSEL (Deep Underground Science and Engineering Laboratory) by the National Science Foundation. Several reports were done by a consortium of companies concerning geological and geotechnical studies performed at 4850 level. In this paper a summary of these studies are presented. The geotechnical information was used for the development of new geomechanical characterization models using Data Mining techniques in the scope of the DUSEL project. Models for RMR, Q and GSI were developed using several algorithms, as well as models applying Bayesian networks.

Pes ost r - Carbon Sequestration Monday, 25 June, 5:30 pm – 6:30 pm

ARMA 12-173 On the stress-fluid coupled behavior of discontinuous rock mass Kamemura, K. Fukada Geological Institute, Tokyo, Japan ABSTRACT: In the design of rock structures such as tunnels and underground caverns, a continuity analysis considering the nonlinearity of rock has been used in many cases. On the other hand, the mechanical and hydraulic behavior of hard rock is governed by discontinuities of various sizes and numbers contained in rock mass. Therefore, the EDZ (excavation disturbed zone) assumed based on the result of the continuity analysis may differ from that of obtained by the analysis considering discontinuities explicitly. This means that the performance evaluation result of rock structures may change by evaluating discontinuity explicitly or not. In the performance evaluation of the high-level radioactive-wastes disposal facility and of the water-sealing type underground storage facility for gas and oil, it is necessary to examine a stress-fluid coupled behavior, because the requested performance to these facilities is greatly depending on the quality of sealing and water-tightness. In such examination, not only a mechanical stability but also a hydraulic performance such as extremely low permeability for long period is examined in detail. Here, the techniques concerning to stress-fluid coupling analysis which has been adopted up to now is reviewed and problems in the performance evaluation to important and highly reliable rock structures are examined.

84 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-249

CO2 Sequestration in Unmineable Coal Seams: An Experimental Approach Dlamini, B. Department of Mining Engineering West Virginia University, Morgantown, WV, USA Mishra, B. Department of Mining Engineering West Virginia University, Morgantown, WV, USA

ABSTRACT: To study and quantify the effect of CO2 injection on sorption induced strain (swelling) and coal elastic properties, specifically ultrasonic velocity (Vp and Vs) and elastic moduli, an experimental approach was followed. A cuboid coal sample with approximate dimensions of 25cm (9.8 inches) x17cm (6.7 inches) x 6cm (2.4 inches) was prepared. The coal sample used was from the Lower Sunnyside Coal Seam of the Books Cliffs Coalfields in Utah. A specially designed steel frame was used to contain the sample. To provide some degree of confinement, the sample was loaded bi-axially to about 12 MPa (1800psi) using hand (pressure) pumps. The conventional pulse transmission method was used to determine P-wave and S-wave velocities. This method uses transducers to send an ultrasonic wave through the sample, where corresponding transducers on the other end of the sample then pick up the signal. Pre-injection measurements of ultrasonic velocity (Vp and Vs) were taken using the OYO New Sonic-Viewer. From Vp and Vs, other pre-injection properties such as Poisson’s ratio, shear, bulk and Young’s modulus (dynamic) were calculated. Digital deformation gauges were also strategically placed on the sample to measure strain during injection phase. CO2 was injected into the sample at 4 MPa (600psi) injection pressure and 12 MPa (1800psi) confining pressure. Injection into the sample proceeded for five days (25 hours of actual injection). An increase in compressional velocity (as high as 21%) was measured at 12 MPa confining pressure and 4 MPa injection pressure. Since the dynamic elastic moduli are influenced by velocity, increases in elastic moduli were also observed with velocity increases. A maximum adsorption strain of 0.9% was measured at 12 MPa confining pressure and 4 MPa injection pressure. The coal stiffened during active injection due to the possible adsorption of CO2 into the coal matrix. Along with stiffening of the coal, strain (swelling) of the coal was also measured. The combination of stiffening and swelling is indicative of possible CO2 adsorption into the coal matrix.

ARMA 12-255

Role of Geometrical Influences of CO2 Sequestration in Anticlines Amirlatifi, A. Missouri University of Science and Technology, Rolla, MO, USA Eckert, A., Nygaard, R., Bai, B., Liu, X., Paradeis, M. Missouri University of Science and Technology, Rolla, MO, USA ABSTRACT: Most of the parametric fluid flow simulation studies are conducted using simplified horizontally layered basins or two-dimensional models. These simple structures usually do not represent the structure of preferred structural and stratigraphic trap systems for geologic CO2 sequestration. This paper presents a thorough parametric modeling study of generic anticline structures and investigates the influence of layer thickness, wavelength and amplitudes at different depths and under different boundary conditions on the maximum CO2 storage amount. We present a new approach for generating more realistic three dimensional generic models using finite element analysis preprocessors and converting them into finite difference grids for fluid flow simulations under different geometrical and physical conditions. The results of this study show that CO2 sequestration simulations should not be conducted under simplified conditions and that the combination of geometrical parameters and fluid flow boundary conditions have a significant influence on the amount of 2CO that can be injected in anticline trap systems.

85 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-295

Geomechanical Issues and Solutions for CO2 Sequestration in Depleted Hydrocarbon Sandstone Reservoirs Fang, Z. and Khaksar, A. Baker Hughes, London/Kuala Lumpur/Perth, UK/Malaysia/Australia

ABSTRACT: CO2 sequestration in depleted sandstone hydrocarbon reservoirs could cause a number

of geomechanical problems associated with well drilling, completions, and CO2 injection. The depletion narrows the operational drilling mud weight window, which could exacerbate wellbore instabilities while drilling. Well completions may need to consider the potential of solids flowback to the injectors

when injection is interrupted due to CO2 supply or required system maintenance. CO2 injection alters the temperature in the near wellbore region, which could cause fault reactivation or thermal fracturing. In addition, the injection pressure may exceed the maximum sustainable storage pressure for avoiding fracturing and fault reactivations. Through a case study, this paper demonstrates a systematic approach for geomechanical risk assessments for CO2 storage in depleted reservoirs. The study used offset well drilling and wireline log data to derive field stresses, formation pressures, rock strengths and elastic properties. A practical workflow was developed to characterize the interaction between pressure depletion and fracture gradient changes. In this particular case if an operating mud-weight window of 0.5 ppg is required, the well inclination should be below 65º towards the minimum horizontal stress Shmin orientation, or less than 45º towards the maximum horizontal stress SHmax azimuth to mitigate drilling risks. Sanding evaluations indicate no sand control installation would be needed for injectors. Fracturing and faulting assessments confirm that the critical pressures for fault reactivation and fracturing of caprock are significantly higher than the planned CO2 injection and storage pressures. However, the initial CO2 injection could lead to a high risk that a fault with a cohesion of less than 780 psi could be activated, due to the significant effect of reduced temperature on field stresses.

ARMA 12-323 Impact of Boundary Conditions on the Evolution of Coal

Permeability during CO2 Injection under Variable Temperatures Qu, HY. School of Mechanical and Chemical Engineering, The University of Western Australia, WA 6009, Australia Liu, J. School of Mechanical and Chemical Engineering, The University of Western Australia, WA 6009, Australia Pan,, Z., and Connell,, L. CSIRO Earth Science and Resource Engineering, Private Bag 10, Clayton South, Victoria 3169, Australia

ABSTRACT: CO2 is commonly injected at lower temperature than that of the targeted coal seams in the field for sequestration. Under this condition, coal matrix swelling due to the thermal expansion and shrinkage induced by the decreasing adsorption capacity with increasing temperature complicate the permeability evolution and may lead to acceleration or delay of the permeability switch from reduction to recovery depending on the reservoir boundary conditions. In this study, a permeability switching model for CO2 sequestration in coal has been developed to represent the evolution of coal permeability under variable temperatures. The combined effects of coal deformation, gas flow and transport are evaluated through explicit simulations of the dynamic interactions between coal matrix swelling/shrinking and fracture aperture alteration, and translations of these interactions to permeability evolution for a series of hypothetical CO2 injection cases. Our results have revealed the transition of coal matrix swelling from local swelling to macro-swelling as a novel mechanism for the simultaneous switching of coal permeability from the initial reduction to the late recovery. Model predictions are consistent with typical laboratory and in-situ observations available in the literature.

86 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-332 Forecast of Gas Production from Coal Seams: The Impact of Effective Permeability Chen, D. and Liu, J. School of Mechanical and Chemical Engineering, The University of Western Australia, WA 6009, Australia Pan, Z. and Connell, L. D. CSIRO Earth Science and Resource Engineering, Private Bag 10, Clayton South, Victoria 3169, Australia ABSTRACT: The coalbed methane (CBM) extraction usually begins with dewatering the coal seams to reduce the reservoir pressure. Then the gas desorbs from coal matrix into coal cleats and flows towards production wells. The CBM extraction requires a thorough understanding of the interactions among gas desorption, transport, capillary pressure and coal deformation. Although this issue has been investigated comprehensively in recent years, their combined impact is still poorly understood. There are two reasons for this: one is a lack of effective permeability models that take the effective stress changes into consideration, and the other is the mechanical influences are not rigorously coupled with the gas transport and water flow system. In this work, such permeability models are developed and implemented into a fully coupled finite element (FE) model of coal deformation, water flow and gas transport. The FE model represents important non-linear responses due to the effective stress effects that cannot be recovered where mechanical influences are not rigorously coupled with the water flow and gas transport system. The FE model is verified through the history matching of the gas and water production profiles in the Powder River Basin, and applied to forecast the gas production for a series of hypothetical production scenarios.

ARMA 12-369 Modeling of a Well-bore Composite Cylinder System for Cement

Sheath Stress Analysis in Geological Sequestration of CO2 Haider, M. G. Faculty of Engineering and Industrial Sciences, Swinburne University of Technology, Melbourne, Victoria, Australia Sanjayan, J. Faculty of Engineering and Industrial Sciences, Swinburne University of Technology, Melbourne, Victoria, Australia Ranjith,P. G. Department of Civil Engineering, Monash University, Melbourne, Victoria, Australia

ABSTRACT: For the geological sequestration of atmospheric CO2 to be viable, it is important that cement sheath integrity of the well-bore is preserved for a long period. A Apart from other modes of failure, the early age damage to the annular cement seal can initiate leakage of CO2 caused by excessive well-bore pressure and temperature increase/decrease. A composite axi-symmetric multi-cylinder well-bore model has been studied using both analytical and numerical techniques. Static structural and thermal analysis has been performed to investigate e the variation of stresses along cement radius for different combinations of well-bore internal and external pressures and temperatures. In addition to that, linear mechanical properties s of different cement systems have been investigated to compare the suitability y of different cementing materials in well-bore situation. It has been demonstrated from the analysis results that cement with low Young’s modulus experiences lower tensile stresses s than cement with high Young’s modulus for some cases of wellbore internal and external pressures. From the analysis, it also turns out that temperature increase or decrease can develop tensile radial stresses in the cement sheath. In the end, a failure analysis has been presented for different cement systems using Mohr-coulomb failure theory.

87 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-376

Image-based Evaluation of the Effect of CO2-Rich Brine on the pre-existing Fracture system within wellbore cement under dynamic flow-through conditions Ozyurtkan, M. H. Petroleum and Natural Gas Engineering Department, Faculty of Mines, Istanbul Technical University, Istanbul, Turkey Detwiler, R. Civil and Environmental Engineering Department, The Henry Samueli School of Engineering, University of California, Irvine, California, United States Radonjic, M. Craft and Hawkins Petroleum Engineering Department, Louisiana State University, Baton Rouge, Louisiana, United States

ABSTRACT: The effect of greenhouse gas CO2 on global warming has motivated numerous studies and projects around the world, which investigate new technology named Carbon Capture and Storage

(CCS). Effective implementation of CCS technology will require containment of injected CO2 into subsurface geological formations over hundreds of years. The performance of structural seals overlying reservoirs targeted

for CO2 storage will rely upon the integrity of well-bore cements in active and abandoned wells subjected to fluids rich in CO2. Micro fractures within the well-bore cement and micro-annulus at the casing-cement and formation-cement may lead to seepage of CO2 to the surface and/or fresh water aquifers. Thus, understanding

CO2-induced changes to the imperfections in the cement matrix is vital for safe and effective implementation of CCS and the impact such changes can have on the overall hydraulic conductivity of a wellbore system. This paper presents an experimental study that depicts changes of cement’s internal structure due to the interaction with acidic brine through a system of purposefully induced fractures within the cement matrix. The

reported study is unique in that it employs advanced imaging analyses to quantify CO2-induced alteration of well-bore cements. Helical computerized axial tomography and high resolution micro-computed tomography was used to visualize several sub-volumes of flow-through cores. Furthermore, a complementary high- resolution surface profilometry allowed quantification of changes of the roughness of fracture walls and their impact on the fracture aperture as a result of cement-acidic brine interaction over 100 days.

Pesost r - Drilling and Wellbore / Reservoir Geomechanics Monday, 25 June, 5:30 pm – 6:30 pm

ARMA 12-106 Geomechanical Approach to Address Extended-Reach Wellbore Instability in Laminated Formations Li G., Allison D., and Bai J. Halliburton, Houston, Texas, USA ABSTRACT: Modern exploration and development of oil and gas fields requires more cost-effective designs for drilling and production programs than in the past. Drilling high-departure wells using extended- reach drilling (ERD) techniques plays an important role in meeting this challenge. However, there are unique wellbore instability challenges related to ERD techniques that limit the progression of the vertical depth and

88 46th US Rock Mechanics/Geomechanics Symposium horizontal departure length of ERD wells. In this study, characteristics of ERD are investigated to identify and address wellbore instability in highly deviated wells. A case study with field observation is introduced and a best practice for ERD problems. An approach based on both analytical and numerical analysis is recommended for ERD under different in-situ stress conditions. 3D numerical simulation is applied for a case study of a high- angle deviated well in thinly laminated sand and shale formations. The simulated failure mechanism concurs with the observation of the wellbore enlargement/collapse, attributable to both shear and tension failure, and can be used for mud-weight optimization and to establish drilling guidelines to mitigate wellbore instability problems. As a result of this study, an integrated solution for wellbore instability under ERD conditions has been developed considering both poromechanical influence and anisotropy of formations.

ARMA 12-128 Hydraulic Fracturing Design for Horizontal Wells in the Bakken Formation Jabbari, H. and Zeng, Z. Department of Geology and Geological Engineering, University of North Dakota, Grand Forks, ND 58202 USA ABSTRACT: Horizontal drilling and hydraulic fracturing play major roles in enhancing the hydrocarbon production from the Bakken Formation, Williston Basin. This paper presents an integrated fracture/reservoir simulation, coupled with economic analysis to compare different fracture treatment scenarios for the Bakken horizontal wells. To accomplish this, three main tasks were carried out: First, a commercial hydraulic fracture simulator was used to develop basic equations of mass balance, elasticity, height growth, and dynamics of fluid flow. Then, reservoir simulation was performed for the purpose of post-frac production analysis for various fracture treatment cases with different well/fracturing treatment parameters. These variables included: fracturing fluid type and volume, proppant type and size, fracture half-length, number of fracture stages, and lateral length. Finally, a proper cash flow model was constructed for each treatment scenario, and the corresponding net present values (NPV) were calculated along with internal rates of return (IRR). These two useful parameters were utilized for comparing the financial advantages of alternative treatments and to analyze the economical feasibility of different scenarios. This study demonstrates how the design and economics of hydraulic fracturing depend highly on the reservoir characteristics and on the operational parameters and costs.

ARMA 12-155 A Geomechanical Approach to Reduce Drilling Time Sare, A. R., Alvarellos, J., Villarroel, F. M. and Ward, C. Baker Hughes/RDS, Houston, Texas, USA Vazquez, L.A. and Aguilera, L.F.N. Petróleos Mexicanos (Pemex), Poza Rica, Veracruz, Mexico ABSTRACT: Geomechanics is a powerful tool to manage unexpected drilling and production problems. This paper shows a successful example of how to reduce non-productive drilling time by using a geomechanical model. For our study, due to data limitations a real-time model was applied to help avoid drilling issues and allow for fast decision making during the drilling process. As a result, the calibrated model updated on a daily basis with new information, provided a better understanding of the stress field, pore pressure and formation mechanical strength. The updated geomechanical model was used to better predict collapse pressure, pore pressure and fracture gradient; which helped the drilling team to make better decisions while drilling. Our experience has shown that with the use of a geomechanical model, major geomechanical issues can be mitigated, drilling time may be reduced up to 50% and cost can be decreased significantly. Results presented here show how a geomechanics study can add value to drilling projects.

89 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-195 Calculation of Friction Coefficient and Downhole Weight on Bit with Finite Element Analysis of Drillstring Wu, A. and Hareland, G. University of Calgary, Calgary, Alberta, Canada ABSTRACT: The real-time calculated friction factor between drillstring and wellbore can be used to identify possible hole cleaning problems, stuck pipe, differential sticking, formation change and mud lubrication problems. The correct calculation and analysis of downhole weight on bit (DWOB) is important for drilling operation and optimization. This paper introduces a practical finite element analysis (FEA) model and program, which can simulate the working behavior of drillstring during the drilling operation. Given the hookload, wellbore geometry and some other drilling parameters, the FEA program can automatically backcalculate the friction factor or coefficient between drillstring and casing or formation. The program developed in this paper can also be used to calculate the actual DWOB in a vertical, directional, horizontal, and any complex well path under different drilling operational modes. The friction coefficient in a well is back-calculated using off bottom data. Based on the friction coefficient the actual DWOB can be obtained using the FEA program. The friction coefficient calculated from the FEA program is reasonable. The FEA program will play an important role in a new Autodriller system which will be used for real-time drilling optimization, rock strength prediction, and solving some other drilling problems.

ARMA 12-214 Preliminary Tool to Assess Fluid Flow Effects on Reservoir Stresses Using Coupled Geomechanics and Fluid Flow Albinali, A. and Kazemi, H. Colorado School of Mines, Golden, CO,USA ABSTRACT: The work presented in this paper investigate developing a mathematical formulation using finite-difference techniques to solve the geomechanics equations consistent with the mathematical formulation for solving fluid flow equations. The key considerations are consistency of the mathematical formulation (finite-difference technique) for both geomechanics and fluid flow calculations, and ease of implementing this formulation. Results show that it successfully model the induce stress changes (Δσ) in the reservoir rock created by either fluid production or injection. Also, the results obtained from applying finite-difference technique in solving the geomechanics equations are comparable to that obtained from using finite-element techniques. The experience obtained from this work indicates that fluid withdrawal or injection can have a great impact reservoir stresses. The provided solution can be used as a preliminary geomechanics and fluid flow modeling tool to assess impact of fluid movement on reservoir stresses. A more advanced modeling workflow/software package can be sought if required.

90 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-241 New Approach in Mechanical Modeling of Inserts of the Rollercone Bits B. Rashidi, G. Hareland, A. Wu University of Calgary, Calgary, Alberta, Canada Y. Lin, Y. Yang Southwest Petroleum University, Chengdu, Sichuan, China ABSTRACT: It has been well understood that the inserts or cutters on the cones of a rollercone bit directly interact with the rock at the bottom of the hole. Therefore, mechanical modeling of inserts while interacting with the rock is important in simulating/predicting drilling rate of rollercone bits. This paper addresses the modeling of cutter-rock interaction in terms of the geometry of the generated craters as well as the applied operational and design parameters. The model is developed based on an experimental study which was conducted using different levels of loadings, rotational speed, cone offsets, inserts and rock types. It has also been well recognized that the mechanism of rock-cutter interaction is a complicated phenomenon which makes it difficult to establish an analytical model to simulate this behavior. The complexity can be either due to modeling of the forces while a single insert penetrates into the rock or due to the sophistication in modeling the generated craters’ geometry. In this study, multi-variables regression analysis method was implemented to analyze and process the available laboratory data. The introduced models/correlations reflect the interaction mechanism between a rollercone bit and the rock and are capable of estimating formation drillability of a specific bit type (IADC code) considering integrated effects of the existing parameters. Moreover, the implementation of the mechanical model makes the drilling simulator predict more accurate rate of penetration values which helps improve drilling performance of the rollercone bits. The comparison between the simulator result before and after implementing the new models are also conducted which validates the feasibility of the developed mechanical models in predicting the rate of penetration of rollercone bits utilizing field data.

ARMA 12-243 Intelligent Prediction of Wellbore Stability in Oil and Gas Wells: An Artificial Neural Network Approach Jahanbakhshi, R. and Keshavarzi, R. Young Researchers Club, Science and Research Branch, Islamic Azad University, Tehran, Iran. Jahanbakhshi, Ro Department of Geology, Shiraz Branch, Islamic Azad University, Shiraz, Iran. ABSTRACT: Wellbore stability is one of the great challenges during drilling oil and gas wells due to complicated geological and stress conditions which can lead to wellbore instability problems. Wellbore instability can results in many drilling problems such as lost circulation and stuck pipe. In addition, wellbore stability can be affected by natural discontinuities and geological conditions. In this way, wellbore stability should be taken into account and predicted in any drilling planning. Artificial intelligence methods such as artificial neural network (ANN) are engineering tools which are able to solve many different engineering problems by considering the effective parameters. In this study, the data of stability/instability of some wells in one of the Southern oilfields in Iran has been considered. So, an ANN approach was developed in such a way that in-situ stresses, drilling string properties, drilling operation, geological conditions and mud properties were the inputs and wellbore stability/instability was the output. Eventually, the results obtained from the developed ANN were compared with the real condition in drilled oil wells in the related field which were so promising. The developed ANN approach can be used in drilling planning and predicting wellbore stability in any oil or gas wells in the related oilfield as well as reducing the costs of drilling problems originated from wellbore instability.

91 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-244 Real-time Prediction of Rate of Penetration during Drilling Operation in Oil and Gas Wells Jahanbakhshi, R. and Keshavarzi, R. Young Researchers Club, Science and Research Branch, Islamic Azad University, Tehran, Iran. Jafarnezhad, A. Department of Petroleum, Omidieh Branch, Islamic Azad University, Omidieh, Iran. ABSTRACT: The researchers in the drilling engineering fields are always looking for the prediction of unexpected events and optimizing the related parameters. Predicting the Rate of Penetration (ROP) is of a great attention for drilling engineers due to its effect on the optimization of various parameters that leads to reduction of the costs. Artificial neural network (ANN) has an efficient capability of combining different parameters to predict different situations. According to ANN structure, it can get the effective parameters as the inputs to predict and evaluate the value of the target parameter(s) as an output. Since formation type and rock mechanical properties, hydraulics, bit type and its properties, weight on the bit and rotary speed are the most important parameters that affect ROP, they have been considered as the input parameters to predict ROP. In this study, ROP has been investigated and predicted in one of Southern Iranian oilfields through an ANN model. Finally, ROP has been predicted prosperously by the developed ANN which has been checked with the field measurements of drilled wells. The results indicate the efficiency of ANN in this field which can be used in drilling planning and real-time operation of any oil and gas wells in the related field that can result in costs reduction.

ARMA 12-246 The Two-Term Rollercone Rate of Penetration (ROP) Model with Integrated Hydraulics Function Kowakwi., I. and Chen, H. New Mexico Institute of Mining and Technology, Socorro, New Mexico Hareland, G. and Rashidi, B. University of Calgary, Calgary, Alberta, Canada ABSTRACT: Drilling rate models have been used extensively to increase drilling efficiency by introducing the optimum operational and bit design parameters for known formation types. Several authors have attempted to develop drilling rate models through investigating the effect of the associated parameters for rollercone bits. Among them, the two-term model developed by Warren in 1981 produces accurate results in the presence of a sufficient hydraulic level at the bit as well as with no bit wear effects. It was found that the hydraulic energy at the bottom of the hole can significantly influence the rate of penetration by removing the generated cuttings. In a real drilling operation, the generated cuttings might not be properly removed due to insufficient hole cleaning underneath the bit. Consequently, some portion of the bit’s energy will be spent on re-grinding of the cuttings which reduces the drilling rate. This paper presents the integration of a simple normalized hydraulics model in the two-term rollercone bit ROP model and verifying it through utilizing laboratory data. The modified model can be applied to estimate correct rate of penetration values considering available hydraulic level at the bit. It can also help determine the required hydraulic energy for a given set of operational parameters and a known formation type. Verification of the proposed model will also be carried out using sets of field data. Preliminary results indicate an acceptable match between calculated ROP values and those reported from the laboratory experiments. The application of the new model will initially be utilized to predict rock strength but will further be used as an input to predict porosity and permeability of the rock formations being penetrated.

92 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-315 Use of Multiple Lithology and Rock Property Indicators to Evaluate Wellbore Failure in Layered Formations Bai, M. Halliburton, Houston, Texas, USA Li, G. Halliburton, Houston, Texas, USA Meng, F. ConocoPhillips, Houston, Texas, USA ABSTRACT: To identify suitable correlations between UCS and sonic velocity for a variety of lithologies, this paper analyzes the variations of formation lithology (e.g., shale, sand, or limestone) and the transitional lithology (e.g., sandy shale, shaly sand, tight limestone, and porous limestone) and examines their relations to the mechanical properties of the respective formation (e.g., UCS). Interpreting the characteristic responses from various wireline logs, such as gamma ray (GR), spontaneous potential (SP), resistivity (RES), sonic (DT), neutron porosity (NPHI), and formation density (RHOB), more accurate formation identification is sensibly obtained than the conventional method of using GR as the sole lithology indicator. The proposed methodology is illustrated using an actual wellbore stability case study in an oil field of the Gulf of Mexico (GOM). After the lithologies are defined, the correlated mechanical properties are determined (e.g., UCS, friction angle, cohesion, Young’s modulus, and Poisson’s ratio). The proposed method is used to evaluate the lower bound of safe mud weight windows in assessing the wellbore stability in drilling, invoking the shear failure gradient. The evaluation is based on each formation layer where the desired correlations between layer lithology and mechanical properties are provided. The calculated shear failure gradient will be used with the determined fracture gradient (or closure pressure) to define the safe mud weight window. With the reasonable sensitivity study, the match between the calculation and the observation can be ensured.

ARMA 12-362 Numerical analysis of Experiments in Sand Control Measures Using Stand Alone and Open Hole Gravel Pack Completion Vargas Jr, E.A., Velloso, R.Q., Richie, R., Pessoa, T.F.P and Mejia, L.A.C. Dept. of Civil Engineering, Catholic University, Rio de Janeiro, RJ, Brazil Gonçalves, C.J. and Block, M. Petróleo Brasileiro S.A., Rio de Janeiro, RJ, Brazil Villarroel, F.M.G. Baker Jughes, Rio de Janeiro, RJ, Brazil ABSTRACT: The present paper presents numerical analysis of experiments performed in a large polyaxial frame in order to understand the interaction mechanisms between the rock formation and the linings for two specific conditions: stand alone, where lining has limited contact with the formation and the installation of gravel pack. All cases were studied on an artificial cubic rock samples of 30 cm side lengths with a centered hole of 6.0 cm in diameter. The block was then compressed by hydraulic actuators in two perpendicular orientations. In the numerical analysis studies, two different approaches were used: continuum only and coupled continuum-discrete techniques. The paper presents results of the experimental program carried out and of the numerical analysis carried out using the above mentioned techniques. Comments are made regarding the match between experimental and numerical analysis and the adequacy of the latter for modeling the types of sand control measures focused in the work.

93 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-373 Numerical simulations of sanding under different stress regimes Younessi, A. and Rasouli, V. Curtin University, Perth, Western Australia, Australia Wu, B. CSIRO, Melbourne, Victoria, Australia ABSTRACT: Laboratory experiments of sand production conducted under true-triaxial stress conditions were simulated numerically using ABAQUS program. The experiments were performed in a true-triaxial stress cell on 100x100x100 mm3 cubes of synthetic sandstones. Two and three dimensional numerical analyses were conducted to investigate the impact of the magnitude of far-field intermediated principal stress and pore pressure on the failure in the vicinity of a borehole. Different stress boundary conditions were modeled for this purpose. The results provide a better understanding on how the stress anisotropy may have an impact on borehole failure and sand production mechanism. The simulation was used as a tool to optimize and plan the future tests conducted in the laboratory on cube samples. The results of the numerical models will be presented and interpreted.

ARMA 12-396 Terminal Failure of Plastic Zone around the Openings Geilikman, M. B. Shell International Exploration & Production Inc. Houston, Texas, USA Wong, S.-W. Shell International Exploration & Production Inc. Houston, Texas, USA ABSTRACT: Growth of plastic zone around boreholes is described in a model with post-failure non-linear power-like strain softening. The failure itself is defined by conventional Mohr-Coulomb criterion. Growth of plastic zone around the inner opening is considered for a hollow (thick-wall) cylinder geometry. It is found that the growth of plastic zone as a function of the outer load is not unlimited but encounters a terminal instability before reaching the outer boundary of hollow cylinder. Without post-failure softening the plastic zone growth does not encounter that type of instability except for the trivial one when the plastic zone spreads throughout the sample to the outer boundary. This terminal instability is reached at some critical load, and plastic zone cannot grow further at a higher load. Instead the plastic zone experiences a brittle failure, and only after that the entire cylinder collapses. It is shown that the terminal instability is characterized by singular response to the load of Considére type. The critical load and final size of plastic zone depend on the softening parameters. Softening-oriented measurements in triaxial tests on stiff machines can provide parameters of post- failure softening and allows us to predict terminal failure in hollow (thick-wall) cylinder samples under load. The model also provides geometric scaling of the data obtained in hollow (thick-wall) cylinder test, and applied for sand production prediction.

94 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-408 Characterization of two shallow aquifers for produced water injection Hettema, M. H. H., Jøranson, H. Statoil, Stavanger, Norway and Larsen, L. Statoil, Stavanger, Norway (now with Kappa Eng.) ABSTRACT: The Statfjord field is an old field that has now entered its late life phase where the current strategy is deep depressurization to produce solution gas. The large amounts of water produced were initially planned to be disposed through injection in overlying shallow aquifer reservoirs. In order to be able to optimize sustainable injection design, two well tests were performed with long fall-offs. The main parameters determined are the reservoir connectivity, minimum stress, flow capacity and pore volume compressibility. This article presents the results of these well tests and to increase the confidence of our interpretation, we compare them with results from other wells and independent testing methods. We discuss the ambiguity and uncertainties of our interpretation. As a general conclusion we demonstrate that it is challenging to properly characterize shallow reservoirs. This article contributes to an oil industry workflow leading to a better understanding of the design of large scale shallow reservoir injection schemes.

ARMA 12-423 Limitations of Log-Based Wellbore Stability Analysis in an Unconventional Conglomerate-Rich Reservoir in the Southern North Sea Hilgedick, S. A. and Nygaard, R. Missouri University of Science and Technology, Rolla, Missouri, US Hellvik, S. and Hoel, E. Lundin Norway AS, Oslo, Norway Skurtveit, E. Norwegian Geotechnical Institute, Oslo, Norway ABSTRACT: The reservoir section of a recent North Sea discovery consists of both sandstone and conglomerate formations. The conglomerate is comprised of a sandstone matrix with granite clasts of varying size and distribution. The field will be developed with deviated and horizontal wells. One of the risks associated with the development is the stability of inclined wells in the conglomerate. To address this concern data from the vertical exploratory wells was used to conduct a wellbore stability analysis for the deviated wells with rock deformation and rock strength properties calculated from well logs. Later triaxial tests were performed to verify these results. While the log-based strength and deformation values exhibited very good predictability for the sandstones, large variation was found between the values derived from log analysis and the rock mechanical testing for the unconventional conglomerate zones. The reason for this discrepancy was observed in the rock mechanical tests where it was clear that the limiting factor of conglomerate strength was the bonding between the clasts and the matrix. Based on the rock mechanical testing it was determined that the conglomerate had lower strength and the limiting factor of mud weight selection was the conglomerate and not the sandstone as first predicted. This demonstrates how careful consideration must be taken when extending rock mechanical correlations to unconventional rock types.

95 46th US Rock Mechanics/Geomechanics Symposium Pesost r - Stability and Support of Underground Openings Monday, 25 June, 5:30 pm – 6:30 pm

ARMA 12-105 Physical Simulationg on Mechanical Characteristics of Rock Surrounding Retreeting Roadway in Steeply Dipping Coal Seam Yang, K. 1 Anhui University of Science and Technology, Huainan,Anhui Province, P.R.China; 2 Chongqing University, Chongqing,P.R.China; 3 Huainan Mining Industry Group Co., LTD, Huainan,Anhui Province, P.R.China. Xie, G. 1 Anhui University of Science and Technology, Huainan,Anhui Province, P.R.China; ABSTRACT: In order to investigate into mechanical characteristics of rock surrounding entry with using bolt support system technology to control rock stability in large dip coal seams (LDCS) whose obliquity are from 25° to 45°, self-design rotatable experimental frame of similar material simulation was used to build the 30° model of solid-side entry based on analyzing geological and technological conditions in Huainan coal mines. Excavating and mining induced stress development, deformation characteristics, and breakage modes of rock surrounding gateway in LDCS have been synthetically analyzed. Results show that, influenced by large dip, asymmetrical characteristic of stress redistribution and deformation is to be serious and strata behaviors, such as roof falling and breaking, high-rib heaving and caving, floor heaving, and low-rib collapsing etc., are to be shrewd. All above utmost extent lead it is more difficultly to implement bolt support to control gateway rock stability in LDCSs mining. The high- rib and roof of entry in solid coal are the key sections to control in bolt support implementing. Effecting and Acting mechanism by large dip on mechanical characteristics of surrounding rock and bolt support system are opened. Engineering practice show that it is the key issue to use unsymmetrical bolt-net-cable support system to control rock stability of extracting gateway based on unsymmetrical characteristics of structure and strata behaviors. And it is also very important to improve support material, optimize support parameters, and enhance excavating management.

ARMA 12-144 The application of the 3-D hydraulic fracturing stress measurement in the deep underground cavern project Guo, Q., Bao, L., Ding, L., Xu, J. Institute of Crustal Dynamics, China Earthquake Administration, 100085 Beijing ABSTRACT: Determining the in-situ stress of wall rock is extremely important in the underground cavern project. The principal stresses at one site can be obtained by hydraulic fracturing stress measurement at different parts of the borehole. Moreover, by measuring the stresses in boreholes with three different orientations at one site, the principal stresses in different orientations at this site and the three-dimensional (3-D) stress state can be obtained. Here we show one example of the 3-D hydraulic fracturing stress measurement in a deep underground carven project located in Eastern China. Compared to the results of stress measurement by the overcoring technique, the results from the 3-D hydraulic fracturing measurement are more reliable. From relationships of stress variations against depth, it is even possible to clearly recognize the stress relaxation curve, the stress concentration region and the original stress distribution in the shallow part of the cavern wall. This example indicates that results of 3-D hydraulic fracturing stress measurement can well demonstrate the stress distribution of the wall rock in the deep underground cavern project.

96 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-165 3D elasto-plasticity damage numerical analysis method of large underground cavern groups excavation based on the irreversible thermodynamics theory Yue, X. School of Civil Engineering, Shandong Jianzhu University, Jinan, P.R. China Li, X. Ministry of Education Key Laboratory of Geotechnical and Underground Engineering,Shanghai, P.R. China and School of Civil Engineering, Shandong Jianzhu University, Jinan, P.R. China Shi, X. School of Civil Engineering, Shandong Jianzhu University, Jinan, P.R. China ABSTRACT: The engineering geological conditions of large underground cavern groups are complicated. The reasonable excavation and support sequence is important for the stability of rock mass. In order to simulate rock mass veritably and analyze its damage in construction, the elasto-plasticity damage model and damage evolution equation is presented on the base of the irreversible thermodynamics theory. The 3D elasto-plasticity damage finite element code D-FEM is programmed by FORTRAN language, which has the capabilities of simulating excavation and support, computing quickly and group function. 3D numerical model of underground cavern group is established, input initial geo-stress is inversion of field stress measurement.

ARMA 12-200 Preliminary Experimental Study of Surrounding Rock Properties for Underground Coal Gasification in Western North Dakota Pei, P., Zeng, Z., Liu, H., and Ahmed, S. Department of Geology and Geological Engineering, University of North Dakota, Grand Forks, North Dakota, USA ABSTRACT: Underground coal gasification (UCG) is a promising technology to recover the vast unmineable, low-rank coal resources. Major challenges associated with the UCG process, such as surface subsidence, groundwater pollution, and product gas leakage, are significantly controlled by the mechanical and transport properties of the surrounding rocks of the target coal seam. During the UCG process, the surrounding rocks experience stress changes due to gasification-induced excavation and high temperatures. At the same time, fluid saturation in the rocks also changes. Stability of the “pressure arch” in the surrounding rocks over the gasification zone is essential to the safety and success of an UCG project. This paper presents the laboratory testing results on the specimens collected from the overburden of Harmon lignite bed (Fort Union Formation) in western North Dakota. The results can help understand the rock behavior in the UCG process. The laboratory testing system simulated the in-situ stress conditions in the “pressure arch” during and post the UCG process. The purpose of the tests is to understand the failure mechanism and fracturing features of the rocks in the “pressure arch”, as well as how the rock mechanical and transport properties change with the variation of the in-situ stresses. The results indicate that the rocks have a low strength, but are relatively impermeable. In the test, the permeability of the specimens decreased as the axial stress or confining stress increased. Based on the testing results, the properties and behavior of the rocks and their effects to the UCG process are discussed.

97 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-325 Analysis of the Properties of Seepage Rate and Seepage force around Tunnel Circumference under the Groundwater Table Wu, Z. Geo-Disaster Prevention Lab.2, Dept. of Civil and Structural Engineering, Kyushu University, Fukuoka, Japan Chen, G. Geo-Disaster Prevention Lab.2, Dept. of Civil and Structural Engineering, Kyushu University, Fukuoka, Japan ABSTRACT: The threat of seepage to the stability of underground structure has always been remarked by a number of experts, and there engineering subjects collapsed because of the effect of seepage force. Some pursuers on the seepage have got invaluable results to solve the problems developed by the seepage force. In this paper, the author has reviewed the analytical solutions of the inflow, the hydraulic gradient and the seepage force have been obtained, and then described the importance of seepage to the stability of tunnel; the numerical analysis by Midas GTS has been also used to simulate the seepage, and illustrated the distribution of seepage rate around the tunnel circumference, and analyzed the effect of the tunnel depth, the space and the relative location on the distribution and the maximum values of seepage rate along the tunnel circumference. Finally, based on the Darcy’s law the most instable location induced by the seepage force along the tunnel circumference has been represented for the single tunnel and the twin-tunnel, and the application range of the analytical expression has been also discussed, which will be advantage to the tunnel construction and reinforcement.

ARMA 12-354 A New Workflow for LiDAR Scanning for Change Detection in Tunnels and Caverns Delaloye, D. Queen’s University, Department of Geological Sciences and Geological Engineering, Kingston, Ontario, Canada Hutchinson, J. Queen’s University, Department of Geological Sciences and Geological Engineering, Kingston, Ontario, Canada Diederichs, M. Queen’s University, Department of Geological Sciences and Geological Engineering, Kingston, Ontario, Canada ABSTRACT: Measuring change in underground environments is an important aspect of geological engineering. Recently, methods for using light detection and ranging (LiDAR) to measure change and convergence in tunnels and other underground environments have been demonstrated. To properly apply these new methods, it is important that an appropriate workflow is followed. The workflow proposed in this paper includes recommendations for choosing scan resolution settings and scan locations based on the level of change to be measured. The workflow follows through to the extraction of cross-section data for convergence measurement and back calculation.

98 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-392 Experimental and Numerical Analysis of Salt Cavern Convergence in Ultra-Deep Bedded Formation Ma, H. & Yang, C. State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, The Chinese Academy of Science, Wuhan 430071 China Qi, Z. & Li, Y. Research Institute of Exploration and Development, Jianghan Oilfield Company, SINOPEC, Wuhan 430223, China Hao, R. Hengda Century (Beijing) Geophysics Technology Co., Ltd, Beijin, 100101, China ABSTRACT: In order to investigate the convergence of underground gas storage (UGS) salt cavern in ultra-deep formation, creep tests in high temperature and numerical simulation are performed. The effects of temperature and deviatoric stress are investigated. Creep test results show that increasing of deviatoric stress or temperature can both increase steady-state creep rate, but the effect of deviatoric stress is stronger than temperature in ultra-deep formation. Higher deviatoric stress can strengthen the temperature effect. Stress is the dominant factor while temperature is the secondary factor. The influence mechanism of stress and temperature to creep is different. The new transient creep phase will never be performed by temperature increasing while can be performed again by deviatoric stress change. Numerical analysis demonstrates that volume convergence has business with the value of inner pressure, rather than injection and withdrawal. The volume convergence trend looks like the creep curve, which grow faster in the beginning and becomes slower by the creep time. The first five years is the most important volume monitoring time. The designed minimum and maximum inner pressures for Qianjiang UGS are 17 MPa and 32 MPa.

