JANUARY 2012 The “Better Business” Publication Serving the Exploration / Drilling / Production Industry Geosteering Improves Bakken Results By Kevin O’Connell, NPE is drilling and developing two blocks, in Divide, Williams and McKenzie coun- David Skari, aggregating approximately 50,000 net acres ties. Wells are being drilled to target zones Aaron J. Wheeler in the heart of the Bakken Shale in Divide, located between 9,000 and 11,000 feet and Allan Rennie Williams, Dunn and McKenzie counties, true vertical depth. The horizontal pro- N.D. (Figure 1). Led by a highly experienced, ducing sections of the wells average 8,000 DENVER–Developing tight oil and technologically focused management team, feet of lateral, which is cased, perforated gas-bearing formations often requires a the company prides itself on customizing its and fractured in multiple stages. The two dense pattern of wells with long lateral drilling and completion methods to the primary intervals targeted within the oil sections. To produce such fields econom- unique geological and geophysical charac- reservoir are a clean dolomite member of ically, producing sections of wells must teristics of its core project blocks. the Three Forks formation and a 15-foot be positioned accurately within the targeted zone below a tight limestone within the Drilling History intervals, while drilling costs are kept to Bakken Middle Member. a minimum. Since early in 2010, Ensign Rigs Nos. Initially, the horizontal production wells A cost-effective solution has been de- 89 and 118 have been working for NPE required drilling a vertical pilot hole that veloped that includes predrill modeling was sidetracked, deviated from vertical of logging-while-drilling measurements FIGURE 1 to build the curve, then drilled laterally along the trajectory of a planned well to North Plains Energy LLC Area of within the producing zone. Wireline logs compare with real-time LWD data. This Operations in North Dakota and cores were run in the initial pilot provides the ability to support geosteering hole to determine the landing point for to and within the target formation. This the sidetrack and to evaluate the optimal geosteering technique has been utilized interval within the reservoir to target. to develop Bakken Shale oil assets. The There was limited regional structural wells have been navigated to land consis- control in planning the laterals. The initial tently in the reservoir, and have successfully well required a sidetrack because it inad- maintained position within the primary vertently drilled into the Upper Bakken target zone for more than 90 percent of Shale. NPE decided that a single geosteered the lateral sections. well trajectory would be more cost effec- North Plains Energy LLC (NPE) is a tive, and the resulting smoother well Denver-based company focused on ac- profile should reduce the risk of losing quiring, developing and enhancing oil the bottomhole assembly. It also would and gas assets within the continental make the completion less problematic. In United States. NPE operates acreage in addition, using LWD tools in the region part of the Williston Basin on the west would provide valuable experience and flank of the Nesson Anticline. A 2008 knowledge about the subsurface geology U.S. Geological Survey assessment of the of the target formations while drilling. undiscovered resources in the Upper De- vonian-Lower Mississippian Bakken for- Geosteering Partnership mation of the Williston Basin Province in Prior to geological steering methods, Montana and North Dakota estimated the success of a directional drilling oper- mean undiscovered volumes of 3.65 billion ation depended largely on steering the barrels of oil, 1.85 trillion cubic feet of well through a target reservoir with an associated natural gas, and 148 million assumed position fixed in geometric space. barrels of natural gas liquids. However, a success in geometric terms Reproduced for Schlumberger with permission from The American Oil & Gas Reporter www.aogr.com Oil & Gas Shales could be a failure in economic terms if were utilized to calculate the expected urements. Because these measurements the assumed and actual geometric locations LWD response of formations into which were similar to wireline resistivity meas - of the reservoir differed. horizontal wells were to be drilled. LWD urements, the LWD logs were correlated Effective well placement in horizontal data types typically modeled included with similar wireline logs to locate im - drilling requires that geological changes gamma ray, resistivity, density-neutron portant geological features. Because the be detected quickly, and that the well (imaging), and sonic measurements. wave propagation measurements were plan be adjusted in a timely fashion. With The objective of geological steering well characterized, the LWD log response this challenge in mind, a dependable ge - depends on the section of the well. In the was predictable under most conditions ological steering partnership was developed build section, where