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3fd INVITATIONAL WELL-TESTING SYMPOSIUM "Well Testing in Low Permeability Environments"
PtOC ^—J March 26-
Earth Sciences Division |Lij Lawrence BerkelBerkelef y Laboratory • University of California kaiI BerkeleyB , California 94720 Thb work was supported by the Assistant Secretary for Resource Applications, Office of Industrial and Utilily Applications and Operations Division of Geo thermal Energy of the U.S. Department of Energy under Contract No. W-7US-ENG-4S. m*mv* w n&MCDMn is MUTOD LBL-1Z076 UC-70 CONF-800344
THIRD INVITATIONAL WELL-TESTING SYMPOSIUM "Well Testing in Low Permeability Environments"
March 26 - 28, 1980 MASTER Thomas W. Doe and Werner 0. Schwarz Editors
Earth Sciences Division University of California Lawrence Berkeley Laboratory Berkeley, California
March 1981
This work was supported by the Assistant Secretary for Resource Applications, Office of Industrial and Utility Applications and Opera tions Division of Geothermal Energy of the U.S. Department of Energy, under Contract No. W-7405-ENG-48.
KtMiniOH Of THIS DOCUMENT IS IMUMEO CONTENTS
Preface vi
OPENING SESSION
R. C. Schroeder, Lawrence Berkeley Laboratory - Chairman
S. N. Davis, University of Arizona, Tucson, Arizona "Waste Isolation" 1 R. Agarwal, Amoco Research, Tulsa, Oklahoma, "Oil and Gas" 2 Don Banks, USA, Waterways Experiment Station, U.S. Army Corps of Engineers, Vicksburg, Mississippi "The Role of Well-Testing in Civil Engineering" 3
L. Aamodt, Los Alamos National Laboratory, Los Alamos, New Mexico "Geothermal Engineering (HDR & Stimulation)" 11
CASE HISTORIES AND RELATED PHENOMENA
R. C. Schroeder, Lawrence Berkeley Laboratory - Chairman
L. A. Rogers, "Well-Testing in Tight Gas Sands" 14
K. E. Almen, L. Carlsson, and K. Hansson, "Some Experience from Well-Testing in Precambrian Rocks of Sweden" 15 J. C. S. Long, P. A. V.'itherspoon, C. R. Wilson, and A. 0. DuBois, "Large-scale Permeability Testing at Stripa". ... 38 M. Voegele, R. McCain, and H. Pratt, "In Situ Permeability Measurements for an Underground Compressed Air Storage Project 45
D. Katz, "Capillary Effects in Rocks of the Earth; Influence on Well Behavior" 51 P. Nelson and R. Rachiele, "Randon as an Indicator of Wellbore Infiltration Rates in Uraniferous Igenous Rock" 64 E. Peterson and P. Lagus, "In Situ Low Permeability Measure ments in Salt at the WIPP Site" 66 WELL TEST DESIGN IN LOW PERMEABILITY FORMATIONS
J. Gale, University.of Waterloo, Ontario, Canada - Chairman
G. Thompson, "Considerations for Tracer Tests in Low Permeability Formations" 67 C. Forster and J. Gale, "Injection Versus Pressure Pulse Borehold Tests in Fractured Crystalline Rock" 74 T. Doe and J. Remer, "Analysis of Constant-head Well Tests in Nonporous Fractured Rock" 84
G. Grisak, "Solute Tracer Tests in Fractured Media" 90
D. Updegraff, K. Kennedy, A. Bakr, C, Culver, and J. Kam, "Testing Low to Moderately Permeable Units in Basalt Rocks" 94
ANALYSIS AND INTERPRETATION OF WELL TEST DATA
S. Papadopulos, Potomoc, Maryland - Chairman
C. Neuzil and J. Bredehoeft, "Measurement of In Situ Hydraulic Conductivity in the Cretaceous Pierre Shale" 96 D. P. Theiry, "Analysis of Pumping Tests Performed in a Horizontal Rectangular Fracture" 103 G. S. Bodvarsson and C. F. Tsang, "Thermal Effects in Well Tests of Fractured Reservoirs" 110 B. Kanehiro and T. N. Narasimhan, "The Response of Aquifers to the Earth Tides" 120
H. Ramey, Jr., "A Drawdown and Build-up Type Curve for Interference Testing" 130
INSTRUMENTATION FOR WELL TESTS
T. W. Doe, Lawrence Berkeley Laboratory - Chairman
F. Patton and W. Black, "Multiple Pressure Measurements and Water Samples in Small Diameter Boreholes 135 A. F. Veneruso and T. D. McConnell, "Pressure Measurements in Low Permeability Formations" -. 136 H. 0. Miller, "Instrumentation for Determining Rock Mass Permeability by Hydro-Pneumatic Pressure Testing" 153 M. Zoback, "Fracture Characterization in Crystalline Rock with Borehole Televiewer" 157 K. Kennedy and W. Miller, "Oownhole Double Packer Instrumentation with High Pressure Resolution Capability and Immediate Surface Monitoring Above, Below, and in the Straddled Interval" . 158 List of Participants -169— Name Index PREFACE
Thomas W. Doe and Werner J. Schwarz
The goal of the LBL invitational Well Testing Symposiums has been to encourage the interchange of ideas and technology between the fields of Reservoir Engineering, Hydrogeology, Civil Engineering, and energy related Earth Sciences. The initial symposium in 1977 included papers of a wide variety of interests in geothermal well testing. For the second symposium, the subject of injection of fluids underground was selected to focus the symposium proceedings. Following the precedent of the second symposium, a topic was chosen focusing the proceedings of the third symposium on the testing of low permeability rocks. Unlike the previous symposiums, which were primarily geothermal in nature, the testing of low permeability rocks is a problem common to waste disposal, fossil energy resource develop ment, and underground excavation for civil or mining purposes as well as to geothermal energy development. The development of well-testing in some of these fields has proceeded somewhat independently of the others, hence an interdisciplinary symposium on this topic was felt to be most appropriate. During the last decade the need for low permeability well-testing has increased significantly. Within the energy resource field there has been the development of hot dry rock geothermal systems, exploita tion of tight gas sands, and the development of in situ processing for oil shale and coal. The waste isolation area has seen both radioactive and toxic non radioactive waste disposal in tight formations become an urgent national concern. In the civil and mining areas the use of underground excavations for housing power structures and deep mining for increasingly scarce resources are requiring more and better ground water flow information. The basic challenge of low permeability well testing is the performance of a test within a reasonable length of time, within the sensitivity of the instrumentation, and affecting a significant volume of rock. Although the governing equations for fluid are not greatly changed by the low value of a rock's permeability, well test techniques