ARMA 12-534 Long term tunnel behaviour and support response analysis using 2D numerical modelling methods Paraskevopoulou, C. Vlachopoulos, N. Diederichs, M.S. GeoEngineering Centre, Queen’s-RMC, Kingston, Ontario, Canada ABSTRACT: Numerical modelling is an integral part of modern tunnel engineering design, enabling assessment of rock-structure interaction and stability as well as assisting in the optimum choice of both excavation method and support measures being employed. Problems and challenges in numerical analysis for underground works arise from simulating the long term behaviour in underground works where time-dependency issues such as swelling or creep occur. In order to deal with creep in the conventional sense, engineers tend to use variations of the two following alternatives: a) viscoplastic analysis or, b) strength degradation modelling. Long term tunnel behaviour is widely discussed in the geotechnical literature [1, 2, 3]; however, practical references for the ultimate simulation of long term tunnel stability and support response are limited. This paper summarizes practical approaches regarding the long term tunnel behaviour and the support measures applied by comparing the two alternatives. This paper approximates time-dependent behaviour for deep tunnels in weak rock using industry norm, conventional 2D methods [4, 5] with emphasis on the support measures being applied. Long term behaviour does not always follow the same path and specifically depends on the loading history and the deferred process. This paper serves to highlight the caveats and concerns associated with the practical modelling of long-term response in a relevant 2D analysis. The numerical modelling results presented herein demonstrate the variability of resulting long term tunnel behaviour based on the software used as well as the assumptions associated with the input parameters. Further, this paper summarizes the limitations of adequacy of these methods concerning the relation between the tunnel long term response and the support measures utilized.

99 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-607 Estimating Fractal Parameters of Rock Fracture Roughness by a Heuristic System Babanouri, N. and Karimi Nasab, S. Department of Mining Engineering, Shahid Bahonar University of Kerman, Iran Sarafrazi, S. Department of Electrical Engineering, Shahid Bahonar University of Kerman, ABSTRACT: Since the fractal theory has been suggested as a suitable tool to quantify roughness of rock fractures, special attention has been paid to estimate the fractal dimension of roughness profiles, D. However, the findings in this issue reported in the literatures are in contrast. In this paper, a new method is presented to estimate D reliably. First, a large number of fractional Brownian profiles with different values of the fractal parameters were generated and their statistical features were extracted. Then, a hybrid algorithm consisting of two algorithms, a particle swarm optimization (PSO) algorithm and a multi-layer perceptron (MLP) neural network, was developed. The inputs of the system were the statistical features of profile. In each it- eration of thenhybrid system, the PSO and MLP algorithms exchanged information with each other to optimize values of the fractal parameters. Finally, the system provided the best set of fractal parameters for a given profile. The effectiveness of this method was shown by estimating the fractal parameters of a testing set of profiles.

ARMA 12-626 Geomechanics Study of West Orebody Crown Pillars at Coleman Mine Razavi, M. Vale Limited, Sudbury, Ontario, Canada Yao, M. Vale Limited, Sudbury, Ontario, Canada ABSTRACT: The main goal of this study is to evaluate how the mining of the West Ore body (WOB2 and WOB3) affects the stress conditions in the crown pillars as mining progress upwards. Also, this analysis determines the “transition zone” in crown pillar at which significant changes are likely to occur, and when changes to the mining method and ground support are required. The intent is to determine the minimum crown pillar thickness that could be mined with current post pillar cut-and-fill method. The West Ore body is divided into two mining zones, WOB2 and WOB3 with the current back elevations of 9095 (cut 7) and 8702 (cut 4), respectively. This study includes two and three dimensional numerical models .A finite element program “Phase2” was used to plastically estimate the displacement and stress at the core of crown pillars. The Bob’s Lake Fault and backfill were incorporated into the model. The 3D boundary element program “MAP3D” was used to obtain the elastic stress and displacement at different locations and elevations. Also, the 3D analyses were used to evaluate the effects of mining in Main Ore body on the West Ore body. The two and three dimensional numerical analysis results along with field observation and historical microseismic data suggest that; 1) Due to the narrow nature and dip of the ore body in WOB2, the cut -and-fill mining may need to be converted to bulk mining from Cut 10/Cut 11 and above. 2) As mining advances upwards in WOB3, the very high deviatoric stresses zone would form in the back at Cut 15. In WOB3, the crown pillar thickness should be limited to a minimum of 90 ft.

100 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-665 An estimation of the height of fracture zone in longwall coal mining Majdi, A. School of Mining Engineering, College of Engineering, University of Tehran, Tehran, Iran Email: [email protected] Hassani, F.P. Department of Mining and Materials Engineering, Faculty of Engineering, McGill Email: [email protected] Nasiri, M.Y. Khavar Tunnel Consulting Engineering Inc., Tehran, Iran ABSTRACT: Longwall mining is one of the most widely used underground mining methods most suitable in relatively flat-lying, thick, and uniform coalbeds. Due to extraction of the coal seam in the panel, the roof above the mined-out zone will be collapsed and distressed and then the panel roof loads will be transferred to the front and the neighboring solid sections where the face, adjacent access tunnels and the intervening barrier pillars are located. The height of distressed zone, in this paper, called the height of fractured zone, plays a vital role in an evaluation of the amount of loads which will be transferred towards the solid sides. The paper describes the mechanism of development of the height of this zone. Two new simple, yet conclusive, mathematical approaches to estimate the height of fracture zone are proposed. The results are compared with each other and with the only comparable model as well. Finally, the results are compared with both the in-situ measurements and those empirically inferred and extracted from the available literature. The comparative results confirm that the models’ results are in reasonable agreement with both the in-situ-measurements and those proposed empirically gathered from a brief and highly selective literature review that is provided in this paper.

Pesost r - Rock Properties and Rock Mass Characterization Monday, 25 June, 5:30 pm – 6:30 pm

ARMA 12-119 The Characteristics of Rock Mechanics and Acoustic Wave Parameters of Carbonate Rock in the North-east Sichuan Y.T. Guo, C.H. Yang and H.J. Mao State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, The Chinese Academy of Sciences, Wuhan, P.R. China. J.H. Chen Sinopec Research Institute of Petroleum Engineering, Beijing, P.R China. Y. Luo Key Laboratory of Ministry of Education for Exploitation of Southwest Resources and Environment Disaster Control Project, Chongqing University, Chongqing, P.R. China. ABSTRACT: Carbonate reservoirs have a significant proportion of the known petroleum reserves, with its characteristics of pores and fractures development. A series of laboratory testing have been performed. Using high pressure water jet cutting the artificial crack (different angles and different lengths for dolostone & limestone), in order to simulate the natural fractures. We have measured P-wave velocity and S-wave

101 46th US Rock Mechanics/Geomechanics Symposium velocity on carbonate rock for original specimens and artificial crack specimens. Results from laboratory research are as follows: 1) as the fractures exist, P-wave velocity and S-wave velocity decreased, the fracture has more influence on S-wave velocity than P-wave velocity; 2) under uniaxial compression, the curves of axial strain and the compression velocity can be divided into three stages: 3) the fracture has an important influence on mechanical parameters of carbonate rock. Increasing fracture angle and length will result in decreasing the strength parameters under uniaxial compression; 4) under condition of confining pressure, P-wave velocity increases with the increasing of confining pressure. The growth rate of dolostone’s P-wave velocity is larger than limestone. The research results can be used for better analysis the mechanical and acoustic wave characteristics of carbonate rock in deep drilling engineering and provide technology parameters for exploration in carbonate reservoirs.

ARMA 12-152 Study of punch tip effect on creep of materials in impression creep test Rassouli, F.S. and Mehranpour, M.H. Graduate student of School of Mining Engineering, University of Tehran, Tehran, Iran Moosavi, M. Associate professor of School of Mining Engineering, University of Tehran, Tehran, Iran ABSTRACT: Applying supports like buttresses or boughs in underground structures such as tunnels and mines cause indentation of the support into the bearing floor due to the creep, which is caused by constant load from the support. Since creep behavior is a time dependent characteristic of rocks, it is hard in practice to investigate the indentation depth of the support, the changes in profile of the floor due to the indentation creep, and the best support tip shape. It seems that for this kind of investigation impression creep test is a suitable one to obtain the creep behavior of the material of the floor in small scale and in short periods of time. In this study, the effects of different kinds of punch tip are compared experimentally and numerically. For this purpose, four different shapes of punch tip (cylindrical with flat end, two conical shapes and cubic) are used to perform impression creep tests under different loading levels. These tests are carried out on rock salt because of its softness and creep behavior. Furthermore, all of these experiments were investigated numerically using commercial finite element analysis (FEA) software, ANSYSTM, to acquire the profile of material beneath the punch during the experiment.

ARMA 12-181 Evaluation of the Brazilian Test Size Effect using Discrete Element Modeling Tomac, I. and Gutierrez, M. Department of Civil and Environmental Engineering, Colorado School of Mines, Golden, Colorado, USA ABSTRACT: The paper presents the results of a micromechanical study using the Discrete Element Method (DEM) to critically evaluate the determination of the tensile strength of brittle rocks using the Brazilian test. The Brazilian test is performed on model cylindrical specimens loaded with two diametrically positioned plates and fails by splitting the cylinder. In the study, a series of DEM models of the direct tensile and Brazilian tests was conducted in controlled conditions to establish the relationship between the bond strength between rock grains/particles and the tensile strength from the Brazilian test. The modeling was focused on size effects and micromechanical insights into the splitting and fracture propagation processes in the Brazilian test. The results of the micromechanical study lead to a scaling relationship to account for the effects of Brazilian test specimen size, and for practical recommendations to obtain more accurate estimations of the nominal tensile strength of the rocks from the Brazilian test data.

102 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-215 Experimental study of size effects of rock on UCS and point load tests Masoumi, H., Douglas, K.J. School of Civil and Environmental Engineering, University of New South Wales, Sydney, NSW, Australia Naydam, S. and Hagan, P. School of Mining Engineering, University of New South Wales, Sydney, NSW, Australia ABSTRACT: A number of studies have investigated the size effect of intact rock mostly focusing on the uniaxial compression test. The most widely used being that by Hoek and Brown [1]. The authors have conducted a suite of uniaxial compressive and point load tests on some igneous and metamorphic rocks to assess the effect of size on the results. The results illustrate that the trend of the Hoek and Brown [1] size relationship is not applicable to the tested rock samples particularly at small diameters. It was also found that the size effect relationship differed for the point load and unconfined compressive tests. The authors present the results and provide a discussion as to the potential reasons for the varying size effects at different stress paths. The results have implications for designers when considering potential testing programs and estimations of strength parameters for their designs in rock.

ARMA 12-277 Strength and wave velocity variation during chemical attack on some masonry rocks Marques, E. A. G. Universidade Federal de Viçosa, Viçosa, Minas Gerais, Brazil Sossai, F. J. M. GEOFT Engenharia e Consultoria LTDA, Belo Horizonte, Minas Gerais, Brazil ABSTRACT: This paper presents the results of a comprehensive study carried out on five different Brazilian rocks commonly used as masonry (building stone) submitted to a chemical attack with hydrochloric acid, potassium hydroxide and detergent. As there is no Brazilian standards for these type of rock tests, authors have followed the methodology and chemical reagents concentrations suggested by the Brazilian standard for ceramic plates used as facing. After each 10 cycles of chemical attack, rock specimens were submitted to point load tests and results were compared to point load strength for sound rock. Rock specimens were also submitted to wave velocity determination and has presented a similar behavior, showing a reduction on strength and wave velocity up until 20 cycles and a small increase after that and up until the end of cycling tests, in a total of 50 cycles. All rocks have presented severe visual damage and noticeable changes on physical properties (specific weight, porosity and absorption capacity) after chemical attack.

103 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-278 Strength variation during freezing and thawing cycling on some masonry rocks Sossai, F. J. M. GEOFT Engenharia e Consultoria LTDA, Belo Horizonte, Minas Gerais, Brazil Marques, E. A. G. Universidade Federal de Viçosa, Viçosa, Minas Gerais, Brazil ABSTRACT: This paper presents the results of a comprehensive study carried out on nineteenth different Brazilian rocks commonly used as masonry (building stone). Rock specimens were submitted to freezing and thawing cycling and uniaxial compressive strength tests. The freezing and thawing cycling were based on Brazilian standards (NBR 12769) while uniaxial compression was based on ISRM suggested methods. All rock specimens were submitted to uniaxial compressive strength prior to cycling. After 20 freezing – thawing cycling test all specimens were submitted to other set of uniaxial compressive strength tests. The results obtained before and after cycling were compared and used to calculate the weakening coefficient, defined as the relation between the uniaxial compressive strength after cycling divided by the result obtained on natural rock samples. The major physical properties (specific weight, porosity and absorption capacity) were also tested and were correlated to strength results. Generally, the obtained results suggest that strength variation for tested rock samples are related to physical and some chemical changes observed during the study. The 20 cycles specified by the Brazilian standard were not sufficient to cause significant damage on the rocks under study.

ARMA 12-366 Evaluation of engineering properties of coal samples using ultrasonic pulse and compressive strength Weidong, P. China University of Mining and Technology, Beijing, China Yousheng, Z. Fenxi Mining Group of Shanxi Coking Coal, Xiaoyi, Shanxi, China ABSTRACT: During the underground mining, it is very important to have the engineering properties of coal seams completely and timely. Hopefully, this objective will be come true by ultrasonic detection in the future. In this study, ultrasonic pulse was taken as the main device to reflect the difference of similar coal samples in different situations. In the laboratory test, the hydraulic pressure servo testing system and ultrasonic detection instrument were used together, which can measure the parameter values of ultrasonic pulse propagation dynamically. The same research mentality can also be applied in situ without changing. The results showed that, it is possible to analyze the fracture mechanics of coal measure rocks using ultrasonic pulse. If the measure range is short, the amplitude of ultrasonic is more sensitive than velocity. Following the change of stress values, the curve of amplitude values fit quadratic function relationship. In the further research, the power of ultrasonic pulse detection should be improved, and the safety precautions should be strengthened to avoid causing explosion in the coal mine.

104 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-397 Drained Behavior of Granular Soil during Rotational Shear Yang L.-T., Wanatowski D., Yu H.-S., and Li X. Nottingham Centre for Geomechanics, University of Nottingham, UK ABSTRACT: This paper presents an experimental investigation on the drained behavior of saturated sand in rotational shear conducted in a hollow cylinder apparatus. In the tests, samples were subjected to cyclic rotation of principal stress axes while the magnitudes of principal stresses were maintained constant. Special attention was placed on the stress-strain behavior, deformation characteristics of granular soils at different stress ratios. The test results demonstrate that volumetric strain during rotational shear is mainly contractive and the amount of the strain increases with the increase in the stress ratio. A significant plastic deformation is induced during rotational shear despite the magnitudes of principal stresses remaining constant. Most of strains are generated during the first 20 cycles. When principal stress rotation continues, the sand samples appear to be gradually stabilized and the strain trajectory in the deviatoric plane approaches an ellipse.

ARMA 12-431 Peak Shear Displacement of Rock Fractures Rashidian, S. and Chang, L.C. The Catholic University of America, Washington, DC, USA ABSTRACT: Barton suggested 1% displacement as a “rule-of-thumb” for peak shear displacement of fractures (δpeak=0.01L). In addition, he introduced an empirical equation for δpeak based on JRC (Joint Roughness Coefficient) and the fracture length (L). The effect of normal stress was eliminated in Barton’s equation and δpeak has a linear relationship with JRC. Asadollahi suggested another equation for δpeak, in which δpeak increases with the normal stress applied on the fractures and it decreases with JRC. In this paper, a database of the results of constant normal stress direct shear tests is investigated by pattern recognition techniques as well as statistical method to find the best equation to predict the peak shear displacement. The rock fractures within the database are classified into four classes, which are the combination of rough and planar joints as well as soft and hard rock. Both Asadollahi’s and Barton’s equations are used to predict δpeak and the results are compared for each class.

ARMA 12-443 Viscous Oil Carbonates at Elevated Temperature Shafiei, A. and Dusseault, M.B. Department of Earth & Environmental Sciences, University of Waterloo, Waterloo, Ontario, Canada ABSTRACT: Carbonate rocks cover over 20% of the earth crust; they contain over 20% of the world’s endowment of viscous oil estimated at over 2 trillion barrels mainly reported in Canada, the United States and the Middle East. To date, only steam injection processes look promising in accessing this immense resource commercially. High T and p prodution processes have a profound impact on geomechanical behavior of viscous oil carbonate reservoirs. Massive geomechanical effects occure in carbonates when subjected to thermal stimulation; dilating natural fractures can show changes in flow capacity of several orders of magnitude from wedging or shear dilation around the thermally stimulated zone. In this article, the importance of thermal geomechanics effects during viscous oil production from carbonate rocks is emphasized. Approaches to calculating thermally-induced stresses are described. Thermal available experimental data and field evidences. Finally, a practical example of thermal geomechanics effects during thermal oil production operations into viscous oil naturally fracture reservoir is demonstrated. Thermal viscous oil production changes reservoir behavior, generally leading to production enhancement although thermal stimulation can generate operational issues such as thermally induced casing shear and seal breaching.

105 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-462 Experimental Studies of Liquefaction-induced Ground Deformation with Different Sand Permeability Wang B. Dept. of Civil and Structural Engineering, Kyushu University, Fukuoka, Japan Chen G.Q., Kasama K. and Li Y.G. Dept. of Civil and Structural Engineering, Kyushu University, Fukuoka, Japan ABSTRACT: Lateral flow of mildly ground is one of the most pervasive and costly types of liquefaction- induced ground failure. This paper presents the results of six shaking model tests of liquefaction-induced lateral flow by using a rigid soil container. Toyoura sand was used in this study to make the liquefiable sand deposits with gently sloping at relative density about 40%. The sloping deposits were saturated with water or a polymer fluid, which has more viscous than water. Therefore, sand deposits with different permeabilities could be modeled. These tests were subjected to sinusoidal base shaking with step increased accelerations: 100, 200, 300 and 400 Gals for 3 seconds. Detailed discussions and comparisons were presented to examine the effects of sand permeability and ground surface gradient on the post-liquefaction lateral flow of liquefied ground.

ARMA 12-488 Residual strength properties of a reservoir cap rock Santos, E. S. R, Ferreira, F. H, Borba, A. M. Petrobras Research Center – CENPES, Rio de Janeiro, RJ, Brazil Vargas Jr, E. A Dept. of Civil Engineering, Catholic University, Rio de Janeiro, Brazil. ABSTRACT: In a scenario where overburden rock coring in the petroleum industry seldom occurs, the fault reactivation analyses lack of real fault material retrieval for peak and residual strength characterization. The strength properties of a fault are commonly defined based on personal judgments of experienced rock mechanicists. This work attempts to deliver more realistic residual strength parameters for artificial slip planes produced in triaxial and direct shear tests performed on shale samples. These artificial planes do not account for rock heterogeneity, fault roughness or breached zones, but may produce a lower boundary of strength properties for robust fault reactivation risk analyses. The individual results matched the expected stress-strain behavior pattern for a frictional material under shear stresses and the final residual strength envelope was consistent. During slippage the specimens presented slickenside features natural to clay-rich rocks which might have affected the friction angle. This behavior is supported by literature experience on soils. As expected, the final strength values were lower than the usually adopted values in the numerical analyses.

106 46th US Rock Mechanics/Geomechanics Symposium Ses s ion 17: U nconventional Reservoir Geomechanics Tuesday, 26 June, 8:00 am – 9:30 am Chairs: David Yale, Ali Mese

ARMA 12-664 The Role of Mechanical and Acoustic Anisotropies on Reservoir Characterization and Field Development in North American Fractured Unconventional Shale Reservoirs Tutuncu, A. N. Colorado School of Mines, Golden, Colorado, USA ABSTRACT: The strong anisotropic characteristics of unconventional reservoirs and their seal formations impact the reservoir characterization and field development plans significantly. When the input parameters needed to run reservoir flow simulators and geomechanical models in these formations are obtained using isotropic assumptions and the associated in situ stress and direction dependences are not incorporated, the prediction often compromise significant deviation from the field observations. These consequences in the modeling stages typically impact all major operations including drilling design and implementations, completion integrity and hydraulic fracturing design, fracture monitoring via surface and downhole microseismic monitoring for seal integrity and environmental impact minimization as well as long term depletion and seal integrity surveillance and risk assessment and sensitivity analysis. Ever since the drilling industry started to take on harsh environment drilling applications from drilling horizontal wells with multistage fracturing to unlock unconventional gas and oil resources to extended reach or multilaterals wells in complex geological environments such as sub-salt plays in the cases for remote ultra deepwater locations with high formation integrity issues, the role of formation anisotropy became substantial for economically viable and technically sound field development and production in these challenging environments. A comprehensive research study have been conducted using field data from several fractured gas and oil shale reservoirs in North America in order to study the impact of inclusion of anisotropic mechanical properties and strength on alteration of mechanical characteristic of the field. Seal shale formation data was also used to compare similarities and differences between seal and resource shale formations. Well logs, seismic and drilling data, laboratory velocity and deformation anisotropy measurements have been evaluated with and without anisotropic rock property assumption to confirm the role of anisotropy in the changes with the two assumptions.

ARMA 12-562 Drainage of Poroelastic Fractures and Its Implications on the Performance of Naturally Fractured Reservoirs Bedayat, H. and Taleghani, A.D. Department of Petroleum Engineering, Baton Rouge, Louisiana, USA ABSTRACT: Large volumes of natural gas and oil are stored in low-permeability fractured reservoirs around the world. Extensive field and lab measurements have revealed presence of natural fracture in different scales and their fractal distributions. The log normal distribution of fractures length and width and their consistency throughout the formation is well documented for different basins in the literature, but the mechanical implication and the potential role of these distributions on fluid flow behavior in the rock is not yet studied. This paper provides poroelastic analysis for a single micro-fracture subject to fluid withdrawal (production) through the fracture. Formation is assumed to be a low permeable poroelastic medium. The main drive behind studying this problem was the fact that core flooding measurements in laboratory studies indicate that permeability of tight formations rock samples is in

107 46th US Rock Mechanics/Geomechanics Symposium the order of nanodarcy, however the rate of production from the stimulated and even non-stimulated wells are leading us to average values for shale permeability, which are orders of magnitudes higher than the permeability measured in the lab. In this paper, we are trying to verify the role of natural fractures and their poroelastic properties to explain discrepancy in the measured permeability using different methods. To achieve this goal, we provide analytical solution for fracture volume changes due to fluid withdrawal (production). The roles of differential in-situ stress and formation pressure in determining the crack volume changes were found to be significant. The results could be used to relate the significant reduction in production from some of the shale gas wells to the closure of microfractures or even larger non-propped fractures. In general having the knowledge of mechanical and hydraulic behavior of natural micro-fractures in low permeability reservoirs could be a key to predict the production decline in these formations and provide insight to more sophisticated stimulation techniques in future.

ARMA 12-194 Microcrack nucleation in porous solids under predominantly compressive stress states with applications to shale gas exploration Choi, J.-W. Bureau of Economic Geology, The University of Texas at Austin, Austin, TX, 78713, USA Duncan, I. J. Bureau of Economic Geology, The University of Texas at Austin, Austin, TX, 78713, USA Rodin, G. J. Institute for Computational Engineering and Sciences, The University of Texas at Austin, Austin, TX, 78712, USA ABSTRACT: The paper analyzes microcracks nucleation under predominantly compressive stress states. It is proposed that microcracks are nucleated from pores, and the nucleation is driven by a local tensile stress. It is shown that local tension can be readily induced by remote compression, as long as the remote stress state is sufficiently different from pure hydrostatic pressure. The mechanism is analyzed in a setting involving pressurization and depressurization of a macroscopic tunnel crack. It is shown that the mechanism is microcrack nucleation can be enhanced upon unloading, as long as the pressurization induces plastic deformation.

ARMA 12-330 Creep Behavior of Barnett, Haynesville, and Marcellus Shale Li, Y. and Ghassemi, A. Texas A&M University, College Station, TX, USA ABSTRACT: In order to assess the contribution of creep to closure rate and conductivity loss of hydraulic fractures in gas shale, the viscoelastic characteristics of gas shale have been investigated. A series of creep tests were conducted on gas shale core samples. First, a few uniaxial creep tests were performed on several selected samples, and then multi-stage triaxial creep tests were carried out at room temperature. Samples used in the tests come from three different gas shale reservoirs. It is found that the creep strain can be described by a power-law function of time. The clay and carbonate contents of these gas shale samples vary noticeably, and it is observed that rocks with more cement and less clay have higher elastic modulus. Pseudo-steady state creep rate increases linearly with deviator stress, and higher confining pressures increase the amount of creep strain under the same deviator stress.

108 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-321 Geomechanical evolution of fractured reservoirs during gas production Huang, J. Texas A&M University, College Station, TX, USA Ghassemi, A. Texas A&M University, College Station, TX, USA ABSTRACT: In tight shale gas reservoir, coupled process between matrix deformation and fluid flow is important for predicting reservoir behavior, pore pressure evolution and fracture closure. In this work the dual permeability method (DPM) is implemented to the Finite Element Model (FEM) to investigate fracture deformation and closure and its impact on gas flow in a fractured reservoir. Within the framework of DPM, the fractured reservoirs are treated as dual continuum. Two independent but overlapping meshes (or elements) are used to represent this kind of reservoirs: one is the matrix elements denoting the reservoir deformation and fluid flow within matrix domain; while the other is the fracture element simulating the fluid flow only through fractures. Both matrix and fractures are assumed to be permeable and the fluid can be transported via these two. A quasi steady-state function is used to quantify the flow between the rock matrix and the fractures. By implement the concept of equivalent fracture permeability, and the shape-factor within the transfer function into DPM, the fracture geometry and orientation are numerically considered and the complexity of the problem is reduced. The stress-dependent fracture aperture can be updated explicitly as time elapse. Simulation results show that the time evolutions of gas pressure, effective stresses, fracture aperture and permeability are strongly affected by desorption gas during production, especially in the near-wellbore region. Gas desorption retards the influence of the effective stress increase associated with pore pressure reduction during production. Combination of in-situ stress condition and gas desorption mechanism governs the fracture deformation behavior in fractured reservoirs.

ARMA 12-291 Proppant Embedment and Conductivity of Hydraulic Fractures in Shales Alramahi, B. ExxonMobil Upstream Research Company, Houston, TX, USA. Sundberg, M.I. ExxonMobil Upstream Research Company, Houston, TX, USA. ABSTRACT: We present a study of proppant embedment in shales and its effect on hydraulic fracture conductivity. We present an analytical model to predict the stress-dependent conductivity of hydraulic fractures based on simple laboratory measurements of proppant embedment. We also study the relations between rock mineralogy, mechanical properties, fluid composition and proppant embedment. Initial results show a close correlation between the amount of proppant embedment at a given stress and the rock stiffness which, in turn, is affected by the mineral content, mainly the amount and type of clay minerals present in the rock. These correlations are being utilized to predict the amount of conductivity loss due to proppant embedment in a variety of unconventional resource plays worldwide.

109 46th US Rock Mechanics/Geomechanics Symposium Ses s ion 18: C oal Mine Strata Behavior - II Te u sday, 26 June, 8:00 am – 9:30 am Chairs: Erik Westman, Anil Ray

ARMA 12- 211 Effect of Mesoscale Fracture during the Uniaxial Compression Process of Coal Containing Gas with CT Scanning Method- An Experimental Approach Nie, B., 1,2, He, X. 1,2, Chen, W., 1,2, Li, X.,1,2, Li, H. 1,2 1. State Key Lab of Coal Resources and Safe Mining(China University of Mining & Technology), Beijing 10083, China 2. School of Resource and Safety Engineering, China University of Mining & Technology, China, 100083 ABSTRACT: The computerized tomography (CT) scanning experimental system of uniaxial compression for coal or rock containing gas was developed. The system includes the industrial CT scanning system, uniaxial compression equipment for coal or rock containing gas, and equipment for measuring stress and strain and other equipments for measuring the fracture process of coal or rock containing gases dynamically and to obtain the pictures during the fracture process. The experiments were done to show that mesoscale fracture rules during the uniaxial compression process of coal containing gas with this system. Experimental results show that coal is one kind of heterogeneous material, and the ability of coal absorbing gas is also inhomogeneous in different parts of coal. Also, the fracture type is different between coal and coal containing gas, with the fracture of the coal without gases being crisp and the one of the coal containing gases being plastic due to the existence of gas. The results can provide the mesoscale proof for understanding the fracture process of coal containing gas and mechanism of gas affecting mechanical characters of coal.

ARMA 12-242 Evaluation of roadway in-stability in the presence of stress anisotropy in underground coal mines Kushwaha, A Central Institute of Mining and Fuel Research, Dhanbad-826015 (India) Sharma, D. N. Kothagudem Area, Singareni Collieries Company Limited (India) Tewari, S., Bhattacharjee, R. and Sinha, A Central Institute of Mining and Fuel Research, Dhanbad-826015 (India) ABSTRACT: Stability of coal mine roadways is found to be a major problem in presence of in situ horizontal stress anisotropy especially in geologically disturbed zones. On most of the occasions, geological discontinuities become more prominent in a particular direction. Such condition causes instability in the roadways some times severely. In the present paper, authors have dealt with a case study of Singareni Collieries Company Limited (India), where the instability in one set of the roadways was found to be due to the major horizontal in situ stress acting perpendicular to the roadways. Based on field investigations, geo-technical mapping and underground observations of development roadways, orientation of the major and minor horizontal stresses were established. 3-dimensional numerical modelling has been used to simulate the failure pattern of the level and dip-rise galleries and accordingly magnitude of major and minor in situ horizontal stresses have been estimated. Using these in situ horizontal stresses in 3D numerical modelling, best possible stable orientation of the roadways has been proposed. Accordingly, required support system of the roadways has been designed. Mine management

110 46th US Rock Mechanics/Geomechanics Symposium oriented the roadways of bottom section of King seam as per the study recommendations and developed the whole area of the mine up to its boundary successfully.

ARMA 12-308 Estimating Mining Recovery Factor and Cavity Stability of Commercial Scale Underground Coal Gasification Plants Pei, P., and Zeng, Z. Department of Geology and Geological Engineering, University of North Dakota, Grand Forks, North Dakota, USA ABSTRACT: During the development of an underground coal gasification (UCG) plant in commercial scale, multiple gasification cavities are arrayed as a set of “parallel tunnels” in the coal seam. The in-situ stress field is perturbed by the induced stresses due to excavation, gasification pressure and thermal effect. The volume of the gasification cavities determines the mining recovery factor and economics of the UCG plant. This paper presents an analytical study on the stability of the cavities and the mining recovery factor of the coal seam. The developmental procedure of a UCG plant is divided into three phases. We have examined the stress field and interactions between these parallel cavities at different production phases. The allowable size of the UCG cavities and reasonable spacing between the cavities are estimated based on the stress profile and safety consideration. The results indicate that the radius of the cavities, the spacing, and the mining recovery factor are largely determined by the properties of the coal-bearing formation. The mining recovery factor is significantly affected by the presence of discontinuity in the target gasification formation. The methodologies and results in this paper provide a convenient and fast approach to estimate the economics of a UCG plant, once the fundamental properties of the coal-bearing formation are known.

ARMA 12-324 The Coal and Gas Co-extraction Technology in China J.C. Wong, L. Wang, Y. Li and R.L. Yi. College of Resources & Safety Engineering, China University of Mining & Technology, Beijing, China ABSTRACT: In the last ten years, China has imported numerous advanced technologies of gas extraction and oil exploitation from other countries, and it has made some achievements, especially for the coal seam with a better gas permeability. But for the most coalfield, the surface longhole drilling is not effectively used in original coal seam with poor gas permeability, low-gas pressure and low-saturation. These disadvantages also cause lower gas production and smaller gas- extraction range of the hole. In order to solve these problems, the ideas and technologies of the underground gas extraction are presented in this paper, which depends on the de-stressed zone and fracture zone caused by coal mining. These two zones could promote not only the gas desorption rate and the flow rate, but also could increase gas permeability. Under this condition, gas extraction along with the coal mining can be achieved at the same time, and it is called coal and gas co-extraction. The paper introduces the project case in Huainan coal area in central China, where the gas extraction technologies had been employed in upper and lower coal seam of first mining coal seam in the process of multi-seam mining.

111 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-370 Optimization of coal measure rocks stress relief to increase the efficiency of the degassing process: numerical modeling using FLAC software Zinovyev, A.A. Novosibirsk State University, Novosibirsk, Russia Patutin, A.V. and Serdyukov, S.V. Institute of Mining, Siberian Branch, Russian Academy of Sciences, Novosibirsk, Russia ABSTRACT: One of the most significant problems of underground mining is sudden methane outbursts occurred during the production. To reduce the probability of these incidents and bring down the level of emission it is necessary to carry out actions for preliminary degassing of rock mass. According to experimental data there is the relationship between the gas flow from the coal seam and its stress state which is characterized by opening of natural fracture system and release of methane during process of mass stress relief. It is proposed to use this relationship to increase the effectiveness of degasification work by hydraulic fracturing in degassing wells or excavating of slots. This paper presents the results of mathematical modeling of rock mass stress-relieving process performed using Itasca’s FLAC finite-difference software. The main goal was determination of the optimal geometry and location of slots or fractures to increase the stress-relief area of the coal measure rock. The resulting stress pattern was analyzed and recommendation for degasification works of coal seams was made.

ARMA 12-471 Review of fundamental geotechnical mechanisms of valley closure subsidence effects Zhang, C. The University of New South Wales, Sydney, New South Wales, Australia Mitra, R. and Hebblewhite, B.K. The University of New South Wales, Sydney, New South Wales, Australia ABSTRACT: The paper presents a description of the hypothesized mechanisms of valley closure and related valley floor upsidence when mining beneath or in the vicinity of valleys and other forms of irregular surface topography. Research coupled with mining experience over the past few decades in Australia, has identified the mining induced valley related movements as being very significant parts of what is referred to as non-conventional subsidence effects, in situations where the surface terrain above and in close to underground coal mining contains changing topographies. Attempts have been made by subsidence engineers and researchers to improve the understanding of this phenomenon and to enhance the ability to predict such subsidence effects, through both empirical and numerical modeling methods. Based on the comprehensive database of measurements of valley closure and upsidence, which has primarily been collected in the Southern Coalfield of New South Wales, there are many widely hypothesized mechanisms that are regularly postulated as possible contributing factors in this behavior. The objective of this paper is to bring a review of these existing models and possible mechanisms relative to the closure and upsidence movements of valleys. Only with better definition of the numerous factors and mechanisms contributing to the valley related movements, improvements can be achieved regarding the prediction of valley closure subsidence effects

112 46th US Rock Mechanics/Geomechanics Symposium Ses s ion 19: F oluid Fl w, Geomechanics and Geophysics of Cracked and Fractured Media Tuesday, 26 June, 8:00 am – 9:30 am Chair: Bill Dershowitz

ARMA 12-296 Numerical Studies on Coupled Flow and Geomechanics with the Multiple Porosity Model for Naturally Fractured Tight and Shale Gas Reservoirs Kim, J. Earth Sciences Division, Lawrence Berkeley National Laboratory. Berkeley, CA, USA Moridis, G. J. Earth Sciences Division, Lawrence Berkeley National Laboratory. Berkeley, CA, USA ABSTRACT: We performed numerical simulations on coupled flow and geomechanics for naturally fractured reservoirs, using the multiple porosity model, dynamic permeability and porosity. From numerical tests, geomechanics affected flow regimes, changing permeability and porosity, followed by pressure, because permeability and geomechanical moduli at the fracture are functions of strain (or effective stress), leading to highly nonlinear coupled systems between flow and geomechanics. We found differences of pressure, permeability, porosity, and Young’s modulus between the uncoupled flow-only and coupled flow-geomechanics simulations. Thus, neglecting the dynamic characteristics of flow and geomechanical properties may cause large errors in naturally fractured reservoirs. Nonlinear and dynamic flow and geomechanical properties, related to geomechanically sensitive naturally fractured reservoirs, can properly be captured by an appropriate model for coupled flow and geomechanics, such as the multiple porosity model used in this study.

ARMA 12-469 Experimental Study on Relationship between Hydraulic Aperture and Rock-Water Dissolution of Granite Shen, L. Department of Energy and Resources Engineering, College of Engineering, Peking University, Beijing, P.R. China Feng, X., Pan, P., and Yang, J. State Key Laboratory of Geomechanics and Geotechnical Enginnering, Institute of Rock and Soil Mechanics, Chinese Academy of Science, Wuhan, Hubei,P.R China ABSTRACT: Coupled hydro-mechanical-chemical experiments were conducted to study the hydraulic aperture and water-rock dissolution of granite. The granite specimens used in the experiments were from the potential site for high level nuclear waste disposal in Beishan, Gansu province, China. An artificial fracture was created by splitting the specimen in the vertical direction to represent the discontinuity. A constant axial compressive load 150MPa and confinement 10MPa were applied on the specimen. A chemical solution (Na2SO4) was injected into the rock specimen with 1MPa hydraulic pressure. Experimental results show a significant influence of water-rock dissolution on hydraulic aperture and fracture surface modification. Fracture surfaces were smoother after experiment under chemical solution and widely distributed etch pits can be found on mineral surface. Results indicate high Gibbs energy is generated by stress application leading to fluid-rock dissolution far from equilibrium and acceleration of reaction rate. Meanwhile, these dissolutions mainly occur at loaded face obeying the model of “water film diffusion”.

113 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-481 Permeability Estimation from Seismic Velocity based on Crack and Grain Models Yamabe, H., Tsuji, T. and Matsuoka, T. Kyoto University, Graduate School of Engineering, Kyoto, Japan ABSTRACT: Estimation of underground fluid state has been paid great attention in subsurface explorations (e.g. oil reservoir development, carbon capture and storage). Permeability is the most important parameter in considering subsurface fluid flow, and seismic-wave velocity is the most popular and trusted parameter derived from geophysical surveys. The objective of this study is estimating permeability from seismic velocity by revealing the relationship between permeability and seismic velocity. Although these two parameters have no direct relationship, the pore geometry of rock can be a bridge of them because it is dominant factor to govern permeability and seismic velocity. Since pore geometry of rock mass is highly complicated, two rock models (cracked rock model and granular model) are adopted for the research. For the calculation of permeability, lattice Boltzmann simulation is conducted in this research. Self-consistent approximation and finite element method are applied to calculate seismic velocity on cracked model and granular model, respectively. As a consequence of the research, permeability can be estimated from seismic velocity using the information of pore geometry: (1) crack aspect ratio and intensity for cracked model and (2) grain-size sorting for granular model.

ARMA 12-553 Staged Differential Effective Medium (SDEM) Models for the Acoustic Velocity in Carbonates M. T. Myers, Shell International E&P, Houston, Texas, USA L. A. Hathon, Shell International E&P, Houston, Texas, USA ABSTRACT: The limitations of using Reuss and Voight averages are discussed. These difficulties are handled by interpolating between these two bounding limits with the use of an effective medium model. A modeling parameter L which takes on values between zero and one is introduced. Zero represents a Reuss average (iso-stress) of the materials and one the Voight (iso-strain) average. The model which is developed includes critical concentration models as a special case and reproduce the published literature. A relation between L and the Biot coefficient is then derived. The critical porosity solutions obtained for dry and brine saturated rocks are then used to examine effects of fluid substitution and Gassman’s equation is obtained. The influence of vugs on the velocity in carbonate rocks is then examined. It is found that vugs in general have a much smaller influence on the velocity than matrix porosity.

ARMA 12-565 Seismic Detection of Flow Paths in a Air-Filled Fracture under Stress Choi, M. K. School of Civil Engineering, Purdue University, West Lafayette, IN, USA Pyrak-Nolte, L. J. Department of Physics, Purdue University, West Lafayette, IN, USA School of Civil Engineering, Purdue University, West Lafayette, IN, USA Department of Earth and Atmospheric Sciences, Purdue University, West Lafayette, IN, USA Bobet, A. School of Civil Engineering, Purdue University, West Lafayette, IN, USA

114 46th US Rock Mechanics/Geomechanics Symposium ABSTRACT: Laboratory experiments were performed to determine the spatial variability of seismic fracture specific stiffness and the dominant flow path within a single fracture subjected to normal stress. Two cylindrical granite specimens were used in the study: an intact sample and a fractured sample with the fracture oriented perpendicular to the load. Compressional and shear waves were measured for the samples in dry conditions and during fluid invasion. The normal fracture specific stiffness increased with increasing stress (0 – 18.9 MPa), while the shear fracture specific stiffness started to approach an asymptote at around 10 MPa. During fluid invasion, the amplitude of both the compressional and shear waves decreased as water filled the fracture while the velocity of the waves increased. By tracking the arrival time changes of the waves, the fluid invasion path was identified. The fluid first invaded portions of the fracture that had a relatively low fracture stiffness and then spread to the regions with higher stiffness. In conclusion, the fluid front can be detected seismically and the spatial variation of fracture stiffness is correlated to the fluid flow path.

ARMA 12-676 Topology analysis method for water flows in 2D discrete fracture networks Xu, Z.H. Shandong University, Jinan, Shandong, China The University of Western Australia, Perth, Western Australia, Australia ([email protected]) Ma, G.W. The University of Western Australia, Perth, Western Australia, Australia ([email protected]) Li, S.C. Shandong University, Jinan, Shandong, China ([email protected]) ABSTRACT: A new 2D numerical simulation method for water flows in discrete fracture networks is proposed. Firstly, hydraulic analysis of a single fracture is carried out. Each fracture in a discrete fracture network is treated as a weighted branch with a start node and an end node in a directed network. Node and branch laws of water flow in discrete fracture networks are derived based on the conservation of mass and energy. The topology theory is applied in order to search the subways of water flow, and to calculate water pressures and flow rate in each branch of a weighted, directed and connected path. Identification of water flow pathways and tree cutting are considered in the developed method. An example is analyzed. It shows that the proposed topology analysis method (TAM) is effective in analyzing water flow in discrete fracture networks. The advantages of TAM include: 1) Boundaries and fractures are unified with the same form of governing equation, which makes it possible to obtain water flows in a network analytically; so TAM is actually an efficient analytical method for analyzing water flows in discrete fracture networks; 2) Solutions of water pressures and flow rates in discrete fracture networks are obtained by solving a system of nonhomogeneous linear equations; 3) Results demonstrate that the developed method is effective and promising for more complex applications and engineering purpose.