the deviation increases observed. between NPE and PathFinder, a Schlum - from the kickoff point until the well enters The LWD resistivity tools have multiple berger company, for providing directional the reservoir, the goal is to steer the well transmitter-receiver spacings and multiple drilling and MWD/LWD services, sup - so that it enters the reservoir at a desired frequencies. The resistivity measurement ported by the company’s PayZone Steer - inclination and direction. In the lateral from each spacing and frequency responds ing™ services at the well site. The real- section, the goal is to position the well’s differently to a resistivity interface located time forward modeling software assists path to optimize well bore exposure to away from the well bore. Since the nature in geologically steering deviated well tra - the reservoir. of the resistivity interface is known from jectories by combining petrophysical data These goals have been achieved con - the offset well logs, multiple resistivities from LWD logs run in offset wells, the sistently through interpreting real-time can be leveraged to obtain a profile to geological earth model, and the directional LWD measurements, gamma ray in the help maintain the well’s position within well plan to create a model of the forma - build section, and gamma ray combined the target interval at a distance from the tions being drilled. with resistivity in the lateral section. These interface. During the early stages of the project, LWD measurements were selected by During drilling, an experienced service company staff, working in close evaluating the log response characteristics geosteering field engineer compared the consultation with the operator’s technical within and adjacent to selected target measured LWD responses with the mod - team, focused on learning the geologic zones of the Bakken Middle Member and eled synthetic responses to determine the setting in the area. Effective communica - Three Forks formations. position of the well’s path within the ge - tions among the team allowed it to as - ological sequence. The engineer also ref - semble local earth models based on avail - LWD Resistivity erenced all other relevant information, able seismic data, structural information, Electromagnetic wave propagation re - such as cuttings sample observations from and information from selected offset wells. sistivity tools delivered the standard deep- the mud logging geologist, to support the geosteering interpretation. Wireline and LWD data from offset wells sensing LWD array wave resistivity meas - The resulting geologic interpretation, which incorporated observed differences FIGURE 2 between expected and measured LWD Prewell Model of the Projected Landing Point (Holland No. 9-19H) responses, combined with additional drilling-related data, was communicated GAPI CHMM CHMM 1,000 RT_RHTE to NPE to allow the drilling and geology RSPH_M 9,690 RMPH_M team to make time-critical decisions effi - 100 RDPH_M y t i v RDAL_M i t ciently about adhering to or modifying s i s e R d 10 e the well plan. l Upper Bakken e d o M The team was able to adjust the drilling 1 Modeled Resistivity Response 9,720 plan as the horizontal well was drilled, GAPI ORR_S using actual well bore trajectory data and 120 LWD logging measurements. In consul - P O tation with NPE, the team incorporated R / y a 80 R 9,750 a interpretations to reconcile the local geo - m m a G logic model with real-time data, allowing D V 40 R Modeled Gamma Ray Response the well bore position to be maintained 0 within the target zone. feet 9,690 9,780 Lower Bakken Refining Results 9,720 Planned Well Trajectory Real-time LWD data acquired from 9,750 Projected landing point within the zone of interest not only were D V T at 9,806 feet TVD based 9,810 correlated with the synthetic model, but on initial geologic model 9,780 Three Forks target interval also were back-correlated with previous identified by red lines and well plan measured data from the same well as the 9,810 trajectory moved upstructure or down - structure within the target formation. All feet 0 40 80 120 1 10 100 1,000 9,760 9,840 9,920 10,000 10,080 Gamma Ray Resistivity decisions regarding changes to the well Oil & Gas Shales FIGURE 3 trajectory considered BHA capabilities, Geologic Interpretation Displaying the Well Bore Position the original directional well plan, and Within the Three Forks Formation Target Interval completion requirements in consultation with NPE. Continuous control of the well API OHMM OHMM 1,000 RT_RHTE bore trajectory delivered reduced tortuosity Vertical Depth Correlation RSPH_A y t i v i t 1s 00 and dogleg severity, leading to quicker i RMPH_A s e R RDPH_A e m well bore completion and production. i 10 RDAL_A 9,740 T - l a e Upper Bakken R LWD data and forward modeling in - 1 Real-Time Resistivity Measurements terpretation results were delivered at the OHMM 1,000 Modeled Resistivity Response RT_RHTE well site and remotely, using secure Web- RSPH_M y t i 1v 00 i RMPH_M t based applications.