-vi- developed for production of fluids in high permeability rocks may not be appropriate due to such factors as the time required for the test or well bore storage. The instrumentation needs are also important as flowmeters and pressure gages need greater reliability and sensitivity for injection tests, interference tests, and other techniques. Although there is much work yet to be done in low permeability well- testing, the papers presented in this volume are a fair representation of the significant progress that has been made in the last few years. The Earth Sciences Division selected a third symposium organizing committee, under the chairmanship of Professor Paul A. Witherspoon. Members were Thomas W. Doe, T. N. Narasimhan, Ron C. Schroeder and Werner 0. Schwarz. The symposium and the proceedings were edited by Thomas W. Doe and Werner J. Schwarz. The symposium provided a forum for the over 130 participants in which to exchange ideas and present new information on low permeability rocks. The emphasis was on reviewing existing capabilities, identify ing current limitations, and generating new ideas for meeting the Department of Energy/Division of Geothermal Energy goals. The opening session was chaired by Ron C. Schroeder and Professor Paul A. Witherspoon who gave the keynote address. The participants represented the major national laboratories, federal and state governments, industry, utilities, independent con sultants, 9 major universities, Canada, England, Germany, Mexico, and Sweden. Abstracts and papers from non Lawrence Berkeley Laboratory authors are being reproduced unchanged. Lawrence Berkeley Laboratory papers were reviewed by the Earth Sciences Division's Publications Committee and by the Technical Information Department. ABSTRACT
PERMEABILITY OF DENSE ROCK WITH PARTICULAR RELATION TO THE ISOLATION OF HAZARDOUS WASTE
S. N. Davis
University of Arizona Tucson, Arizona
Curing the past decade, the determination of the permeability of very dense rocks has been of increasing importance owing to activities such as 1) the geologic isolation of hazardous wastes, 2) the storage of hydrocarbon fuels, 3) the design of dry-rock geothermal schemes, 4) the study of the distribution of ore deposits, and 5) the investigation of the generating mechanisms of earthquakes. Hazardous wastes must be isolated for periods of time ranging from a few years to more than 10,000 years. Rock permeability, which con trols the rate of redistribution of the waste by groundwater, is not entirely a predictable property over the longer time spans. As a consequence, geochemical techniques of dating water and secondary minerals are being considered as a means to reconstruct the history of permeability changes within a rock with the objective of trying to predict the nature and possible magnitude of future changes.
-l- ABSTRACT
ROLE OF MASSIVE HYDRAULIC FRACTURING IN THE EXPLOITATION AND DEVELOPMENT OF OIL AND GAS RESERVES IN LOW PERMEABILITY FORMATIONS
Ram G. Agarwal Amoco Production Company Tulsa, Oklahoma
Massive hydraulic fracturing (MHF) appears to be a proven stimulation technique for commercially developing natural gas resources contained in low permeability formations. This paper briefly reviews the locations of major tight gas basins in the U.S. and points out the limitatons of the conventional analysis methods (normally applied to high permeability formations) in predicting reserves for tight gas wells. Methods are discussed to evaluate and predict the performance of low permeability gas wells stimulated by MHF. Field examples are included to demonstrate the applicability of such methods. Portions of this talk are taken from Reference 1.
Reference 1. Agarwal, R. G., Carter, R. D., and Pollock, C. B.: "Evaluation ana Performance Prediction of Low-Permeability Gas Wells Stimulated by Massive Hydraulic Fracturing," J. Pet. Tech. (March, 1979) 362-372D; Trans., AIME, 267.
-2- TEE ROLE OF WELL TESTING IN CJ VIL ENGINEERING
Don Banks Chief, Engineering Geology and Rock Mechanics Division U. S. Army Engineer Waterways Experiment Station
Vicksburg, Mississippi
Civil engineering involves the application of art and science to the
investigation, evaluation, design, construction, operation, and maintenance
of worthwhile projects, Projects on whioh well testing results are Important
to the civil engineer are obviously those In which the subsurface flow of
water potentially Impacts upon safety and economical considerations. A few
examples include: flow of water (a) through foundations and abutments of
dams, (b) within slopes, or (c) into subsurface excavations and underground
openings; development of underground water supplies; and leakage from reservoirs
and canals. Closely akin to the cited examples are control measures to
prevent flow (i.e., grouting) and to reduce pore water pressures (i.e., drains)
and construction techniques. To the above-listed, more traditional examples
of civil engineering projects, new projects of national interest with new needs are being Identified. Projects requiring a renewed interest In the understanding of underground flow of water are exampled by needs for under ground storage of radioactive or other forms of hazardous wastes; underground storage of energy-producing products; development of alternate forms of energy reserves (i.e., geotherraal); and concern over pollutant migration. Significantly, experience has shown that the most successful approach In solving the more traditional projects, thereby indicating a similar approach to the more newly
Identified projects, has been when the civil engineer works as a team member with engineering geologists, hydrogeologists, and groundwater hydrologists.