115 46th US Rock Mechanics/Geomechanics Symposium Ses s ion 20: F ailure Response Tuesday, 26 June, 8:00 am – 9:30 am Chairs: Marc Loken, Shugang Wang

ARMA 12-367 Compactant features observed under true triaxial states of stress Ingraham, M. D. Clarkson University, Potsdam, NY, USA Issen, K.A. Clarkson University, Potsdam, NY, USA Holcomb, D.J. Sandia National Laboratories, Albuquerque, NM, USA (Retired) ABSTRACT: Features similar in size, appearance and orientation to previously reported compaction localization features were found in a suite of constant mean stress true triaxial tests. Tests were run at five different stress states ranging from axisymmetric compression to axisymmetric extension at five constant mean stresses ranging from 30 to 150 MPa. Most of the specimens that formed compaction localization- like features exhibited a plateau in the stress - strain curve without a stress drop, suggesting that these specimens represent a deformation mode that is transitional between true compaction localization and bulk compaction. Compaction localization features were observed in all of the stress states above 75 MPa mean stress. As the deviatoric stress state shifts from axisymmetric compression to axisymmetric extension, a higher mean stress is required to cause compaction localization. These results suggest that compaction localization may be more common than previously thought.

ARMA 12-566 Multi-scale investigations on the mechanisms affecting the strength and the elastic modulus of a marble varying in texture Bandini, A. and Berry, P. Department of Civil, Environmental and Materials Engineering (DICAM), University of Bologna via Terracini 28, 40131, Bologna, Italy ABSTRACT: The study on the mechanisms affecting the strength and the elastic modulus of a crystalline rock has been focused on a marble, variable in texture, despite an almost monomineralic calcitic composition. A wide experimentation was conducted on three levels: macro-scale (scale of the laboratory sample, order of centimeters), mesoscale (several grains) and grain-scale (order of mm). The experimental results have confirmed, on the various scales, the theoretical models which assume failure occurs from preexisting flaws, acting as stress concentrators in controlling the rock’s strength. On the grain- and meso-scales, the indentations cause the brittle failure of the calcite grain along its cleavage planes and the indents are influenced by microcracks (intra- granular and inter-granular), whatever the indenter’s shape (Berkovich, Vickers, Knoop). On the macro-scale, the texture markedly affects the strength, the stress-strain behavior and the failure mechanisms in Rock Impact Hardness Number (R.I.H.N.) test of the investigated rock. Furthermore, the more intense open microcracking inside the granoblastic marble causes lower values of elastic modulus, strength and P-waves velocity compared to xenoblastic marble.

116 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-448 Formalized approaches to defining damage thresholds in brittle rock: Granite and Limestone Ghazvinian, E. Perras, M. Diederichs, M. GeoEngineering Centre, Queen’s University, Kingston, ON, Canada Labrie, D. CANMET – MMSL, Natural Resources Canada, Ottawa, ON, Canada ABSTRACT: Brittle spalling is the failure mechanism that is commonly observed in the walls of underground excavations in rocks with high ratio of compressive to tensile strength (brittle rock). Extensile crack damage that is controlling spalling in brittle rock is rarely capable of leading the failure mechanism of the rock in laboratory strength tests due to geometric constraints within the test. The onset of crack damage thresholds in brittle rock can be identified by acoustic emission monitoring or rigorous strain measurements during a laboratory compressive test. Crack initiation (CI) and crack propagation (CD) stresses correspond to long-term and yielding (short-term) in situ strength of the rock. The repeatability and subjectivity of interpretation of the existing algorithms for calculation of crack damage thresholds is evaluated through inter-laboratory comparisons for Smaland granite and since initially these algorithms were all developed for granitic rocks, their accuracy and robustness is determined for Lindsay Cobourg limestone as a sedimentary rock. This paper presents the latest guidelines that are to be included in the ISRM “Suggested Method” for defining damage thresholds in brittle rocks.

ARMA 12-615 The effects of bridge length and material on surface crack growth and coalescence under uniaxial compression Yin. P., Wong. R.H.C. and Chau. K.T. Civil and Structural Engineering Dept. of the Hong Kong Polytechnic University, Hong Kong, China ABSTRACT: The objective of this study aims at increasing the understandings of the effects of bridge length and material on surface crack growth and coalescence. Both granite and PMMA specimens containing two parallel pre-existing surface cracks were tested under uniaxial compression. The bridge length of the granites specimens were varied from 16.5 mm to 26 mm. Two observation systems were used including CCD camera and acoustic emission (AE) system. Results are summarized as follows: (i) shorter bridge length facilitated the growth and coalescence of surface cracks; (ii) in granite material, two pre- existing surface cracks were coalesced together by a trust movement of the rock at the bridge area when the bridge length was 16.5 mm, and by a shear displacement at the bridge area when the bridge length was 26 mm; (iii) in granite material white patches appeared as the sign of the emanation of macrocracks, while cracks in PMMA material occurred just in a sudden form; (iv) in granite material petal cracks initiated first inside the specimen, and in PMMA material wing cracks emanated first on the specimen surface; (v) petal cracks inside the granite specimens propagated from the anti-wing crack side towards the wing crack side, whereas petal cracks in the PMMA specimens extended from the wing crack side to the other tip of the pre-existing surface crack; and (vi) petal crack coalescence appeared in both granite material and PMMA material representing as a special character of 3-D cracks.

117 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-306 Stress-Dependent Brittle-to-Ductile Deformation of Tuff in Geothermal Wells Lee, J.S., Chesapeake Energy Corporation, Oklahoma City, OK, USA Maharidge, R.L., Franquet, J.A. and Dick, A. Baker Hughes, Houston, TX, USA ABSTRACT: This study discusses the stress-dependant brittle-to-ductile deformations observed in a tuff formation of the Newberry Volcano field in Oregon, USA, which is encountered in geothermal wells drilled to 3066 m (10,060 ft). Laboratory tests investigate the mechanical behavior of the tuff during drilling and deformation conditions. Ultrasonic velocity, unconfined, and triaxial compressive tests are performed to characterize the elastic and plastic deformations of the tuff, and the results of these tests are used to complement bottomhole drilling simulator tests for bit performance. Triaxial compressive tests show significant differences in rock strength and brittle-to-ductile transition zones between 2.5 cm (1 in.) and 3.8 cm (1.5 in.) diameter core samples. As a result, the deformation behavior of the tuff depends on confining stress and specimen dimension, which is typically called a scale effect. The results show that 3.8 cm samples produce more representative in-situ rock deformation behaviors. Our data explain why the bottomhole drilling simulator test using a bigger tuff sample indicated typical ductile (plastic) deformation that showed inefficient drilling performance when using a Tricone® bit. For this tuff formation, it is observed that a more aggressive steel tooth bit improves drilling efficiency markedly.

ARMA 12-624 Relationship between shear stress and shear strain at post-peak curves of rocks subjected to direct shear tests G. Zhang, Y. Li, C. Yang, W. Jing State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences, Wuhan, Hubei 430071, China ABSTRACT: Direct shear tests are usually carried out to find the shear strength parameters, and few attention is paid on the post-peak curve. An experimental and theoretical study on the relationship between the shear strength parameters and the post-peak curve were carried out. Analysis on the shear stress-strain curves showed that when normal stresses σn satisfy certain conditions, the post- peak curve is interrelated to the shear strength parameters by (1) τdrop=τd-τr=c and (2) υ=arctan(τr/ σn), where τdrop, τd, and τr are the shear stress drop, the peak shear stress, and the residual shear stress respectively. Based on the theoretical analysis of above phenomena, an approximate method was proposed by using post-peak curves to obtain shear strength parameters of rocks, and its concrete calculating process was presented. Finally, through further study on the slope of shear stress-strain curves during the shear stress drop, a shear stress-strain constitutive equation for the whole curve was proposed: τ= f(ε, σn). It implies visually the physical meaning of post-peak curves: the whole dropping course of shear stress is the releasing course of the cohesion.

118 46th US Rock Mechanics/Geomechanics Symposium Ses s ion 21: Production Geomechanics at the Sand Face Tuesday, 26 June, 11:00 am – 12:30 pm Chairs: Gang Han, John Cook

ARMA 12-266 The Effect of FracPacks on Sand Stability during Depletion Walters, D.A. Taurus Reservoir Solutions Ltd., Calgary, AB, Canada Han, G. HESS Corporation, Houston, Texas, U.S.A. ABSTRACT: Fracpack completions are widely used as the most efficient sand control method in deep GOM fields. For fracpacked wells, rock stability issues are often no longer considered when well drawdown is decided. While fracpacks can prevent sand from entering the wellbore, it is not unusual to witness skin increase and productivity loss over production time. Contradictory to conventional thought that productivity loss results from flow-related fines migration or mechanical failure of completion equipment, this paper documents a field study where it is found the fracpack stimulation and completion surprisingly increases the risk of rock failure around the fracture resulting in severe production decline. The well studied is a fracpacked condensate producer from a high permeability turbidite sandstone reservoir with a strong water drive. After 2-3 years of production, well productivity declines more quickly than expected. Well test analysis attributed the productivity loss to skin at the fracture face and additional permeability damage around the fracture. Extensive rock lab tests have shown that, despite high fluid flow rate, little fines are produced. However, significant permeability reduction occurs when the loading stress increases to a threshold level. The solids produced and collected consist of mainly sand chips and particles. In preparation for geomechanical modeling a rock constitutive model has been developed and calibrated to drilling events, logs, and core data. A detailed geomechanical model with an embedded fracture has been coupled with fluid flow near the wellbore to simulate the fracpack followed by drawdown and long-term depletion investigating rock stability around the fracture. Simulation results indicate that the placement of a propped hydraulic fracture during fracpack operations has two side effects: on one hand, it increases rock strength at most locations around the fracture, which is consistent with what industry has believed; on the other hand, there are certain areas, especially surrounding the fracture tip that have been weakened due to elevated shear stress levels. Rock failure occurs at a certain level of drawdown and depletion, either in shear failure mode or compaction failure mode, depending on the location with respect to the fracture, rock strength, and stress path. It is postulated that this depletion induced failure mobilizes the fines which are then transported to the fracture resulting in plugging of the completion. A stress path analysis is used in conjunction with the calibrated cap and cone failure surface to estimate the critical drawdown and depletion causing rock failure. This analysis can be used to manage drawdown as well as investigate variations of the fracpack completion to reduce the risk of fines mobilization.

119 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-489 Effect of Mechanical and Physical Properties of Rocks on Post-Failure Cavity Development — Experimental and Numerical Studies Wu, B. and Choi, S.K. CSIRO Earth Science and Engineering, Clayton South, Victoria, Australia ABSTRACT: This paper presents a combined laboratory experimental and numerical modeling study on fundamental mechanisms of sand production-induced post-failure cavity development. The laboratory component of the study utilized a sand production apparatus that accommodates a cylindrical sample with a pre-drilled central hole. The experiments were conducted by producing a fluid from the central hole of the pre-stressed sample. The failure condition of the central hole was monitored using a borescope. Experimental results demonstrated that sanding behavior and post-failure cavity development were vastly different for different types of rocks tested. At a constant external stress and drawdown pressure, transient sand production was observed for competent sandstones where a breakout type cavity was developed. By contrast, continuous sand production was observed for weak and porous sandstones where a thin- slot type cavity was formed. Little sand production was observed for low permeability ductile sandstone where classic shear band type of failure was developed. For compacted unconsolidated sands, continuous sand production was observed where no open cavity was developed. To understand the factors responsible for such distinctly different sanding behavior and cavity development, the laboratory experiments were simulated preliminarily using a hybrid discrete element-finite element (DE-FE) model. The numerical results showed that the properties and characteristics of the cementation between sand grains have a determining role in the post-failure cavity development. In particular, the cement strength, distribution, degree of brittleness, the degree of cementation and the properties of the pore fluid affect what type of cavities that will be formed and how sand production will evolve.

ARMA 12-482 Scale effect in volumetric sand production Berntsen, A.N. SINTEF Petroleum Research, Trodheim, Norway Papamichos, E. Aristotle University of Thessaloniki, Greece and SINTEF Petroleum Research, Trondheim, Norway ABSTRACT: The scale effect of the hole size on the onset and development of sand production was studied in a series of sand production tests with fluid flow on outcrop sandstone specimens. The onset of sand production was shown to vary inversely with hole size, in agreement with established results. The rate of produced sand was dependent on the hole size only for some types of rock. This dependency is explained on the basis of the cavity geometry and area of potential erosion for the different sandstone classes. For brittle sandstones showing slit-like erosion pathways, hole size dependency is negligible, while for sandstones where breakouts are the main source of sand production, sand rate scales roughly as the square of the hole size.

120 46th US Rock Mechanics/Geomechanics Symposium ARMA 12- 671 Sand prediction by different criteria and validation through a hollow cylinder test Wang, Y. Petro-Geotech Inc, Calgary, Alberta, Canada Papamichos, E. Aristotle Univ of Thessaloniki, Greece and SINTEF Petroleum Research, Trondheim, Norway ABSTRACT: The onset of sand production in a hollow cylinder test is evaluated by three different sanding models, i.e. shear failure, cohesive tensile failure, and EPS (Equivalent Plastic Strain) failure. The comparison of the results with experimental results from a hollow cylinder test shows that the shear failure model provides the most conservative prediction, while the EPS can provide the closest results to those from the test.

ARMA 12-126 Sand production model based on episodic functions Cerasi, P. R. SINTEF Petroleum Research, Trondheim, Norway Vardoulakis, I. NTUA, Athens, Greece ABSTRACT: A new sand production model is presented in this paper, based on a stochastic formalism offered by the so-called episodic functions. Starting from simple physical considerations such as porosity increase coupled to flow in porous media, the model is refined step by step to take more physical assumptions into account. The simulation results show striking resemblance, qualitatively at least, with laboratory sand prediction experiments. The sand rate in the model is taken proportional to the fluid drag force, if above a certain grain transport threshold. The drag force itself is also moderated by solid friction between sand grains. The porosity evolution law, a natural consequence of losing sand grains under sand production is itself made dependent on the stress level (above sandstone failure stress).

ARMA 12-374 The effect of stress anisotropy on sanding: An experimental study Younessi, A. and Rasouli, V. Curtin University, Perth, Western Australia, Australia Wu, B. CSIRO, Melbourne, Victoria, Australia ABSTRACT: Sand production experiments were carried out under true-triaxial stress conditions. The experiments were conducted on 100•100•100 mm3 cubes of synthetically made samples. The samples were prepared based on an established procedure developed in the laboratory to produce samples with identical physico-mechanical properties and representing weakly consolidated sandstone. Using a true- triaxial stress cell (TTSC), the samples were subjected to 3D boundary stresses and radial fluid flow from the boundaries. The fluid flows through the sample uniformly and discharges from a hole drilled at the center of the sample. The experiment setup and procedure are explained in detail in this paper. The experiments were performed under three different states of stress to study the effect of the intermediate principal stress (in this study, the minimum lateral stress) on the development of the failure zone. The dimension (i.e. width and depth) of the failure zone developed around the borehole were investigated at the end of the experiments. The results of these experiments will be presented and discussed.

121 46th US Rock Mechanics/Geomechanics Symposium Ses s ion 22: Suppo rt and Reinforcement in Hard Rock Mining - II Tuesday, 26 June, 11:00 am – 12:30 pm Chairs: Murali Gadde, Brijes Mishra

ARMA 12-150 Stress heterogeneity and complexity: implications for mining Beck, D.A. Beck Engineering Pty Ltd. Sydney, Australia Windsor, C. R.Western Australian School of Mines / Cooperative Research Centre Mining. Kalgoorlie, Australia Reusch, F. Beck Engineering Pty Ltd. Berlin, Germany Player, J. MineGeoTech Pty Ltd. Kalgoorlie, Australia ABSTRACT: Stress fields in a disturbed discontinuum such as the Earth’s crust should be complex, and yet most mines make do with a handful of measurements not sufficient in coverage or number to capture the complexity of this fundamental input to mine design. Observations confirm that at a mine scale and smaller, the variability in stress gradients is sufficient to affect excavation performance. At a number of example mines, an effort was made to explain and match the measured variability by numerically simulating aspects of the geo-mechanical history. By accounting for the structural geometry, topography or a simple interpretation of the geological history, these simple numerical models help explain the variability between measurements and confirm measured heterogeneity of the stress field at a scale that is relevant to mine performance.

ARMA 12-298 Ten Months of Ground Imaging Ahead of TBM Using Seismic Reflector Tracing Descour J. M. C-Thru Ground, Inc., 5436 West Indore Dr., Littleton, CO, 80128, USA Morino A. GD Test srl, via Pigafetta 17, 10129 Turin, Italy Maffucci M., and Pinheiro F. Ghella S.p.A., Piazzale Cardinal Consalvi, 9, 00196 Rome, Italy Elsner P. Babendererde Engineers, Markt 2, 23611 Bad Schwartau, Germany ABSTRACT: Forty surveys using Tunnel Reflector Tracing (TRT) developed by C-Thru Ground (CTG) were conducted in Brazil over 3.8 km of the TBM-driven tunnel, excavated mostly in granite-gneissic rock. Each survey extended around 200 m ahead of the face. A hand-held swept frequency source was applied at the rock surface through openings in the TBM shield. Seismic S-waves were measured by an array of accelerometers coupled to the tunnel walls within 20 m behind the sources. Later, the TRT images were compared to the TBM data, the rock types, and the water discharge locations. Approximately 90% of significant features were predicted by the surveys including an anomaly which produced around 3000l/min inflow of water. It was first detected approximately 175 meters ahead of the TBM, and confirmed when at 51

122 46th US Rock Mechanics/Geomechanics Symposium m ahead. The analysis also included: differences in wave polarity, a significance of adjusting the attenuation correction between surveys to accommodate for changing features, particularly for longer image ranges, and for detecting smaller features near larger anomalies. Prospects for assessing wave velocity ahead of the face were also investigated.

ARMA 12-412 Revisiting the design challenge of permanent bolts and shear reinforcement in laminated ground above large caverns Crockford, A.M. and Diederichs, M.S. Department of Geological Sciences and Geological Engineering, Queen’s University, Kingston, Ontario, Canada ABSTRACT: This paper addresses the challenges associated with using fully grouted rock bolts in shallow to moderate depth underground cavern design in laminated ground. Laminations in a rockmass have the capacity of being either an asset or challenge to a cavern design. If supported adequately the rockmass acts as structural beams in the roof which enable a stable large span excavation. Fully-grouted rock bolts can be used to support against layer dissociation due to displacement along the shear plane, where even minor movement can cause instability. The mechanisms affecting the effectiveness of the bolts are complex and understanding the interactions of the three materials (the rockmass, grout and steel bolt) are critical. Preliminary models of a fully grouted rock bolt in shear have previously been used to determine the viability of using three-dimensional Finite Difference Method (FDM) numerical modelling to represent the behaviour of bolts when sheared. In this paper, focus is therefore given to the individual effects of the various parameters influencing the efficiency of a rock bolt to support a beam undergoing shear: confining stresses, joint conditions, installed bolt angle and the thickness of the grout annulus.

ARMA 12-476 Methodology to Determine Peak Particle Velocity in Underground Drift Developments Caceres, C. A. University of British Columbia, Vancouver, B.C., Canada Pakalnis, R.T. University of British Columbia, Vancouver, B.C., Canada ABSTRACT: This paper presents a linear scaled distance methodology to estimate peak particle velocity (PPV) originated from blasting rounds, developed specifically for tunneling and drifting operations. It considers input parameters that are characteristic of different rock mass qualities, such as propagation velocity and resonance frequency, and explosive characteristics such as velocity of detonation (VOD) and the geometry of the blasting round. The final PPV value of any particular blasthole of the round is determined through the linear superposition of multiple waveforms, generated for a number of small incremental charges, each scaled by the distance from the explosive source to the point of interest. In addition, every waveform is shifted in time from the difference of their respective arrival times as they arrive to the point of interest. As a result of these considerations, the proposed methodology can yield a much more precise estimation of the PPV levels, which is a fundamental parameter to assess the damage potential the rock is being subjected to.

123 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-532 Reliability based support design for an excavation in brittle rock Langford, J. C. Queen’s University, Kingston, Ontario, Canada Diederichs, M. S. Queen’s University, Kingston, Ontario, Canada ABSTRACT: Spalling damage can pose significant risks to the service life of underground excavations in brittle rock. While deterministic analyses have traditionally been used in the design of these structures, reliability based design (RBD) methods provide a more rational approach to quantify spalling risk by directly incorporating uncertainty in the input variables into the design process and evaluating the probability of failure for the system. While RBD concepts are relatively new to geological engineering, they require little additional effort beyond conventional analyses and provide a more complete definition of risk and safety. This paper outlines a method for the selection of appropriate Hoek-Brown parameters for variable brittle materials using a combination of the Damage Initiation and Spalling Limit (DISL) method and Griffith’s theory of microcrack initiation. A standard RBD approach for support design in brittle material using the Response Surface Method (RSM) and the First Order Reliability Method (FORM) is then presented and used to assess bolt performance for a deep excavation in limestone.

Ses s ion 23: C arbon Sequestration on the Reservoir Scale Tuesday, 26 June, 11:00 am – 12:30 pm Chairs: Mark Zoback

ARMA 12-579 Shared Earth Models Give Model Consistency in Simulations; Application at a Shallow Carbon dioxide Sequestration Site Akpan, I. C., Govindarajan, S., Nygaard, R., Eckert, A., and Baojun, B. Missouri University of Science and Technology, Rolla, Missouri, USA ABSTRACT: Sequestering carbon dioxide with the goal to reduce greenhouse gases has been mainly been investigated and implemented for depleted oil reservoirs and deep saline aquifers where the carbon dioxide is stored under supercritical conditions. We investigate the potential to sequester carbon dioxide in relatively shallow depths of 550 m to 650 m at which it may not always be in its denser supercritical state. An extensive though mostly readily accessible dataset ranging from regional geological and topographical maps, hundreds of water wells, core observations and well logs are used to develop a 19 layer characterized shared earth model representing the storage site. Regionals stress analysis and rock properties characterization were determined. Application of the developed shared earth model is demonstrated in subsequent closed volume injection simulations which suggests that potential exists to inject up to 20.7 Mm3 in a single well and 44.7 Mm3 using multiple (9) injection wells over a 100 year injection timeframe. Critical factors affecting injection quantities in shallow formation injection such as formation pressure and fluid properties are also examined. This paper describes a methodology which can be applied in the evaluation of other potential shallow and deep sequestration sites.

124 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-319 Influences of Anticline Reservoir Geometry on Critical Pore

Pressures Associated with CO2 Sequestration Paradeis, M. A. Missouri University of Science and Technology, Rolla, Missouri, USA Eckert, A. and Liu, X. Missouri University of Science and Technology, Rolla, Missouri, USA ABSTRACT: In this study we use three-dimensional Finite Element Analysis to determine the influence of specific geometrical relationships on the feasibility of CO2 injection into anticline reservoir settings under different in situ stress regimes. Anticline structures as an example of folded sedimentary layers are among the most common structural traps for hydrocarbon reservoirs and thus become a prime target of the emerging challenge of safe geologic sequestration of CO2. This study shows how stress field heterogeneities within generic anticline structures affect geomechanical risks associated to CO2 injection. The method used to assess the geomechanical risk is the calculation of the critical pore pressure increase that the reservoir can withstand without the reactivation of existing fractures or the formation of new second-order fractures. The specific characteristics evaluated in this study include the relative thickness of the reservoir layer, the amplitude of the anticline and the wavelength of the anticline. Our results show that anticline structures exhibit a highly heterogeneous state of stress, and the geometrical parameters of wavelength and amplitude contribute to the stress heterogeneity. The results further show that the critical sustainable pore pressure also varies with respect to horizontal location in the structure. The most significant factor controlling stress heterogeneity in the anticline structures is the prevailing stress regime. Compared to horizontally layered basin models our results suggest that for extensional and strike-slip regimes anticline structures provide safer conditions than horizontally layered basins. This study shows that in order to realistically assess geomechanical risks associated with CO2 sequestration, three-dimensional models which realistically resemble the reservoir structures are necessary. Models based on horizontally layered basins represent an oversimplification and do not account for mechanical contributions, which are associated with the geometry of the structure, when geomechanical risks are analyzed.

ARMA 12-459 Evaluation of leakage potential considering fractures in the caprock for sequestration of CO2 in geological media Jaewon Lee and Ki-Bok Min Department of Energy Systems Engineering, Seoul National University, Seoul, South Korea Jonny Rutqvist Earth Sciences Division, Lawrence Berkeley National Laboratory, United States of America

ABSTRACT: In the context of Carbon Capture and Storage (CCS), the injection of CO2 induces a geomechanical change in the reservoir, which is an important issue for the stability of CO2 sequestration.

The injection of CO2 makes the fluid pressure increase, resulting in ground heaving. In addition, the increased fluid pressure is expected to be a source of shear slip of fractures in the caprock, which leads to the leakage of CO2 and microseismicity. In this study, we conduct a multi-phase coupled thermo-hydromechanical analysis to investigate the geomechanical aspect of CO2 storage focusing on ground heaving and leakage of CO2. In order to describe the caprock, fractures are considered implicitly and explicitly. For the analysis using implicit fractures, the fracture orientations were generated using the Latin Hypercube Sampling (LHS) method. In order to investigate the effect of orientation of principal stresses, we considered three kinds of stress regimes with the pore pressure evolutions calculated using a TOUGH-FLAC analysis. Based on these generated fracture orientations and stress distribution information, the probability of fracture shear

125 46th US Rock Mechanics/Geomechanics Symposium slip was examined using Mohr-Coulomb failure criteria. This study allows for a quantitative description of ground heaving and leakage potential induced by shear slip of fractures, which is an important parameter for performance assessment of CO2 reservoir.

ARMA 12-522 Probabilistic analysis of a faulted hydrocarbon reservoir during

CO2 injection Pereira, F. L. G., Oliveira, M. F. F. and Roehl, D. M. Computer Graphics Technology (Tecgraf) and Department of Civil Engineering, Pontifical Catholic University of Rio de Janeiro (PUC-Rio), Rio de Janeiro, Brazil Almeida, A. A. D. Department of Civil Engineering, Fluminense Federal University, Niterói, Rio de Janeiro, Brazil ABSTRACT: Carbon Capture and Sequestration have great potential for climate change mitigation,

but it still brings a list of concerns. In the case of CO2 injection in hydrocarbon reservoirs, for instance, modifications in the stress field can lead to the reactivation of geological faults. This phenomenon makes them a likely path for the escape of CO2 to other shallower layers or even to the surface. There are several methodologies to estimate the reactivation pressures in literature. However, even the most sophisticated solution can be unreliable depending on the uncertainty of the input data. The aim of this study is to investigate a probabilistic methodology using the program NESSUS® to efficiently characterize the uncertainties associated with the problem parameters. A synthetic geological cross-section with a single fault was analyzed by both a simplified analytical approach and a numerical FE modeling. The maximum admissible injection pressure to prevent fault reactivation is given in terms of a cumulative distribution curve. A sensitivity analysis is performed to determine the effect of parameter variations on results for both analytical and numerical methodologies.

ARMA 12-544 The Effects of Sequestration/ Water Floods on Exterior Stress Fields Dunayevsky, V.A. Shell International E&P, Houston, Texas, USA Myers, M.T. Shell International E&P, Houston, Texas, USA Bennett, M.B. Shell International E&P, Houston, Texas, USA ABSTRACT: The Eshelby like approach is used to successfully model the stress, strain and displacement fields associated with a depleting/inflating reservoir. A modified Cam-Clay material model is implemented as the constitutive equations for the reservoir material. The exterior of the reservoir is modeled as an infinite homogeneous linear elastic material and body forces are not considered. These assumptions allow a semi- analytical approach to be applied. The stresses exterior to the fault are induced by the depleting reservoir. The fault is represented as an elastic-plastic (modified Cam-Clay) high aspect ratio ellipsoidal inclusion loaded by the calculated exterior stress field. Two mechanisms are discussed as criteria for fault activation, runaway instability and negative rate of work of plastic strains. Two initial conditions are considered for the fault material model. First where the parameters for the material model are supplied by the user. Second where the initial effective mean stress and shear stress are assumed to be in the immediate vicinity of the intersection of the critical state line and yield surface. The differing predictions that follow from these two assumption are discussed. We find that fault activation is more likely to occur in the scenario when we

126 46th US Rock Mechanics/Geomechanics Symposium are inflating the reservoir rather than depleting the reservoir. This is due to movement of the stress path towards more unstable regions of the MCC material model under inflation scenarios.

ARMA 12-653 Passive Seismic Imaging for Carbon Sequestration Monitoring, Verification, and Accounting Fahrman, B. P., Slaker, B. A. and Westman, E. C. Department of Mining and Minerals Engineering, Virginia Tech, Blacksburg, VA, USA ABSTRACT: Double-difference seismic tomography was performed on travel time data from a carbon sequestration site at the Aneth oil field in southeast Utah as part of a Department of Energy initiative on monitoring, verification, and accounting (MVA) of sequestered CO2. A total of 1,211 seismic events were recorded from a borehole array consisting of 22 geophones. Most likely because of the poor geophone arrangement, a low-velocity zone in the Desert Creek reservoir can only be detected when voxels containing the highest ray path coverage are considered. MVA accuracy and precision could be improved through the use of a receiver array that provides more comprehensive ray path coverage. A synthetic analysis was performed to determine the effect of receiver arrangement on the success of passive seismic tomography as an MVA tool for varying CO2 plume sizes and locations. Seismic event locations were generated to represent induced seismicity from injection, and five geophone arrays were created to monitor this artificial seismicity. A quantitative comparison was made between each calculated velocity model and its corresponding synthetic model.

S ES Ion 24: HETEROGENEITY IN ROCKS Tuesday, 26 June, 11:00 AM - 12:30 PM Chairs: Roberto Suarez-Rivera, Alexander Chudnovsky

ARMA 12-189 Structural Integrity of Oil Storage Caverns at a Strategic Petroleum Reserve Site with Highly Heterogeneous Salt and Caprock Sobolik, S.R. and Ehgartner, B.L. Sandia National Laboratories, Albuquerque, New Mexico, USA ABSTRACT: This paper presents computational analyses to evaluate the effects of heterogeneous salt creep properties, com-promised caprock mined for sulfur, and pressure loss in an abandoned brine storage cavern, on cavern wellbore and surface struc-tures at an underground oil storage facility. These analyses represent a first attempt to combine several complex, non-homogen-eous processes in a dome-scale, three-dimensional geomechanical analysis using caverns meshed to measured geometries. The salt dome is characterized by heterogeneous salt properties, and nonuniformly-damaged caprock due to sulfur mining. Separate computational analyses in this report model the weakened caprock and identify a priority list for cavern borehole inspections, attempt to develop a set of salt creep properties from which predicted cavern volume closure matches measured values for individual caverns, and evaluate what effect that a damaged abandoned cavern may have on nearby caverns and their boreholes.

127 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-444 Scaling Problem in Heterogeneous Rock Fracture Chudnovsky, A., and Zhang, H. University of Illinois at Chicago, Chicago, IL, USA Wong, G. Shell Exploration and Production Company, Houston, Texas, USA Dudley, J.W. Shell International Exploration and Production, Inc., Houston, Texas, USA ABSTRACT: A well-recognized hierarchy of defects from microheterogeneities on the grain level to a large-scale network of cracks and layering structures creates a challenge for adequate fracture propagation modeling. The core of the problem is the constitutive equation for such a complex system and the formulation of strength and facture toughness criteria. The concept of a representative volume is commonly used in modeling statistically heterogeneous material by an effective homogeneous continuum. The foundation of this concept and its limitations are discussed. The necessity of an additional scaling rule in dealing with properties like strength and facture toughness that exhibit a scale effect is addressed. An example of brittle fracture in a concrete structure, and the determination of a scaling rule for the scale effect in fracture toughness are presented. The fracture of brittle materials like rocks and concrete appears in the form of highly tortuous, stochastic paths. This reflects a complex interaction between a crack and preexisting as well as newly formed micro-defects controlled by chance, and results in a large scatter of all fracture related parameters. A brief exposition of Statistical Fracture Mechanics (SFM) that addresses the statistical aspects of fracture is also presented. SFM is a formalism that combines Fracture Mechanics methods with Probability Theory and serves as the basis for an adequate modeling of brittle fracture.

ARMA 12-509 Rock Heterogeneity from Thermal Profiles using an Optical Scanning Technique Popov, Yu., Parshin, A., Chekhonin, E., Gorobtsov, D., Miklashevskiy, D., and Korobkov, D. Schlumberger Research Center, Moscow, Russia Suarez-Rivera, R. and Green, S. Schlumberger Innovation Center, Salt Lake City, USA ABSTRACT: The optical scanning (OS) technique and instrumentation has been developed for continuous high-resolution, noncontact profiling of rock heterogeneity and simultaneous measurements of thermal conductivity, thermal diffusivity and, as a result, volumetric heat capacity of rock samples. The OS technique is based on scanning a sample surface with two (for heterogeneity and thermal conductivity profiling) or three (for simultaneous profiling and thermal conductivity and thermal diffusivity measurements) infrared temperature sensors in combination with continuously operated, concentrated optical heat source. The OS technique provides for determining the principal values of thermal conductivity and diffusivity tensor components from scanning along two (for 2D anisotropy) or three (for 3D anisotropy) directions for anisotropic rocks. Spatial resolution on rock heterogeneity profiling was determined to be approximately 0.2 mm. Other merits of the new technique include freedom from constraints for sample size (1 to 80 cm sample length) and shape and quality of mechanical treatment of the sample surface, a contactless measurements mode that provides high-quality experimental data, short time of the measurement for each sample, ability to measure on a flat or cylindrical sample surface, and the possibility for measuring full-size cores and core plugs.

128 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-577 Shale Rock Properties: Peak Strength, Acoustic Anisotropy and Rock Fabric Hathon, L.A. Shell International E & P, Inc., Houston, TX, USA Myers, M.T. Shell International E & P, Inc., Houston, TX, USA ABSTRACT: A suite of strength tests, in compression and extension, acoustic properties measurements, and sample characterization using several techniques have been performed on a suite of mud rocks. The samples range from Miocene through Late Jurassic in age, occur at in situ stresses ranging from 1100 – 4000 psi, and range from deep water deposits associated with turbidite sandstones to over-mature, organic rich source rocks that are shale gas play targets. Peak strength in compression controlled by the strongest is always greater than peak strength in extension which is controlled by the weakest. The ratio of these strengths varies from 3 for weakly consolidated samples up to 14 in shale gas samples. The measured acoustic polar anisotropy in deep water Gulf of Mexico mud rocks increases with increasing compaction and ranges between ~9-20%. Shale gas samples, however, display polar velocity anisotropy on the order of 40%. This is a results recrystallization of clay minerals at elevated temperatures, and to preferential alignment of components like organic matter. Strong relationships are observed between the acoustic properties and peak strength in both compression and extension.

ARMA 12-611 The Influence of Fieldscale Heterogeneity upon Dynamic and Quasistatic Processes: Shock-Induced Damage and Injection Induced Surface Deformation Morris, J. P. Schlumberger-Doll Research, One Hampshire St, Cambridge, MA 02139 ABSTRACT: Rock heterogeneity and fabric can control mechanical response at a range of spatial scales. In this paper we review several examples which demonstrate the role of heterogeneity and fabric at the field scale specifically. In addition, heterogeneity and fabric play a role in processes at all time scales. Our discussion ranges from short time scales involving shock loading to consideration of perturbations resulting from fluid injection that manifest over years. Accounting for the influence of three-dimensional heterogeneity in detail presents challenges in terms of characterization, development of suitable material models and ultimately export to suitable 3-D computational tools. The examples presented in this paper demonstrate that the current generation of characterization methods, geological modeling tools and high fidelity 3-D computational geomechanical codes enable new understanding of the influence of 3-D heterogeneity and fabric in detail.

ARMA 12-649 Effect of Anisotropy and Heterogeneity on the Bending of Geologic Structures J. Burghardt and R. Suarez-Rivera Schlumberger Innovation Center, Salt Lake City, Utah, USA ABSTRACT: Bending of geologic strata occurs in the formation of a variety of geologic structures. Such bending deformation causes redistribution in the stress and strains within the formation and may result in the formation of fractures. Quantitative estimates of the stress redistribution as well as estimation

129 46th US Rock Mechanics/Geomechanics Symposium of the location and orientation of natural fractures is critical to many aspects of oil and gas production including wellbore stability, fracture containment, and production. Geomechanical analysis of folded structures commonly assumes that the rock is isotropic and homogeneous, which results in relatively simple mathematical formulas that are convenient for the estimation of the stress state, the location and orientation of induced fractures, as well as the change in permeability due to the fractures. However, such an approach ignores the rock properties as well as the heterogeneity present in many formations. The consequent spatial variability in properties within the rock unit can have a strong influence on where the rock mass deforms, where the maximum stresses occur and therefore where and how fractures are likely to form. The purpose of this paper is to review the literature on this topic and to illustrate the coupled effects of anisotropy and heterogeneity on the bending of geologic structures. A series of simple case studies is used to demonstrate which rock properties are most important to correctly characterizing folded geologic structures. It is demonstrated that when both lateral and vertical heterogeneity of the rock are accounted for, the in-situ stress state and the possible modes of failure become more complex and difficult to predict. Understanding these consequences is critical to the geomechanical analysis of folded structures and to applications to the oil and gas industry.

Ses s ion 25: I rnteg ation of Microseismic Monitoring into Natural and Hydraulic Fracture Characterization in Shale Reservoirs Tuesday, 26 June, 2:00 pm – 3:30 pm Chairs: Norm Warpinski, Ted Urbancic

ARMA 12-276 Understanding Hydraulic Fracture Variability Through Geomechanical Integration of Microseismic and Seismic Reservoir Characterization Maxwell, S.C. Schlumberger, Calgary, Alberta, Canada Norton, M. Progress Energy, Calgary, Alberta, Canada ABSTRACT: Economic recovery of shale gas reservoirs requires effective hydraulic fracturing in order to stimulate production. In this paper, a case study is presented from the Montney Shale in NE British Columbia, where microseismic and reservoir characterization data were used to understand some of the constraints on the fracture geometry. The study found that when wells were close to pre-existing faults, the hydraulic fractures were found to interact with these faults and act as a barrier to fracture growth. The microseismicity associated with the fault activation was found to have relatively large magnitudes and anomalous frequency-magnitude characteristics. In cases where the wells were far from pre-existing faults simple, planar hydraulic fractures were observed. However, there was a tendency to grow towards regions of low Poisson’s ratio identified through amplitude versus offset inversion of the seismic reflection data, which are believed to correspond with lower stress regions. Integrating microseismic interpretations and fracture treatment data with enhanced reservoir characterization has been used to rethink well placement and completion designs, resulting in improved well performance.

130 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-201 Microseismic Responses from Two Hydraulic Fracture Stimulation Strategies of One Horizontal Well in a North American Shale Mahrer, K.D. APEX HiPoint, Englewood, CO, USA Engelbrecht, L. and Fuller, B.N. HiPoint Reservoir Imaging, Littleton, CO, USA Mickey, K.D. APEX HiPoint, Englewood, CO, USA ABSTRACT: The goal of hydraulic fracture stimulations in unconventional reservoirs (e.g., shales) is creating an extensive, high-density fracture network. In December, 2010 the ~3050-m horizontal section of a ~3200-m deep well in a North America shale was stimulated using two strategies over a 30-stage stimulation. Stages 1-22 used ball-actuated, sliding-sleeve technology to open pre-existing wellbore casing slots, giving the stimulation fluid access to the surrounding rock; Stages 23-30 used pump-down- perforation-guns-with-plugs technology to deploy the plugs between stage sections and shoot casing perforations, again giving access to the surrounding rock. The whole stimulation was microseismically monitored using one, vertical, 45-level, 2,164-ft long, 3-component geophone array with its deepest geophone package deployed at the approximate depth of the stimulated well. The array recorded 1,388 stimulation-induced microseisms, 519 induced by Stages 1-22 and 869 induced by Stages 23-30. The microseismic data showed (a) the sliding sleeve stages generated sparse, narrow, somewhat-isolated microseismic event clouds, indicating a less-developed, but deeper-penetrating fracture network and (b) the plug and perforation stages showed dense, highly-overlapping microseismic event clouds, indicating a more-extensive, less-penetrating fracture network. In support of these findings, a data set from an unconventional reservoir comparing oil production using the two stimulation strategies from different wells, showed plug-and-perforation stimulated wells substantially out produced sliding sleeve wells.