-3- The purpose of well testing Is to derive a value of the permeability of
the geologic medium or to directly measure the velocity or quantity of
fluid flow. In the former situation, a change of the in-hole water pressure
is created and the resulting response of the system is measured. Through
interpretation of the response measurements by means of appropriate ccnceptucl models, the permeability of the medium can be derived. In the latter situation, borehole velocity meters or tracers, as examples, are used to measure the rate at which water is flowing in the medium. Once the tects are analyzed, a site- specific, boundary-valued problem Is solved to permit design decisions to be made. Past civil engineering interest has generally focused on flow in the near-surface environment (or, in the case of tunnels, in the new-bore environment).
Thus, equipment and procedures were generally developed to operate to nominal
depths - say 200 to 300 ft. Secondly, because of traditional interests,
pertinent tests have been conducted in the more pervious zones with the result
that test equipment has been relatively simple. Thirdly because the usual use of the data was to make a design decision (e.g., whether or not to grout: the type of draining or dewatering scUeme to be employed; si2ing of pumps, etc.), relatively simplistic models have been employed. The inherent variability of geologic media and the general application of the results from well testing have given the civil engineer some degree of comfort in satisfying the oft-an quoted "criteria" of determining a measure of the permeability "within an order of magnitude." Perhaps with new projects and more stringent needs, the civil engineer must now work even more closely with the engineering geologist or hydrogeologlst to better define the medium in which the tests are being conducted and to improve equipment and analysis procedures for use in geologic media exhibiting much Inwer permeabilities than were previously of importance.
-4- Civil engineering projects are quite varied by nature, and thus, without
the interjection of site-specific considerations on personal preferences,
cause a variety of techniques to be employed. The types of Celts (with
attendant depth of investigation limitations; typically employed on civil
engineering projects are;
Simple borehole tests
—Water gain/loss during drilling
—Variable or constant head tests In open boreholes
. Packer or pressure tests in boreholes
—Single packer assembly
—Double (or at times multiple) packer assemblages
Pemteameter •' ^sts
—Sealed individual piezometers
—Continuous borehole piezometers
Well pumping tests
In-hole tests using well flow meters or tracer tests
While general, good practice requires records to be maintained by the
drilling inspector or on-site geologist of water losses or gains during
drilling, the understanding of subsurface flow of water is Jiuch more
complicated than would be indicated by total reliance on this type "test."
In fact, except in cases whi;re there is a total loss of water into cavernous
limestones, the observations can lead to an incomplete and erroneoLs picture.
Variable or constant head tests In open boreholes are frequently conducted
in near-surface settings. Generally, these tests are limited to the most pervlouo of Jiaterials. In the case of water flowing Jnto the media, fines may
-5- clog conduits to cause an «i»der-estimate of the permeability of the media; In
the case of water flowing from the media, fines may wash from the conduits
to cause an over-estimate of the permeability.
Packer tests are normally conducted, either with single, double, or multiple assemblages when (a) distinct stratification of materials is
Indicated, (b) the number of borings is limited, or (c) the depths of
interest indicate that the conduct of interference-type tests (i.e., well
pumping) may be exceedingly expensive. In the packer test one or more packers are inflated to isolate the section between the packer and the bottom of the hole or between successive packers. A standpipe, either free or connected to a pump, and a source of water are used to elevate the pressure
In the isolated section. Observations of the relationship between the quantity of flow and the active pressure in the isolated section, along wih assumptions regarding the geologic media, lead to an estimate of the perme ability of the zone being tested. It is often thought that if a sufficient number of tests are conducted, along with detailed geologic observation of the rock core or of the borehole wall, then meaningful, relative information can be obtained. However, it is well known that the test results are strongly influenced if fines in the injected water tend to clog the fractures. Similarly, it is known that the results can bj completely misleading depending upon the location of the borehole and packer with respect to the joint system present in the rock mass.
Generally, in civil engineering practice (with variations depending upci the purpose of the project), if the average permeability as deduced from the simple tests descrlbei above does not vary over an order of magnitude,
-6- then further testing and definition .la not considered to be required. The
completion of the project will generally be made with occasional single
piezometers installed in selected boreholes to Indicate seasonal changes in
the groundwater flow or construction relit ted changes as caused by excavation
or drainage or as retarded by grouting measures.
Where the results indicate strata of'extremely high or low permeabilities,
then multiple piezometers are many tlmss installed. These multiple piezometer
installations can be of single piezometers .located In a close cluster of bore
holes, each to a different depth, or several piezometers installed in a single
borehole.
Most pieroraeters are carefully installed vith a protecting filter or
screening material placed around the tip. Permanent seals are placed both above
and below the screen. The piezometer will be developed by bailing, pumping,
i:ad surging before being declared operational. Generally, a falling head
or rising head test will be performed tj give yet another measure of the
permeability of the strata In which the piezometer tip is placed. Observa
tion of the piezometrie levels with time gives detailed Information of the
response of the geologic media to changes in flow as caused by excavation
or drainage or as retarded by grouting measures.
These type tests are recognized as affecting only a local volume of material and, on projects in which an interpretation of the mass characteristics
is sought, may be supplemental or used in conjunction with well pumping tests or tracer tests. When well pumping tests or tracer tests are employed, generally near-surface flows are of concern. Deeper flows are determined only on projects of major importance.
-7- While these types of tests are usually employed, test equipment, test
conduct, and interpretation of results are almost as varied as the nunber of people conducting the tests. A review of the literature will indicate numerous
papers describing adaptations or variations of traditional tests purportedly
to meet site-specific requirements but at times, it is suspected, to meet the
personal preferences of Individual engineers. By themselves such adaptations
should not be criticized, but where unnecessary, adherence to established
guidelines would greatly al.l in the portability of data or In establishing meaningful data bases for use in similar situations. Detailed descriptions
for various t.ests can be found in the Earth Manual of the formerly-known
Bureau of Reclamation; In the U. S. Army Technical Manual TM 5-818-5
(April 1971), Dewatering and Groundwater Control for Deep Excavations (also numbered NAVFAC P-418 and AFM 88-5, Chap. 6); in Time Lag and Soil Permeability In
Groundwater Observations by hvorslev, WES Bulletin No. 36 (1951); In the suggested procedures of the International Society for Rock Mechan.cs Commission on Standardization of Laboratory and Field Tests, "Suggested Methods for
Determining Hydraulic Parameters and Characteristics of Rc:k Masses" (Part 5) and "Suggested Method for Determining Permeability by Water Injection Out of
Three Cells Separated by Packers in a Borehole" (Part 6).
Such standardized approaches to obtaining a measure of the flow of water through geologic media have generally been sufficient in past civil engineering applications. However, with new needs, such as previously described, the civil engineer and his coworkers must critically reexamine past approaches.
The reexamination must cover the areas of:
a_. Flow phenomena.
b. Test equipment and equipment control.
-8- _c. Teet procedure.
a\ Interpretation of teat results.
£. Numerical modeling to extend the results over the volume of interest.
f_. Well-documented case studies Indicating successful applications and
importantly, unsuccessful applications with stated reasons.
To a large extent, continuation of symposia, such as this one, will
provide the forum for researchers, practitioners, equipment developers,
and modelers to assemble and discuss the results of reexamination and
improvement in describing fluid flow In geologic media.
New problem needs by their nature imply a determination of flow charac
teristics at greater depths than generally Involved in civil engineering
practice and in materials of low permeability. Work being performed by the
groundwater hydrologlsts, engineering geologists, hydrogeologists, civil
engineers, petroleum engineers, geothermal engineers, theoreticians, and
numerical modelers all have a significant place to play.
If it can be assumed that the fluid flow in the deep, low permeability
environment will be dominated by flow through discontinuities, then problems
of accurately defining the presence and characteristics of the network of
discontinuities are Immediately evident. Once descriptions are obtained from
core or borehole observation techniques, a major problem involves the extrap
olation of the information to unexplored regions of interest, i.e., a descrip
tion of the heterogeneity of the flow system. Then superimposed upon this boundary description is a description of the response of the system to changes
in pressure, temperature, possible mixed fluid flow, possible unsaturated flow,
-9- and possible variable flow lavs. I.e., laminar, transitional, and turbulent flow. These considerations must precede the design and selection of equipment, determination of test procedure, interpretation of teat results, and application of results to obtain a successful solution of the engineering problem.
The tasks are many. Coordinated reexamination and continued development by many workers in several disciplines will be required to successfully come to grips with the solution of fluid flow in low permeability environments.
I, for one, applaud the efforts of personnel at the Lawrence Berkeley Laboratory as individual workers and in hosting this symposium. I am looking forward to hearing of the advances described In the technical papers.
-10- HOT DRY ROCK GEOTHERMAL RESERVOIR ENGINEERING
R. Lee Aamodt Los Alamos National Laboratory Resource Engineering, G-5 Los Alamos, NH 87545
History The Los Alamos Hot Dry Rock Geothermal Energy project is locatea on the Jemez plateau, in northern New Mexico, about two miles (3.2 km) west of the ring fault which bounds the Valles Caldera. Two wells, GT-2 and EE-1, were originally drilled to a depth of 9600 ft (2.93 km) and 10,000 ft (3.05 km), respectively, and, after some difficulties, including re- drilling of the bottom portion of GT-2, a good fracture connection was made between EE-1 and GT-2B, as the modified GT-2 was called. Water entered this fracture from EE-1 at a depth of 9020 ft (2.75 km) and emerged from several exits in GT-2B. The main exit was located at 8760 ft (2.67 km). This circulation system was studied extensively for the purpose of establishing a number of fracture properties. Techniques were developed tc determine orientation, geometry, heat exchange area, volume, flow impedance and impedance distribution. A much larger fracture system was then created from a depth of 9620 ft (2.93 km) in EE-1. Similar studies are underway or have been com pleted on this system, Figure 1 shows schematically the system as it appears today. The techniques used and results obtained in the study of the new and old fracture systems are discussed below. Fracture Creation All fractures created in EE-1 and GT-2 by hydraulically pressurizing the wellbore appear to have been weakly cemented natural fractures, as no breakdown-pressure peak has been seen. The fractures may not be oriented at right angles to the least principal horizontal earth stress. They appear to stay partially open after their formation, possibly because of a shear component in the earth stress acting on the fracture, with a resulting displacement of the faces relative to one another. When the gradient in earth stress 1s considered, normal hydraulic fracture equations usually do not apply. Quasi 3-D machine calculations by A. Vol Ian and T. Wacker of Dornler System GmbH, West Germany1 show that with a fracturing fluid such as water, fractures will generally assume an elongated pear shape, eventually running away in the upward direction. Pumping at high flow rates reduces this effect, maximizes shear displace ment of the fracture faces, and opens up the maximum number of joints of various orientations.