ARMA 12-594 Integrating Microseismic with Surface Microdeformation Monitoring to Characterize Induced Fractures in the Immature Eagle Ford Shale Walser, D. W. Pinnacle, a Halliburton Service, Houston, Texas, USA Roadarmel, W. H. Pinnacle, a Halliburton Service, Houston, Texas, USA ABSTRACT: High-node-count, high-frequency-downhole-offset microseismic mapping was employed in conjunction with surface microdeformation (tilt) monitoring over an exploratory horizontal completion located in an oil-window Eagle Ford horizon where the magnitude of the maximum principle horizontal stress was close or equal to the overburden stress. The two far-field mapping technologies were merged in an effort to take advantage of the relative strengths of each, and to provide independent verification of various deliverables. A new deterministic calculation regime for the estimation of Stimulated Reservoir Area (SRA) and Stimulated Reservoir Volume (SRV) was implemented and compared to more conventional calculations of SRA performed with microseismic event positioning. A number of interpretive conclusions were drawn for each technology. It became apparent that with respect to the microseismic mapping effort, microseismicity alone may not always be sufficient to fully describe far-field fracture placement, geometry and orientation, and multi-planar joint inflation in shallow mapping scenarios.

131 46th US Rock Mechanics/Geomechanics Symposium The surface microdeformation diagnostics suggested that additional confidence in the combined interpretation was possible. Herein the overall mapping effort in terms of both technologies, and the various stress regimes are characterized in terms of their relationships to the induced fracturing orientation and the interaction with pre-stressed, naturally occurring geological features. It is shown that a geomechanical inversion based on surface microdeformation is capable of resolving the spatial distribution, orientations, and the principle fracture components of the complex network. The added knowledge of localized induced fracture distribution, orientation, geometry, and feature count per unit of SRA can be useful (and even fiscally material) in the shallower portions of the oil-window Eagle Ford.

ARMA 12-618 Microseismic and 3D VSP for infill evaluation in Greater Tindilpie, Cooper Basin, Australia Camac, B. A., Santos Ltd, 60 Flinders Street, Adelaide, S.A. Australia 5000 Waldron, A.W., Donley, J. A. and Hunt, S. P. Santos Ltd, 60 Flinders Street, Adelaide, S.A. Australia 5000 ABSTRACT: The Greater Tindilpie (GT) region located in the Patchawarra Trough (South Australia) is proving to be one the premier hydrocarbon producing regions of the Cooper Basin. To date, approximately 0.3 Tcf of condensate-rich gas has been booked as reserve. The development of these reserves and further resource conversion in GT is currently requiring a consistent and sustained approach. The reservoir section, the Early Permian Patchawarra Formation, is comprised of a series of stacked sands, silts, shales and coals deposited in a fluvio-lacustrine environment. Gas is reservoired within tight sands (Perm range: 0.1-10 mD) and silts; with coals and shales providing source and seal. Prediction of gas pay (Porosity >4%; water saturation <70%) has proven difficult in the GT area due to a large variation in the lateral and vertical distribution of channel, point bar and splay sand bodies, resulting from the complex depositional system. This paper reports on a microseismic project that was implemented in the Cowralli Field defining frac geometry in a well described strike-slip stress environment. Uncertainty around the effect of channel body geometry on fracture propagation led to the acquisition of a 3D VSP survey in a nearby field at Nephrite South Field, west of Cowralli, as optimum drainage will be governed by both frac geometry and channel body architecture influencing frac containment.

ARMA 12-554 Fracture Network Engineering: Combining Microseismic Imaging and Hydrofracture Numerical Simulations Pettitt, W.S., Pierce, M., Damjanac, B., Hazzard, J., Lorig, L., and Fairhurst, C. Itasca Consulting Group, Inc., Minneapolis, Minnesota, USA Sanchez-Nagel, M., and Nagel, N. Itasca Houston, Inc., Houston, Texas, USA Reyes-Montes, J.M., and Andrews, J. Applied Seismology Consultants Ltd., Shrewsbury, Shropshire, UK Young, R.P. University of Toronto, Toronto, Ontario, Canada ABSTRACT: Fracture Network Engineering (FNE) is the engineering design of rock mass disturbance through the use of advanced techniques to model fractured rock masses numerically, and then correlate field observations with simulated fractures generated within the models. Microseismic (MS) monitoring

132 46th US Rock Mechanics/Geomechanics Symposium is a standard tool for evaluating the geometry and evolution of the fracture network induced during a hydraulic treatment, principally by source locating MS hypocenters and visualizing these with respect to the treatment volume and infrastructure (Figure 1). The integrated use of Synthetic Rock Mass (SRM) modeling of the hydraulic fracturing with Enhanced Microseismic Analysis (EMA) provides a feedback loop where the SRM is constrained by the information provided by the MS data, and the in-situ behavior of the fracture network is better understood, which leads to informed decisions on future field operations. This paper discusses the technologies used in FNE and some of the developmental challenges we face in order to provide a more efficient and robust application of the approach.

ARMA 12-667 Induced hydraulic fractures or reactivated natural fractures? Modeling the response of natural fracture networks to stimulation treatments Williams-Stroud, S. C. and Barker, W. B., MicroSeismic, Inc., Houston, TX, USA Smith, K. L. EnCana Oil & Gas (USA), Dallas, TX, USA ABSTRACT: Microseismicity induced by hydraulic fracture stimulation of a horizontal well was mapped with a near-surface buried array. Distinct linear trends of events were not parallel to the direction of fast shear wave polarization measured in the reservoir with a crossed-dipole anisotropy tool. Analysis of core from a nearby well revealed numerous calcite-filled fractures that did not induce shear wave polarization, but did significantly impact the failure behavior of the reservoir rock during the stimulation treatment. Hydraulic fracture simulation with DFN modeling and source mechanism analysis supports the interpretation of reactivated existing fractures rather than the formation of hydraulically-induced tensile fractures.

Ses s ion 26: Sta bility and Support of Caverns and Tunnels Tuesday, 26 June, 2:00 pm – 3:30 pm Chair: Essie Esterhuizen

ARMA 12-123 Rock mechanical considerations associated with the construction of a deep nuclear waste disposal in clay rock Amann, F. Swiss Federal Institute of Technology, Engineering Geology, Zurich, Switzerland Martin, C.D. University of Alberta, Department of Civil & Environmental Engineering, Edminton, Canada Thoeny, R. Swiss Federal Institute of Technology, Engineering Geology, Zurich, Switzerland ABSTRACT: This paper discusses some fundamental rock mechanical issues relevant for the construction and the design of a nuclear waste underground repository associated with the short-term “excavation phase” and long-term “open drift phase”. Of particular interest is the development of the pore pressure field around a repository tunnel in the short-term, the dissipation of excess pore pressures in the long-term, the resulting loads in a stiff tunnel lining, and the effects of de- and re-saturation cycles.

133 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-135 Ground Conditions Encountered and the Support System Installed in the Realigned Starter Tunnel for the Lake Mead No.3 Intake, Nevada. Berry, T. W. Arup, London, UK Pollak, S.E. Arup America, Houston, Texas, USA Piek, M. L. Arup America, San Francisco, California, USA ABSTRACT: In 2008 the Southern Nevada Water Authority (SNWA) awarded Contract No. 070F 01 C1 for Lake Mead Intake No. 3 – Shafts and Tunnel to a joint venture between Impregilo SpA and SA Healy, the Vegas Tunnel Construc- tors. Following award, the 9m diameter, 185m deep access shaft and 20m wide, 10m high and 50m long TBM launch chamber were successfully constructed. Difficult conditions encountered in the original starter tunnel during 2010 resulted in its abandonment and sealing in early 2011. Vegas Tunnel Constructors commenced excavation of a realigned starter tunnel thereafter to allow the installation and erection of the 7.22m diameter 190m long Herrenknecht AG Dual Mode Mixed Shield TBM. This paper describes the ground conditions encountered during the excavation of the realigned starter tunnel, discusses the excavation production data and summarizes the support system employed to successfully complete the starter tunnel.

ARMA 12-343 Characteristics of Rock Deformation and Fractures in an Underground Powerhouse Caverns Wei, J.B., Deng, J.H., and Zheng, H.C. State Key Laboratory of Hydraulics and Mountain River Engineering, College of Water Resources and Hydropower, Sichuan University, Chengdu, Sichuan, China ABSTRACT: The deformation and fracture characteristics of a large underground caverns with high in-situ stress are analyzed and correlated with its geology, data from monitoring and geophysical surveying, and construction process. Comparing with low to medium in-situ stress, under high in-situ stress and low strength-to-stress ratio, the deformation of rock mass is no longer controlled by the “opening displacement” of major structure planes, the proportion of deformation induced by rock fractures increases. The deformation magnitude and EDZ depth are relatively large. The EDZ depth of sidewall is 9–15 m in generally, some is greater than 15 m. The deformation magnitude increases with the extending of EDZ depth, the development of rock mass deformation with time should be understood as the progressive failure of rockmass, which is different with normal rheologic deformation behavior of soft rock. Cracks at the downstream arch of powerhouse chamber and transformer chamber are caused by the unloading splitting and outward buckling failure of layered rock mass under high stress, which leads to the increasing of measured displacement at the downstream arch abutment. Cracks at the upstream sidewall of transformer chamber are tensional and are caused by the compression fracture of rock mass due to stress concentration.

134 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-497 New Technology for Measuring the In Situ Performance of Rock Bolts Hyett, A. YieldPoint Inc., Kingston, Ontario, Canada Spearing, A.J.S. Southern Illinois University Carbondale, Carbondale, Illinois, USA ABSTRACT: Understanding the interaction between rock bolts and underground rock movement is critical for safe and cost effective underground excavation design. Although early research on this subject involved a balance of theoretical analysis and field measurement, recent work has been heavily focused on analytical and numerical studies. This paper describes technology that has the potential to redress the balance through instrumentation of rock bolts deployed under routine operating conditions in underground mines Almost all previous instrumented rock bolt studies have used core technologies based on resistive strain gauges according to two scenarios (i) load cells positioned at the head of the bolt, and (ii) resistance strain gauge arrays recessed into grooves along the length of the bolt. Both approaches are complimentary with the selection criterion for each depending on factors such as whether the rock-bolt is fully grouted or end-anchored. A new product is introduced in this paper. The d-REBAR involves an array of small-diameter long-base-length displacement sensors recessed into grooves along the entire length of the bolt. The transducers are interfaced with on-board digital signal conditioning and telemetry. Methodologies for the deployment of the new instrumentation are presented, and guidelines are presented for the interpretation of results obtained based on data obtained from field trials. The results demonstrate the viability of these new technologies and moreover provide important insight into rock bolt/rock mass interaction.

ARMA 12-677 Subway Project in Istanbul, Turkey Ozturk, C. A. Istanbul Technical University, Istanbul, Turkey Simdi, E. Avrasya Metro Group, Istanbul, Turkey ABSTRACT: Kadikoy-Kartal subway tunnels will be the part of solution for Istanbul’s heavy traffic problem. The subway consists of two underground tubes having approximately 56.1 km length. Sixteen stations are going to be constituted on the subway line. The geological formations are Trakya, Kartal, Kurtkoy, Aydos, and Dolayoba, respectively. These formations could be mostly classified as weak and/or medium rock mass classes based on geotechnical studies. The depths of the tubes also change from 18 m to 44 m due to the topographical diversity. The excavations and support of underground structures including tubes, connection tunnels, and stations in this project was started in July 2008 and completed in August 2011. The first 9 km of the tubes was driven by tunnel boring machine (TBM) while the rest of constructions were excavated by excavators and loaders. The initial support systems of the underground opening are mainly based on lattice girders, shotcrete and bolts. The aim of this paper is to give the basic stages of the subway construction project as well as the initial support systems of the underground tubes based on the geometry of the underground openings and the engineering properties of geological formation.

135 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-378 Effects of Initial Geostress on the Displacement of Underground Powerhouse Caverns Deng, J. H. State Key Laboratory of Hydraulics and Mountain River Engineering, Sichuan University, Chengdu 610065, China Chen, F. School of Civil Engineering, Southwest Jiaotong University, Chengdu 610031, China Cai, D. W. Monitoring Center, Hydrochina Chengdu Engineering Coorporation, Chengdu 610072, China Wei, J. B. & Gao, C. Y. State Key Laboratory of Hydraulics and Mountain River Engineering, Sichuan University, Chengdu 610065, China ABSTRACT: Measured displacements are analyzed for 5 large-scale underground powerhouse caverns in Southwest China. Their principal stresses lie between 18 and 35MPa, however their displacements demonstrate completely different characteristics. In order to clarify the effects of stress, a term of stress index λ is defined to describe their stress state; Then the displacement is correlated with the stress index; And finally displacement characteristics is compared at various stress state.

Ses s ion 27: Rock Fall and Slope Analysis Tuesday, 26 June, 2:00 pm – 3:30 pm Chairs: David Potyondy, Lee Petersen

ARMA 12-493 Perforation of rockfall protection barriers by normal block impact Hambleton, J.P, Buzzi, O., Giacomini, A., Spadari, M., and Sloan, S.W. Centre for Geotechnical and Materials Modelling, The University of Newcastle, Callaghan, NSW, Australia ABSTRACT: Flexible rockfall protection barriers are used ubiquitously to safeguard people and infrastructure against falling rock fragments along weak or fractured slopes. Performance of these barriers is often quantified in terms of the level of impact (kinetic) energy that can be withstood, referred to here as the “critical energy.” As pointed out in recent papers, however, there is no single representative value of critical energy for a given barrier. Instead, critical energy decreases as the block size decreases, a phenomenon referred to as the “bullet effect.” With a view towards explaining and predicting the bullet effect, the paper presents a simple analytical model for perforation of a flexible barrier caused by normal impact. The model rests on a two-dimensional idealization of the full three-dimensional impact problem, as well as a balance of energy between the initial kinetic energy of the block and the energy absorbed by the barrier. The model predicts a strong dependence of the critical energy on the block size, and the predicted trend agrees well with data available in the literature. Ramifications for practical applications and possible future refinements to the model are also discussed.

136 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-631 Effect of Rockfall Shape on Normal Coefficient of Restitution Vijayakumar S., Yacoub T. and Ranjram M. Rocscience Inc., Toronto, ON, Canada Curran, J.H. Rocscience Inc. and Civil Engineering, University of Toronto, Toronto, ON, Canada ABSTRACT: In the lumped mass model which is used in various commercial software (eg. CRSP and Rocfall 4.0), the division of kinetic energy into translational and rotational components is done through a combination of energy balance and empirical relationships. Other than slope geometry, the required input data are the normal coefficient of restitution, the tangential coefficient of restitution and the coefficient of rolling friction. In order to accommodate shape and rotational effects in lumped mass models, two empirical factors related to size and normal impact velocity are employed. Using the lumped mass model, values of normal coefficient of restitution greater than 1 were reported in many field observations, with values as large as 2 obtained. This makes the application of the lumped mass model questionable in some situations. We have proposed a two-dimensional shape-dependent mechanistic model where only two material parameters, namely the normal coefficient of restitution and the friction coefficient, are used. The proposed model uses the shape, size and point of contact of the rock to calculate the translational and rotational components of the kinetic energy. Through this new approach which incorporates complete two-dimensional rigid body dynamics, we are able to predict an apparent normal coefficient of restitution greater than 1 while, at the same time, not violating the principle of conservation of energy.

ARMA 12-484 Comparison of 2D and 3D DDA in rockfall analysis Chen, G. Kyushu University, Fukuoka, Japan & Visiting Prof. of Institute of Earthquake Science, China Zheng, L. Kyushu University, Fukuoka, Japan Jiang, Z. Institute of Earthquake Science, China Earthquake Administration, China ABSTRACT: It is important to estimate the trajectory and motion behaviors of falling rocks in rockfall preventive measures such as rockfall hazard and risk assessment, design and performance evaluation of rockfall protection structures. The trajectories of falling rocks can be described as combinations of four types of motion: free fall, rolling, sliding and bouncing of a falling block. This study shows that these four basic types of motion can be simulated by DDA with high accuracy. A close comparison is carried out on motion behaviors between 2D and 3D DDA simulation. The merits and nota bene in the application of DDA are explored in this paper.

ARMA 12-267 Rigid body dynamics for rock fall trajectory simulation Basson, F. R. P. Newmont Asia Pacific, Perth, Western Australia, Australia ABSTRACT: Rock falls are difficult to model accurately, partly because the readily available simulation packages simplify problems to either two dimensions and ignore the fall body geometries with particle models. Lumped-mass models concentrate the fall body mass into a single point, ignore the fall body shape and can only simulate sliding movement. Rotation is mimicked by assigning a zero friction angle to

137 46th US Rock Mechanics/Geomechanics Symposium the interaction between the fall body and slope. In reality, falling rocks often free fall, bounce, slide, and roll during a single trajectory, and the falling body shape and size, and the three dimensional topography largely determine the trajectory path and associated energy. The author developed a rock fall simulation package, Trajec3D, using existing technologies. The resulting software is a three dimensional rigid body rock fall analysis program that can simulate the trajectory of volumetric bodies during free fall, bouncing, sliding and rolling. The physical interaction between materials is a function of the combined properties of the fall body and the impact surface, with only three input parameters required; the coefficient of restitution, and the static and dynamic friction angles.

ARMA 12-122 Modeling and Remedial Measures of Rock Slope Stability and Rockfalls Problems along Werka Descent Road West of Saudi Arabia Sadagah, B. H. King Abdulaziz University, Jeddah, Saudi Arabia El-Shanooty, S. I. Geotechnical consultant office of soils and foundations, Jeddah, Saudi Arabia ABSTRACT: A great attention has been given to construct a number of descent roads, at the Kingdom of Saudi Arabia government development plans. Werka descent constructed two years ago and recently harmed due to rainstorm. Werka mountainous road subjected to rockfalls, manmade slope failures and debris flow along the road both sides. Intensive geotechnical study includes the RMR and GSI rock masses classifications were applied indicates that the rocks are medium to poor quality. The integrated techniques such as graphical method, modeling, and simulation are utilized to assess rock slope instability and rockfalls by using DIPS, RocFall, RocPlane and Swedge programs, on Werka descent road and recommend the remedial measures for the natural and manmade slope cuts and rockfalls. The seismic coefficients of 0.1 to 0.4 were taken into consideration in modeling. Two man-made slope cuts were studied and modeled utilizing the integrated techniques is to eliminate the risk of slope failures and rockfalls through the construction of remedial measures. The analyses indicate that the intensity of rainfall, joints set attitudes with the slope face attitude, Jv, block size; block shape, specific gravity, coefficients of restitution and the slope geometry are the main factors in rock slope failure and rockfall’s problems. The factors of safety of the slopes decrease as the seismic coefficients increase.

ARMA 12-237 A case study of slope stability evaluation of cut-slopes of switchyard site of Tapovan-Vishnugad Hydropower Project, Uttarakhand, India. Y. R. Dhar Indian School of Mines, Dhanbad, India D. John O.N.G.C. Mumbai, India ABSTRACT: The paper embodies technical findings of slope stability investigations of the switchyard section of the Powerhouse Complex of Tapovan-Vishnugad Hydroelectric Project, at Helong village, situated on the left bank of the Alaknanda River. The switchyard area has to be of 130 m length and 40 m width and was proposed to be laid on a slope with length striking NW-SE, at an elevation of 1377 m. Consequently, the slope on the hillside in the North-East of the switchyard was to be cut to make a bench

138 46th US Rock Mechanics/Geomechanics Symposium of the desirable dimension at an elevation of 1377m. As a result of this, a steep slope cut of around 14 m height could get created on the North-East side of the proposed location. Kinematic analysis for the original ground slope facing the switchyard area shows that the slope is fairly stable. On cutting to create a leveled space of 40 m width at an elevation of 1377 m, the inclination of the slope face would increase. So in the study a maximum slope inclination value (N230°/83°) was considered for the south-west facing slope in the switchyard area. The studies deliberate on procedures adopted for stability investigations, rock reinforcement, using shotcrete with wire mesh, tensioned anchors, horizontal and vertical bolting, bolt spacing and drainage measures for the slope.

Se ssion 28: Mapping and Imaging Tuesday, 26 June, 2:00 pm – 3:30 pm Chairs: Steve Glaser, Sarah Wilson

ARMA 12-531 Characterization of Damage in Anisotropic Rock Due to Buried Explosions Martin, R. J. and Boyd, P. J. New England Research, Inc., White River Junction, VT, USA ABSTRACT: In July 2008, five small (61 to 122 kg) chemical explosions were detonated in a low fracture density, homogeneous granite in Barre, VT. The physical properties of the granite were measured before and after the explosions on cores recovered in the vicinity of each shot. The changes in the post- shot properties were used to quantify damage at the micro, meso, and macro scales. The Barre granite is transversely isotropic; the elastic anisotropy is on the order of 20%. The anisotropy is due a planar array of microcracks, frequently referred to as the rift. After the shots were detonated, cores were recovered at various distances from each shot point. The pre-shot cores contained few preexisting fractures. In contrast, the post-shot cores show extensive damage; the intensity of the damage decreased with range. The damage zone extended laterally to 7 meters for the 122 kg shots. Five distinct damage zones were identified. Near the emplacement, the rock was highly pulverized and granulated. Outward and above the emplacement level, the granite was characterized by high angle fractures parallel to the rift. This zone transitioned to a mostly intact matrix with few randomly oriented fractures out to the elastic region. At the microscale, damage was quantified by measuring the differences in ultrasonic wave speeds between the pre- and post- shot values on specimens of intact matrix rock. Near the working point, the P wave velocity decreased up to 12%. Damage at all scales was greatest above the emplacement level of the charge and parallel to the trend of the rift. The shapes of the zones of equal damage were non spherical. These results were used to interpret the seismic data collected on this experiment.

139 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-494 Uncertainty of Volumetric Fraction Estimates Using 2-D Measurements Tien, Y.M., Lu, Y.C., Chang, H.H., and Chung, Y.C. Department of Civil Engineering, National Central University, City, Jhongli, Taoyuan 320, TAIWAN Lin, J.-S. Department of Civil and Environmental Engineering, University of Pittsburgh, Pittsburgh, PA 15261, USA Lee, D.H. Department of Civil Engineering, National Cheng Kung University, Tainan 701, TAIWAN ABSTRACT: This paper presents an analytical solution to quantify the uncertainty of volumetric fraction (Vf) estimates in a heterogeneous material using 2-D probes. The analytical solution was derived based upon the concept of representative volume (RVE). The results show that the uncertainties of the estimates depend upon the size of blocks, measurement area, and level of Vf. The analytical solution has been verified via numerical simulation. The latter was carried out by first generating spherical blocks to various level of Vf, which was then sampled by 2D probes in obtaining the Vf estimates and the associated uncertainties. Application examples are given at the end.

ARMA 12-456 On Site Visualization as a new visual scheme for risk and safety management for rock engineering applications Akutagawa, S. Kobe University, Kobe, Japan Abe, R. and Izumi, C. Oriental Consulting, Bangalore, India Nomura, M. CTC, Tokyo, Japan ABSTRACT: Sensors of the new type are developed for simultaneous monitoring and visualization of risk conditions for geomechanics applications to achieve an advanced safety management scheme using “color of light” as a key technology of the proposed method. These sensors are designed and built based on the new monitoring concept called “On Site Visualization” and capable of 1) sensing data and 2) visually outputting the measurement results simultaneously by using LED for workers and all concerned. This new monitoring scheme may be applied to tunneling, rock slope cutting, open-cut excavation problems, etc., whereby real-time visual presentation of monitored information may be fully incorporated to achieve an advanced safety management scheme.

ARMA 12-368 Comparison of Standard Structural Mapping Results to 3-D Photogrammetric Model Results: Boundary Transformer Banks Rockfall Mitigation Project, Metaline Falls, Washington Gates, W. C. B. Jacobs Associates, Seattle, Washington, USA Haneberg, W. C. Fugro GeoConsulting, Inc., Houston, Texas, USA

140 46th US Rock Mechanics/Geomechanics Symposium ABSTRACT: The Boundary Dam hydroelectric power plant on the Pend Oreille River in northeastern Washington has been producing a significant proportion of Seattle’s electricity since 1967. Six hydro- generating units are housed in a large machine room within a dolomitic rock massif with individual step-up transformers in rock bays, located at the bottom of a 150 m high cliff above the tailrace. Transmission lines exit the bays on concrete outriggers, run nearly vertically up the rock face to stand-off structures, and then into the power grid. Rockfall has been a constant problem, causing damage to outriggers, power line accessories, and appurtenances. Because of electrical interference and difficult access, traditional mapping of the geologic structure was complemented with close range terrestrial photogrammetric 3-D models on which discontinuities could be mapped remotely. Rock mass discontinuity orientations from historical mapping data, new tunnel mapping, and photogrammetric modeling of the face agreed well and fell into distinct sets. This facilitated evaluation of the rock mass structure and kinematic analyses used in tunnel design and rock face protection. Remote techniques such as photogrammetry are important tools that complement manual rock face mapping. However, they cannot and should not replace traditional hands- on-the-rock geological fieldwork, observation, and interpretation.

ARMA 12-552 Verification of a 3-D LiDAR point cloud viewer for measuring discontinuity orientations Otoo, J. N., Maerz, N. H. Missouri University of Science and Technology, Rolla, MO, USA Li, X., Duan, Y. University of Missouri, Columbia, MO, USA ABSTRACT: LiDAR (Light Detection and Ranging) scanners are increasingly being used to measure discontinuity orientations on rock cuts to eliminate the bias and hazards of manual measurements which are also time consuming and somewhat subjective. Typically LiDAR data sets (point clouds) are analyzed by sophisticated algorithms that break down when conditions are not ideal, eg. when some of the discontinuities are obscured by vegetation, or when significant portions of the rock face are composed of blast fractures, weathering generated surfaces, or anything that should not be identified as a discontinuity for the purposes of slope stability analysis. This paper presents a simple LIDAR point cloud viewer that allows the user to view the point cloud, identify discontinuities, pick 3 points on the surface (plane) of each discontinuity, and generate discontinuities orientations using the three point method. A test of our 3-D LiDAR viewer for discontinuity orientations on three rock cuts in the Golden Gate Canyon Road area of Colorado is also presented.

ARMA 12-186 Numerical modeling of strain transfer from rock mass to a fibre optic sensor installed inside a grouted borehole Madjdabadi, B. M. Civil Engineering Department, University of Waterloo, Waterloo, Ontario, Canada Valley, B. Geomechanics Research Centre, MIRARCO – Mining Innovation, Sudbury, Ontario, Canada Dusseault, M.B. Earth and Environmental Sciences Department, University of Waterloo, Waterloo, Ontario, Canada Kaiser, P.K. CEMI, Sudbury, Ontario, Canada

141 46th US Rock Mechanics/Geomechanics Symposium ABSTRACT: Strain measurements in underground excavation are usually done locally, with extensometers or similar devices placed within 10-15 meters of adit or stope faces, mainly to gage development of the EDZ (excavation damaged zone) and assess its evolution and impact on local safety (rock falls, rapid deterioration of wall condition...). However, the calibration of three-dimensional stress analysis models used to assess excavation geometry and sequencing requires strain (displacement) measurements in those parts of the rock mass that are in the elastic domain for some or all of their active design life. Recently developed distributed fibre optic sensors are now being used to measure local linear displacements continuously in a large rock mass volume in real mining conditions in Canada. Grouted inside a borehole and therefore encased in a material of far lower stiffness that the rock mass, an optical fibre may register strains different from those actually occurring in the rock mass. A number of factors affect the process of rock mass strain conveyance through the grout to the fibre. This paper reports a study that simulates the borehole-grout-fibre interaction to find how the strain transfer takes place and whether there are any issues serious enough to warrant alterations in installation procedures and grout materials.

Ses s ion 29: M odeling of Hydraulic Fracture Interactions in Naturally Fractured Formations Tuesday, 26 June, 4:00 pm – 5:30 pm Chairs: Tom Doe, Azra Tutuncu

ARMA 12-668 Static & Dynamic Data Integration for Improved Characterisation of a Fractured Gas Reservoir Rogers, S. Golder Associates Ltd, Burnaby, British Columbia, Canada Lim, D.H. Golder Associates Inc, Redmond, Washington, USA Fejer, P. Hess Corporation, Kuala Lumpur, Malaysia Han, G. Hess Corporation, Houston, US ABSTRACT: A common characteristic of many fractured reservoirs is the low level of data density that often results in the non uniqueness of any interpreted description of the role and influence of natural fractures upon reservoir performance. Therefore approaches that integrate both static and dynamic data sources provide a means to help reduce some of this conceptual uncertainty. A workflow is described below for a thick Permian aged fractured carbonate gas reservoir where relatively low data density and highly variable well performance provides considerable uncertainty. A variety of different structural elements from micro-fractures, meso-scale fractures and major faults are seen from core, log data and seismic imaging. Understanding their contribution is critical if development decisions are to be made that exploit the positive impacts of fractures on reservoir deliverability. Using Discrete Fracture Network (DFN) based analysis and characterisation methods, the data base of both static and dynamic data were considered in order to understand a range of fracture related properties including their geometric, spatial and dynamic contributions. In order to help synthesise these observations into a predictive model for estimating the field scale distribution of fracture intensity and also estimated initial production, a multivariate statistical analysis was

142 46th US Rock Mechanics/Geomechanics Symposium utilised. Drawing on a range of independent field scale fracture variables such as structural curvature, fault proximity, reservoir thickness, porosity etc were correlated against both calculated fracture intensity and initial production (IP) rates. This lead to the development of 3D predictive models that can be used in field development planning. ARMA 12-209 Shale Gas Resources: Energy Potential and Associated Exploitation Challenges for Coupled Geomechanics and Transport Characteristics Liu, C.H., Tutuncu, R.S.A. Petroleum Engineering Department, Colorado School of Mines, Golden, Colorado, USA ABSTRACT: Natural gas systems are of great value in terms of providing clean energy solution to the growing energy demand in the world. From the statistical analysis carried out by the US National Petroleum Council, Department of Energy in 2009, both natural gas and coal will meet around 25% of the energy demands of the world by the year 2030. Such sharp increase in demands especially from fast growing economies many influences the geopolitical scenario of the world. To maintain a level play field for sustainment of the world economies, it is necessary to look into unconventional resources that are available in plenty on the earth in almost all the continents and may offset the energy dependence of countries on outer sources. Natural gas from unconventional resources like Coal Bed Methane (CBM), Tight Gas Sands, and Shale Gas has been identified to be economically exploitable. From the speculative studies carried out by Energy information Agency that looked into 48 basins in 32 countries totaling around 70 shale formations was an exhaustive study and provides a lot of new information about the resource potential of these shales in term of the extent, maturation, generation and technical recoverability of the gas from these basins. However, there are certain environmental issues associated with development of natural gas from these unconventional resources like contamination of natural resources.

ARMA 12-657 How important is the poroelastic effect to completion design on tight shales? Suarez-Rivera, R. Schlumberger Innovation Center, Salt Lake City, Utah, USA Fjær, E. SINTEF Petroleum Research and Norwegian University of Science and Technology, Trondheim, Norway ABSTRACT: The poroelastic effect addresses the coupled deformations of the solid framework and the fluids in a porous rock. It also studies the effective stresses that result from this coupled behavior. Because fluids can move through the porous medium, at a rate controlled by their permeability, local increases in pore pressure, resulting from local pore strains, dissipate as a function of time. This behavior makes the poroelastic effect time-dependent, and is long-lasting for low permeability rocks. For some applications (e.g., borehole stability in low permeability rocks), evaluating the transient effect is critical to anticipating and preventing failure. For other applications (e.g., evaluating the in-situ effective stress), the equilibrated steady- state condition is needed. The Biot and Skempton coefficients are the two fundamental rock properties that are needed to understand the poro-elastic effect. In this paper, we discuss a methodology for evaluating the Biot’s coefficient and to evaluate its variability along the directions parallel and perpendicular to bedding. We also discuss implications of the poroelastic effect for applications to oil and gas producing tight shale reservoirs. The effects are illustrated by examples, using data from laboratory tests. Most importantly, we provide values of Biot’s coefficients that could be used for applications in organic-rich mudstone reservoirs.

143 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-441 Montney Shale Geomechanical Challenges: 2D and 3D FEM/ DEM Numerical Simulations of a Layered Material Fracturing in Compression Keneti, S. A. R. EBA, A Tetra Tech Company, Oceanic Plaza, 9th Floor, 1066 West Hastings Street, Vancouver, V6E 3X2, British Columbia, Canada Pak, R. A. Golder Associates Ltd., 500 - 4260 Still Creek Drive, V5C 6C6, Burnaby, British Columbia, Canada Wong, R. C. K. Department of Civil Engineering, Schulich School of Engineering, University of Calgary, T2N1N4, Calgary, Alberta, Canada ABSTRACT: In this study a series of numerical analysis have been carried out to assess the suitability of the FEM/DEM technique to simulate UCS test of a horizontally layered material, the Montney shale. The strength parameter of the Montney samples reported by Keneti and Wong (2011) were used as the input data to 2D and 3D models in the ELFEN program. When the failure criterion within the intact material was met in the model, a new crack was generated which could be visualized by re-meshing the updated geometry with the pre-existing foliations and the new cracks. The results were analyzed in terms of the “global mechanical response” obtained by assessing if the fracturing response is comparable to the recorded behavior in the UCS test of the Montney shale. The entire fracturing process was shown to be simulated well by ELFEN during fractures initiation and propagation processes.

ARMA 12-292 Numerical Modeling of Hydraulic Fractures Interaction in Complex Naturally Fractured Formations Kresse, O., Weng, X., Wu, R., and Gu, H. Schlumberger, Sugar Land, Texas, USA ABSTRACT: A recently developed unconventional fracture model (UFM) is able to simulate complex fracture network propagation in a formation with pre-existing natural fractures. A method for computing the stress shadow from fracture branches in a complex hydraulic fracture network based on an enhanced 2D Displacement Discontinuity Method (DDM) with correction for finite fracture height is implemented in UFM and is presented in detail including approach validation and examples. The influence of stress shadow effect from the hydraulic fracture network generated at previous treatment stage on the hydraulic fracture network propagation and shape at new stage is also discussed.

ARMA 12-238 A Microscopic Numerical System for Modeling Interaction between Natural Fractures and Hydraulic Fracturing Han1, Y., Damjanac1, B., and Nagel2, N. 1. Itasca Consulting Group, Inc., Minneapolis, Minnesota, USA 2. Itasca Houston, Inc., Houston, Texas, USA ABSTRACT: In this paper, we present a microscopic numerical system for simulating the interaction between the natural fractures and hydraulic fracturing. In this system, the intact rock mass is represented by bonded particle model in Particle Flow Code (PFC); the pre-existing natural fractures are simulated

144 46th US Rock Mechanics/Geomechanics Symposium by smooth-joint contact model; the fluid flow in the porous media and fracture and the buildup and dissipation of pore pressure are modeled by the pipe flow over the network connecting all the pores; and, the hydraulic fracturing is treated as dynamic mechanical and hydraulic pressure boundary or interior conditions along the hydraulic fractures. In our model, the hydro-mechanical response of the porous matrix, the fluid flow in the pore channels, the coupling of the matrix volumetric deformation and the pore fluid dissipation, and the reactivation and further development of natural fractures, are modeled naturally and realistically in a physically correct manner. After each component of the system is described in great details, an example is provided to illustrate the complete procedure of applying the developed system in solving practical problems.

Ses s ion 30: Advances in In Situ Stress Determination Tuesday, 26 June, 4:00 pm – 5:30 pm Chairs: Takatoshi Ito, Doug Schmitt

ARMA 12-168 Wireline hydraulic fracturing stress determinations in the ANDRILL South McMurdo Sound Drill Hole Schmitt, D. R. University of Alberta, Edmonton, Alberta, Canada, City Wilson, T.J. Ohio State University, Columbus, Ohio, U.S.A. Jarrard, R.D. University of Utah, Salt Lake City, Utah, U.S.A. Paulsen, T.S. University of Wisconsin, Oshkosh, Wisconsin,U.S.A. Pierdominici, S. Int. Nazionale di Geofisica e Vulcanologia , Rome, Italy Handwerger, D. Schlumberger Terra-Tek, Salt Lake City, Utah, U.S.A. Wonik, T. Leibniz-Institut für Angewandte Geophysik, Hannover, Germany ABSTRACT: A set of hydraulic fracturing stress measurements were carried at depths of up to 1400 m below the rig floor at the bottom of the ANDRILL South McMurdo Sound borehole. The measurements were accomplished in open hole through indurated and low permeability glacial diamicts and shales. A 2000-m long wireline hosted straddle packer system was used that allowed for relatively rapid deployment; and seventeen successful measurements were made. Good breakdown pressures were observed in most of the tests; and this allowed constraints to be placed on the magnitude of the greatest horizontal compression. Correspondingly, the vertical stress was calculated by integrating the densities obtained from physical property logging of the nearly continuous core. In all cases, this vertical stress magnitude was intermediate between the horizontal stress values, and consequently indicating a strike-slip stress environment exists at this location.

145 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-461 Review of borehole in situ stress measurement techniques for various ground conditions and numerical stress estimation considerations Gaines, S., Diederichs1, M.S., and Hutchinson1, D.J. Dept. of Geological Sciences and Geological Engineering, Queen’s University, Kingston, ON, Canada 1GeoEngineering Centre, Queen’s-RMC, Kingston, ON, Canada ABSTRACT: Evaluation of in situ stress conditions is important for determining wellbore stability in the oil and gas industry, or assessing excavation stability for mining and civil engineering projects. As a result, accurate and reliable methods of in situ stress determination are necessary to adequately define stress conditions in order to optimize engineering design of a given structure. Since it is challenging to collect reliable stress information at significant depth from surface, observational methods based primarily on borehole reconstruction tools have increasingly been used to constrain stress conditions. This paper provides an overview of some of the traditional methods used for determining in situ stress conditions in deep boreholes, including a summary of the methodology and a critical assessment of the limitations associated with each technique. Some of the issues associated with properly assigning material properties are examined, both in terms of scale dependency and the variation of material properties from the borehole wall to the rock mass. Particular emphasis is placed on the use of these methods in a variety of difficult ground conditions including high stress environments and horizontally layered sedimentary rock.

ARMA 12-169 Study on effect of residual aperture and system compliance in in-situ stress measurement by hydraulic fracturing method Dong, Y.K., Li, H. and Wang, H.Z. Key Laboratory of Crustal Dynamics, Institute of Crustal Dynamics, CEA, Beijing, China ABSTRACT: Residual aperture causes pressure penetration into the fracture prior to its reopening, and system compliance makes the measured reopening pressure unequal to the real value. Both of the two factors are ignored in the conventional theory. Taking account of residual aperture and system compliance effects, we analyzed the phenomenon that measured reopening pressure Pr (a)decreases with the repeated test cycles, and considered that Pr (a) gradually approaches to the real value Pr0 due to the increased dVc/ dP and residual aperture effect. Furthermore, we present two critical values, critical crack length Lc and critical crack capacity Cc, to explain the phenomenon that Pr (a) is less than Ps. It is concluded that Pr (a) is between Pr0 and Ps when Cc appears earlier than Lc. Comparing experiments by hydraulic fracturing in 3 boreholes of about 5 m away from each other were carried out. For the phenomenon Pr (a) is less than Ps at 2 test sections, that is different from others at the same depth, we concluded that it’s not caused by high stress difference, and modified the 2 abnormal data to average lever based on residual aperture and system compliance theory.

ARMA 12-254 Stress changes at the crest of dipping structures Nikolinakou, M.A. Bureau of Economic Geology, The University of Texas at Austin, Texas, USA Flemings, P.B. Jackson School of Geosciences, The University of Texas at Austin, Texas, USA

146 46th US Rock Mechanics/Geomechanics Symposium ABSTRACT: We use a coupled poro-elastic model to calculate the change in stresses at the crest of dipping structures, due to a regional over-pressured field. We show that localized flow field at the crest of the structure may increase horizontal and vertical stresses above the lithostatic value, and therefore very high leakoff values, even greater than the overburden, are possible at the crest of these dipping structures. We also show that principal stresses may rotate, and the direction of the least principal stress can become vertical. Furthermore, the elevated pore pressures can lead to very low effective stresses, and hence localized fractures. We also explore how the stress field is affected by permeability anisotropy: higher horizontal permeabilities lead to more significant changes in the horizontal stress. Our analyses illustrate that traditional basin-modeling assumptions - such as a vertical stress equaling the overburden and a horizontal stress equaling a fraction of the overburden - are not valid at the tip of dipping structures and may misrepresent borehole stability and trap integrity.

ARMA 12-447 Borehole breakout formation and stress estimation in unconsolidated deepwater sediments Chang, C. Department of Geology, Chungnam National University, Daejeon, South Korea Moore, J. C. Earth and Planetary Sciences Department, University of California, Santa Cruz, CA, USA ABSTRACT: Borehole breakouts were commonly observed in the boreholes drilled in unconsolidated deepwater sediments near the Nankai Trough, SW Japan. The use of borehole breakouts enabled us to constrain in situ stress states. While it was straightforward to estimate the stress direction based on the breakout azimuth, an ambiguity occurred that the breakout width to constrain stress magnitudes widened significantly with time in an order of hours. Two independent borehole wall images of the same depth interval, captured at the bottom and the top of the 30m long logging-while-drilling (LWD) bottom-hole- assembly, indicate that breakout widths grew from 42° immediately after bit to 135° about an hour later. Triaxial compression tests in cores revealed that all the specimens failed in brittle mode immediately when stress condition reaches that required for failure, suggesting that for the purpose of stress estimation, the use of breakout width immediately after the drill-bit passes through the depth is appropriate.