-ii- Fracture 0.ientation Seismic signals accompanying fracture growth delineate regions of high pressure. The signals are observed with a downhole seismometer having three sets of four seismometers oriented at right angles. Signal direction can be determined, with 180° ambiguity, from the first P-wave cycle, while distance is deduced from the time difference between P- and S-wave arrivals. A pressure sensor at a different point in the wellbore can remove the directional ambiguity. Geometry Information about joint systems can be derived in a single well by borehole televiewer and dipmeter logs. Correlation of logs in nearby wellbores is also informative. Spinner and temperature logs taken under flowing conditions identify the major entrance and exit points. The top of the fracture can be located by passing sound waves between well bores, if the fracture lies between them. Since temperature reel/ery in radial geometry is faster than in plane geometry, the bottom of the fracture can be located after a few weeks of no flow, if it is close enough to one wellbore. Heat Exchange Area Figure 2 shows the fit obtained between calculations and observations of temperature drawdown in the old fracture system during the 75-day test. The new fracture is now undergoing a flow test. The heat exchange area is one of the most reliable numbers obtained during a flow test. Volume Fracture volume is obtained by injecting a slug of concentrated dye into the reservoir. Figure 3 shows results for both the old and new frac tures. The new volume is •OZ.OOD gallons (122 m3), if the volume at the peak of the returning dye concentration is used. This is about ten times the volume of the old fracture. Flow Impedance and Distribution Flow impedance is defined as the difference in pressure between the exit and entrance points of a flowing well-pair, divided by the flow rate. The overall impedance requires a correction for the difference in pres sure of water in the hot and cold legs of the reservoir. An entrance and exit impedance may be derived from the prompt change in pressure when the wells are shut in.
Reference 1. MAGES. Report submitted to the Executive Committee for the Program of Research and Development on Han-Hade Geothermal Energy Systems under the auspices of the International Energy Agency, 1979.
-12- KO s MAJOR ^ \ NATURAL JOINTS
2590 m (eSOO'J ?7 »
«»Msasur«d drawdown Temp t — Firil ordir analytical modtl, A* 8000m2 A 8 2 outlat numtrlca'modtl, R-60m / MAIN FRACTURE J i t 1 • • 1 95% OF FLQW^ O S
2750 m^ (9020!) Time Ways)
A / HIGH-IMPEDANCE Fig. 2. Calculated and observed temperature 8% OF FLOW-^ / FRACTURE drawdown curves.
FREE CASING
2930 m (9620'1'/^
Fig. 1. Present configuration of reservoir (schematic).
VOLUME (10 gal)
ntsracsmu* I-1 (LBP) l-f'HBPI
SCCOMO HCSEman
2-IILtP)* 2-2IHBPI i-S(lWI»2-*ILW>
'"I I"- 40 90 FRACTURE SYSTEM VOLUME Fig. 3. Dye tracer recovery curves. ABSTRACT WELL TESTING IN TIGHT GAS SANDS L. A. Rogers Institute of Gas Technology Chicago, Illinois Department of Energy tests of geopressurad-geothermal wells in Louisiana and Texas are providing data from which reservoir analysis and potential production can be made. IGT is participating in the geopressured-geothermal program in obtaining the reservoir data, making laboratory measurements on core samples, and performing computer simulation of the well production. Computer modeling of the Edna Oelcambre well test provided an understanding of the anamolous excess free gas above that dissolved in the brine. Projections based on test data are providing information from which production and economic analyses can be made. -14- SOME EXPERIENCES FROM WELL TESTING IN PRECAHBRIAN ROCKS OF SWEDEN K-E. Almen, L. Carlsson, and K. Hansson Geological Survey of Sweden Uppsala, Sweden BACKGROUND The Swedish Stipulation Law requires that before starting new nuclear reactors it must be shown how and where the high level waste can be handled and stored in a safe way. The KBS:s pro posal (KBS 1977, 1978) for final storage of the high level nuclear waste comprises a repository at a depth around 500 meters in Swedish crystalline rock. A great number of drillings, well tests and other investigations were performed to show the existence of sufficiently large volumes of rock with very low groundwater flow suitable for a repository. The well tests performed also gave relevant values of the hydraulic conductivities to be used in model calculations of groundwater flow and transport times (Stokes and Thunvik 1978, Stokes 1979, Axelsson and frisson 1979). In total about 12,000 meters of boreholes were drilled and in vestigated within the work of KBS. In the two areas Finnsjbn and Sterno, see Figure 1, almost 7,700 meters of boreholes were investigated and the results formed the basis for the KBS safety-analysis for a repository in crystalline rock in accordance with the requirements of the Stipulation Law (KBS 1977, 1978). In this paper a brief review will be presented of the hydraulic well-test performed and some experiences from the testing and the results. AREAS INVESTIGATED Finnsjon The Finnsjo area is located in northeastern Uppland, about 120 km north of Stockholm, see Figure 1. The topography is -15- very flat, characterized by a Subcambrian peneplane formed more than 570 million years ago. The bedrock is made up of different rock-types found within the Sveco-Fennian area in Sweden. Granodiorite with an age more than 1 800 million years is the dominating rock type. Other rock- types to be found are leptite, granite, metabasite, pegmatite and aplite. The area has a high frequency of fractures, 3-4 fractures per meter on the rock surface. In the area seven fully cored bore-holes with a diameter of 56 mm were drilled to lengths varing between 494 and 691 m. All the bore-holes were core-logged and hydraulic well tested. Some of them were also geophysical well-logged. The location of the bore-holes and major fracturezones is shown in Figure Z. Sterno The Sternb area is a peninsula in the Baltic Sea, about 400 km SSW of Stockholm. The peninsula is about 1 500 m wide and the highest point about 50 m above the sea level. Near the surface the rock type is a fine-grained gneiss, called Coastalgneiss, intersected by veins and bodies of pegmatites and granites. At depths the rock type turns over to a gneissic granite and to a granite called Karlshamnsgranite. The transi tion from gneiss to granite is gradual and not characterized by any tectonic or other structural zone. The fracture frequency is low, about O.ii per meter on the rock surface. Through the area a 150 - 250 m wide dolerite-dike runs in north-south direc tion. -16- Five bore-holes with lengths between 577 and 803 m were drilled in the area. The same kind of investigations as in the Finnsjo area were performed in the bore-holes in SternB. The location of the bore-holes and major tectonic features is shown 1n Figure 3. HYDRAULIC TESTING Method Two types of hydraulic tests were carried out with respect to equipment used, single- and doublepacker water injection tests. Due to the large number of tests to be carried uut during a limited time (Carlsson et al 1979) a rather simple method was applied. Water was injected at constant head into a tested sec tion of fixed length (2 or 3 m), with a pressure of 0.2, 0.4 and 0.6 MPa in excess of the hydrostatic head. The flow was measu red at the imposed head difference when an apparent steady state had been reached. The hydraulic conductivity was calcu lated by the formula used by Banks (1972): k =-S (1 + In-M 2TT-L-AP 2r When k = the hydraulic conductivity of the test section Q = injection flow rate r = bore-hole radius L = length of the test section 4p = head difference Transient methods with constant head or constant water injection flow were performed in some sections in order to compare the hyd raulic conductivity values obtained by different methods (Carlsson et al 1979). -17- The values of the hydraulic conductivity thus obtained are values of the rock mass where the sum of the conductivities of each individual fracture in the test section is averaged over the section. With the knowledge of fracture spacing and geometric data the obtained rock mass conductivity can be transformed to a hydraulic conductivity of an equivalent set of hypothetical average fractures jnd of each individual fracture. Equipment The equipment used was constructed in 1977 - 78 and the tests performed until the end of 1979. The same equipment was used in the two types of tebt, but the single packer tests were made with the two packers placed together and water injected beneath them, see Figure 4. The packers used were of rubber-type with a length of 0.3 m. They were mechanically expanded by using oil-hydraulics. Water was injected through a stem of steel-pipes with 10 mm inner and 20 mm outer diametres, each pipe 2 m in length. They were joined by inside screwthread and 0-ring packing. The packer equipment was held in the hole by the steel-pipes. Water injection flow was monitored by flow-meters of rotameter type. Six different flow-meters were used, which overlapped one another. The lowest measurable flow rate in practice was 0.85 ml/min. The injected water was marked with Rhodamine which made it possible during later pumping and sampling to see whether the water obtained was contaminated by the injection or not. Results tojbj/sjjacjcer measurements_ Results of the double and single packer measurements given as hydraulic conductivity versus depth are presented by Hult et al 1978, Gidlund et al 1979, Carlsson et al 1979 and Ekman and -18- a decrease in hydraulic conductivity over longer sections might be seen below 400 m i:i the diagrams. It has sometimes been pointed out that the use of long test section will give a mean value of the rock mass hydraulic conductivity. The length chosen should depend on among other things the fracture frequency and distribution in the borehole. An average hydr- lie conductivity of each bore-hole both from single and double packer tests is given in Table 1. Good agree ment is obtained for the two types of measurements in Sterno but for Finnsjon the agreement is poor in spite of higher con ductivity values. Table 1. Valaei oA the hydnaulic conductivity (oi each boKehole. (lorn iingle packet mea&unement and jAom caZcuZationi baied on doable, pactwi meaiWiemenXi iia&ed on 3 meXeJii teAi itcttom. Borehole section m beiow Hydraulic conductivity m/s ground surface Double packer Single packer Fi 4 52 - 590 5.4-10"7 6.2-10'8 Fi 6 100 - 691 5.8-I0"7 6.8-10"8 Ka 1 3(1 - 779 9.3-10"10 1.3-10"10 Ka 2 100 - 576 5.4-10"9 8.4-10"9 Ka 3 50 - 765 2.6-10"8 2.0-10"8 Ka 4 48 - 553 6.MO"8 2.9-10"8 Ka 5 100 - 578 6.3-10"9 2.6-10"9 19- Gentzschein 1980. In Figures 5 and 6 the hydraulic conductivities are shown in groups of half-decade values versus depth together with the fracture frequency obtained from core-logging. In general the high hydraulic conductivity values are combined with high frac ture frequency. A slight decrease in hydraulic conductivity with depth is observed for the high fractured zones. The much higher fracture-frequency in the Finnsjb area compared to th.? Sternb' area observed on the rock surface are also observed from the boreholes. The bore-holes were placed and drilled to illustrate and con firm fracture zones and other geological units or features within the areas. For instance bore-hole ;:•. 3 (Sternb) was placed to confirm a fracture zone (tectonic line) and to illustrate its hydraulic conductivity. The bore-hole crossed that tectonic line at the depth of 300 - 350 m which is shown in Figure 6. Thus the distribution of the hydraulic conductivity along the bore-holes and between them differs. Despite that it is assumed that the bore-holes together in each area might show some gene ral distribution of the hydraulic conductivity of the rock mass down to about 500 - 600 m. In Figure 7 zones in a normal distri bution diagram are shown of the distribution of the hydraulic conductivity in the two areas Finnsjbn and Sterno, calculated from each bore-hole. The diagram thus gives an indication of the hydraulic properties within the areas and a comparison between them. Figures 8 and 9 show how much of the bore-holes at different Q depth has hydraulic conductivity lower than 10 m/s. In some -20- of the bore-holes in Finnsjon no sections occur with conduc- q tivity lower than 10" m/s. On the other hand some