ARMA 12-588 Laboratory Verification of the Diametrical Core Deformation Analysis (DCDA) Developed for In-situ Stress Measurements Funato, A. OYO Corporation Ito, T. and Shono, T. Institute of Fluid Science, Tohoku Univ. ABSTRACT: DCDA is a new method for evaluating the in-situ stress of rocks based on the elliptical deformation of boring cores with stress relief. When a rock core sample is carved out by drilling, it becomes free from in-situ stress, and the expansion should occur elastically. If the condition of in-situ stress is anisotropic, the core must deform in an asymmetric manner. With the precise measurement of core diameters in each directions, the deviatoric stress SHmax—Shmin and azimuths of SHmax and Shmin could be determined from the circumferential variation of the measured diameter. In order to confirm the reliability of DCDA, laboratory verifications were conducted. The estimated stresses by DCDA agreed well with the applied stresses, and the directions of dmax coincide to the directions of the applied stresses. From these results, the effectiveness of DCDA was confirmed.

147 46th US Rock Mechanics/Geomechanics Symposium Ses s ion 31: D iscrete Simulations in Geomechanics Tuesday, 26 June, 4:00 pm – 5:30 pm Chairs: Ali Fakhimi, James Hambleton

ARMA 12-501 A Flat-Jointed Bonded-Particle Material for Hard Rock Potyondy, D. O. Itasca Consulting Group, Inc., Minneapolis, MN, USA ABSTRACT: The bonded-particle model (BPM) consisting of parallel-bonded disks or spheres suffers from the limitation that if one matches the unconfined-compressive strength () of a typical hard rock, then the direct-tension strength () of the model will be too large. This limitation can be overcome in two dimensions by introducing a polygonal grain structure to provide rotational restraint arising from intergranular interlock. The flat-jointed BPM (in which each disk-disk contact simulates the behavior of a finite- length interface between two disks with locally flat notional surfaces such that even a fully broken interface continues to resist relative rotation) provides such a structure and supersedes the parallel-bonded BPM by mimicking more of the micro- and macro-mechanisms associated with rock damage.uqtσ

ARMA 12-212 Simulation of carbonate rocks elastic properties using 3D X-Ray computed tomography images based on Discrete Element Method and Finite Element Method Jouini, M. S. The Petroleum Institute of Abu Dhabi, Abu Dhabi, United Arab Emirates Vega, S. The Petroleum Institute of Abu Dhabi, Abu Dhabi, United Arab Emirates ABSTRACT: Standard analytical models that estimate effective elastic properties of porous media present some limitations in carbonate rocks. Indeed, carbonates can reveal very heterogeneous grains and pores structures produced by diagenesis at several scales. In this paper, we estimate the elastic properties of core plug samples from a Middle East carbonate reservoir using X-ray computed tomography scanner images. First, we simulate the elastic properties by solving the elasticity equation using the finite element method. Then, we use the discrete element method to investigate its ability to predict the elastic properties using a Hertzian and a Hookean contact models. Furthermore, in order to validate the numerical simulations we compared our results with experimental measures at ambient pressure. Simulations results show a relatively good agreement for samples with relatively homogeneous pore spaces distribution for both methods. However, a mismatch is revealed for the highly heterogeneous samples. Finally, we analyze and discuss both numerical simulations methods and provide possible future improvements.

ARMA 12-416 Distinct Element Model Analysis of Unstable Failure of Rock Discontinuities Gu, R., Ozbay, U. Colorado School of Mines, Golden, Colorado, USA ABSTRACT: Unstable shear failure along large discontinuity planes is one of the major causes of rockburst events that occur in deep mines and civil excavations. Improved understanding of such failures

148 46th US Rock Mechanics/Geomechanics Symposium could help alleviate destructive effects of rockburst. This paper presents findings on unstable discontinuity failures obtained from a series of numerical modeling studies performed for cases of both laboratory and in situ conditions. The numerical program, Universal Distinct Element Code (UDEC), is used for simulations of rock discontinuity failures. A series of double shear tests are modeled to verify the program’s ability in differentiating stable and unstable failures of discontinuities. The in situ modeling studies investigate the stability of a bedding plane loaded by an advancing underground excavation. The loading system stiffness of the double shear tests is considered. It is shown that unstable failures can be modeled with the application of the continuously-yielding joint model. The studies confirm that unstable failures occur when the loading system stiffness is smaller in absolute value than the post-peak stiffness of the discontinuities. It is observed in the in situ model that the intensity of unstable failures is affected by the shear stress mobilized on the bedding plane and local mine stiffness.

ARMA 12-457 Direct shear tests to model the shear behavior of rock joints by PFC2D Bahaaddini, M. School of Mining Engineering, The University of New South Wales, Sydney, Australia Shahid Bahonar University of Kerman, Kerman, Iran Sharrock, G., Hebblewhite, B.K. and Mitra, R. School of Mining Engineering, The University of New South Wales, Sydney, Australia ABSTRACT: This paper investigates the shear behavior of rock joints in a direct shear test using PFC2D. PFC2D is a distinct element software in which the rock is represented by a dense packing of non- uniform sized circular particles bonded at their contacts and damage process under loading is represented by breakage of the bonds. Two approaches have been used in PFC for generation of joints, namely: bond removal method and the smooth joint model. In bond removal method, joints are generated by removing bonds between particles within a specified distance on either side of the joint track. It is found that this approach is unable to reproduce the sliding behavior of joints due to micro-scale roughness of joint surface and reduction of friction coefficient of unbonded particles or increase of unbonded band width cannot improve this deficiency. In the smooth joint model, particles can overlap and pass through each other rather than move around one another. This method is investigated by undertaking direct shear test on planar joints. It is found that at shear displacements more than the minimum particle size, particle interlocking occurs, due to the inability of this approach to recognize the upper and lower blocks particles. To overcome this problem, a new shear box genesis method is proposed. In order to study the ability of the suggested method in reproducing the shear behavior of rock joints, direct shear tests on three joint profiles of saw- tooth triangular joint with the base angle of 25°, standard JRC 12-14 and 18-20 are carried out. Results of numerical models are compared against the Patton, Ladanyi and Archambault and Barton and Choubey models and good agreement are found.

ARMA 12-651 Modeling direct shear tests with FEM/DEM: Investigation of discontinuity shear strength scale effect as an emergent characteristic Tatone, B. S. A., Grasselli, G. Department of Civil Engineering, University of Toronto, Toronto, Ontario, Canada ABSTRACT: The mechanical behavior of rough rock joints can vary as a function of scale. Characterization of this scale effect can be problematic due to the difficulties in performing shear tests on larger rock joint specimens. This paper investigates the use of the 2D Combined Finite-Discrete Element

149 46th US Rock Mechanics/Geomechanics Symposium Method (FEM/DEM) as tool to perform numerical direct shear tests. Direct shear models of a 400 mm long joint and 200, 100, and 50 mm subdivisions thereof are constructed and numerical direct shear testing is performed. The results show that the relative influence of scale on shear stiffness is captured. In contrast, a decrease in the average shear strength as a function of scale is not observed. The variation in the stress and dilation between specimens decreased as longer specimen lengths were considered and the upper bound shear strength showed a clear, albeit minor, scale effect.

ARMA 12-632 Mechanical, Failure and Flow Properties of Sands: Micro- mechanical Models Manchanda, R.; Olson, J.E. and Sharma, M.M. The University of Texas at Austin, Austin, Texas, U.S.A. ABSTRACT: There is incomplete understanding of the influence of shear failure observed in field operations in sand formations. This work explains the effect of shear failure on permeability anisotropy and dilation in sands. Three-dimensional discrete element modeling is used to model the behavior of uncemented and weakly cemented sand samples. Mechanical deformation data from experiments conducted on sand samples is used to calibrate the properties of the spherical particles in the simulations. A rolling resistance strategy is applied in the simulations, incorporating the stiffness of the specimens due to particle angularity, aiding in the calibration of the simulated samples against experimental data to derive optimum granular scale elastic and friction properties. A flexible membrane algorithm is applied on the lateral boundary of the simulation samples to implement the effect of a rubber/latex jacket. Simulations are extended to non-cylindrical specimen geometries to simulate field-like anisotropic stress regimes. Pore network fluid flow simulations are conducted before and after mechanical deformation to observe the effect of failure and stress anisotropy on the permeability anisotropy and dilation of the granular specimen. The effect of confining pressure, stress anisotropy, and particle size distribution on failure, permeability and dilation is studied. The effect of shear failure on the permeability is confirmed and calculated. The shear failure plane alignment is observed to be parallel to the maximum horizontal stress plane. Flow simulations confirm the increase in permeability due to shear failure and show a significantly greater permeability increase in the maximum horizontal stress direction. Permeability anisotropy is observed and permeability tensors are calculated.

Ses s ion 32: Static & Dynamic Response of Rocks Tuesday, 26 June, 4:00 pm – 5:30 pm Chairs: Erling Fjaer, Laura Pyrak-Nolte

ARMA 12-610 A Numerical Investigation of the Scaling of Fracture Stiffness Morris, J. P. Schlumberger-Doll Research, One Hampshire St, Cambridge, MA 02139 ABSTRACT: The goal of our study was to understand how the properties obtained from a deformation test performed on a relatively small portion of a fracture under laboratory conditions can be related back to the in situ properties of the entire fracture. In this paper, we present results of a numerical investigation into the scaling of fracture stiffness with increasing fracture length. Using an efficient boundary element method we were able to simulate hundreds of virtual normal stress tests on entire fracture surfaces and on

150 46th US Rock Mechanics/Geomechanics Symposium “sub-fractures” cut from them. In the paper we draw specific attention to the need to perform appropriate numerical processing of the aperture distribution in order that the simulations be representative of relevant experimental configurations. Our results reflect the expected trend with test results performed at small scale resulting in stiffer fracture response than the full fracture according to a power law. In addition, we found that the exponent of the power-law was stress dependent, with less size effect evident as the stress was increased. In this manner, this work provides preliminary insight into the complicated relationship between scale, fracture roughness, stiffness and stress.

ARMA 12-294 Shear Specific Stiffness of Fractures and Fracture Intersections Abell, B.C. Purdue University, West Lafayette, IN, USA Choi, M.-K. Purdue University, West Lafayette, IN, USA Pyrak-Nolte, L.J. Purdue University, West Lafayette, IN, USA ABSTRACT: Fractures in rock masses influence strongly the mechanical and hydraulic properties of a rock mass. Thus, the detection and characterization of fractures using geophysical methods is of critical importance for maintaining the integrity of sub-surface infrastructure and subsurface waste or storage repositories. While the effects of single fractures or sets of parallel fractures on seismic wave propagation have been studied by many scientists and engineers, little research has been performed to determine the role of fracture intersections on seismic wave attenuation and velocity. A fundamental question is whether the specific stiffness or compliance of an intersection is the same or differs from the stiffness of any of the individual fractures within two intersecting sets of fractures. In this paper, we show from experimental and numerical studies that the stiffness of fracture intersections can be less than, equal to, or greater than the stiffness of the individual fractures depending on the applied bi-axial loading conditions.

ARMA 12-307 Interface Waves along Fractures in Anisotropic Media Shao, S.S. Purdue University, West Lafayette, IN, USA Abell, B.C. Purdue University, West Lafayette, IN, USA Pyrak-Nolte, L.J. Purdue University, West Lafayette, IN, USA ABSTRACT: The detection of fractures in an anisotropic medium is complicated by discrete modes that are guided or confined by layers, as well as by fractures, and that travel with velocities close (~92%) to the shear wave velocity. For instance, fractures can “mask” the presence of textural anisotropy in a rock, and can change the apparent shear wave velocity anisotropy. In this study, we examine the effect of fracture interface waves on the interpretation of shear wave velocities for two orthogonal polarizations propagating through a layered medium with fractures. These experimental results demonstrate that competing textural and structural properties can affect the interpretation of rock properties from seismic data. Interpretation in the presence of fractures in isotropic or anisotropic media can be unambiguously interpreted if measurements are made as a function of stress, which eliminates many fracture-generated discrete modes.

151 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-523 When to use static or dynamic moduli in geomechanical models Mossop, A. Shell / NAM, 9400 HH Assen, The Netherlands ABSTRACT: The increased use of computer simulation methods in geomechanics (e.g. finite element), allows for complex heterogeneous structures to be modeled. It is relatively trivial, using these approaches, to create layered or block type linear elastic models with moduli that vary from formation to formation. Such models are frequently used to understand and predict the displacements and stress perturbations induced by industrial processes such as reservoir depletion or fluid injection over periods of many years. Because inertial terms are negligible for deformations on these time scales it is often assumed that static moduli are the appropriate parameters to apply, and a simplistic comparison to laboratory data would appear to confirm this view. Indeed, there are a number of studies in the literature that describe methods for deriving static properties to populate such numerical models. However, it is reasonable to assume that the majority of the difference between static and dynamic moduli can be ascribed to simple poroelasticity and that the appropriate time scales that define the static and dynamic end member cases are governed by pressure diffusion. A straightforward analysis that simply considers the most basic drained and undrained cases, and rudimentary diffusion, makes it apparent that in most cases the use of static moduli is only really appropriate for formations that are being actively depleted. Other formations will generally exhibit undrained or dynamic behavior on time scales of years or millennia.

ARMA 12-537 Combining static and dynamic measurements for evaluation of elastic dispersion Fjær1,2, E. Stroisz1, A.M. Holt1,2, R.M. 1 Norwegian University of Science and Technology, Trondheim, Norway 2 SINTEF Petroleum Research, Trondheim, Norway ABSTRACT: Earlier studies on dry, clay free sandstone have shown a linear increase in the non-elastic compliance upon unloading, apparently starting from zero at the turning point of the stress path. It is argued that the offset seen at the turning point in other rocks may be interpreted as a result of dispersion. A method, based on this assumption, for estimation of the velocity dispersion in the range from seismic to ultrasonic frequencies, using only standard rock mechanical tests with acoustic velocity measurements is presented. Application of the method is demonstrated by experimental data. The results show no measurable dispersion in a clay free sandstone, and relatively large dispersion in a shale. The results for a sandstone with some clay content show moderate dispersion, and also indicate that the dispersion decreases with increasing stress. The method requires good quality data, but the requirement for accuracy is not extreme.

ARMA 12-542 Static vs. Dynamic Behavior of Shale Holt, R. M. NTNU and SINTEF, Trondheim, Norway Nes, O.-M., and Stenebråten, J.F. SINTEF, Trondheim, Norway Fjær, E. SINTEF and NTNU, Trondheim, Norway

152 46th US Rock Mechanics/Geomechanics Symposium ABSTRACT: From experiments performed with outcrop and overburden shales it is observed that dynamic elastic moduli measured at ultrasonic frequencies by far exceed static moduli. The data do, however, indicate a relation between static and dynamic moduli. If properly established, this would facilitate estimation of in situ static parameters such as e.g. strength and brittleness from seismic or sonic log data. This may enable improved characterization of potential reservoirs and/or cap rock in terms of identifying optimum drilling sites and procedures during subsequent drilling and possible hydraulic fracturing. Our experiments point to strain amplitude effects and frequency dependence as primary sources of discrepancy that need to be understood in order to establish the required relationships.

Pesost r - Formation Characterization and Mechanical Earth Modeling Tuesday, 26 June, 5:30 pm – 6:30 pm

ARMA 12-118 Experimental Study on the Tensile Strength Weakening of Mudstone in Leaching Process of Bedded Salt Cavern Yang, C., Shi, X., Li, Y. State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences, Wuhan, Hubei, China Yang, J. School of Materials & Engineering, Wuhan Institute of Technology, Wuhan, Hubei, China Wei, D. Petrochina Beijing Gas Pipeline Corporation Limited, Beijing, China ABSTRACT: The existence of indissolvable muddy interbeds leads to many adverse effects for building salt cavern storages by solution mining. It is an urgent technical problem that how to forecast and control the collapse of indissolvable interbed in the salt cavern leaching process. Some experiments are carried out in order to reveal the tensile strength weakening discipline of interbed mudstone immersed in brine. The test results show that the lower the brine concentration is or the longer the immersed time is, the more obvious the weakening degree of the mudstone strength will be. The mudstone in bedded salt rock contains mainly clay mineral and also some dissolvable salt grains. The solution of salt grains and the softening and expansion of clay mineral are implied to be the key factors relative to the mudstone strength weakening, and the two factors promote each other during weakening process. It is also showed that mudstone samples with different salt content rates behave different weakening disciplines: immersed in brine with concentration close to field brine concentration, the tensile strength of mudstone samples with low salt content rate are weakened lightly and slowly; the samples with middle salt content rates are weakened obviously when immersed in middle concentration brine, and the solution of salt grains and the softening and expansion of clay mineral play a key role in strength weakening of mudstone; immersed in unsaturated brine, the samples with high salt content rate weaken quickly, and the primary reason is the failure of the material framework caused by solution of salt grains.

153 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-221 Geomechanical Modeling of an Anisotropic Formation-Bakken Case Study Ostadhassan1, M., Zeng1, Z., Zamiran2, S. 1- Dept. of Geology and Geological Engineering, University of North Dakota, Grand Forks, ND 58202 USA 2- Department of Civil Engineering, Science and Research Branch, Islamic Azad University, Markazi, Iran ABSTRACT: Production of hydrocarbon causes changes in pore pressure and effective stresses acting on the reservoir rocks. This will be followed by reservoir compaction, surface subsidence and may lead to fault reactivation, casing or wellbore failure and closure of micro-cracks. Nonetheless, acquiring a good understanding of rock strength, pore pressure and in-situ stress will be critical to successful horizontal drilling and hydraulic fracturing. Bakken Formation of Williston Basin, North Dakota, which is identified by three distinct members, is a huge unconventional, self-sourced, naturally-fractured reservoir. It is one of the least studied sedimentary rock units in the basin. The over pressured nature of this formation have made the study of its geomechanical properties even more important. Natural fractures are also considered as another major source of problems in this reservoir. To investigate these problems, Mechanical Earth Model (MEM), a numerical representation of the reservoir properties, was built. This enabled to predict the alterations and changes of the geomechanical properties in the reservoir. The results show that the lower and upper members are mechanically transverse isotropic whereas the middle member is isotropic. Besides, the numerical geomechanical modeling demonstrate that the elastic anisotropic characteristics of the upper and lower members will result in elastic failure of the region around the wellbore following a shear failure phase but the elastic isotropic middle member will mostly stay in the shear failure state.

ARMA 12-233 An experimental investigation of the properties of weak rocks surrounding mine workings Geng, Y., Wanatowski, D. and Stace, L. R. Nottingham Centre for Geomechanics, Faculty of Engineering, The University of Nottingham, United Kingdom ABSTRACT: This paper describes the program of laboratory testing of soft rock samples that has been carried out at the University of Nottingham to characterize weak materials. This work, which is part of the EU RFCS project “Geosoft”, has been conducted to examine alternative methods of obtaining physical properties of soft rock when conventional rock mechanics testing methods are not appropriate. This is because the weakness of these strata types often results in samples breaking up into pieces when being collected at the working face, during transport to the laboratory or during sample preparation. In this study, tests were conducted on intact, reconstructed and broken samples to obtain the strength and stiffness parameters that could be fed into numerical modeling of underground situations. The Unconfined Compressive Strength (UCS) of intact and reconstituted rock samples was determined in the stiff press. The friction angle and cohesion of reconstituted and broken soil-like samples were determined using conventional soil element testing techniques such as the shear box and triaxial cell. The experimental data obtained from all the tests are compared and analyzed in this paper.

154 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-309 Near-salt stress and wellbore stability: A finite-element study and its application Luo, G., Nikolinakou, M.K., Flemings, P.B., and Hudec, M.R. Bureau of Economic Geology, Jackson School of Geosciences, The University of Texas at Austin, Austin, Texas, USA ABSTRACT: We develop finite-element models to simulate stresses around salt bodies, and use these results to calculate wellbore stability and optimal mud weights for a vertical wellbore near these salt bodies. In the finite-element models, salt bodies are simulated by viscoelastic material, sediments are elastic, and pore pressure is assumed to be hydrostatic in sediments. We show that near-salt stresses are perturbed; near-salt wellbore instability tends to happen at the places with low minimum principal stress and high shear stress; in these locations, safe mud weight window is narrow. Near a salt sphere, wellbore instability tends to occur above and below the salt sphere due to low minimum principal stress, and at the lateral edges of the salt sphere due to high shear stress. Near an irregular salt sheet, wellbore instability tends to occur at the convex curves of the salt body; if shear stress is very high and minimum principal stress is very low in these locations, safe mud weight window may be impossible. These results show changes of stresses, optimal mud weights and safe drilling window around salt bodies, and provide some insights into the drilling and mud weight programs near salt bodies.

ARMA 12-310 A new approach to the sedimentation and compaction of basin based on continuum mechanics concepts Guilmin, A.-L. IFP Energies nouvelles, 1 et 4 avenue de Bois-Pr.au, 92852 Rueil-Malmaison, France Barthélémy, J.-F. IFP Energies nouvelles, 1 et 4 avenue de Bois-Pr.au, 92852 Rueil-Malmaison, France Sassi, W. IFP Energies nouvelles, 1 et 4 avenue de Bois-Pr.au, 92852 Rueil-Malmaison, France ABSTRACT: This work aims at simulating basin sedimentation subjected to tectonic effects with a poro-mechanical approach. A code is built to solve the fundamental equations of mechanics in a mixed formulation (displacement and pressure). In the range of depth of interest, material is assumed to have an elasto-plastic behaviour. It is adapted for large strains using different assumptions from [1]. Material properties such as porosity or permeability are computed and updated at each step of the compaction. Although this simulation tool is designed to deal with complex cases, we checked that the reference relationships between porosity and depth for oedometric compaction are still satisfied.

ARMA 12- 387 Effect of osmotic force on apparent fracture toughness Rozhko, A.Y. Schlumberger Norge AS, Division: M-I SWACO, Stavanger, Norway ABSTRACT: This paper studies the mechanical effect of osmotic force on the strength of rock using the fracture mechanics approach. Calculations are based on consideration of representative volume element: elliptical crack inside porous, clay-bearing rock. Clays are considered as semi-permeable membranes for osmotic diffusion, while the osmotic diffusion is driven by difference of water activity of shale and surrounding fluid. A new analytical solution for apparent fracture toughness as a function of water activities, temperature and poro-elastic parameters is derived in a long term limit. A new solution can be used directly in wellbore stability analysis and during modeling of hydraulic fractures.

155 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-404 Building a Mechanical Earth Model: a Reservoir in Southwest Iran Fattahpour, V. The University of Tehran, Tehran, Tehran, Iran Pirayehgar, A. and Dusseault, M.B. University of Waterloo, Waterloo, Ontario, Canada Mehrgini, B. The University of Tehran, Tehran, Tehran, Iran ABSTRACT: Decreasing development costs and risks involves optimizing field development plans, refining drilling programs and making good predictions of production rate. In achieving these goals, it is important to investigate the geomechanical behavior of the reservoir. All data and information recorded during exploration, drilling and production are used for estimating the mechanical properties and earth stresses in the stratigraphic section by constructing a Mechanical Earth Model (MEM). We focus here on building a 1D MEM for one well in a reservoir in southwest Iran, and then we apply the model to well design and construction for field development through generation of a drilling mud weight strategy based on the MEM. General lack of calibration data, especially for stress measurements, means it is necessary to use different methods to determine the rock properties and the stress state. Since there is limited knowledge about the stress state, different stress states are discussed and possible principle stresses are determined based on the comparisons of drilling reports, image logs, and wellbore stability conditions. These considerations and comparisons suggest that the ratio of horizontal to vertical stresses should be less than 0.7, which means that the stress regime of the study area is one of normal faulting.

ARMA 12-434 Inferring In Situ Stresses in a Naturally Fractured Heavy Oil Field Shafiei, A. and Dusseault, M.B. Department of Earth & Environmental Sciences, University of Waterloo, Waterloo, Ontario, Canada ABSTRACT: Delineation of in situ stress field (magnitudes and orientations of the principal stresses) has several applications in petroleum industry such as better drilling management, effects of oil production on stress regime change, stress change effects on permeability, increasing the stability of boreholes, enhancing the oil production from stress sensitive reservoirs, subsidence due to stress changes, and optimal drilling and field development. In this article, magnitudes and orientations of the in situ principal stresses in the study area was estimated with combination of various available data and techniques including core analysis, image logs (FMI and UBI logs), World Stress Map, and geological and geotectonics evidences. The orientation of maximum and minimum horizontal stresses was obtained NE-SW and NW-SE. In addition, magnitudes of the in situ principal stresses and pore pressure were estimated. Estimates made in this study using multiple sources such as core analysis, and image logs are in a good agreement with estimates suggested by World Stress Map, and geological and geotectonic evidences. Results obtained from this study will help manage the geomechanical issues related to drilling and production more efficiently.

156 46th US Rock Mechanics/Geomechanics Symposium Pes ost r - Numerical, Analytical and Constitutive Modeling Tuesday, 26 June, 5:30 pm – 6:30 pm

ARMA 12-146 Investigation of the effect of in-situ stresses and loading rate on blasting induced fracture propagation Aliabadian, Z.1 Sharafisafa, M. 1 Mortazavi, A. 1 1 Amirkabir University of Technology, Tehran, Iran ABSTRACT: Rock blasting process is very complicated and is affected by many factors such as internal and external factors. Internal factors are related to controllable parameters such as blasthole and bench dimensions and explosive parameters. External factors are uncontrollable and in blast design must be determined precisely. These factors such as magnitude and direction of in situ stresses, rock properties, ground water and rock jointing dominate the amount of fractures induced by an explosive. In underground blasting, the effect of in situ stresses is more sensible and extent and direction of fractures depend on theses stresses. On the other hand, the blast loading rate (i.e. applied pressure waveform) which depends on explosive properties and also blasthole dimensions are controllable and affect the pattern of different fracture zones around blasthole. Therefore, to control overbreak and to aim desired breakage of rock mass, all parameters specially two mentioned parameters should be considered and measured carefully. For this purpose, two dimensional distinct element code (UDEC) was used to study fracture initiation and propagation process in a rock domain. Mohr-Columb material model was employed to allow rock failure. The analysis consists of two different parts. At part one, the in situ stress effect on fracture pattern is investigated. The results of conducted analysis demonstrate that magnitude and direction of these stresses have significant effect on the amount and direction of blasting induced fractures. The main fractures are intended to more propagation in the direction parallel to main stress and in directions which are perpendicular to major stress, there are a few long fractures. In the second part, the effect of stress waveform on fracture initiation and propagation was examined. The main features in this part were the dimensions of fracture zones generated around blasthole and the length of major fractures. The results indicate that higher stress-loading rate increases the number of radial cracks, thereby releasing intense magnitude of stress around the running cracks. At lower stress-loading rates, the number of cracks and crack arrest caused by stress released at adjacent cracks were reduced. This led to longer crack extension. These analyses showed that when the preferential cracks developed earlier, crack extension was longer.

ARMA 12-159 The Influence of Drilling Direction on RQD Values of Rock Mass with Multiple Sets of Discontinuities and RQD Data Acquisition for In-depth Analysis Chen, G. Department of Mining & Geological Engineering Fairbanks, Alaska 99775 University of Alaska Fairbanks College of Engineering and Mines

157 46th US Rock Mechanics/Geomechanics Symposium ABSTRACT: The RQD values are frequently used as an important index in rock mass rating systems for convenient assessments of rock mass quality. It has been revealed that RQD values are strongly correlated to the distribution of discontinuities. However, many argued that, although convenient to be acquired from rock cores, RQD has its limitations to be used to characterize the rock quality. Some claimed that RQD is unreliable and can be of widely ranged values that vary significantly with drilling directions. In this paper, studies are conducted to statistically analyze the relationship between the drilling direction and the RQD. With the assumption of negative exponential distributions for discontinuity spacings, which has been commonly accepted in rock mechanics studies, a statistical model is developed to characterize fractures of drill cores acquired in rock masses with multiple sets of discontinuities. Studies have indicated that RQD may vary significantly over different drilling directions, especially when the number of discontinuity sets in the rock mass is small. In order to fully characterize and understand the rock properties, a practical approach is proposed in this study to utilize RQD values from multiple drill holes/scanlines at different directions to acquire detailed probability distribution parameters for individual discontinuity sets. Analysis indicates that it is necessary to have the number of nonparallel drill holes and scanlines equal to the number discontinuity sets in rock mass in order to solve for all the probability distribution parameters. With the probability distribution parameters estimated for each individual discontinuity sets, the distribution of RQD values over any direction range in the rock mass can then be evaluated.

ARMA 12-160 3D Geological and Structural Geology Modeling and 2D Open Pit Mine Slope Stability Analysis by the Synthetic Rock Mass (SRM) Method Paredes Otoya, C.E. Ausenco Environment and Sustainability (E&S), Lima, Perú Barreto da Fontoura, S.A. Pontifícia Universidade Católica do Rio de Janeiro, PUC-Rio, Rio de Janeiro, Brasil ABSTRACT: Rock Mass must be characterized prior to the evaluation of slope stability. Therefore, geological, structural and rock mass models, components making up the geotechnical model, were constructed as per the recommendations of the Large Open Pit project (LOP), an international research project dedicated to open pit mine stability research. The rock mass stability of each geotechnical model may be subsequently evaluated using methods such as limit equilibrium, finite elements and discrete element methods. Methods will be selected according to factors such as the influence of structural elements (defects), need for analysis and available information. The SRM (Synthetic Rock Mass) model was used to evaluate the slope stability of an open pit mine in Peru. The SRM model is a new approach to the simulation of fractured rock mass mechanical behavior, taking into account the propagation of fractures and anisotropic effects. This method employs two well-known techniques: BPM (Bond Particle Model) to represent intact rock and SJM (Smooth-Joint Contact Model) to represent the structural fabric of the PFC program, while the DFN (Discrete-Fracture Network) method is used for structural modeling. The Petrel program was used to design the geological and structural models and the PFC2D program was used to analyze slope stability using the SRM model.

158 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-250 Combined Microscopic-Macroscopic Modeling of Rock Damage and Failure Lu, Y.L.1,2 1 State Key Laboratory for Geomechanics and Deep Underground Engineering, China University of Mining and Technology, Xuzhou, Jiangsu 221008, China Elsworth, D.2 2EMS Energy Institute, Energy and Mineral Engineering & G3 Center, The Pennsylvania State University, University Park,PA 16802, USA ABSTRACT: Composed of heterogeneous mineral grains and microdefects at the microscopic scale, natural rocks are strongly heterogeneous. This typically results in macroscopically non-linear mechanical response under the action of external forces including thermomechanical and thermochemical effects. Classical macroscopic constitutive equations fail to describe the complex evolution of damage and its progress to failure. Recently, micromechanical damage models have been developed to address the complex macroscopic behavior of rock material. These models allow the evolution of real damage microstructures, including the initiation, growth and coalescence of defects with the result that this method links microscopic damage evolution to macroscopic mechanical response. We present a combined microscopic-macroscopic model that embeds the micromechanical model into a macroscale finite element model (FEM). The method is implemented in FEM with each grid block treated as a microscopic element (i.e. REV) of rock material. The evolution of both microcrack damage and of the macroscopic effective constitutive equation is then evaluated for each grid block. On this basis, the global stiffness matrix of the entire object is established and FEM used to solve practical rock engineering problems. A uniaxial tension experiment is simulated to validate the method. The stressstrain relations recovered for this numerical experiment replicate the experimental results including the evolution of damage and failure of the rock sample. This method provides an effective approach to study problems of rock damage and failure in engineering.

ARMA 12-260 A Double Structure Constitutive Model for Expansive Clays: Problems for Verification in Sierra Mechanics Bean, J.E. Sandia Staffing Alliance LLC, Albuquerque, New Mexico, USA Sánchez, M. Texas A&M University, College Station, Texas, USA Argüello, J.G. Sandia National Laboratories, Albuquerque, New Mexico, USA ABSTRACT: An important application of expansive clay materials is their use as engineered barriers or seals in radioactive waste repositories. The low permeability of clays and the chemical interactions (e.g. sorption) between the clay minerals and radionuclides present in the radioactive waste are essential for reducing the migration distance of the radionuclides over time scales of interest for repository design. This paper describes the efforts underway to incorporate a constitutive model for expansive soils into the Sierra Mechanics finite element code framework being developed at Sandia National Laboratories. Several simple verification problems are described for evaluating the implementation of the model.

159 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-406 Sensitivity Numerical Analysis of Orientations and Sizes of Forepoles for Underground Excavations in Weak Rock Oke, J. Vlachopoulos, N. Diederichs, M.S. GeoEngineering Centre, Queen’s-RMC, Kingston, Ontario, Canada ABSTRACT: Despite recent progress, there are still fundamental deficiencies in recognition, prediction, and mitigation of underground construction hazards associated with complex geological conditions in weak rock and soil works. These fundamental deficiencies that exist in regards to design, could be addressed by improving the geomechanical analytical models. This improvement would provide better insight into underground infrastructure performance. Additionally, one issue that is unclear with regards to behaviour, are the guidelines associated with the installation of forepole temporary structural support members. This paper focuses on 3 critical design parameters of forepole supports: spacing between forepoles, positioning, and size of the forepoles. Two-dimensional (2D) and Three-dimensional (3D) numerical analysis have been used in order to determine the influence of these design parameters. The results summarize commonly used design values while also providing practical ranges associated with the design parameters investigated. Furthermore, the results confirm that the industry norm 2D numerical analyses are inaccurate and can lead to under/over design.

ARMA 12-411 Effect of model scale on mechanical properties of rocks based on PFC3D modeling Ding, X. Department of Civil Engineering and Engineering Mechanics, University of Arizona, Tucson, Arizona, USA Zhang, L. Department of Civil Engineering and Engineering Mechanics, University of Arizona, Tucson, Arizona, USA ABSTRACT: This paper studies the effect of model scale on the simulated mechanical properties based on PFC3D modeling. The uniaxial compression tests of intact rocks are simulated. Three different particle size ratios, all having a uniform particle size distribution and the same average diameter, are considered. For all simulations, the same model length to diameter ratio of 2 and the same microscopic mechanical properties are utilized. By changing the model size represented by the model length to the average particle diameter ratio (L/d) at each particle size ratio, the unconfined compressive strength (UCS), Young’s elastic modulus (E), and Poisson’s ratio are determined based on the PFC3D simulations. The results show that the coefficients of variation of the simulated mechanical properties in PFC3D decrease significantly as L/d increases. To reach a specific variation level for the simulation results, the related minimum model size should be used. The results also show that both UCS and E increase with larger L/d, although the rate of increase decreases with L/d. The analysis indicates that the increase is caused by the decrease of model porosity with larger L/d. As for the Poisson’s ratio, the scale effect can be ignored when L/d is large enough.

160 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-413 Comparison of approaches for modelling dilation of brittle rockmasses around circular excavations and associated issues Walton, G. Queen’s University, Kingston, Ontario, Canada Diederichs, M.S. GeoEngineering Centre, Queen’s-RMC, Kingston, Ontario, Canada ABSTRACT: Conventional numerical modelling tools for analyses of underground excavations are well suited for modelling elastic behaviour and yield response of geomaterials with very simple constitutive behaviour. Non-dilatant elastic and perfectly plastic behaviour is most commonly used for preliminary analyses in the absence of the data required to consider more complex behaviours such as strain-weakening and dilation. This results in inaccurate predictions (normally non-conservative) of tunnel wall displacements and support loading which leads to a tendency of arbitrary conservatism in support design. For truly brittle models, this deficiency is more acute. This problem is largely a function of a poor understanding of how inelastic dilation occurs in different types of rockmasses, the rate controls on strength loss and volume change during yield, and the complexities of rock-support interaction in yielding conditions. Recently, efforts have been made to understand and quantify the complexities of dilation angles in rock, including dependency on confinement stress and plastic shear strain incurred. These current approaches will be reviewed and compared. The effects of dilation on numerical model results are examined for different material types, most notably those exhibiting brittle behaviour. A dilation angle model based on lab testing data is compared to an empirically determined method for estimating wall displacements around an excavation. Deficiencies in existing strategies for addressing dilation in numerical models are analyzed critically, and key areas for future work are identified.

ARMA 12-422 Identifying Unstable Failure in Brittle Rock using the Finite Difference Method Garvey, R. Colorado School of Mines, Golden, CO, USA Ozbay, M.U. Colorado School of Mines, Golden, CO, USA ABSTRACT: A series of uniaxial and triaxial compressive strength tests were simulated using the explicit finite difference software FLAC3D to simulate and identify unstable failure in rock. A slender cylindrical specimen was calibrated using the Mohr-Coulomb strain-hardening/-softening constitutive model to behave as a weak, brittle coal. Instability was induced within the specimen through a relatively soft compressive loading system with an applied elastic response. Unbalanced forces, accelerations, velocities, and shear strain rates were recorded during the FLAC3D simulations and were all found to have a strong positive correlation with other indications of unstable failure. The use of numerical identifiers of unstable failure was shown to provide a potential method for detecting instability within an explicit finite difference model at a higher resolution than existing methods.

161 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-429 Three-Dimensional Discrete Element Modeling of Disc Cutting Applications Bahr, K., Frenzel, C., Nakagawa, M. and Smiley, E. Colorado School of Mines, Golden, CO, USA ABSTRACT: With increasing use of mechanical excavation techniques in mining and civil engineering projects, it has become increasingly important to understand the fracture mechanisms involved in disc cutting. Two-dimensional Discrete Element Modeling has traditionally been used with some success in illuminating fracture behaviors; however, rock fracturing is an inherently three-dimensional problem with challenges including matching the bulk properties of real rocks and cutting down computation time by reducing the number of particles needed to obtain realistic results. In this paper we discuss some of the challenges facing three-dimensional modeling of rock cutting. Additionally, we suggest the potential for alternative solutions such as boundary conditions and tensile strength calibration as a preliminary step toward a full three-dimensional understanding of rock fragmentation.

ARMA 12-458 Statistical analysis of the effect of joint geometrical parameters on the mechanical properties of non-persistent jointed rock masses Bahaaddini, M. School of Mining Engineering, The University of New South Wales, Sydney, Australia Shahid Bahonar University of Kerman, Kerman, Iran Sharrock, G., Hebblewhite, B.K. and Mitra, R. School of Mining Engineering, The University of New South Wales, Sydney, Australia ABSTRACT: This paper investigates the effect of joint geometrical parameters on the uniaxial strength and deformation modulus of the non-persistent jointed rock mass. The synthetic rock mass (SRM) approach which has shown promising results in numerical modeling of rock masses was used for this study. In order to acquire a sound understanding of the influence of joint geometrical parameters and reduce the number of numerical experiments, the experimental design technique was employed. Using this technique, twenty five joint configuration models were generated. These joint configuration models were inserted into intact rock models and uniaxial compression tests were carried out. Results of numerical experiments were analyzed by analysis of variance (ANOVA). It is found that the joint orientation angle has the greatest influence on the uniaxial strength and deformation modulus. Five failure modes of intact rock failure, planar, block rotation, step-path and semi-block generation were observed and it is found that the failure mode is controlled dominantly by joint orientation angle and step angle.

ARMA 12-496 Modeling of Blast Waves Propagation through Jointed Rock Masses: a Case Study at the Gol-e-Gohar Iron Ore Mine (Iran) Babanouri, N., Karimi Nasab, S., and Mansouri, H. Department of Mining Engineering, Shahid Bahonar University of Kerman, Iran ABSTRACT: The prediction of blast-induced ground vibrations across fractured rock masses is of great concern to rock engineers in evaluating the stability of rock slopes in open pit mines. At the present work, the ‘hybrid method’ was used at the Gol-e-Gohar iron ore mine to simulate the production blast. Then,

162 46th US Rock Mechanics/Geomechanics Symposium the simulated production blast seismograms were used as input to predict particle velocity time histories of blast vibrations in the mine wall using the three-dimensional distinct element method. By back analysis of measured blast waveforms, mechanical properties of in-filled faults of the study area were determined. In combination with the numerical model, a ‘simulated annealing’ search algorithm was employed to find the optimum values of unknown parameters. Simulated time histories of particle velocity showed a good agreement with the measured production blast time histories.

ARMA 12-571 A Numerical Approach of Failure Mechanism of Transversely Isotropic Rocks Shimelies, A. A. Clemson University, Clemson, SC, USA Nadarajah, R. Clemson University, Clemson, SC, USA ABSTRACT: Stress-induced rock failures occur during the construction of underground structures, which draws a considerable attention of geotechnical, mining, and petroleum engineers to understand the failure mechanism of rocks. This paper presents a numerical experiment for evaluating the strength and deformation characteristics of transversely isotropic rock specimen, 5 cm in diameter and 10 cm in height, using advanced finite element software PLAXIS. A mesh refinement study was conducted to select the appropriate finite element mesh for the proposed study to ensure that the computed responses are independent of the finite element mesh. Seven orientations of bedding plane (15, 30, 45, 60, 75 and 90°) and four confining pressures (0, 2.5, 5 and 10 MPa) were considered in this study. The Mohr-Coulomb failure criterion was employed for each isotropic layer joined by an interface bonding. The results indicate that the failure strength is, in general, dependent on confining pressure and bedding plane orientation. The largest failure strength is obtained for case with maximum bedding plane, and the smallest strength is obtained when the bedding plane angle is between 400 and 60°. The predicted ultimate strengths are compared with the experimental results of Yi Shao et al. (1999). A reasonable match between the numerical and experimental approaches is observed, especially at low confining pressure.