sections in the bore-holes in Sternb have 100 % of their lengths lower than 10"9 m/s. ^ijyje_packer meas£rm^J:s_ajid_com£ariscm j>etween !ij!92e_ajid_ doiibtejp«ter measurements^ By using up to about 100 times longer test sections in the single packer measurements compared to the 3 m sections used in double packer measurement, the measuring limit can in theory be lowered about two orders of magnitude. Most of the single packer measurements were made by lowering the packer 50 m at a time in the boreholes. The obtained trans- missivity values from each test gave base-values for calculation of the hydraulic conductivity for each individual 50 m section. Figures 10 and 11 show the results from some of thp boreholes both from single and double packer measurements and calculations. In some of the calculated sections a substraction of two very similar transmissivities gave negative values and were excluded in the diagrams of the single packer measurements. The negative values imply that the difference between the two basic flow rate- measurements in question is within the experimental errors at the two packer positions. Figure 11 shows that in Sternb a marked change in the hydraulic conductivity in general occurs near 300 - 400 meters depth. Above this change values of 10 m/s are found and below it about 10-10 m/s or lower prevail. Such an abrupt change can not clearly be distinguished in the diagrams from Finnsjbn, Figure 10. However -21- The influence of test section length is illustrated in Figures 12 and 13 in which single packer measurements are compared with the calculated values from double packer measurements using 2 or 3 meters sections. For the very low hydraulic conductivity in shorter sections no good agreement exists illustrated at depth in Sternb Ka 3. The same disagreement is found for long sections with high hydraulic conductivity as in Finnsjbn Fi 6. All individual single packer measurements and corresponding calculations from double packer measurements are compared in Figure 14. In general the hydraulic conductivity calculated from double packer measurements is higher than corresponding single packer measurements. It must be kept in mind that the test sec tions are picked out without any respect to fractures or other tectonic zones, and that leakage is likely to occur both within the rock between the test section and borehole and between the packers and the bore-hole wall. This leakage affects the calcu lated value of hydraulic conductivity less in single packer mea surements than in double packer measurements, because it is spread over a longer section in calculation and also because a longer packer is used in the single packer measurement. The differences showed in Figure 14 might indicate a leakage which corresponds to -9 -8 a hydraulic conductivity of up to 10 - 10 m/s, equivalent to 6-60 ml/min at double packer measurement with 3 meter test sec tion and a head difference of 0.2 MPa. DISCUSSION The leakages observed as disagreements between the two types of measurements might in a theoretical discussion be distinguished in two types. First a very small leakage which probably has to do with insufficient closure between packers and bore-hole wall -22- and other imperfections In the measuring system. This leakage affects the very low conductivity measurements as shown in the Sterno measurements. Usually this leakage represents the mea suring limit of the double packer equipment used. For a conti nuous set of 75 individual 3 m sections between 350 and 575 m depth in bore-hole Ka 2 in Sterno this leakage was determined as 2.23 + 1.59 ml/min at 0.2 MPa excess head. The second type of leakage occurs in rock with a high fracture frequency where water might be transported *hrough the fracture system as short-circuit flow between the test section and the untested part of the fc-re-hole. As a high frequency of fractures, which also can transport water, indicates high hydraulic con ductivity this second type of leakage occurs in and affects the measurements of high hydraulic conductivity when using small test section and short packers. This type of leakage is illustra ted by some of the measurements in Finnsjb'n. To avoid or minimize the leakages mentioned it is recommended to use longer packers and to use information of the locations of highly fractured parts of the borehole in order to make sui table applications of the instrument and method for measurements of hydraulic conductivity in these parts. -23- REFERENCES Axelsson, C-L., Carlsson, L. 1979: Model calculations of ground water conditions on Sternb peninsula. KBS technical report 79 - 10, Stockholm 1979. Banks, D. C. 1972: In situ measurements of permeability in basalt. Proceedings of the Symposium on Percolation Through Fissured Rock. Stuttgart 1972, pp. Tl - A. Carlsson, L., Gentzschein, B., Gidlund, G., Hansson, K., ?vensson, T., Thoregren, U. 1979: Supplementary measurements of permeability in the Finnsjo area (In Swedish). KBS technical report (in print). Stockholm Sept. 1979. CarSsson, L., Gidlund, G., Hansson, K., Klockars, C-E. 1979: Estimation of hydraulic conductivity in Swedish Pre- cambrian crystalline bedrock. Proceedings of the NEA/IAEA Workshop on Low-Flow, Low-Permeability Mea surements in Largely Impermeable Rocks, Paris March 1979, pp. 97 - 114. Ekman, L., Gentzschein, B. 1980: Supplementary geohydrologic investigations in Sterno (In Swedish). KBS technical report 80 - 01 (in print). Stockholm March 1980. Gidlund, G., Hansson, K., Thoregren, U. 1979: Supplementary hydraulic conductivity measurements in the Karlshamn area (In Swedish). KBS technical report 79 - 06. Stockholm 1979. Hult, A., Gidlund, G., Thoregren, U. 1978: Measurements of hyd raulic conductivity (In Swedish). KBS technical re port 61, Stockholm Jan. 1978. KBS 1977: Handling of spent nuclear fuel and final storage of vitrified high level reprocessing waste. Report in five parts from the Nuclear Fuel Safety Project, KBS, Stockholm 1977. -24- KBS 1976: Handling and final storage of unreprocessed spent nuclear fuel. Report in two parts from the Nuclear Fuel Safety Project, KBS, Stockholm 1978. Stokes, J., Thunvik, R. 1978: Investigations of groundwater flow in rock around