Pesost r - Slope Stability and Open Pit Mining Tuesday, 26 June, 5:30 pm – 6:30 pm

ARMA 12-222 Analysis of the Influence of Low Conductivity Formations on Slope Stability of Open-Pit Iron Ore Mines Ventura, L. C. Geoestável Consultoria e Projetos, Belo Horizonte, MG, Brazil Bacellar, L. A. P. University Federal of Ouro Preto, Ouro Preto, MG, Brazil ABSTRACT: This article presents the analysis of the possible influences of low-conductivity phyllites of the Batatal Formation on the flow pattern and on the slope stability of the bottom pit of the Tamandua, Pico and Capitao do Mato iron-ore mines, in the Quadrilátero Ferrífero region, in southeastern Brazil. Typical cross-sections of these mines were selected after a careful analysis of geological, hydrogeological and geotechnical data. The patterns of flow were simulated with SEEP/W® software assuming some boundary

163 46th US Rock Mechanics/Geomechanics Symposium conditions and recharge rates provided by adapted characteristic curves for each outcropping units. Limit equilibrium stability analyses were performed with SLOPE/W®, with Bishop, Janbu and Morgenstern/Price methods. From the parametric analysis it can be concluded that: it is better to use unsaturated conductivity curves indirectly determined than to adopt evenly distributed recharge rates through all the geological units; slope stability analyses coupled with flow analyses showed to be very effective; vertical components of flow are important to establish the slope safety factor and can determine local failures; for this reason, high conductivity layers in Batatal Formation, such as metacherts, increase the stability factor; permeability values obtained through back analyses in previous studies suggest that there is a reasonable flow through the Batatal formation rock masses.

ARMA 12-263 Smart Phone Application for the Cut Slope Management System in Korea Ho-Bon, K., Sang-Woo, B., Seung-Hyun, K., Ferdinand, B.E. Korea Institute of Construction Technology, Goyang City, Gyounggi Province, South Korea Seok-Pyo, H. Ministry of Land, Transport and Maritime Affairs, Gwacheon City, Gyounggi Province, South Korea ABSTRACT: The accessibility of the cut slope location, geotechnical information, failure history, mitigation measures and other information at the field is very crucial in the scientific and systematic management of cut slopes. But since the data is stored in an office computer, data access at the field is difficult if not impossible. Slope Navigation (SLOP-NAVI) was previously developed to store basic cut slope information in a memory card but it was not sufficient to store all the slope information. With the development of the CSMS (Cut Slope Management System) Smart Phone application, all the slope information in the slope database can not only be accessed from the field, it can also be modified. Slope inventory and field investigation that were previously performed using a mobile PC can now be performed using the smart phone and encoded data is directly stored in the server thereby reducing the risk of data loss. The slope navigation function was also incorporated in the application and upgraded by adding the augmented reality function that conveniently guides the user to cut slope location. The CSMS Smart Phone application will not only make cut slope management systematic and efficient, it will also serve a vital role in diadter prevention by warning the public of a possible slope failure landslide or rockfall which will save both lives and property.

ARMA 12-337 Visualization and determination of removal blocks by stereo- analytical method in discontinuous rock masses Zhang, Z.X. Department of Geotechnical Engineering, College of Civil Engineering, Tongji University, Shanghai 200092, China Lei, Q.H. Department of Geotechnical Engineering, College of Civil Engineering, Tongji University, Shanghai 200092, China ABSTRACT: Block theory has been well applied to solve practical problems in rock engineering associated with the stability of discontinuous rock masses. Traditional methods of block theory are difficult to determine the actual locations of blocks, and they are always limited to the analysis of convex blocks constructed with relatively few discontinuities that are assumed to be infinitely persistent. However, the occurrence of finite discontinuities including joints and faults can produce numerous blocks with not only

164 46th US Rock Mechanics/Geomechanics Symposium convex but also concave geometries. In order to overcome these shortcomings, a new block visualization technique based on the stereo-analytical method is introduced to systematically describe block geometries. The proposed visualization method would provide basis for computer modelling and mechanical calculating of large-scale rock mass systems. Furthermore, examples of a slope excavation and a tunnel excavation in rock masses are presented to prove the validity and high performance of this methodology.

ARMA 12-356 Reliability analysis of soil nailed walls and rock slope excavation through Monte Carlo simulation method Hamed, A.A. Ms student of Islamic Azad University, Central Tehran Branch, Tehran, I.R .Iran Moghadaripour, M Ms student of International Institute of Seismology and Earthquake Engineering, Tehran, I.R. Iran Siavoshnia, M. Assistant Professor of Islamic Azad University, Central Tehran Branch, Tehran, I.R .Iran ABSTRACT: Uncertainties and inherent variability of soil strength parameters, scatter in the data or systematic testing and modeling discrepancies are commonly found in geotechnical problems. The same is true for soil nailed walls as an example of geotechnical problems, which is similar to rock bolt method being used for reinforcing rock mass. Because of these issues, engineers cannot evaluate and identify the rate of available risk by deterministic methods such as limit equilibrium method. In probabilistic methods, most of the existing uncertainties in analysis processes can be considered. This research studies uncertainty in soil nail walls based on a case study and rock slope excavation using Monte Carlo simulation. The results were then compared with those of the deterministic method.

ARMA 12-379 Automatic Detection of Landslides Induced by the Wenchuan Earthquake and Subsequent Rainstorm Li, Y. G. Kyushu University, Fukuoka, Japan Chen, G.Q. Kyushu University, Fukuoka, Japan & Visiting Prof. of Institute of Earthquake Science Tang, C. Chengdu University of Technology, Chengdu, Sichuan, China Zheng, L. & Wang, B. Kyushu University, Fukuoka, Japan ABSTRACT: We developed a two-step detection approach to map landslides in Chenjiaba area, Beichuan County, Sichuan Province, China after the 2008 Wenchuan earthquake and a strong rainfall four months later. First, the variance information was assessed by image fusion technique. Different from traditional usage of image fusion technique, this paper aims to enhance the interesting features through combing multispectral image with high resolution and panchromatic image with relatively lower resolution. Four fusion technologies (PCA, Brovey, IHS and Wavelet) were tested. All the results contain the spectrum information of both earthquake and rainfall-induced landslides except the one by wavelet transform based fusion method. The fusion results were assessed by visual inspection and IHS transform based fusion image shows the best performance. Second, fusion image was semi-automatically interpreted. The image interpretation was based on object-oriented analysis which not only the spectral information in pixel-based

165 46th US Rock Mechanics/Geomechanics Symposium method was considered, but also the spatial and texture information of the image. Various landscape elements were classified by K Nearest Neighbor algorithm for landslide detection. Accuracy assessment was carried out by comparing those extracted ones with a manually prepared landslide inventory map. Results showed that this approach is capable of mapping different temporal landslides quickly and efficiently.

ARMA 12-382 Slope stability analysis under dynamic loading at Choghart Iron Mine, Iran A. Zarei School of Mining Engineering, The University of Tehran, Iran. M. Moosavi School of Mining Engineering, The University of Tehran, Iran. ABSTRACT: Earthquake is a major trigger for instability of natural and man-made slopes. Often the instability of slopes due to an earthquake causes mass failures in open mines which in turn stops mine production. Therefore, large mines should be designed for possible future earth shakes. Choghart Iron Mine is one of the most important and large active mines in central Iran which has an important contribution to the overall countries iron ore production. The possibility of a large size mass movement at its southern wall has raised concerns about the stability of the mine and its continuous production which necessitated a research into this subject. Presence of numerous faults and major weathering in this zone and also occurrence of few smaller size slope instabilities together with the fact that the mine is located in a very active seismic region necessitated a dynamic slope stability analysis in addition to usual static study. To account for all the important factors in this stability analysis, massive in situ joint mapping and rock mechanics studies have been performed to gather the basic information required for a numerical analysis. A seismic study is also performed to investigate the effect of dynamic loading on the safety factor in case of a possible earthquake. The present study shows that most parts of the southern wall will be unstable if it is subjected to an earthquake similar to the ones that have been recorded in the region’s history.

ARMA 12-438 Numerical modeling of volcanic slope instability and related hazards at Pacaya Volcano, Guatemala Schaefer1, L.N., Oommen1, T., Corazzato2, C. and Tibaldi2, A. and Rose1, W.I. 1 Michigan Technological University, Houghton, MI, USA 2 Università degli Studi di Milano-Bicocca, Milan, Italy ABSTRACT: This study uses numerical modeling to determine the possibility of an edifice collapse at the active Pacaya Volcano in Guatemala. Stability analyses using the Limit Equilibrium Method (LEM) and the Finite Element Method (FEM) were performed on the south-western flank using the physical- mechanical material properties of Pacaya’s intact rocks and rock mass characteristics based on field observations and laboratory tests. The Hoek and Brown failure criterion was used to calculate the friction angle, cohesion, and rock mass parameters in a determined stress range. Volcanic instability was assessed based on the variability of the Factor of Safety and Shear Strength Reduction using deterministic, sensitivity, and probabilistic analyses considering static conditions. Results indicate the volcanic slope is stable under gravity alone, but the possible presence of a layer of pyroclastics significantly reduces the stability of the slope. Future work will focus on verifying the presence of this layer and evaluating the effect of external loading mechanisms such as earthquake load and magma pressure on the slope stability at Pacaya.

166 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-526 An Analysis to Compare Factor of Safety Values Between the Limit Equilibrium Method and Shear Strength Reduction Technique Ureel, S.D. Call & Nicholas, Inc., Tucson, AZ USA Killian, J.R. Call & Nicholas, Inc., Tucson, AZ USA Ryan, T.M. Call & Nicholas, Inc., Tucson, AZ USA ABSTRACT: Computer modeling for large-scale rock slopes has become essential to assess factor of safety (FOS) values to predict slope instability and estimate potential failure. The limit equilibrium method (LEM) provides FOS values according to force and moment equilibrium; the shear strength reduction (SSR) technique calculates FOS using stress- and deformation-based analyses. Currently, both methods are used by geotechnical engineers to analyze large-scale rock slopes for mining and civil engineering projects. Both methods can be used simultaneously to check critical slip surface locations and FOS values. This study was performed to understand similarities and differences in FOS calculations between the two computer modeling programs for high rock slopes greater than 600 meters. The FOS values obtained indicate a SSR generates results roughly 0.1 lower than the traditional LEM when dealing with homogeneous rock slope geometry. However, when additional geology is included within the rock slope, resulting FOS values between the two methods may be higher or lower depending on the modeling program limits. Several sensitivities were run using different pore pressure conditions, in situ

ARMA 12-551 Impacts of saturation on rainfall-triggered slope failures at the Simbal Landslide, Pakistan Ahmed, M.F. Department of Geological Science and Engineering, Missouri University of Science & Technology, Rolla, MO, USA (On leave from University of Engineering and Technology Lahore, Pakistan) Rogers, J.D. Department of Geological Science and Engineering, Missouri University of Science & Technology, Rolla, MO, USA Farooq, K. Department of Civil Engineering, University of Engineering and Technology Lahore, Pakistan ABSTRACT: On August 10, 2005 a landslide of approximately 133,000 m3 occurred along the Lahore-Islamabad Motorway (M-2) near the village of Simbal, in the Salt Range area of Pakistan. A program of research was undertaken to evaluate the likely impacts of percent saturation and bulk density on mobilized shear strength along the basal rupture surface of the Simbal Landslide. A series of direct shear tests [1] were performed on remolded samples at different densities. The percent saturation was then varied on these samples to evaluate its impact on mobilized shear strength. The results of these tests suggest that soil cohesion and friction tended to decrease with increasing percent saturation. The tests also showed that the shear strength parameters tended to increase with increasing dry density; however, all of the samples exhibited a noticeable loss of shear strength with increasing degree of saturation, independent of soil density.

167 46th US Rock Mechanics/Geomechanics Symposium Limit equilibrium slope stability analyses were performed along the most probable failure planes, based on shear strength parameters corresponding to degrees of saturation, varying between 20% to 100% over a wide range of in-situ densities. The results of these analyses suggests that the factor of safety drops significantly, (from FS = 1.6 down to 0.41) as the degree of saturation approaches unity. These results suggest that the causative factor in triggering the Simbal Landslide was the partial saturation of the zone that developed the basal rupture plane. As rain infiltrated the slope, the bulk unit weight of the soil increased along well the pore water pressure, while the shear strength along the developing plane of rupture decreased sufficiently to concentrate shear strain when the material became more than 60% saturation (FS < 1.0).

ARMA 12-675 Progressive failure analysis and support design of blocky rock mass based on extended key block method Fu, G.Y. School of Civil and Resource Engineering, the University of Western Australia, Perth, WA, Australia Ma, G.W. School of Civil and Resource Engineering, the University of Western Australia, Perth, WA, Australia ABSTRACT: Traditional rock support design methods of rock slopes and tunnels are reviewed. Towards a more rational support design, not only the effects of blocks inside the rock mass on the key blocks daylighting into the excavation directly are considered, but also whether or not these day-lighting blocks are anchored to blocks inside and forming large key blocks after support is checked. Through a realistic numerical representation of three-dimensional rock mass, different batches of key blocks are searched successively. Then the sliding forces of the key blocks in the later batches are transferred to key blocks in the earlier batches batch by batch until the first batch according to a force transfer algorithm. The resultant forces of the key blocks in the first batch are finally utilized for support design. After selection of a rock bolting scheme, the stability of the reinforced rock mass is re-assessed. Stability analysis of individual key blocks and block groups connected by rock bolts are carried out. Compared with the previous rock support methods, the present support design based on advanced key block analysis is safer and more rational for blocky rock support design.

Pesost r - Fracture Mechanics and Fracture Flow Tuesday, 26 June, 5:30 pm – 6:30 pm

ARMA 12-129 Hydraulic Fracture Propagation in Unconventional Reservoirs: The Role of Natural fractures Keshavarzi, R. Young Researchers Club, Science and Research Branch, Islamic Azad University, Tehran, Iran Mohammadi, S. and Bayesteh, H. School of Civil Engineering, University of Tehran, Tehran, Iran ABSTRACT: Recovering hydraobarbon from unconventional reservoirs is always a challenge since it requires cost-effective fracture simulation treatments to make production economic. Meanwhile, the interaction between pre-existing natural fractures and the advancing hydraulic fracture is a key challenge especially in unconventional reservoirs, because without fractures, it is not possible to recover hydrocarbons

168 46th US Rock Mechanics/Geomechanics Symposium from these reservoirs. During hydraulic fracture propagation, any diversion or abrupt change in hydraulic fracture path caused by natural fractures, increases the possibility of premature screenout which leads to job failure. In another hand, the activation of natural fractures commonly found in shale reservoirs can create a network of connectivity within the reservoir and potentially improve the production. In this study, an extended Finite Element Method (XFEM) model has been developed to investigate the hydraulic fracture propagation and interaction with a natural fracture in unconventional reservoirs. The results indicate that hydraulic fracture diversion as well as natural fracture activation takes places even several stages before intersection. Also, it is clearly observed that hydraulic and natural fracture behaviors after intersection are strongly controlled by the in-situ horizontal differential stress and the orientation of the natural fractures.

ARMA 12-148 Tensile strength and failure criteria of analog lithophysal rock Nott, J.A. U.S. Corps of Engineers, Retired, Civil Engineer, Las Vegas, Nevada, USA. Rigby, D.B. U.S. Nuclear Waste Technical Review Board, Senior Professional Staff, Arlington, Virginia, USA. Karakouzian, M. Department of Civil and Environmental Engineering, Professor, University of Nevada, Las Vegas, Nevada, USA. ABSTRACT: This project determines the indirect tensile strength of lithophysal analog rock and presents possible failure criteria. The analog rock was made from Hydro-Stone TB cement and has mechanical properties similar to the estimated rock mass mechanical properties of welded nonlithophysal Topopah Spring Tuff in western Nevada. Three, 102 mm cubical specimens were tested in direct tension, and twenty, 102 mm diameter, specimens were tested by the indirect tensile Brazilian test method. Test results showed the elastic tensile modulus of elasticity was within two percent of the compressive modulus of elasticity, which was determined from previous tests. Brazilian tests determined the indirect tensile strengths and established the effect of lithophysal porosity on the indirect tensile strengths. Results showed that the indirect tensile strength of the specimens was approximately 10 percent of the compressive strength. Test data were obtained from specimens with 0, 6.2, 12.5 and 18.7 percent lithophysal porosities. Computer simulations were made using Itasca’s UDEC program to predict cracking patterns and tensile strengths. Results showed that the Mohr-Coulomb, Mohr-Coulomb-Tresca, Griffith and Power analyses can be used to predict failure of lithophysal rock.

ARMA 12-208 Effect of Dilation Parameter on the Stress Intensity Factor at the Crack Tip Using RKPM Hajali, M. Florida International University, Miami, Florida, USA Abishdid, C., PhD, PE. Florida International University, Miami, Florida, USA ABSTRACT: Reproducing Kernel Particle Method (RKPM) is a mesh-free technology which has proven very useful for solving problems of elastic-plastic fracture mechanics. In this study, the stress intensity factor (SIF) at the crack-tip in a work-hardening material is obtained using RKPM. Ramberg- Osgood stress-strain relation is assumed and the crack-tip SIF before and after formation of the plastic zone are examined. To impose the essential boundary conditions, penalty method is used. To construct the shape functions in the vicinity of the crack and crack-tip, both the diffraction and visibility criteria are employed and the crack tip region is also refined using more particles in two

169 46th US Rock Mechanics/Geomechanics Symposium various model particle arrangements. The effects of different dilation parameters on SIF under plane- stress and plane-strain conditions are studied for plane-stress and plane-strain conditions. Results show that dilation parameter has a great impact on the performance of the RKPM and especially on the SIF value for the edge crack problems. The main objective is to study the effects of different dilation parameters on SIF value under plane-stress and plane-strain conditions at the crack-tip using diffraction and visibility criteria.

ARMA 12-226 Simplified approach of gas production effect on nuclear waste repository stability DUVEAU1, G., 1 Université Lille Nord de France, F-59000 Lille, France and LML, CNRS, UMR8170, F-59650 Villeneuve d’Ascq, France and Polytech’Lille, Dept GTGC, F-59655 Villeneuve d’Ascq cedex, France JIA1 Y., SHAO1 J.F., POUTREL A.2 2 ANDRA,1/7 rue J. Monnet, 92298 Châtenay Malabry, France ABSTRACT: In the context of feasibility study for nuclear waste disposal, numerical modelling of the underground facilities construction is necessary in order to study the different physical processes occurring during the live-time of the nuclear waste. This paper consists to study the gas-mechanical coupling effect on a claystone using a mechanical model coupled with a two-phase flow model formulated in the framework of Biot theory. A two dimensional simplified geometry is studied. Pore pressure evolution and plastic deformations evolution during gas injection in the different components will be discussed. Comparison between calculations performed with and without gas allow us to draw some conclusion on the gas coupling effect on such low permeable materials.

ARMA 12-274 Fracture Propagation under Poroelastic Loading Chun, K.H. Department of Petroleum Engineering, Texas A&M University, College Station, TX, USA Ghassemi, A. Department of Petroleum Engineering, Texas A&M University, College Station, TX, USA ABSTRACT: In this work, the fracture propagation in a homogeneous poroelastic rock is considered. A two-dimensional poroelastic displacement discontinuity method is developed and used to model the fracture propagation and to calculate stress and pore pressure distributions around the crack. The model can accurately calculate very short time (undrained) and long time (drained) solutions. A poroelastic crack tip element is also developed and implemented to accurately compute the stress intensity factors at the crack tips. The maximum principal stress criterion is used to predict the crack propagation path. Numerical experiments are carried out to study fracture propagation trajectories compared with elasticity solutions. The numerical results indicate that the fracture growth under undrained condition does not show distinctive differences because the crack growth is so fast that the pore pressure diffusion effect is negligible. However, the fracture grows to the different direction under drained condition due to the impact of pore pressure loading.

170 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-283 Three Dimensional Modeling of Hydraulic Fracturing Process in Oil Reservoirs Hamidi, F. & Mortazavi, A. Department of Mining and Metallurgical Engineering, Amirkabir University of Technology, Tehran, Iran ABSTRACT: In this study a three-dimensional Distinct Element Methods (DEM) scheme was used for the simulation of initiation and propagation of the hydraulically induced fractures in a typical reservoir. Due to the fact that modeling the initiation of an induced fracture in DEM is difficult, a fictitious joint technique was introduced to simulate the process. The analysis results show that the success of the hydraulic fracturing process not only depends on controllable parameters such as fracture fluid properties and the injection rate, but also on the uncontrollable parameters such as stress regime, orientation of principal stress, and in-situ rock mass properties. Moreover, a sensitivity study of input variables was performed to examine the effect of different field conditions. These involved the orientation and magnitude of principal stress components, fracture fluid properties, injection rate and rock parameters. In addition, the results obtained from numerical modeling were compared with analytical solutions indicate that an obvious connection exists between them.

ARMA 12-293 Stress Dependent Seismic Wave Velocity of Randomly Micro Fractured Rocks Almrabat1, A., Katsuki2, D., Gutierrez3, M., Affiliations: 1-3 Division of Engineering, Colorado School of Mines, Illinois St., BB 269, Golden, CO 80401, U.S.A. ABSTRACT: Propagation of elastic waves in fractured rocks is investigated, both theoretically and experimentally. Mechanical properties of microfractured rocks have been characterized from the computation of seismic velocities. Published experimental studies indicate that normal and shear rock stiffness is a stress level dependent parameter in fractured rocks. This study reveals that a new physical parameter (n) affect the normal stiffness of fractured rocks. The stress dependent normal stiffness in fractured rocks is modeled as an empirical power law function of effective normal stress, which is a modification of the Goodman’s model. The stress dependent shear stiffness in fractured rocks is modeled as a linear function of normal stress based on experimental data. This empirical relationship is compared with extensive measurements of the normal compliance C obtained by Malama, and Kulatilake (2003) on rock fractures. The parameter (n) is a best fit for the existing experiment data. The observed variation in (n) value suggests that it may be a function of the rock fracture properties or pre-existing stress loading history. Consequently, the empirical relationship is integrated with the simple theoretical model to develop a new model for stress dependent seismic velocity in micro fractured rocks. In addition, velocities in dry and water-saturated Berea sand stone samples have been measured under different confining pressure. The new experimental and existing published data have been used to validate the new predicted model.

ARMA 12-333 A 3D Thermal-Poroelastic Model for Naturally Fractured Geothermal Reservoir Stimulation Wang, X. Texas A&M University, College Station, TX, USA Ghassemi, A. Texas A&M University, College Station, TX, USA

171 46th US Rock Mechanics/Geomechanics Symposium ABSTRACT: One of the most important tasks for geothermal reservoir development is engineering a fractured reservoir and predicting its future performance. For this purpose, numerical modeling of fluid flow and deformation of fractured rock is necessary. This work focuses on utilizing a stochastic fracture network to simulate the thermal-hydro-mechanical response of the reservoir during the stimulation process, and to assess the permeability enhancement in the stimulated zone. The reservoir stimulation process is simulated using a system of rock blocks some of which contain stochastically-distributed fractures and fractured zones. The effect of the fractures on permeability is introduced into the model by using the equivalent permeability approach. The rocks matrix is assumed to be poroelastic and the fractures are allowed to deform and to slip. Heat transport within the fractures, and heat conduction between adjacent rock mass and the fluid in the fracture are also considered. A series of simulations are carried out to analyze the rock mechanical response and permeability evolution for a Newberry-type reservoir. Results show the significant role of fracture distribution and its mechanical deformation in EGS design and development. This model provides a tool to predict the performance of natural fracture networks, and to analyze the stimulation response and future production performance.

ARMA 12-395 Open-System Geomechanics of Rocks with Variable Solid Mass Geilikman, M. B. Shell International Exploration & Production Inc. Houston, Texas, USA Wong, S.W. Shell International Exploration & Production Inc. Houston, Texas, USA ABSTRACT: The Open-System Geomechanics Model (OSG) provides a fully coupled description of stress/strain, solid and fluid masses evolution initiated by phase transformation (desorption, dehydration, or dissolution/precipitation) between solid and fluid components. The model consists of new constitutive relationships, which capture variation of eigen-strain caused by variation of solid and fluid mass and new equations of equilibrium for solid phase, fluid mass and heat transfer equations. A new model of coalbed methane (CBM) permeability is derived based on OSG approach. The new model of sorption-induced permeability vs. pressure provides significantly better agreement with experiment data compared to previously published permeability models.

ARMA 12-525 Coupled plastic failure and permeability in rocks: a modeling approach Kelkar1, S., Karra1, S., Zyvoloski1, G., Pawar1, R., and Rapaka2, S 1 Los Alamos National Laboratory, Los Alamos, NM, USA 87545 2 now at Siemens Corporate Research, Princeton, N.J., USA 08540 ABSTRACT: The coupled interactions in fractured geological media between thermal-hydrologic- mechanical (THM) and chemical effects are expected to be important in many engineering applications

including CO2 sequestration, geothermal energy production, oil and gas production, nuclear waste isolation, and arctic permafrost. Large changes in pressures and temperatures can result due to injection/withdrawal of fluids or emplaced heat sources, which can potentially lead to mechanical failure (fracturing) of the cap rock, or reactivation of existing geological faults. Shear and tensile failure on pre-existing or induced fractures can enhance the permeability and accessible surface area of the formation, and also generate microseismic events. Chemical changes associated with large temperature changes can enhance or diminish porosity and permeability along with plastic rock deformation. The work presented here focuses on the coupling between flow and plastic deformation through a model that varies the permeability with plastic strain. We describe a general purpose computational code,

172 46th US Rock Mechanics/Geomechanics Symposium FEHM, developed for this purpose, that models coupled THM processes during multi-phase fluid flow and transport in fractured porous media. The code uses a continuum mechanics approach, based on control volume – finite elements. It is designed to address spatial scales on the order of tens of centimeters to tens of kilometers. The equations representing the processes being considered – thermal, hydrologic, and mechanical - are formulated simultaneously in a consistent fashion. Nonlinearities in the equations and the material properties are handled using a full Jacobian Newton-Raphson technique. Stress-strain relationships are assumed to follow linear elastic/plastic behavior. The code incorporates several models of fracture aperture and stress behavior combined with permeability relationships. The nonlinear coupled equations describing the system can be solved in any of the fully coupled implicit, iteratively coupled, or explicitly coupled modes.

ARMA 12-678 Exploring the physicochemical processes that govern hydraulic fracture through laboratory experiments Alpern, J., Marone, C., and Elsworth, D. College of Earth and Mineral Sciences, The Pennsylvania State University, University Park, PA 16802 Belmonte, A. Department of Mathematics and of Material Sciences & Engineering, The Pennsylvania State University, University Park,PA 16802 Connelly, P. Chevron Exploration Technology Company, Houston, TX 77002 ABSTRACT: Hydrocarbon recovery is potentially maximized with an open, complex fracture network of large surface area to volume ratio that penetrates the reservoir. We study the hydraulic rupture of a solid, homogenous cube of Polymethyl methacrylate (PMMA) containing model boreholes as an analog to hydraulic fracturing with various fracture-driving fluids. The transparency of PMMA allows for the visualization of fracture propagation using high-speed video. The cubes are constrained by prescribed triaxial far-field stresses with the borehole-parallel stress set to zero. The cube is ruptured by overpressuring the borehole at controlled rates with fluids present as both liquids and gases pre- and syn- failure. We measure the fracture breakdown pressure, rates of fracture propagation and the physical characteristics of the resulting fractures and how they vary between fluid types. Further research extends these experimental methods to bluestone and granite, with additional tests that determine the permeability of these materials and its effect on creating a complex fracture network.

Pesost r - In Situ Stresses Tuesday, 26 June, 5:30 pm – 6:30 pm

ARMA 12-108 The Determination of the In Situ Stress Tensor as an Inverse Problem de Mello Franco, J.A. Rock Mechanics Engineering Consultant, Rio de Janeiro, Brazil Vargas Jr., E. A. Department of Civil Engineering, Catholic University, Rio de Janeiro, Brazil

173 46th US Rock Mechanics/Geomechanics Symposium ABSTRACT: This paper aims to show why the determination of the in situ stress tensor is an inverse problem, as well as describing a Bayesian inverse problem technique for finding the components of the in situ stress tensor or the initial boundary conditions of the site using existing knowledge. Techniques for the evaluation of the reliability of calculated results will also be explained. Synthetic examples will be used in order to exemplify the calculations. Preliminary methods for calculating the in situ stress tensor as the initial data, if no previous tests are available, will also be shown. A synthetic example will be used to illustrate the application of the Bayesian Technique and evaluate the reliability of its answers, for two cases, considering 3D conditions in a continuous, homogeneous, isotropic and linearly elastic rock mass.

ARMA 12-134 Using Borehole Breakouts to Estimate In Situ Stresses at Depth Simon, R. Ecole Polytechnique de Montreal, Montreal, Quebec, Canada Labrie, D. CANMET-MMSL, Natural Resources Canada, Ottawa, Ontario, Canada ABSTRACT: This paper presents an ongoing study on the use of borehole breakouts to estimate in situ stresses at depth in a Canadian underground mine. The breakouts were identified using an acoustic televiewer (ATV) probe. Rock samples were tested in laboratory to determine their failure curve. Breakouts analyses were performed using a multiaxial failure criterion. Analyses were carried out using both short- term (peak) and long-term strengths (considered here as being represented by the damage initiation threshold DIT). The analyses have shown that the use of the long-term strength leads to results that are more coherent with stress measurements performed in the area.

ARMA 12-197 Case Studies on Stress Pattern around Salt Bodies in Deep Water Formations Shen, X. Halliburton, Beijing, China ABSTRACT: Two major aspects in the description of a stress pattern are the effective stress ratio and tectonic facture. This paper presents two case studies focusing on the stress pattern around salt bodies in the deepwater. The salt body geometries are modeled on the basis of a set of sectional seismic data. The geometry of the geomechanical model used in the calculation for a field at the Gulf of Mexico is a block with a height, width, and thickness of 10 km. An inclined cake-shaped salt body with a diameter of 6927 m is embedded in the model. A similar geometric scale is used for the second case study from the Campos basin of offshore Brazil. In this case, a salt body with an irregular geometry has a thickness of 6024 m along the trajectory of wellbore. An anticline structure was modeled at the bottom surface of the salt body. Numerical results obtained with the FEM for each study include: 1) sectional views for the distribution of both the effective stress ratio and tectonic factor, and 2) diagrams of the distribution of the effective stress ratio and the tectonic factor along specific paths below and above the salt body, respectively. The anticline structure was found to have a significant influence on the distribution of stress pattern within the subsalt formation; the rang of effective stress ratio varies from 0.65 to 1.2.

174 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-389 The integrated use of hydraulic fracture and deformational measurements in permeable rock stress state estimation Pavlov, V. A. Institute of Petroleum geology and geophysics, Novosibirsk, Russia Serdyukov, S. V. and Martynuk, P. A. Institute of Mining, Novosibirsk, Russia ABSTRACT: The method of stress state estimation is proposed. This method is based on subsequent measurement of circular contour deformations. The mathematical model is created and numerical modeling of circular contour deformations estimation is carried out. The calculations were made for the case with 2 fractures going from the borehole outline with loading by the cover (sleeve).

ARMA 12-473 Characteristics of the regional shallow in-situ rock stress field in the Kyungsang Basin in Korea Park, E.S. and Chae, B.G. Korea Institute of Geoscience and Mineral Resources, Daejeon, Korea Bae, S.H. GeoGeny Consultants Group, Seoul, Korea Jeon, S.W. Seoul National University, Seoul, Korea ABSTRACT: Since late in the 90’s, in-situ rock stress tests have been widely conducted to provide the quantitative information on the stress state of an engineering site at the design stage of an underground rock structure in the Kyungsang Basin, Korea. Totally, 270 in-situ stress measurements were conducted in the surface test boreholes at the depth from 20 m to 300 m by the hydraulic fracturing method using an engine driven wireline hydro-fracturing system. And almost of all the fracture tracing works were carried out using borehole scanning device to obtain more accurate and visualized information on induced fractures rather than conventional oriented impression packer method. In this paper, the overall characteristics of the current in-situ rock stress fields in the Kyungsang Basin are described with the results of measurement data set. The maximum horizontal stresses (SH) range from 1.18 MPa to 20.73 MPa and the minimum horizontal stresses (Sh) from 0.84 MPa to 10.92MPa at less than 300m in depth. Although the stress ratio (K) has strong anisotropies at less than 100 m in depth, it generally has a tendency to decrease and stabilize with depth. The average stress ratio (Kavg) ranges from 0.83 to 4.91 and the maximum stress ratio (KH) from 0.83 to 5.63. The average direction of all SH data set was approximately 84±40.6° from the north (N84°E).

ARMA 12-519 Evaluating the Relationship between Moisture Induced Expansion and Horizontal Stress Orientation in Samples from the Nonesuch Formation Vermeulen, L. Michigan Technological University, Houghton, MI, United States of America Vitton, S., Phd, P.E. Michigan Technological University, Houghton, MI, United States of America

175 46th US Rock Mechanics/Geomechanics Symposium ABSTRACT: High horizontal stresses can cause numerous ground control problems in mines and other underground structures ultimately impacting worker safety, productivity and the economics of an underground operation. Mine layout and design can be optimized when the presence and orientation of these stresses are recognized and their impact minimized. A simple technique for correlating the principal horizontal stress direction in a sedimentary rock mass with the preferential orientation of moisture induced expansion in a rock sample was introduced in the 1970s and has since gone unused in practice. This procedure was reexamined at a proposed mine site near the original White Pine Mine in White Pine, Michigan in order to validate the original research and to consider its usefulness in mining and civil engineering applications in high horizontal stress conditions. This procedure may also be useful as an economical means for characterizing regional stress fields.

Ses s ion 33: Cas l s ic and Novel Wellbore Stability Evaluation Wednesday, 27 June, 8:00 am – 9:30 am Chairs: Sergio Fontoura, Greg Pepin

ARMA 12-317 Determination of Safe Salinity Window in Drilling Shale Formation Huang, L. The University of Tulsa, Tulsa, Oklahoma, U.S. Yu, M., Miska, S., and Takach, N., and Green, A. The University of Tulsa, Tulsa, Oklahoma, U.S. Bloys, B. Chevron, Houston, Texas, U.S. ABSTRACT: A new concept called “Safe Salinity Window” is introduced to help drilling engineers determine the proper salinity level in drilling fluids. Safe Salinity Window can be obtained from a chemo- poro-elastic wellbore stability model, which incorporates drilling fluid-induced chemical osmotic in-situ stress. A multiple solute, non-ideal solution pore pressure transmission model is adopted in this study for accurately predicting the pore pressure term in a wellbore stability model. It has been found that both compressive failure index and tensile failure index are a function of pore pressure. It is also found that the salinity of drilling fluids will cause chemical osmotic pressure and further affect the effective principle stresses. Increasing salinity will decrease the chances of compressive failure but may move the drilled section closer to the tensile failure boundary. A computer program has been developed to find the proper salinity. Mohr-Coulomb criterion gives more conservative salinity value to predict compressive failure than the prediction from Modified-Lade criterion.

ARMA 12-417 Drilling in Fracture Shales: Another Look at the Mud Weight Problem Hemphill, T. Halliburton, Houston, Texas, USA ABSTRACT: Much of the drilling in unconventional resource plays occurs in unstable shales, which are usually fractured and can be easily destabilized. Successful drilling through them can be difficult at

176 46th US Rock Mechanics/Geomechanics Symposium best, and many high-angled holes in these plays are often lost due to mechanical instability. This paper looks at the drilling problems of shale gas drilling from the theoretical perspective of Wellbore Pressure Management, (WPM) and keys in on the effects of Equivalent Circulating Density (ECD) while drilling and on the effects of Equivalent Static Density (ESD) when there is no circulation. In this paper the following questions pertaining to drilling a typical fracture shale are addressed from the WPM perspective: · What mud density do I need to drill a fractured shale? · Why can a typical shale gas play well be drilled with no drilling problems, yet becomes very unstable on the last trip out of the hole before E-logging or running casing? · Why are drilling problems especially acute in laminated shales or similar weak zones? By using a Wellbore Pressure Management approach to understanding instability in fractured shales, the reader can readily see how to best deal with the problem in the field and hopefully improve stability in future wells.

ARMA 12-445 Integrated Wellbore Stability Analysis for Well Trajectory Optimization and Field Development in the West Kazakhstan Field Kadyrov, T. Colorado School of Mines, Golden, Colorado, USA Tutuncu, A. N. Colorado School of Mines, Golden, Colorado, USA ABSTRACT: Several vertical and horizontal exploration wells drilled in the West Kazakhstan field that are located on the Northern margin of the Pre-Caspian Basin, show significant wellbore-stability problems including stuck pipe and mud-shale interactions. A numerical model was developed to diagnose the source of these problems and implement a successful development plan considering the variation of the local in situ stresses, temperature alteration, shale-fluid physicochemical interactions and the effect of the induced fluid flow. The magnitude and orientations of the in-situ stresses, formation properties and strength of the formations drilled have been extensively studied. A field geological model was utilized in conjunction with the well log and drilling data from several of the exploration wells to obtain accurate input parameters for the integrated model. The wellbore-stability model was calibrated using drilling, pressure and cutting data. An integrated risk analysis study, incorporating borehole stability, lost circulation, hole cleaning and differential sticking was implemented to effectively plan future drilling operations in the field and to maximize the drilling margin. History matching for the observed field wellbore-instability cases was conducted using the proposed coupled model, optimizing the drilling fluid programs and well trajectories to minimize the instability problems in future wells in the study area. Based on outcomes of this study, recommendations for field development have been made to reduce non-productive time during drilling operations resulting in sizable cost reduction.

ARMA 12- 453 The challenge of drilling the Ecopetrol’s first well, in the Cupiagua field. A Geomechanics point of view. Mateus, M. C., Carvajal, J. M Ecopetrol_ICP,Piedecuesta, Santander, Colombia Illidge, E. J GEMS, Piedecuesta, Santander, Colombia Lozano, J.A., Ceballos, C. P., Castillo, A. F Ecopetrol_SYA, Bogotá, Colombia

177 46th US Rock Mechanics/Geomechanics Symposium ABSTRACT: Ecopetrol, the national oil company of Colombia, decided to take the operation of the Cupiagua field, in June of 2010, after 20 year of operation by an International Oil Company. This field has very important geomechanical features such as; stresses anisotropy, overpressured shales, overpressured sandstones, fractured zones and presence of coal beds. This area has been considered as a complex tectonic setting, even worldwide, so drilling it is very complicated. The combination of geomechanical features has caused important increases on the final drilling cost. For instance, typical values of non-productive time (NPT) had reached almost 30% of the total drilling time. For all that said, the first well drilled by Ecopetrol was a big challenge for the drilling team, as well as for the geomechanic team. Geomechanical issues were considering since the early planning stages on; then, during drilling operations, meticulous stability monitoring was done in order to help the performance of the well. First of all, it was selected the best location in surface, looking for an appropriate stresses configuration over the wall of the hole. Then, the well trajectory was designed taking into account the best attack angle. After that, the casings seats were established to deal with the pore pressure profile, and finally, the mud weight window was designed based on the stability model. The whole analysis was based on a tridimensional geomechanical model developed for the Cupiagua field. This paper presents the geomechanical analysis methodology involved, as well as, the main geomechanical issues that were considered in the well planning stage. On the other hand, the most important events that occurred during the drilling stage are described, and how they matched with the previous geomechanical model. At the end of the paper, it is presented the final performance and the NPT of the well to show the advantages of involving geomechanic’s studies for drilling operation.

ARMA 12-463 A coupled model for wellbore/reservoir temperature prediction and stress analysis during fluid circulation Wu, B., Zhang, X., Wu, B., Jeffrey, R. G. and Bunger, A. P. CSIRO Earth Science and Resource Engineering, Clayton, VIC 3168, Australia ABSTRACT: In this paper, a pesuo-3D model is presented and simultaneously deals with both heat transfer between the circulating fluid and the surrounding reservoir rocks and the thermally-induced in-plane thermo-elastic (TM) stress changes during fluid circulation. Along the wellbore, the cold water descends through the drill pipe at a constant injection rate and ascends to the ground via the annulus. As a result of fluid circulation, the wellbore bottom temperature will be reduced and this can allievate the local high compressive stress to facilitate hydraulic fracturing. The governing equations are delineated to ensure that most important parameters are taken into account. The formation is assumed to be homogeneous and thermo-elastic, and the wellbore is subject to a non-hydrostatic in situ far-field stress field. In modelling heat conduction, the heat transfer coefficients (HTC) between fluid and formation are dependent on fluid properties and flow behaviours. By using the Laplace transform, analytical solutions are obtained for the temperature evolution of the fluid in the drill pipe and annulus and for the temperature and stress changes in the formation. The numerical results in the time domain are obtained using an efficient inversion approach. In particular, the near-well stresses are compared for the cases with fixed and cooling wellbore conditions. It indicates that the results based on fixed wellbore conditions may mis-estimate the mud weight necessary for hydraulic fracturing.

178 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-533 Potassium Efficacy versus Osmosis and a Biological Analog to Shale-Fluid Interactions Boyd, P. J. New England Research, Inc., White River Junction, VT, USA ABSTRACT: The dichotomy between the fact that the potassium (K+) ion is well known to be a preferred additive in drilling and completion fluids, and the widely held belief that osmosis plays an important role in the clay/shale-fluid interaction problem has been intriguing for several years. This ion dependency alone challenges the osmotic theory of shale stabilization, and over the last two decades a vast amount of research to examine the existence of swelling, and the feasibility of osmosis under wellbore conditions has led to additional doubt. A review of that research is summarized in this paper, and a number of factors that have not been satisfactorily addressed, but are important to the discussion are examined. These factors include a reassessment of laboratory results that promulgated swelling, a simple assessment of whether the accepted osmotic process could create pressure imbalances that would cause dewatering, a compilation of basic ion properties that are important to the analysis, an examination into why there is ion specificity in the manner and results of the ion transfer process (and consequently why K+ is preferable over other cations) and finally a presentation of likely reasons for the stabilizing impact of ion interactions with clay surfaces. Additionally, the ion selectivity structures present in cell walls were found to be an interesting analog to the shale-fluid interactions problem, and their functions will be presented as well.

Ses s ion 34: Su rface Mine Pit Slope Stability Wednesday, 27 June, 8:00 am – 9:30 am Chairs: Loren Lorig, Doug Stead

ARMA 12-133 Evaluation of Structurally-Controlled Failures in Large Quarrying Operations Scarpato, D.J. Haley & Aldrich, Inc., Boston, MA., USA Boakye, K. Dragon Products Company, Thomaston, ME., USA ABSTRACT: Excavated rock slopes, such as those that result from massive exploitation operations in surface mining, can be subject to periodic rock instability events. These events can take the form of relatively localized instabilities such as rock fall, which are risky for quarry operators and equipment, to large-scale slope failures which, apart from evident safety problems, can hinder further exploitation of the ore body sectors or even impact the neighboring environment. This paper summarizes the primary steps for conducting for a comprehensive geomechanical study at a large quarry, where structural geologic controls can induce failures in those portions of a mine that are developed with an over-steepened face profile. A comprehensive geomechanical study will incorporate a rock mass characterization program, and include development of a rock mass structural model, short and long-term slope monitoring, kinematic analyses, limiting equilibrium slope stability analyses, and numerical modeling where appropriate. The paper also synthesizes results of case studies from active quarries where design and controlled blasting are actively being implemented.

179 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-248 Modelling rock bridge failure and brittle fracturing in large open pit rock slopes Havaej, M. Simon Fraser University, Burnaby, British Colombia, Canada Stead, D. Simon Fraser University, Burnaby, British Colombia, Canada Lorig, L. Itasca Consulting Group, Minneapolis, Minnesota, United States Vivas, J. Simon Fraser University, Burnaby, British Colombia, Canada ABSTRACT: As large open pit slopes increase in depth, it is becoming increasingly necessary to investigate nonconventional slope failure mechanisms. The existence of rock bridges can have a significant effect on rock slope stability therefore, it is necessary to further our understanding of the impact of rock bridges and brittle fracture processes. In the first part of this study, the 3D lattice spring code Slope Model allows evaluation of the effect of rock bridges on the stability of a pentahedral or “non-daylighting” wedge. The geometry adopted simulates a 3D equivalent of a conventional 2D bi- planar wedge. As a preliminary analysis, various rock bridge percentages were simulated by the location of intact rock along the basal surface of the wedge. The results demonstrated that 2% rock bridges on the basal surface were required to stabilize the wedge. In the second part of this study, the staged construction of a rock slope containing a pentahedral wedge was modeled to investigate damage at the toe of the slope and the depth at which the wedge would fail. Significant damage at the toe was noted prior to daylighting of the basal surface of the wedge.

ARMA 12-251 Towards a methodology for characterizing intact rock bridges in large open pits Tuckey, Z. Simon Fraser University, Burnaby, BC Stead, D. Simon Fraser University, Burnaby, BC, Canada Sturzenegger, M. Klohn Crippen Berger, Vancouver, BC, Canada Elmo, D. Golder Associates, Burnaby, BC, Canada Terbrugge, P. SRK Consulting, Johannesburg, South Africa ABSTRACT: Despite over four decades of research into rock mass and discontinuity methods for field characterization of discontinuity persistence and Simon Fraser University, three open pit mines based LiDAR, and modified discontinuity survey methods persistence and potential for intact rock bridges. dimensional trace maps at bench, inter-ramp, and based on contrasts in lithology, bench condition, develop preliminary recommendations for an adaptable methodology for assessing dis content, which may be customized according to site practitioner.

180 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-360 Heterogeneous Distribution of the Coefficient of Permeability and an Equivalent Homogeneous Approach Riahi, A. and Hazzard, J. & Lorig, L. Itasca Consulting Group, Minneapolis, U.S.A. ABSTRACT: The effects of variations in the coefficient of permeability and its spatial correlation on the hydromechanical behavior of Large Open Pit problems are studied in a two-dimensional framework by using a probabilistic analysis approach. The results of the probabilistic analyses are compared to the results of models with deterministic values of permeability equal to three statistical means, namely arithmetic, geometric and harmonic mean. It is evaluated if a problem with heterogeneous permeability field can be represented by an equivalent problem in which the heterogeneous permeability distribution is represented by a homogeneous field with the value of permeability taken as one of the three statistical means.

ARMA 12-452 Simulation of Three-Dimensional Pore-Pressure Distribution for Slope-Stability Analysis Liu, H. Itasca Denver, Inc., Lakewood, Colorado, USA Durán del Valle, F. Division Codelco-Chuquicamata , Chile Xiang, J. and S¸ener Kaya, B. Itasca Denver Inc., Lakewood, Colorado, USA ABSTRACT: A 3D groundwater flow model was constructed using MINEDW [1]to simulate pore pressure at the Chuquicamata open pit mine slope in Chile. Three main factors required the implementation of a 3D model for the prediction of pore pressures: (1) discrete zones of recharge in the gravel zone lead to the non-uniform flow field; (2) the low-permeability west fault and shear zones maintain the non- hydrostatic pore-pressure distribution with depth during mining; and (3) the drainage gallery causes localized depressurization. In addition, a zone of relaxation (ZOR) was observed at the site. Simulations of the development of the ZOR according to the mining schedule are important in the prediction of pore- pressure distribution within the slope. The model was calibrated against measured water levels, pore pressures, drains, and seepage rates. The calibrated model was then used to simulate and predict pore-pressure distribution in the pit walls for different time periods. Specifically, the model was able to capture the non-hydrostatic, transient nature of the pore pressures with depth in the granodiorite west of the shear zone, in the shear zone, and along the west fault. The model also simulated the ZOR for the first 150 m below the pit bench with enhanced hydraulic conductivity values according to the excavation schedule. Simulated transient 3D pore-pressure distribution provides a more realistic input to 3DEC slope-stability analyses.

ARMA 12-466 Forensic Evaluation of Pit Slope Instabilities Narendranathan, S. Coffey Mining Pty Ltd., West Perth, Western Australia, Australia Bungard, G.P. and Thomas, R.D.H. Coffey Mining Pty Ltd., West Perth, Western Australia, Australia

181 46th US Rock Mechanics/Geomechanics Symposium Astractb : Over the last few decades there has been a push to standardize most aspects of geotechnical (pit slope) design work. Design standards / guidelines have evolved from the CANMET manuals in the early 1970’s to the most recently developed open pit design guidelines published by CSIRO. One aspect of the geotechnical design and implementation process which still remains highly subjective and has not been effectively standardized across the industry is methodologies to apply when forensically assessing pit slope instabilities or failures. The authors propose a set of guidelines and protocols that in their experience, based on a number of case studies, has proven useful in the field of forensic geomechanics.

Ses s ion 35: Fr acture Processes and Testing Wednesday, 27 June, 8:00 am – 9:30 am Chairs: John Kemeny, Shugang Wang

ARMA 12-401 Fracture initiation and propagation in the Quintner Limestone Perras, M.A., and Diederichs, M.S. Queen’s University, Kingston, Ontario, Canada Amann, F. Geological Institute ETH, Zurich, Switzerland ABSTRACT: Crack initiation and crack damage strength thresholds are key parameters to describe the brittle behavior of rock and are used as input values for numerical models. A set of 15 Quintner limestone samples, with calcite veining, were tested in uniaxial compression. The strength thresholds were determined by acoustic emission and strain methods. Crack initiation values were less variable than crack damage and peak strength. The calcite vein orientation was determined to influence the strength thresholds and stiffness of the samples, which generally increased as the vein angle off the loading direction was increased. The influence was most pronounced on the stiffness and less so on the crack initiation threshold. An influence on crack damage and peak strength is indistinguishable with the small set of samples; however an visual observation suggests that when thick calcite veins were present, the samples tended to be stronger.

ARMA 12-258 Size of process zone in fracture testing of rock Tarokh, A. Department of Mineral Engineering, New Mexico Institute of Mining and Technology, Socorro, NM, USA Fakhimi, A. Department of Mineral Engineering, New Mexico Institute of Mining and Technology, Socorro, NM, USA & Department of Civil and Environmental Engineering, Tarbiat Modares University, Tehran, Iran Labuz, J.F. Department of Civil Engineering, University of Minnesota, Minneapolis, MN, USA ABSTRACT: Fracture of rock involves the formation of a localized region of damage called the process zone, which influences size effects on strength and stability. To study the development of the process zone in rock, physical and numerical experiments are conducted using a three point bending test on beams without a notch. A discrete element model with softening of normal (tensile) bonds is used to capture the quasi-brittle behavior. In the simulations, the normal bond is gradually reduced by increasing the relative normal displacement at the contact point of two particles. The slope of the softening line is assumed to be a material property. It is shown that this property can affect the dimensions of the process zone.

182 46th US Rock Mechanics/Geomechanics Symposium The numerical results are compared with some physical experiments with acoustic emission monitoring. Both experimental and numerical results suggest that as the material becomes less brittle, which means a larger process zone, the size of process zone becomes more dependent on the specimen size. Fracture characteristics are size independent only for brittle materials (a small process zone).

ARMA 12-421 Role of Microstructure Size in Fracture Process Zone Development of Marble Brooks, Z., Ulm, F-J., and Einstein, H.H. Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA ABSTRACT: The fracture process zone (FPZ), a zone of weakened material surrounding the tip of a propagating crack, is common to many brittle materials, and is likely related to brittle material damage mechanisms. This study follows recent investigations of Carrara Marble and asks whether microstructure size, such as the size of marble grains, leads to an different extent of damage for a brittle material. Existing work has used acoustic emissions or laser interferometry and optical microscopy to answer this question, and found a positive relationship between grain size and size of the FPZ. Our study uses nanoindentation to probe the nanomechanical properties of the FPZ for two marbles of varying grain size, and attempts to relate mechanical properties of the FPZ to grain size. The marbles are from Carrara, Italy (typical grain size 300 μm), and Danby, Vermont (typical grain size 520 μm). Grids of nanoindentations were placed within the FPZ regions of Danby and Carrara marble specimens. Both marbles exhibited lower nanomechanical properties near the crack tip and near the area of future wing-crack formation, i.e. the FPZ. However, the Danby (large microstructure) marble exhibited this trend over a larger distance, and thus provides nanomechanical support for the increase of the FPZ with grain size.

ARMA 12-156 Fracture Characterization in Analog Rock and Granite Under Bending Stresses Using Acoustic Emission Hampton, J., Frash, L. and Gutierrez, M. Colorado School of Mines, Golden, CO 80401 ABSTRACT: Brittle heterogeneous rocks emit Acoustic Emission (AE) events from fracture formation during loading which are associated with microstructure dislocation. Notched Beam Fracture Toughness (NBFT) tests were performed on samples of an analog rock and Colorado Rose Red Granite in order to characterize tensile fracture AE signals. All concrete specimen sizes were approximately 45x60x140 mm3 beams. Granite specimen sizes were 40x50x240 mm3 beams. Three point and four point loading methods were used on the concrete and granite samples respectively in order to generate maximum beam moment in the vicinity of an initiation notch. Six AE piezoelectric transducers manufactured by Physical Acoustics Corporation (PAC) were used. PAC’s AE source location software, AEwin, was used in order to triangulate event locations and perform waveform analysis. Attenuation analysis and curve generation was performed for each material tested in order to refine the event source location parameters. Load dependent stages of acoustic emission events were created. Four stages were used in order to characterize the micro crack development leading up to the main fracture formation. Crack location was verified visually post-test and a profilometer was used to generate a digitized fracture surface. An AE event estimated fracture surface was also created and compared with the profilometer data.

183 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-628 Fracturing Behavior of Inclined Cracks under Static and Cyclic Loading Erarslan, N. Geotechnical Engineering Centre, The University of Queensland, Brisbane, Queensland, Australia Williams, D.J. Geotechnical Engineering Centre, The University of Queensland, Brisbane, Queensland, Australia ABSTRACT: This study presents the results of laboratory diametrical compression tests performed on Brisbane tuff disc specimens to investigate their mixed mode fracturing response to static and cyclic loading. Both the static and cyclic loading tests were carried out on Cracked Chevron Notched Brazilian Disc (CCNBD) rock specimens. Static diametrical compression resulted in the opening of the notch cracks at the centre of the specimens (Mode I), up to a 30° crack inclination angle (β), whereas crack closure (Mode II) was observed for β > 33°, with closure becoming more pronounced at the higher crack inclination angles of 45° and 60°. A second series of diametral compression testing with increasing cyclic loading amplitude showed that the failure load decreased between 30% and 45% compared with that under static loading. Comparison of the load–CMOD (crack mouth opening displacement) plots of monotonically and cyclically loaded CCNBD specimens showed that the 45° and 60° chevron notch cracks started to open from the beginning of the cyclic loading test, while under static loading they closed. This outcome is a very important finding for examining rock fatigue damage mechanisms.

ARMA 12-338 The Strength and Crack Behavior of the Rock-like Gypsum under High Strain Rate Zou, C., Ngai, L., Wong, Y., Cheng, Y., School of Civil and Environmental Engineering, Nanyang Technological University, Singapore, Singapore ABSTRACT: The strength of rock and rock-like brittle materials is loading-rate dependent in a wide range of strain rate. Besides, the crack initiation and propagation processes under the high strain-rate loading and quasi-static loading are different. In order to investigate the dynamic fracture performance under the high strain rate conditions, rock-like artificially moulded gypsum specimens with and without pre-existing flaw(s) are loaded under different strain rates. A quasi-static loading is applied to the specimens by a uniaxial compression machine. The dynamic loading is produced by the split Hopkinson pressure bar (SHPB). The strain-time history recorded by the strain gauges attached on the incident and transmitted bars is used to obtain the strain-stress curve in the specimen. At the same time, the entire fracturing process is recorded by a high speed video system at a frame rate of 40,000 frames per second. It is found that the strength of the gypsum specimens increases apparently as the strain rate increases from approximately102 s-1 to103 s-1, while the strength is nearly constant under a quasi-static loading of a strain rate from 10-6 s-1 to 10-3 s-1. With regard to the fracturing processes, for specimens containing a pre-existing flaw, the high speed camera images show that the first tensile wing cracks initiating under the dynamic condition are similar to those under the quasi-static condition. However, the dynamic secondary crack patterns are distinct from those of the quasi-static ones. The experimental findings provide insights into the relationship between the material strength and the dynamic fracture mechanism.

184 46th US Rock Mechanics/Geomechanics Symposium Ses s ion 36: F oluid Fl w & Deformation in Porous Media: Connecting Micro- and Macro- scale Properties Wednesday, 27 June, 8:00 am – 9:30 am Chairs: Jose Andrade

ARMA 12-175 Effect of grain scale geometric heterogeneity on tensile stress generation in rock loaded in compression Bewick, R. P.1,2,3, Valley, B.1,3 Kaiser, P. K.3 1 MIRARCO - Mining Innovation, Sudbury, ON, Canada 2 University of Toronto, ON, Canada 3 Centre for Excellence in Mining Innovation, Sudbury, ON, Canada ABSTRACT: Brittle failure of rock is dominated by tensile mechanisms even in an overall compressive stress field. Heterogeneities play a key role in the development of the localized tensile conditions. However, details on how heterogeneities affect brittle rock failure processes are still open for debate. Through the use of regular honey- comb grain arrangements progressing to highly irregular Voronoi arrangements, the impact of grain geometric heterogeneity through finite element tools and discrete element methods was assessed and it is shown that non-uniformity of grain size distribution is not a critical parameter to evaluate crack initiation, peak strength, or micromechanical behaviour. The results demonstrate that grain boundary orientation and grain system arrangements control tensile stress generation inside a brittle rock specimen under compression and thus impact the crackinitiation stress level. This suggests that crack interaction and peak strength is then affected by the kinematic and allowable degrees of freedom in the grain assembly of the damaged rock. At this stage, grain deformability and more importantly grain breakage is needed to increase the degrees of freedom required for the linkage and formation of a macroscopic rupture. Based on this it is suggested that if it is possible to characterize grain boundary orientations or arrangements, various micro-mechanical behaviour could potentially be forecast.

ARMA 12-253 Multiscale Modeling of 3D Granular Systems by Computational Homogenization Meier, H. A. ExxonMobil Research and Engineering Company, Annandale, NJ, USA Meier, S. W., Liu, F., and Gordon, P.A. ExxonMobil Research and Engineering Company, Annandale, NJ, USA Tran, T.A. ExxonMobil Technical Computing Company, Annandale, NJ, USA ABSTRACT: The numerical modeling of granular materials is often performed with one of two techniques depending on the length-scale of the system of interest. For large-scale problems, continuum approaches such as the finite element method are the standard. These approaches require continuum descriptions of the constitutive relationship between stress and deformation. Since these descriptions do not explicitly consider grain-scale dynamics, modeling of large-scale history dependent phenomena due to permanent grain rearrangement remains a long-standing challenge. On the other hand, small-scale systems are often modeled using discrete element methods that directly simulate grain-grain interactions,

185 46th US Rock Mechanics/Geomechanics Symposium thereby capturing history dependent phenomena. While a successful approach for small-scale systems, discrete element method simulations have been shown to be computationally expensive and impractical for large-scale systems. We demonstrate a scalable multiscale approach for large-scale 3D granular systems where the domain of interest is discretized using the finite element method with the constitutive behavior coming directly from discrete element method simulations of the grain-scale. The coupling between the finite element method model and the discrete element method simulation comes from a computational homogenization approach.

ARMA 12-268 Network Theory, Cracking and Frictional Sliding Ghaffari, H.O. Department of Civil Engineering and Lassonde Institute, University of Toronto, Toronto, Canada Young, R.P. Department of Civil Engineering and Lassonde Institute, University of Toronto, Toronto, Canada ABSTRACT: We have developed different network approaches to complex patterns of frictional interfaces (contact areas developments). Network theory is a fundamental tool for the modern understanding of complex systems in which, by a simple graph representation, the elementary units of a system become nodes and their mutual interactions become links. With this transformation of a system to network space, many properties about the structure and dynamics of the system itself can be inferred. We map the real-time net contact areas to network configurations while we use similarity measures to link the nodes. In other words, we follow the possible collective deformation of contact areas as well as the characteristics of correlated elements. Here, we analyze the dynamics of static friction. We found, under the correlation measure, the fraction of triangles correlates with the detachment fronts. Also, for all types of the loops (such as triangles), there is a universal power law between nodes’ degree and motifs where motifs frequency follow a power law. This shows high energy localization is characterized by fast variation of the loops fraction. Also, this proves that the congestion of loops occurs around hubs. Furthermore, the motif distributions and modularity space of networks –in terms of within-module degree and participation coefficient- show universal trends, indicating an in common aspect of energy flow in shear ruptures. Moreover, we confirmed that slow ruptures generally hold small localization, while regular ruptures carry a high level of energy localization. We proposed that assortativity, as an index to correlation of node’s degree, can uncover acoustic features of the interfaces. We showed that increasing assortativity induces a nearly silent period of fault’s activities. Also, we proposed that slow ruptures resulted from within- module developments rather than extra-modules of the networks. Our approach presents a completely new perspective of the evolution of shear ruptures.

ARMA 12-322 Two-scale characterization and modeling of porous continua from discrete mechanics Andrade, J. E., Vlahinic, I., Lim, K.-W., Mital, U. California Institute of Technology, Pasadena, CA, USA ABSTRACT: A computational tool is proposed to utilize advanced visualization (e.g., X-ray CT and diffraction) that affords geosciences unprecedented access to sub-micron scales. This paper will focus on the multiscale nature of the coupled deformationdiffusion problems in porous rocks and soils and numerical issues related to connecting microstructural information to macroscopic properties for both solid and fluid constituents. We propose that the future of geomechanical modeling relies on incorporating advanced experiential techniques with unprecedented multiscale numerical modeling.

186 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-465 High Resolution Dual Modality (Neutron and X-ray) Imaging of Partially Saturated Sand and Direct Numerical Simulation Based on Realistic Microstructure Kim, F. H., Penumadu, D., and Gregor, J. University of Tennessee, Knoxville, TN,USA Kardjilov, N. and Manke, I. Helmholtz Center Berlin for Materials and Energy, Berlin, Germany Schulz, V. P. Baden-Wuerttemberg Cooperative State University Mannheim, Germany Wiegmann, A. Fraunhofer ITWM, Kaiserlautern, Germany ABSTRACT: High resolution neutron (~13.7 μm/voxel) and X-ray (~11.2 μm/voxel) tomography imaging of partially water saturated sand specimens was performed at Helmholtz Zentrum Berlin (HZB). Two different sand grain morphologies (round and angular) were used. Partially saturated silica sand is a three-phase material consisting of solid (Silica: SiO2), gas (air), and liquid (water) phases. Due to different attenuation characteristics of neutrons and X-rays to these three phases of interest, the neutron and X-ray images presented in this paper provided unique and complementary information. While the water phase contrast is wellidentified with the cold neutron images without using a contrast agent, the detailed structure of the silica sand phase is much clearly shown in the X-ray images due to low attenuation of the air/water phases to X-rays. A detailed description of neutron and X-ray tomography for visualizing and quantifying microstructure of an assemblage of sand grains is provided in this paper. An automatic approach to register the dual modality image information in the same coordinate is also demonstrated, and a technique to match different resolutions from neutron and X-ray imaging techniques is addressed. Direct numerical simulation technique based on a realistic pore geometry obtained from X-ray tomography of a dry sand specimen is also demonstrated. Full morphology model was used to obtain simulated capillary water distributions and a capillary pressure – saturation curve for the dry sand specimen with complex initial void size distribution in three dimensions based on the measured tomography data.

ARMA 12-670 Pore-scale deformation in high-porosity rocks Tjioe, M., Rahmani, H., and Borja, R.I., Department of Civil and Environmental Engineering, Stanford University, Stanford, CA 94305, U.S.A. ABSTRACT: High-porosity rocks have the greatest potential to undergo irreversible compaction due to pore collapse instability. Mechanisms of pore collapse include crystal plasticity in the mineral grains and grain crushing. We develop a mesoscopic scale modeling approach to investigate the interplay between these two fine-scale processes as they impact pore collapse. We focus on the first pore-scale process, namely, crystal plasticity in the mineral grains. We model the solid matrix microstructure using the finite element method with the voids represented explicitly by hollow inclusions. Irreversible deformation in the mineral grains is then modeled using rate-independent crystal plasticity theory.

187 46th US Rock Mechanics/Geomechanics Symposium Ses s ion 37: M nonitori g of Hydraulic Fracturing in Unconventional Reservoirs Wednesday, 27 June, 11:00 am – 12:30 pm Chairs: John Dudley, Marisela Sanchez

ARMA 12-287 A Numerical Evaluation of the Geomechanical Interactions Between a Hydraulic Fracture Stimulation and a Natural Fracture System Nagel, N. B., Sanchez-Nagel, M.A., Garcia, X., and Lee, B. Itasca Houston, Houston, Texas, USA ABSTRACT: Due to the low permeability of many shale gas reservoirs, multi-stage hydraulic fracturing in horizontal wells is used to increase the stimulated volume. However, each created hydraulic fracture alters the stress field around it, and subsequent fractures are affected by the stress field from the previous fractures, which results in higher net pressures, smaller fracture widths, and diminished microseismic emissions. The results of a numerical evaluation of the effect of stress shadowing, as a function of natural fracture and geomechanical properties, are presented, including a detailed evaluation of natural fracture shear failure (and, by analogy, the microseismicity) due to a created hydraulic fracture using both continuum and discrete element modeling approaches. The results show the critical impact that a created hydraulic fracture has on the shear of the natural fracture system, which in-turn, significantly affects the success of the stimulation. Furthermore, the results provide important insight into the mechanisms that generate the microseismicity that occurs during a hydraulic fracture stimulation.

ARMA 12-449 Emergence and Propagation of Delamination Cracks along the Casing- Cement Interface Wang, W., Dahi Taleghani, A., Louisiana State University, Baton Rouge, Louisiana, USA ABSTRACT: Pressure buildup and corrosion at the bottom of the well may result in significantly adverse consequences on the integrity of the cement and casing. Wellbore integrity is highly depending upon the integrity of the interfacial bond between the cement and the formation as well as the bonding between casing and cement. Hence, these interfaces may act as weak paths for failure and potential broaching under the effect of excessive pressure nearby the wellbore. To incorporate the role of the cement sheath on the well integrity, we used cohesive but porous interfacial elements to simulate emergence and possible development of the failure zone. An axisymmetric poroelastic finite element model is built, where cohesive interface elements with zero in-plane thickness are embedded along the interfaces between cement and formation rock and between cement and casing. Nonlinear traction separation law is used to predict fracture initiation. Damage propagation is predicted based on maximum energy release rate criterion, where the parameters for this model could be extracted from the ultrasonic CBL measurements. Using this model, the effects of excessive pore pressure magnitude and positions on wellbore integrity have been shown through some numerical examples. Moreover, the favorable effect of formation permeability on the delamination is investigated. The results show stress and pressure redistribution due to the initiation and propagation of delamination. The proposed approach provides a tool to understand the competition between different interacting physical processes for propagation of failure zone near the wellbore.

188 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-331 Simulation of Hydraulic Fractures and their Interactions with Natural Fractures Sesetty, V. Department of Petroleum Engineering, Texas A&M University, College Station, Texas, USA Ghassemi, A. Department of Petroleum Engineering, Texas A&M University, College Station, Texas, USA ABSTRACT: Modeling the interaction between hydraulic fractures and pre-existing natural fractures is important to geothermal and petroleum reservoir stimulation. This paper presents a boundary element- based method for modeling this interaction during hydraulic fracturing process. The model couples fluid flow to fracture deformation, and accounts for fracture propagation including the transition of natural fractures to a hydraulic fracture. The numerical model is used to analyze a number of stimulation scenarios with results presented in terms of the hydraulic fracture trajectory, fracture aperture, and pressures as a function of injection time. The injection pressure profile shows the complexity of the propagation process and its impact on stimulation design and proppant placement. In addition, sequential and simultaneous injection and propagation of multiple fractures is modeled. Results show that for sequential injection, the pressure needed to initiate the later fractures increases but the geometry of the fractures is less complicated than that obtained from simultaneous injection. It is also observed that when mechanical interaction is present, the fractures in sequential fracturing have a higher width reduction as the later fractures are formed.

ARMA 12-223 Application of the distinct-element method to investigate the influence of natural fractures and in-situ stresses on hydrofrac propagation Zangeneh, N. University of British Columbia, Vancouver, British Columbia, Canada Eberhardt, E., Bustin, R.M. University of British Columbia, Vancouver, British Columbia, Canada ABSTRACT: A hydraulic fracturing operation involves fluid injection into a naturally fractured rock mass. Yet the presence of these natural fractures and their influence on fracture propagation is often not accounted for in hydrofrac design calculations. Presented here are the results of a set of simulations carried out using the discontinuum-based distinct-element method. The simulations have been carried out applying a transient, coupled hydro-mechanical analysis to a naturally fractured rock mass. The inclusion of a voronoi tessellation scheme adds the necessary degrees of freedom to model the propagation path of a hydraulically driven fracture as a function of its interactions with the natural fracture network and in-situ stress state. The results show that key interactions develop with the natural fractures that influence the calculated stimulated volume through additional connected surface area and fracture dilation. These interactions also have the potential to decrease the size and effectiveness of the hydrofrac stimulation by diverting the injected fluid and proppant, and limiting the extent of the hydraulic fracture.

189 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-252 Initiation and Propagation of Secondary Cracks in Thermo- Poroelastic Media Tran, D. Computer Modelling Group Ltd., Calgary, AB, Canada Settari, A. University of Calgary, Calgary, AB, Canada Nghiem, L. Computer Modelling Group Ltd., Calgary, AB, Canada ABSTRACT: When cold fluid is injected into a hot reservoir, secondary cracks may be created perpendicular to the main crack. The difference between the temperature of the fluid in the main crack and the temperature of the formation along with the increase of pressure due to poroelasticity cause a decrease of initial effective stress in the direction parallel to the main crack. The secondary crack is initiated when the value of the minimum effective stress is lower than the rock tensile strength. This crack continues propagating into the formation when constant pressure and temperature are maintained at the main crack surface. The effect of flow into the secondary crack is also examined. Crack initiation, crack width and crack length are discussed. A 2D plane strain simulation model used for this study is presented and its results for a variety of conditions are discussed such as initial effective stress in the formation, Young’s modulus, leak-off, no leak-off and temperature difference. The results demonstrate that i) thermal stresses are the dominant cause of secondary fracturing, and ii) the initiation and propagation of secondary cracks is possible even in short term injection typical of hydraulic fracturing treatments.

ARMA 12-538 Direct measurement of contact area and seismic stress along a sliding interface Selvadurai, P.A. University of California Berkeley,CA,94720 USA Glaser, S.D. University of California Berkeley,CA,94720 USA ABSTRACT: Seismic stress drop is an important metric for understanding the kinematics of injection- induced frictional sliding. Seismic stress drop is commonly estimated from Brune’s corner frequency model and the assumption of a double couple source rather than from direct knowledge of the size of the slipping junction, which is impractical to impossible in the field but can be achieved in the laboratory. A direct shear experiment comprised of PMMA sliding blocks were used as an analog of weak, compliant rock interfaces that might exhibit contact melting. A pressure-sensitive film was employed to localize and size, and measure normal stress upon contact junction. The film allowed measurement of contact asperities with spatial resolution of 5 μm x 5 μm, and contact stresses to within ± 1.5 Pa. Final estimation of junction area were made optically using digital image processing techniques. Initially the surface is repeatedly loaded, at 3.5 MPa for 60 s loading cycles, where real contact area increased ~14 to 48% in low and high normally stressed regions, respectively, in three subsequent tests. These changes were mainly attributed to the healing of the interface; a process commonly observed in rock at scale. Subsequently, the slider was subjected to an impulse shear load, which resulted in full rupture of the interface. Spatial measurements of pre- and post-slip contact area show a ~ 233.6 % increase in low stress contacts (12-17 MPa) and ~ 99.8 % decrease in high stress contacts (37.5-50 MPa). Visualization of the interface, pre- and post-slip, shows evidence of micromechanical processes and elastic-plastic interactions at the junction level.

190 46th US Rock Mechanics/Geomechanics Symposium Ses s ion 38: Behavior of High Porosity Materials Wednesday, 27 June, 11:00 am – 12:30 pm Chairs: Brian Crawford, Yueming Liang

ARMA 12-143 Soil model for rock properties prediction in exploration settings Nikolinakou M.A. Bureau of Economic Geology, The University of Texas at Austin, Texas, USA Chan, A.W. Shell Exploration & Production Company - Upstream Americas, New Orleans, Louisiana, USA ABSTRACT: Pre-drill rock properties, pore pressure and reservoir quality are key factors to exploration success. Typical workflows are based on burial histories, stress evolution and thermal history of the basin and have been successfully deployed in most modern deltaic environments. However, for sands that have experienced complex stress histories, the conventional approach does not provide accurate predictions. Several authors have proposed pragmatic ways to capture the effect of lateral strain into the workflows. These soil-mechanics inspired approaches appear to provide a better estimate of rock and fluid properties than the conventional workflows but several questions regarding their validity remain unaddressed. We conducted several numerical experiments to evaluate the potential impact of complex stress histories on the compaction behavior of poorly consolidated sediments. We used different material models to predict the volumetric strains that develop along K0 consolidation paths. Based on the results, we evaluated the pragmatic stress modifier approaches that translate the three-dimensional in situ stress state into the one- dimensional stress input of the existing simulators.

ARMA 12-182 True Triaxial Compression Tests on a Medium-High Porosity Sandstone and the Effect of the Intermediate Principal Stress on Strength and Fault Angle Ma, X. Geological Engineering Program, University of Wisconsin, Madison, WI, USA ([email protected]) Haimson, B. Geological Engineering Program, University of Wisconsin, Madison, WI, USA ([email protected]) ABSTRACT: True triaxial tests have been carried out on the quartz-rich Coconino sandstone, (porosity 17.5%) to investigate the effect of the intermediate principal stress (s2) on strength and fault angle. In all tests the least and intermediate principal stresses (s3 and s2) were maintained constant, while the largest stress (s1) was raised until failure (at s1,peak), and beyond. For each constant s3, s2 was varied between s3 and s1. Rock strength for a given s3 increases with s2, reaches a peak (up to 10% higher than when s3 = s2), and then gradually drops, but when s2 = s1, it is still higher than the s1,peak when s2 = s3. Brittle failure developed a single fault at lower s3, to multiple parallel and conjugate faults at s3 ≥ 80 MPa. Fault angle under s3 = s2 loading decreased with the rise in s3 from ~80° at s3 = 0 to ~50° at s3 = 150 MPa. However, fault angle increased by up to 15° as s2 was raised above s3. Both strength and fault angle dependence on s2 was lower than in tested crystalline rocks. The results of these tests contradict the Mohr-Coulomb criterion, which neglects s2 effect on strength, and predicts a unique fault angle for a given rock.

191 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-286 Influence of effective stress coefficient on mechanical failure of chalk Alam, M.M. and Fabricius, I.L. Technical University of Denmark, Lyngby, Denmark Hjuler, M.L. and Christensen, H.F. Danish Geotechnical Institute, Lyngby, Denmark ABSTRACT: The Effective stress coefficient is a measure of how chalk grains are connected with each other. The stiffness of chalk may decrease if the amount of contact cements between the grains decreases,

which may lead to an increase of the effective stress coefficient. We performed CO2 injection in chalk, as this process could affect the grain contact cement. If this happens, the effective stress at the grain contacts in a reservoir will change according to the effective stress principle of Biot. In a p′-q space for failure analysis, we observed that a higher effective stress coefficient reduces the elastic region and vice versa. However, as the effective stress working on the rock decreases with increased effective stress coefficient, the reduction of elastic region will have less effect on pore collapse strength if we consider the change in the effective stress coefficient. This finding will help estimate a more precise failure strength of chalk during changed stress state and under the influence of chemically reactive fluids during production of hydrocarbon and geological storage CO2.

ARMA 12-335 Modeling the onset of bifurcation in porous sedimentary rocks Buscarnera, G. Northwestern University, Evanston, IL, USA ABSTRACT: The mechanical response of porous sedimentary rocks is the outcome of a complex interaction between their granular skeleton and the cement matrix originated by lithification. Crustal movements and human activities alter this original microstructure, modify the hydro-mechanical properties and promote the development of localized deformation mechanisms. This paper focuses on the study of mechanisms of localized compaction. For this purpose, an elastoplastic constitutive model for porous sedimentary rocks is combined with a mathematical theory for predicting the initiation of bifurcation processes in elastoplastic continua. The attention is focused on the role played by the mechanical properties of the rock on failure and bifurcation. After discussing the mechanical response observed in typical sedimentary rocks, the paper illustrates the interplay between the material properties, the static-kinematic conditions associated with failure mechanisms and the bifurcation of the predicted response. It is shown that the potential for compactive bifurcation at high confinement evolves during loading and requires prior definition of the parameters related with the potential for pore collapse. The paper provides a modeling strategy to address technical problems involving porous rocks and identifies a set of material properties that can have a major effect on the geomechanical characterization of porous sedimentary formations.

ARMA 12-430 Experimental Study and Modeling of the Hydromechanical Behavior of a Weakly Consolidated Sandstone under Proportional Triaxial Compression Stress Paths 1,2 Nguyen, V.H., 1 Gland, N., 1 Dautriat, J., 2 David, C., 1Guélard, J., and 2 Wassermann, J. 1 IFP Energies nouvelles, 1-4 Av. de Bois Préau, 92852 Rueil-Malmaison Cedex, France. 2 Université de Cergy-Pontoise, Géosciences & Environnement Cergy, 5 mail Gay Lussac, 95031 Cergy- Pontoise, France.

192 46th US Rock Mechanics/Geomechanics Symposium ABSTRACT: Hydromechanical tests under different stress paths (hydrostatic and proportional with constant ratio of vertical to horizontal stress rates) have been performed on a weakly cemented layered sandstone, the Otter Sherwood Sandstone, outcrop analog of the Sherwood reservoir of the Wytch Farm oil field (UK). The elastic and plastic deformation regimes are well identified and the determined yield stresses are fitted using the modified Cam-clay and Elliptic Cap models for all the observed onsets of plastic yielding. Both vertical and horizontal permeability have been measured during loading. For the horizontal flow, the geometrical and anisotropy factors were determined using Finite Element simulations in order to calculate the correct horizontal permeability. Permeability evolutions follow closely the material deformation and are controlled by both volumetric and shear strains. It is possible to infer the effect of the mean pressure and/or the deviatoric stress on the permeability evolution by building isopermeability maps in the stress space. Finally, an application of elasto-plastic modeling to predict the hydromechanical behavior of this sandstone is presented. This approach allows a satisfying prediction of the permeability evolution with stresses, using an exponential function of an effective strain.

ARMA 12-347 Heterogeneity within deformation bands in sandstone reservoirs Torabi, A. Uni CIPR, Uni Research, Bergen, Norway Alikarami, R. Department of Earth Science at UiB and Uni CIPR, Uni Research, Bergen, Norway ABSTRACT: We have investigated the variation in physical and mechanical properties along cataclastic deformation bands exposed in the damage zone of Moab Fault in Waterfall Canyon, Utah. In our research, we have combined field observations including measurements of thickness, permeability (using a Tiny-Perm II) and rock hardness (using a Schmidt hammer) with laboratory measurements of the elastic modulus of the natural samples and microscopic analysis of the rock. In the study area, total local band thickness can vary from 0.5 mm (a single band) to 60 mm (a cluster of bands) in a short distance (cm). Permeability varies up to two orders of magnitude along the bands and shows an inverse relation with the band thickness. Our ultrasonic laboratory measurements reveal higher elastic moduli within bands than the adjacent undeformed host rock, indicating the dense microstructure of the band attributed to cataclasis and porosity reduction. We have employed different approaches to calculate the propagation energy release rate of the bands and found out that the thickness variation along bands can be attributed to variable stress and propagation energy release along the bands. Based on our calculation, the total propagation energy of a single cataclastic band would be very low (~2.5 kJ/m2).

Ses s ion 39: N umerical Modeling of Crack Growth Wednesday, 27 June, 11:00 am – 12:30 pm Chairs: Jianlin Wang, Gang Li

ARMA 12-450 Three-dimensional Boundary Element Modeling of Fractures under Gravity Load Nikolski, D.V. University of Minnesota, Minneapolis, MN, USA Mogilevskaya, S.G. and Labuz, J.F. University of Minnesota, Minneapolis, MN, USA

193 46th US Rock Mechanics/Geomechanics Symposium ABSTRACT: A new three-dimensional boundary element technique is presented for evaluating gravitational stresses in rock containing a single or multiple fractures. The boundary element analysis is based on the use of the integral equation written for the tractions on the boundaries, including internal boundaries from an excavation and existing discontinuities.

ARMA 12-179 Modeling mixed-mode fracture propagation in 3D Meng, C. and Pollard, D. D. Department of Geological and Environmental Sciences, Stanford University, Stanford, CA 94305-2115 USA. ABSTRACT: A planar fracture when subjected to sufficient tensile and shear stresses will propagate off-plane, known as mixed-mode propagation. Predicting the fracture path relies on the propagation criteria. The criterion we present scales the propagation magnitude and direction with the near-tip tensile stress in form of vectors that originate from the fracture tip-line. Boundary element method (BEM) enables us to calculate the near-tip stress field of an arbitrary fracture. We feed the near-tip stress to the propagation criterion to determine the propagation vectors. We grow the BEM mesh by adding new tip-elements whose size and orientation are given by the propagation vectors. Then, we feed the new mesh back to BEM to calculate the new near-tip stress. By running BEM and the propagation criterion in a loop, we are able to model 3D fracture propagation. We use analytical Eshelby’s solution that evaluates near-tip stress of an ellipsoidal fracture to validate the BEM results.

ARMA 12-213 A multi-modal approach to 3D Fracture and Fragmentation of Rock using Impulse-Based Dynamics and the Finite Element Method Paluszny, A., Tang, X.H. and Zimmerman, R.W. Department of Earth Science and Engineering Imperial College, London, United Kingdom ABSTRACT: A numerical method combining the finite element method (FEM) and impulse-based dynamics is proposed for the simulation of 3D fracture and fragmentation. As opposed to existing methods, fragments are not represented as a conglomeration of primitive shapes; instead, their geometry is represented using solid modeling techniques. This allows for continuum-mechanics-based fracture propagation analysis to be carried out within each fragment, with fragment interaction and movement simulated using impulse-based dynamics. This approach models multi-body interaction of non-convex 3D objects which fall, collide, and fragment using impulse-based dynamics, as opposed to a penalty-based method. Instead, object trajectories are used to estimate time-of-impact, and contact between bodies is modeled by collisions at contact locations. This approach allows material properties to be explicitly defined at the macro-scale. A 3D fracture engine models fracture propagation in the individual 3D continua based on local stress intensity factor measurements using the reduced virtual integration technique, as well as decoupled geometry and mesh representation, and on the evaluation of local failure and propagation criteria. Fractures that reach free boundaries lead to further fragmentation. The framework, presented as a multi-modal toolkit, is suitable for meso-scale simulations, and is demonstrated by a mining-specific block caving application.

194 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-593 Study of stress and strain fields around a flaw tip in rock Gonçalves da Silva, B. Massachusetts Institute of Technology, Cambridge, MA, United States of America Einstein, H. H. Massachusetts Institute of Technology, Cambridge, MA, United States of America ABSTRACT: The study of crack initiation and propagation is important for the understanding of rock mass behavior, which affects many rock engineering problems. Such studies can be done experimentally in the laboratory or in the field, or numerically. Here, a numerical study is presented, in which the stress and strain fields around a flaw tip were analyzed using the finite element code, ABAQUS, to better understand the processes involved in crack initiation and propagation. Double-flaw geometries were modeled with ABAQUS with the intent of identifying the differences between stress and strain fields around the flaw tip, relating the stress and strain fields to crack initiation and propagation, and comparing numerical results with those of tests performed on gypsum and marble specimens. Both stepped and coplanar flaw geometries were studied, as well as different stages of crack propagation were modeled based upon laboratory results. For the stepped flaws, both stress and strain field analyses correctly explain wing and shear crack initiation and propagation in gypsum and marble. Furthermore, the two analyses are also capable of describing reasonably well tensile and shear coalescence in gypsum and marble, respectively. For the coplanar flaws, it was found that the stress field analysis is capable of explaining wing crack initiation and propagation observed in tests on gypsum and marble. It is also capable of explaining shear coalescence observed in gypsum, but it is not capable of describing the indirect coalescence observed in marble. The strain field analysis is not only capable of satisfactorily explain what the stress field analysis explains, but it also correctly describes the indirect coalescence that occurs in marble specimens.

ARMA 12-339 2D Frictional crack initiation and propagation analysis using the numerical manifold method Wu, Z. and Wong, L.N.Y. Nanyang Technological University, Singapore ABSTRACT: By using both a physical mesh and a mathematical mesh to formulate a physical problem, the numerical manifold method (NMM) can lead to a very simple meshing task, which allows a direct capture of the discontinuities across the crack surfaces. In this study, verification of the stress intensity factor ahead of flaw tips is first performed to demonstrate that the NMM is capable of analyzing crack problems with a high degree of accuracy. Based on the contact technique of the NMM and the incorporation of the Mohr-Coulomb crack initiation criterion, the effects of the friction and cohesion on the crack growth from a closed flaw (crack) under compression are investigated. The NMM can not only accurately predict the pure tensile or pure shear crack growth, but also satisfactorily predict the development of mixed shear-tensile crack types. The crack type is strongly influenced by the ratio of the compressive strength σ( c) to the tensile strength (σt) of the material. When the σc/σt ratio is between 5 and 7, the mixed type of cracks will typically develop. However within this range of σc/σt ratio, the lateral confining stress, the friction angle between the flaw surfaces and the inclination angle of the flaw may also significantly affect the crack type developed. Large and small flaw inclinations favor the development of oblique-type cracks and coplanar-type cracks respectively. The secondary cracks are not necessarily shear cracks but can also be tensile cracks. This study thus demonstrates the advantages and strong potential of the NMM in dealing with continuous-discontinuous problems.

195 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-190 A Finite-Element Method for Modeling Fluid-Pressure Induced Discrete-Fracture Propagation using Random Meshes Bishop, J. E., Martinez, M.J., and Newell, P. Sandia National Laboratories, Albuquerque, NM, USA ABSTRACT: A finite-element method is proposed for simulating the propagation of discrete fractures resulting from fluid injection within a heterogeneous media. The method only allows new fracture surfaces to nucleate at the inter-element faces of a random mesh. The potential crack paths within the random mesh are viewed as instances of realizable crack paths within a random field representation of the continuum material. Mesh convergence of fracture simulations is viewed in a weak, or distributional sense. The explicit facet representation of fractures within this approach is advantageous for modeling coupled fluid-flow within the evolving fracture network. Flow within the fractures is modeled using Reynold’s lubrication approximation. Within the flow solution the fractures are represented as two-dimensional surfaces with a spatially varying aperture. This fluid-structure coupling has been applied in both the dynamic regime using explicit time stepping and in the quasi-static regime using a dynamic relaxation method. Applications of interest for this coupled multi-physics model include carbon sequestration, engineered geothermal systems, and hydraulic fracturing. For carbon sequestration, this modeling approach is being used to improve our understanding of potential leakage scenarios through the caprock and possible mitigation strategies.

Ses s ion 40: F luid-induced Stabilization and Destabilization of Fractures and Faults Wednesday, 27 June, 11:00 am – 12:30 pm Chairs: Seiji Nakagawa, Hide Yasuhara

ARMA 12-603 Evolution of Induced Seismicity Due to Interactions between Thermal, Hydraulic, Mechanical and Chemical Processes in EGS Reservoirs Izadi, G., Elsworth, D. Department of Energy and Mineral Engineering, EMS Energy Institute and G3 Center, Pennsylvania State University, University Park, Pennsylvania, USA ABSTRACT: We explore the complex interaction of coupled thermal, hydraulic, mechanical and chemical (THMC) processes that influence the evolution of EGS reservoirs in general, and in particular with reference to strong, low-permeability reservoirs with or without relic fracturing. We define and describe dominant behaviors that evolve with the evolution of the reservoir: from short-term stimulation through mid-term production and culminating in long-term decline. The injection of fluid under pressure in a rock mass may change the effective stress at early times and result in micro seismicity induced by shear events on reactivated fractures. Changes in thermal stress and chemical changes in the mid- to long-term injection period may also generate seismic activity at later times. In most geothermal reservoirs the induced seismicity results from fluid injection and migrates within the reservoir with time as driven by the various interactions of thermal, hydraulic, mechanical and chemical processes. These processes migrate through the reservoir as fronts at a variety of different length-scales and timescales. We use a continuum model of reservoir evolution subject to coupled THMC processes to explore the evolution of stimulation- and production-induced seismicity in a prototypical EGS reservoir. The model which is discussed here is capable

196 46th US Rock Mechanics/Geomechanics Symposium of accommodating changes in stress that result from change in fluid pressure as well as thermal stress and chemical effects. This model is applied to both a single injector and doublet geometry to explore the spatial and temporal migration for triggering of seismicity as stimulation evolves into production. We use varied fracture network geometries in our models to examine various stimulation and production scenarios. The individual models are realized by different fracture density, fracture distribution (~1m to 100m) and spacing between fractures (~1m to 10m). The approach is successfully calibrated against short-term observations in the Cooper Basin (Australia) and applied to explore the expected evolution of moment magnitude and the triggering of seismicity. Modeled b-values (~0.68 to 0.72) at different locations and times are in good agreement with observations (~0.7 to 0.8). For longer injection periods, predicted changes in energy release generate moment magnitudes which vary from -2 to 2 for small to large fractures. Tracking of the hydrodynamic and thermal fronts illustrates a transition in the triggering of seismicity with time. At early time (days to months) – higher flow rates driven by the fluid pressure result in larger magnitude events. For later time (>1year) thermal drawdown and potentially chemical influences principally trigger the seismicity but result in a reduction in both the number of events and their magnitude. As a result of this decrease in the number of events (both large and small) both b- and a-values decrease with time.

ARMA 12-151 Long-term Evolution of Rock Permeability in Sandstone and Mudstone under Pressure- and Temperature-controlled Conditions Yasuhara, H. and Kinoshita, N. Ehime University, Matsuyama, Japan Nakashima, S. Yamaguchi University, Ube, Japan Kishida, K. Kyoto University, Kyoto, Japan ABSTRACT: A suite of permeability experiments on intact rocks in sandstone and on a single fracture in siliceous mudstone has been conducted under confining pressures of 3 – 15 MPa, and at temperatures of 20 – 90 °C for several hundred days in each experiment. For the mudstone experiments, oil-flow experiments are also conducted to examine the effect of mineral dissolution on the flow behavior – the oil-saturated condition refrains from the mineral dissolution and enables to certify if mechanical creep occurs under the stressed conditions. Evolution in permeability and dissolved mass fluxes were periodically measured to examine the flow behavior under stress and temperature conditions. In sandstone, the permeability of intact rocks little changed until a couple of hundred days, then started to increase with time. In mudstone, the permeability in a single fracture monotonically decreased with time and reached a quasi-steady state within one month. However, it started to increase with time after ~100 days. This augmentation in the permeability in sandstone and mudstone should be attributed to mineral dissolution within void spaces.

ARMA 12-154 Experimental study on stress wave interaction with rock fractures Wu, W., Zhang, Q., Zhu, J. Ecole Polytechnique Fédérale de Lausanne (EPFL), School of Architecture, Civil and Environmental Engineering, Laboratory of Rock Mechanics (LMR), Lausanne, Vaud, Switzerland ABSTRACT: A split Hopkinson rock bar is developed and utilized to characterize the interaction between stress wave and artificial rock fractures. The non-filled contact fracture is assumed to be the direct contact interface between the incident bar (rear end) and the transmitted bar (front end), while the

197 46th US Rock Mechanics/Geomechanics Symposium filled fracture is simulated by inserting a layer of filling materials, e.g., sand and clay, in the opening at the interface of two bars. The experimental results show that the non-filled contact fracture displays stress equilibrium and displacement discontinuity, however, the filled fracture exhibits stress and displacement discontinuities. The transmission coefficient for the non-filled contact fracture increases with higher loading rate. The filled fracture displays lower strength and larger deformation than the non-filled contact fracture, which likely induces the instability of rock masses. The transmission coefficient for the filled fracture decreases with increasing thickness of the filling materials, and the transmission coefficient for the sand-filled fracture is larger than that for the clay-filled fracture. It is found that stress wave attenuate much highly due to the large fracture aperture and the low stiffness filling materials.

ARMA 12-170 Bubble nucleation in groundwater triggered by seismic stimulation: A laboratory study Crews, J.B. Desert Research Institute, Reno, NV, USA University of Nevada, Reno, NV, USA Cooper, C.A. Desert Research Institute, Reno, NV, USA ABSTRACT: A laboratory study is undertaken to explore the potential for seismic waves to drive bubble nucleation in groundwater formations. A Hele-Shaw cell containing a supersaturated carbonic acid solution is subjected to mechanical pressure perturbations of varying magnitude, and the resulting changes in dissolved gas concentration are found to be qualitatively consistent with a conceptual model

based on low-pressure CO2 solubility data and a first-order approximation of the bubble nucleation mechanism. A correlation between the change in dissolved gas concentration and the magnitude of the pressure perturbation is observed, but with a different constant of proportionality than that predicted in the conceptual model.

ARMA 12-297 Modeling and Numerical Simulation for Coupled Flow and Geomechanics in Composite Gas Hydrate Deposits Kim, J. Earth Sciences Division, Lawrence Berkeley National Laboratory. Berkeley, CA, USA Moridis, G. J. Earth Sciences Division, Lawrence Berkeley National Laboratory. Berkeley, CA, USA ABSTRACT: We investigated composite gas hydrate deposits where the fine scale single porosity model for geomechanics was difficult to apply. To this end, the multiple porosity model was used for the composite reservoirs, upscaling geomechanics but keeping the fine scale for flow. We analyzed the numerical results of the multiple porosity model, comparing them with the reference solutions, the fine scale single porosity system. From the comparison, the multiple porosity model successfully approximated the reference model, providing good accuracy for pressure, saturation, effective stress, and subsidence fields and reducing geomechanical computation. In particular, when geomechanical properties of an upscaled gridblock were the same as those of its subelements, the results of flow and geomechanics between the reference and multiple porosity models were almost identical. Thus, the multiple porosity model can be useful for composite gas hydrate reservoirs.

198 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-400 Coupled Continuum Modeling of Fracture Reactivation and Induced Seismicity during Enhanced Geothermal Operations Wassing, B.B.T., van Wees, J.D. and Fokker, P.A. TNO, Utrecht, The Netherlands ABSTRACT: We developed a coupled code to obtain a better understanding of the role of pore pressure changes in causing fracture reactivation and seismicity during EGS. We implemented constitutive models for fractures in a continuum approach, which is advantageous because of the ease of integration in existing geomechanical codes (FLAC3D), the speed of the calculations and the flexibility of the fracture representation. For modeling the mechanical behavior of the fracture zone the softening ubiquitous joints model was used with random strength properties for the fracture zone. We implemented a hyperbolic deformation with effective stress for the reversible tensile fracture opening, and a linear relationship between plastic shear strain and irreversible fracture opening. The effective permeability of the fracture network was described by a cubic dependence on the fracture aperture. We created a model inspired on the Soultz-la-Forêts GPK3 injection well, intersected by a dominant fracture zone. Due to injection of water, the model reproduced reactivation of the fracture zone and we observed the growth of a zone with large directional permeability. The model was used to perform a sensitivity analysis on parameters like injection rates, in-situ stress regime, fracture strength, and frictional weakening. This allowed us to evaluate the trends of their impact on fracture reactivation, including reactivated area, seismic moment and moment magnitudes.

Ses s ion 41: I nteraction of Natural and Induced Fractures and Stimulated Reservoir Volume Wednesday, 27 June, 2:00 pm – 3:30 pm Chairs: Doug Blankenship, Ahmed Ghassemi

ARMA 12-386 Experiments on Permeability Evolution with Temperature of Oil Shale Yang D. Energy and Mineral Engineering and G3 Center, PSU, University Park, PA, USA 16801 Institute of Mining Technology, Taiyuan university of Technology, Taiyuan, China 030024 Elsworth, D. Energy and Mineral Engineering and G3 Center, PSU, University Park, PA, USA, 16801 Kang Z.Q. and Zhao Y.S. Institute of Mining Technology, Taiyuan university of Technology, Taiyuan, China 030024 Zheng B.S. Energy and Mineral Engineering and G3 Center, PSU, University Park, PA, USA 16801 ABSTRACT: In this paper we use a permeability measuring system developed by Taiyuan University of Technology measure the permeability of oil shale to temperatures in the range 200 to 500°C. Two samples have been tested in this system with N2 as permeant. The samples are from the Daqing (northeastern China) and Changqing (western China) oil shale deposits. The experiments show that temperature has a significant impact on the permeability of oil shale. With different initial permeability of these two samples,

199 46th US Rock Mechanics/Geomechanics Symposium temperature thresholds are shown to be important in the evolution of the permeability. For one sample, permeability first increases and then decreases to a minimum at 400°C (Daqing). For the second sample, the permeability decreases to a minimum at 450°C and then increases significantly after this threshold (Changqing). We conclude from these observations that the transport properties of shale are influenced by the complex interaction of mechanical and chemical processes activated at elevated temperatures.

ARMA 12-436 Simulation of fracture clusters in unconventional reservoir using fully coupled thermo-hydro-mechanical FEM analysis Min, K.S., and Ghassemi, A. Harold Vance Department of Petroleum Engineering, Texas A&M University, College Station, TX 77840, USA ABSTRACT: Understanding of interactions between in-situ stresses, injection fluid pressure and fracture propagation is important for unconventional reservoir development that relies on fracture network design. In this paper, hydraulic fracturing process is investigated using fully coupled Thermo-Hydro- Mechanical analysis. The influences of coupled processes on fracture propagation are investigated using continuum damage mechanics along with the embedded crack element approach. Damage mechanics describes the inelastic response of micro-crack growths, while the macroscopic fracture opening, shear slippage, and the fracture surface friction effects are described by the equivalent crack element modeling. The numerical model of passive/active crack element provides for explicit resolution of discontinuous shear fracturing behavior of fracture clusters by constructing crack tracking algorithm. In this paper, we focus on the fluid-mechanical coupling for various perforation cases and studied hydraulic fracture initiation and propagation using 2D/3D numerical modeling. Residual thermal effects on unconventional reservoir are also important, so the study of thermal effects is remained for future improvement.

ARMA 12-530 Numerical modelling of thermo-hydro-mechanics involving AMR-based thermal fluid flow and geomechanics: application to thermal EOR Guy, N., Enchéry, G. and Renard, G. IFP Energies nouvelles, Rueil-Malmaison, F-92852, France ABSTRACT: Enhanced Oil Recovery methods can involve complex physical phenomena such as thermal and multiphase fluid flow and rock-fluid interactions with geomechanical effects. The numerical modelling of these recovery methods can induce significant cpu time. Here a numerical procedure that performs coupled thermo-hydro-mechanical simulations in an efficient way is presented. This procedure relies on an iterative coupling between a thermal reservoir simulator based on a finite volume method and a geomechanical one based on a finite element method. The coupling method [1, 2] is particular; it allows the use of separate grids for the geomechanical and the thermal fluid flow simulations in order to decrease cpu time. A strong enhancement of the procedure presented here is that it is adapted to allow the use of Adaptive Mesh Refinements (AMR) for the thermal fluid flow simulations in order to further decrease cpu time. The considered AMR method [3] provides a relevant description of the fluid and thermal fronts. The efficiency of this coupling procedure is illustrated on a synthetic but realistic test case involving Steam Assisted Gravity Drainage (SAGD) method. The results show that the proposed modelling procedure provides relevant results and important decrease of the mesh sizes.

200 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-642 Gas Production Induced Stress and Permeability Variations in Coalbed Methane Reservoirs Liu, S. and Harpalani, S. Southern Illinois University, Carbondale, IL, USA ABSTRACT: A sound knowledge of stress and coal cleat permeability, both varying with continued gas production from coalbed methane (CBM) reservoirs, is critical in order to determine how to best produce the reservoir. CBM reservoirs are unique due to their exhibiting shrinkage of coal matrix associated with release of gas, resulting in increased permeability. This paper describes the work carried out focusing on the stress and cleat permeability variations as a function of declining reservoir pressure. A new experimental technique was developed to estimate the variation of permeability and monitor the stress evolution under best replicated in situ condition, namely the uniaxial strain. The experimental results showed that decreasing reservoir pressure resulted in a significant decrease in horizontal stress and increased permeability for methane. The horizontal stress decreased linearly for depletion. Using the laboratory established permeability trend, cleat compressibility was estimated by application of the exponential relationship between changes in effective stress and permeability. The results showed that the cleat compressibility was not a constant during the course of depletion and a bi-model variation was able to describe the variation well.

ARMA 12-425 Radial cracking of a borehole by pressure and thermal shock Tarasovs, S. Texas A&M University, College Station, TX, 77843 Institute of Polymer Mechanics, University of Latvia, Riga, Latvia Ghassemi, A. Texas A&M University, College Station, TX, 77843 ABSTRACT: The problem of radial crack propagation from a borehole is of increasing interest in geothermal and petroleum applications. The injection of cold fluid into hot rocks may cause the formation of several cracks emanating from the borehole and growing a significant length. We study this process using a numerical model that is based on the complex hypersingular integral equation. The model is used to study the conditions necessary for the growth of radial cracks. The influences of the internal pressure, thermal stress, and the in-situ stress anisotropy on the cracks’ lengths are investigated by taking into account the interaction of multiple fractures. Results show that a complex pattern of cracks may form in the vicinity of the wellbore, however, only a few cracks usually grow to a significant length as the cooling front moves into the formation.

ARMA 12-433 Natural Fractures Characterization in a Carbonate Heavy Oil Field Shafiei, A. and Dusseault, M.B. Department of Earth & Environmental Sciences, University of Waterloo, Waterloo, Ontario, Canada ABSTRACT: Fracture system characteristics in naturally fractured carbonate reservoirs seem central to any development plan. In this article, a combination of outcrop studies, core studies, seismic and borehole image logs were used to charactize natural fractures in a naturally fractured carbonate heavy oil field in Iran. A field study of fractures at the surface and in the sub-surface was conducted and regional tectonic fracture systems characterized. Three general orientations of mainly vertical and sub-vertical fractures

201 46th US Rock Mechanics/Geomechanics Symposium were identified and characterized over the crestal area. Two main fracture sets, one shear conjugated and the other clearly a tensile fracture set, were identified. The frequent shear fractures resulted from compressional tectonics forces. This type of fracture is normally tight and impermeable but in this field they have largely been opened as the stress regime changed to a tensile tectonic regime by bending, accompanied by uplifting or drag folding, thus creating high-permeability fractures. Borehole image logs proved as useful tools in identification and characterization of natural fractures in the study area. Results obtained from this study can be implemented in optimizing well placement, reservoir simulation, hydraulic fracture design, and evaluation of studied heavy oil field for appropriate production technology.

Ses s ion 42: C ase Studies in Hard Rock Mining Wednesday, 27 June, 2:00 pm – 3:30 pm Chairs: David Beck

ARMA 12-174 Excavation in hard rock under high in-situ stress at Rana Gruber, Norway Trinh, Q.N. SINTEF, Trondheim, Norway ABSTRACT: The Rana Gruber is an iron mine in the North of Norway, 30 km east of Mo I Rana. The mine is located in a foliated gneiss host rock, and the ore body is about 70 m wide and more than 300 m deep. The mining method now is sub-level caving. Many infrastructures have been developed, and experience during the development is that the rock mass in this area can be classified as hard and brittle rock. A high stress condition is also indicated in the area. Combination of the brittle hard rock and high in-situ stress causes rock bursts of different magnitudes to occur from time to time, putting the excavation and rock support at risk. This paper describes a typical failure associated with high stress together with the excavation and rock support used.

ARMA 12-524 Numerical analysis of room closure rate in an underground potash mine Rahnama, A. Department of Mineral Engineering, New Mexico Institute of Mining and Technology, Socorro, NM, USA Mojtabai, N. Department of Mineral Engineering, New Mexico Institute of Mining and Technology, Socorro, NM, USA Razavi, M. Department of Mineral Engineering, New Mexico Institute of Mining and Technology, Socorro, NM, USA Fakhimi, A. Department of Mineral Engineering, New Mexico Institute of Mining and Technology, Socorro, NM, USA ABSTRACT: A combination of field monitoring, Close Range Photogrammetry (CRP) and 3-dimensional numerical modeling is used in an underground potash mine to study the closure rates in the main panel as well as in large underground storage areas. The main interests is to predict the closure rate and total displacement in the storage area where a large stacker is operating. Due to the considerable dimensions of the storage area, conventional methods of monitoring are not feasible. Numerical modeling was selected as a tool to predict the convergence. A 3-dimensional numerical model using FLAC3D computer program

202 46th US Rock Mechanics/Geomechanics Symposium was employed. The two-component power law model has been selected to express the creep behavior of potash and surrounding salt formations. There is a limited data on the value of n and A parameters in the power creep law. Numerical results are compared with the field measurements in the panels. CRP is being employed as well, which allows measuring the displacement on a cross section between the pillars. This type of analysis provides useful information on both lateral and vertical displacements of the pillars. All structural features, such as clay layers and beddings as well as rock bolts are included in the model.

ARMA 12-599 Rock support design in burst-prone ground utilizing an interactive design tool Cai, M. Bharti School of Engineering, Laurentian University, Sudbury, Ontario, Canada Kaiser, P.K. and Duff, D. J. Centre for Excellence in Mining Innovation, Sudbury, Ontario, Canada ABSTRACT: As mining and civil tunneling progresses to depth, excavation-induced seismicity and rockburst problems increase and cannot be prevented. As an important line of defense, ground control measures and burst-resistant rock support are used to prevent or minimize damage to excavations and thus to enhance workplace safety. Rock support in burst-prone ground differs from conventional rock support where controlling gravity-induced rockfalls and managing shallow zones of loose rock is the main target. Rock support in burst-prone ground needs to resist dynamic loads and large rock dilation due to violent rock failure. After reviewing the rockburst phenomenon, types of rockbursts, damage mechanisms, and rockburst support design acceptability criteria, this paper introduces an interactive design tool for conducting rockburst support design in underground mines.

ARMA 12-679 Mining Remnant Underground Mine Pillars with Large Open Pit Development in a Jointed Rock Mass - Key Elements of Slope Stability Analysis Using Three-Dimensional Numerical Modeling Methods Cremeens, J., Varnier, J.B. and Visca, P. Telesto Solutions, Inc., Fort Collins, Colorado, USA ABSTRACT: The stability of large open pit slopes developed in the presence of remnant underground mine workings is evaluated using three-dimensional numerical modeling methods. A 150 meter high pit with daylighted stopes and three joint sets was modeled using a three-dimensional discrete element software. Details of model construction and execution are presented. The key elements of modeling the interaction of large open stopes located between ore-bearing underground mine pillars and pit slopes that intersect these mine voids are identified and investigated. Key elements considered include the stope dip angle, the vertical location of a stope relative to the pit slope surface, effects of stope backfill on slope displacement, and sensitivity to stope backfill strength. The three-dimensional model results are compared to results from an infinite slope model constructed using a very thin variation on the full width model.

203 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-681 How can an intensive preconditioning concept be implemented at mass mining method? Application to Cadia East panel caving project Catalan, A. Dunstan, G., Morgan, M., Green, S., Jorquera, M., Thornhill, T., Newcrest Mining Limited, Orange, NSW, Australia Onederra, I., and Chitombo, G. The University of Queensland, Sustainable Minerals Institute, W H Bryan Mining and Geology Research Centre, Brisbane, Qld, Australia. ABSTRACT: Broadly speaking, preconditioning as applied to cave mining is a process conducted prior to the initiation of caving in order to alter the inherent characteristics of the rock mass to enhance caving. To date preconditioning using hydraulic fracturing in particular has been implemented and reported to produce measurable and positive outcomes even through there is still on-going debate on the real impact of preconditioning with respect to cave mining performance. The Newcrest Mining Limited’s Cadia East (CE) underground project economically viable required the application of a large scale and low cost underground mass or cave mining method in order to also achieve the required production rates (26Mpta). As such, panel caving was selected as the caving option. The extraction level of the first CE panel cave (PCI) is located 1,200m below surface and for the second lift (PC2) 1,400m also below surface. At Cadia East Project a novel approach locally designated as Intensive preconditioning” is being applied. This uses a combination of hydraulic fracturing (in down-holes) and fully confined blasting (in up-holes). This paper describes the work that has been carried out to date and how technical and operational parameters have been assembled and implemented in order to incorporate the intensive pre-conditioning process.

Ses s ion 43: A pplications of Numerical Modeling Wednesday, 27 June, 2:00 pm – 3:30 pm Chairs:Giovanni Grasselli, Mark Diederichs

ARMA 12-262 Applied back-analysis methods for tunneling using numerical modeling Vardakos, S. Parsons Brinckerhoff Geotechnical and Tunneling, Chicago, IL, USA Gutierrez, M. Professor, Division of Engineering, Colorado School of Mines, Golden, CO, USA ABSTRACT: Back-analysis is a systematic procedure to identify model parameters using the measured response from the construction. The use of back-analysis is particularly appropriate and useful for various tunneling projects, where more information on ground characteristics and monitored response become available as the construction progresses. Most often backanalysis requires that an optimization algorithm handles the task of identifying a set of model input parameters that will minimize the difference between predicted and measured performance. Predicted performance is typically obtained with the use of numerical analysis. The present paper explores the application of various optimization-based back- analysis techniques that are applicable to variable ground conditions and are directly coupled with the finite difference code FLAC. More specifically, this paper compares the performance of a traditional local

204 46th US Rock Mechanics/Geomechanics Symposium optimization scheme versus global optimization strategies and outlines the characteristics and features of each method. The strength and importance of global optimization are discussed for geotechnical engineering applications along with the novel implementation of two global optimization algorithms in geotechnical parameter identification. This paper focuses on the use of these two novel algorithms, namely, the Simulated Annealing (SA) and the Differential Evolution Genetic Algorithm (DEGA) as candidate algorithms for back-analysis with FLAC. SA and DEGA belong to a broad class of heuristic-based methodologies for locating global solutions for nonlinear optimization problems. Specific examples are given showcasing the convergence behavior and efficiency of these methods. It is shown that global optimization schemes are able to overcome the deficiencies of local search optimization methods, especially when non-linear geotechnical problems are investigated. With modern advances in computational efficiency, the back-analysis schemes presented provide easily deployable back-analysis toolboxes which are transparent and efficient in their use.

ARMA 12-272 Impact of post-failure rock mass behavior on excavation response Alejano, L.R., Arzúa, J. & Alonso, E. Natural Resources & Environmental Engineering Department, University of Vigo, Spain ABSTRACT: In this paper the authors combine three ingredients to analyze the response of deep tunnels in granite rock masses. First, some servo-controlled tests on granite rock are presented and interpreted to estimate dilation. Then, the authors recall a method to characterize rock masses behaving in strain-softening manner to estimate the most relevant parameters of three rock masses. Finally, this behavior model is introduced in a numerical model to study the response of a tunnel. Results show that whereas variable dilation models affects significantly tunnel displacement response, post-failure strength models control the extent of the failure zones. It is therefore shown that standard behavior models (namely, perfectly plastic models) may not well represent actual tunnel face response.

ARMA 12- 541 A Generic Stope Model for Investigation of Fracturing Mechanisms in Deep Gold Mines Katsaga, T. Potyondy, D.O. Itasca Consulting Group, Inc., Minneapolis, USA ABSTRACT: A generic mechanical model for rock behavior around advancing stopes has been developed to understand brittle failure mechanisms inherent in deep gold mines in South Africa. The model can reproduce the induced fracture patterns such that fracturing mechanisms can be explored and then related to in-situ conditions. The rock mass consists of finite-thickness horizontal layers separated by zero- thickness parting planes; also, a finite-thickness dyke may be defined ahead of the stope face. The generic stope model consists of a rectangular FLAC model within which may be embedded a rectangular PFC2D inclusion. Both the FLAC-only and the coupled FLAC-PFC2D models produce well-defined fractures similar to those observed in the field.

205 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-672 Effect of micro-parameters on the Hoek-Brown strength parameter mi for intact rock using particle flow modeling Zhang, Q. and Zhu, H. Key Laboratory of Geotechnical and Underground Engineering of Ministry of Education and Department of Geotechnical Engineering, College of Civil Engineering, Tongji University, Shanghai200092, China Zhang, L. and Ding, X. Department of Civil Engineering and Engineering Mechanics, University of Arizona, Tucson, Arizona, USA ABSTRACT: Hoek-Brown strength criterion has been used for analysis of a wide range of problems in rock mechanics and rock engineering. For intact rock, the criterion is mainly controlled by the strength parameter mi which is empirical and developed by trial and error. By representing intact rock as a densely packed cemented granular material, its mechanical behavior can be modeled using the particle flow modeling. In this paper, the three dimensional particle flow code PFC3D is used to conduct numerical tests on intact rock and investigate the effect of micro-parameters on the strength parameter mi. The micro- parameters which may affect the strength parameter mi, such as particle size, contact model type, the normal and shear strength are studied respectively. The results show that the particle size only has minor influence on the strength parameter mi and its effect can be simply ignored. The contact model type and the contact normal to shear strength ratio, however, both have major effect on the strength parameter mi. The parallel-bond model gives higher mi values than the contact-bond model. When the normal to shear strength ratio is smaller than 1, higher shear strength leads to large increase of parameter mi.

ARMA 12-176 Continuum representation of brittle rock failure bulking-induced displacements around tunnels Corkum, A.G. BGC Engineering Inc., Halifax, Nova Scotia, Canada Lorig, L.J. and DeGagné, D.O. Itasca Consulting Group Inc., Minneapolis, Minnesota, USA ABSTRACT: Mining tunnels continue to be excavated at increasingly greater depths, where it is a challenge to design, support and maintain stable openings. For ground support design, it is important to reasonably predict the extent of failure and the deformation behavior of the rock mass. Currently, limited practical tunnel-analysis techniques are available for tensile-failure-dominated brittle rock-mass behavior. This paper describes a numerical continuum-based method of brittle failure analysis that predicts both the extent of failure and provides an adequate continuum representation of brittle bulking deformations. The Damage Initiation Spalling Limit (DISL) approach, modified to account for stiffness degradation due to damage of the failed rock, is implemented into the two-dimensional continuum code FLAC. The technique is compared to empirical methods through an illustrative example and back-analysis of a case study with measured tunnel displacements.

206 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-432 On Using Spatial Methods for Heterogeneous Slope Stability Analysis Allan, F.C. and Yacoub, T.E. Rocscience Inc., Toronto, ON, Canada Curran, J.H. University of Toronto & Lassonde Insitute, Toronto, ON, Canada ABSTRACT: Kriging is a well-documented spatial interpolation technique used in geotechnical engineering problems where a material property is governed by an unknown spatial distribution. This paper studies the effect of kriging on slope stability analysis and compares it to other interpolation methods. Statistical distributions describing the factor of safety (FS) of a trial slope are generated. For reference, purely random Gaussian fields with increasing variance are examined first. Kriging and other spatial interpolation methods are then introduced using subdomains of the random field as input points. The number of known points is found to have a significant effect on the FS distribution, underscoring the importance of good sampling methods. Kriging has a smoothing effect on the input data and kriged predictions revert to the mean of the input points when no input points are nearby. The interpolated fields it produces tend quickly to the reference value of the FS as the number of input points becomes larger. In this respect, kriging outperforms other interpolation methods by supporting the results of homogeneous analyses while accommodating measured deviations from the mean rock properties. However, the smoothed field generated by kriging does not reproduce the statistical features of the original data. It may omit potential failure mechanisms due to localized, probabilistic weakness in the rock mass. Several representative examples of rock slopes are presented in this paper to illustrate the effects of using kriged estimates to calculate the overall FS for a slope stability problem.

Ses s ion 44: Trno a sp rt and Coupled Processes in Natural Fractures and Along Interfaces Wednesday, 27 June, 2:00 pm – 3:30 pm Chairs:Joe Morris, Mileva Radonjic

ARMA 12-206 Experimental Study of Portland Cement/Rock Interface in Relation to Wellbore Stability for Carbon Capture and Storage (CCS) Agbasimalo, N. and Radonjic, M. Craft & Hawkins Department of Petroleum Engineering, Louisiana State University, Baton Rouge, LA 70803, USA ABSTRACT: Primary cementing is carried out during the drilling and completions of wells and the main objective is to provide zonal isolation. For effective cementing, the cement should completely displace the drilling mud (water-clay mixture). In practice, this is never achieved as some of the mud is not displaced and remains in the wellbore. This study investigates the effect of the residual mud on the hydraulic conductivity of the cement-formation interface. Flow-through experiments were conducted at 14.48 MPa (2100 psi) overburden pressure with cement-rock composite cores and brine at a flow rate of 1 ml/min. The cement-rock composite cores had 0% and 10% clay-rich fluid contamination respectively. The pressure drop across the composite cores was recorded throughout the flow-through experiments. Extensive microstructural characterization of the cement-rock interface was carried out before and after the flow-through

207 46th US Rock Mechanics/Geomechanics Symposium experiments. Higher pH values were recorded for the effluent brine from the mud contaminated core and the higher values indicate increased leaching of Ca2+. Micro-CT imaging revealed that the contaminated composite core possessed higher porosity at the interface zone. This shows that clay contamination of cement-rock interface degrades the interface zone and can provide a pathway for injected CO2 to escape from the intended storage zone.

ARMA 12-227 Monitoring slip initiation and propagation along frictional interfaces with seismic wave transmission Hedayat, A. School of Civil Engineering, Purdue University, West Lafayette, IN, USA Bobet, A. School of Civil Engineering, Purdue University, West Lafayette, IN, USA Pyrak-Nolte, L. J. Department of Physics, Department of Earth and Atmospheric Sciences, School of Civil Engineering, Purdue University, West Lafayette, IN, USA ABSTRACT: Slip initiation and propagation along frictional interfaces were studied in the laboratory by monitoring seismic wave transmission across the interface. Slip was imposed on two individual blocks of gypsum with perfectly mated contact surfaces while the interface was continuously monitored using seismic techniques. The contact surfaces were made by casting gypsum against flat surfaces with different frictional characteristics. The specimens were loaded in a biaxal compression displacement rate until final slip occurred. Compressional and shear wave pulses were transmitted through the interface while the shear load on the sample was increased. The normalized amplitude of the recorded shear waves increased as the shear load increased and reached a maximum prior to the peak shear strength of the interface. A significant change of slope of the normalized amplitude of the compressional waves was also observed prior to the maximum shear stress. These can be considered as ‘precursors’ to a failure and can be used to investigate the propagation of slip along the interface. Precursors were detected closer to failure on homogeneous smooth surfaces than on homogenous rough surfaces.

ARMA 12-350 Particle Swarms in Confining Fractures Boomsma, E.R. Department of Physics Purdue University, West Lafayette, IN, USA Pyrak-Nolte, L.J. Department of Physics Purdue University, West Lafayette, IN, USA Dept of Earth and Atmospheric Sciences Purdue University, West Lafayette, IN, USA School of Civil Engineering Purdue University, West Lafayette, IN, USA ABSTRACT: Particle swarms are an attractive potential delivery method for the deployment of nano/ micro-scale sensors to targeted locations in the subsurface because of their coherent group behavior that causes a swarm to travel faster than any individual sensor. We performed experiments to determine the effect of fracture aperture on swarm evolution and maintenance. A single coherent swarm will eventually bifurcate into two separate swarms. The speed of a swarm and its depth at the time of this bifurcation are strongly affected by fracture aperture and the geometry of the apertures. Additionally, there is an optimal range of fracture apertures where swarm bifurcation is suppressed. In this optimal aperture range, swarms travel farther and faster than outside this range because the fracture walls maintain the mass distribution of the swarm through confinement.

208 46th US Rock Mechanics/Geomechanics Symposium ARMA 12-437 Coupled stress and flow along interfaces in the wellbore environment in relation to CO2 sequestration Lewis1, K. Zyvoloski1, G. A. Kelkar1, S. Carey1, J. W. 1Los Alamos National Laboratory, Los Alamos, NM USA

ABSTRACT: Assessment of potential CO2 and brine leakage from wellbores is central to any consideration of the viability of CO2 sequestration. Most existing work on wellbore integrity has focused on field and laboratory studies of chemical reactivity. Very little work has been done on the impacts of mechanical stresses on wellbore performance. In this study, we use the coupled Thermal-Hydrologic- Mechanical (THM) computer code FEHM to simulate key features of a wellbore (casing, annulus and cement) embedded in a system that includes the upper aquifer, caprock, and storage aquifer. We consider two stress-permeability models: tensile-failure and shear-failure. Tensile failure represents the creation of annuli at the steel-cement or cement-rock interfaces. Shear-induced damage is similar to a Mohr-Coulomb slip mechanism used to represent displacements on faults. Two injection conditions were considered: constant pore-pressure above the failure threshold for the well and a constant flow condition with increasing pressure in a confined reservoir. The simulations show that both tension- and shear-failure modes lead to enhanced permeability of the wellbore system. Shear failure leads to a larger damage zone and generally higher leakage rates than tensile failure. In addition, the shear zone extends further into the caprock and is focused closer to the cement-steel interface.

ARMA 12-549 Geochemical controls on fracture evolution in carbon sequestration Fitts, J.P., Ellis, B.R., Deng, H. and Peters, C.A. Dept. of Civil & Environmental Engineering, Princeton University, Princeton, NJ, USA

ABSTRACT: Stored supercritical CO2 will acidify native brines in deep saline aquifers and promote mineral dissolution within the storage formation resulting in varying degrees of calcite saturation. Injection overpressure will force these reactive brines into existing and induced fractures in overlying caprock formations. We present examples from our experimental efforts to understand how these fluids might alter fracture geometry and leakage pathway permeability, with the ultimate goal of predicting caprock integrity. We use mineral-specific imaging analysis to correlate changes in fracture geometry with spatial maps of dissolution and precipitation. Synchrotron-based x-ray spectroscopy and diffraction imaging of thin section sub-samples of the cores from the flow-thru experiments are used to connect mineral-specific dissolution and precipitation processes with the geometric changes in fracture aperture observed with CT images. Results of μXRF, μXANES and μXRD analyses reveal that preferential calcite dissolution and the spatial distribution of relatively insoluble dolomite and silicate minerals produced the non-uniform aperture widening. These results clearly point to the need for predictive models of caprock integrity to consider coupled geochemical processes, mineralogical characterizations, and geometric alterations of flow paths.

209 46th US Rock Mechanics/Geomechanics Symposium ARMA619 Simultaneous anhydrite dissolution and gypsum precipitation in a closed swelling rock system Serafeimidis, K. and Anagnostou, G. ETH Zurich, Zurich, Switzerland ABSTRACT: Anhydritic claystones are among the most problematic rocks for tunneling. Their swelling has led to serious damage and high repair costs in a number of tunnels. One cause of the swelling process is undoubtedly the formation of gypsum. Anhydrite dissolves into calcium and sulphate ions in the pore water and gypsum crystals subsequently precipitate. It is a markedly time-dependent process which in nature might take several decades to complete. Apart from the kinetics of the chemical reactions involved, advection and diffusion are also important factors in the evolution of swelling. The present paper focuses on simultaneous anhydrite dissolution and gypsum precipitation while leaving aside the transport processes. Understanding such a so-called “closed system” represents the first step towards more complex models involving transport. The paper begins with the governing equations and presents estimates of the kinetic parameters. The model is calibrated with experimental results from the literature, and parametric studies are performed in order to investigate the role of the initial volumetric fractions of the constituents and the specific surface areas of the minerals involved. A simplified model of anhydrite hydration is proposed, which identifies the governing process and possible orders of magnitude in terms of the swelling process duration.

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