repositories for nuclear waste. KBS technical report 47. Stockholm Hay 1978. Stokes, J. 1979: Calculations of groundwater movement within the Sterno area in Blekinge, preliminary report (In Swedish). KBS technical report 79 - 08, Stockholm 1979. -25- Fig. 1. The location of the Finnsjo and Sterno area in Sweden. Fig. 2. Map of the Finnsjo area with deep bore-holes and major tectonic lines. f TECTOMC UWS C3 °°"» Fig. 3. Map of the Sterno area with deep bore-holes and major tectonic lines. Fig. 4. Equipment used and packer configuration in the double and single packer measurements. Ft? «IMWM MMtatacT KTMAUUC o c Fig. 5. Hydraulic conductivity versus depth and corresponding fracture frequency in the bore-holes in the Firnsjo area. The hydraulic con-, ductivity is given in groups of half-decades. -28- KB 2 K*5 PIMURI MMUtNCr HTMWLIC MMUC1H"" riltiMi rat cut no maiMutK c Fig. 6. Hydraulic conductivity versus depth and corresponding fracture frequency in the bore-holes in the SternS area. The hydraulic con ductivity is given in groups of half-decades. -29- 10° 10" 10" 10 % Hydraulic Conductivity Fig. 7. Zones in a normal distribution diagram illustrating th> hydraulic conductivity values obtained from measurements in the borehole in Finnsjon and Sterno. -30- FI1 FI4 0 10 100 % 0 10 100 'A 10 MK FI2 FiS FI7 300 fa. 400 .•ffl1.'!"'.'.!"' 600 Fi3 <10"B •% Fig. 8. Percentage of different sections in the bore-holes in Finnsjon with hydraulic conductivity lower than 10"9 m/s. -31- Kal K«4 50 tOO % 0 SO 100 % 200- pill Ka2 Ka5 "fa defective WMWJ.prfc jWi*iSVWWrVWV1 . Ka3 <10"9 •% H.l.VililiV,l,W,iMWMWV Fig. J. Percentage jf different sections in the bore-holes in Sterno' with hydraulic conductivity lower than 10"' m/s. -32- FU ami PKH5 -to .? -a -T DEPTH '*' DE"TH '"It FIB DOUBLE PACKERS SIKLE PACKER I m/s) [ m/s J 10''° 10'' 10"' 10'' 10"' io"s W* 10"' TO"6 IO"1 «** ICf* Fig. 10. Hydraulic conductivity calculated from single and double packer measurements in Finnsjon. Hydraulic Conductivity 10 9 8 10 B 1 10 16' id* 16'° 10 id 16 16' 16 16 ° 10"' m/s S 4 0> S 2 600- Ka 3 h-r 1ZU Fig. 13. Hydraulic conductivity from single packer measurements(full line) with different length of the test section and corresponding value from double packer measurements(broken line) in bore-hole Ka 3 in Sterno. DOUBLE PACKERS Fig. 14. Hydraulic conductivity from single packer measurements and corres ponding value from double packer measurements. Curves are shown indicating leakages corresponding to hydraulic conductivities of 10"8 m/s and 10"9 m/s in double packer measurements. -37- LAtWE-SCALE PERMEABILITY. TESTING AT STRIPA C. S. Long, p. A. Witherspoon, C. R. Wilson, and A. O. OuBois Lawrence Berkeley Laboratory* University of California Berkeley, California 94720 rhe niacropurtneabiliey experiment at Stripa, iwuden, is an attempt to measure the average permea bility oi J very large volune of low-permeability, vi ictured rock. Flow into and pressure surrounding a ii m drift will be measured. This experiment will alsr> netp to determine the size of the repre sentative elementary volume for the Stripa granite. Problems in pressure field characterization include tn« perturoation resulting from drainage into the rest of the mine and vagaries of the fracture sys tem itselt. To measure pressure, 15 boreholes have been drilled front the drift into the surrounding rock and instrumented with 94 packers and 90 pres sure yayes. Inflow to the drift is measured by evaporating the seepage into the ventilation air wnile measuring the jhange in water vapor content oetwuen incoming and exhaust air streams. In order Fig. I. Perspective sectio l through the ventila to measure this change in water vapor content, the tion drift showing air flow pattern and drift has been scaled off and measurements of the hydrology instrumentation boreholes. Mtiimetric pressure, air velocity in the exhaust iiuct, anri the wet and dry bulb temperatures of the inlet and nxhaust air are taken. A test at ambient of the first two of these problems. The third is tempera Lur-? has been completed. Preliminary re not discussed here. sults estimate a hydraulic conductivity of about 11 h.b : i/e As the volume of the fractured rock sample increases from zero, the average permeability will i. MUTIVATIOU FUK LAMJE SCALE TESTING oscillate as either fractured or solid rock is added to the sample. When the volume of rock be The prospect of geologic storage of nuclear comes sufficiently large that permeability is no usee has created a need to determine the hydrologic longer sensitive to the effects of individual material properties of low-permeability iractured fractures, the oscillations will cease. An average rock, 'l'he macropermeability experiment at the permeability can then be assigned to that volume of Stripa mine in bweden is an attempt to improve perm rock which is called the representative elementary eability characterization techniques for the anal volume {REV). Theoretically, volumes of rock the ysis of regional groundwater flow through low perm size of the REV can be treated as porous media for eability rock m the vicinity of a nuclear waste regional groundwater flow analyses. Increasing th<; repository. The experiment is part of the Swedish- volume further may ultimately cause additional ,ttnerican Coaperative Program on Radioactive Waste oscillations if a different realm of fracturing is storage in Hined Caverns in Crystalline Socket»21t encountered. When a single permeability measure At strips we are monitoring flow into, and pressure ment is made on an arbitrary volume of rock there surrounding a 5 n x 5 n K 33 m long drift called is no way of knowing a priori whether or not the the ventilation drift at the 335 m level of the measured permeability lies on the oscillating por btripa mine (Figure 1). This paper examines the tion of the curve. A series of measurements on theoretical problems associated with making such a different scales must be made to determine if there measurement, and describes the actual experiment is a REV smaller than the rock mass itself and to now in progress including preliminary results as of determine the permeability associated with that November iy7y. volume. i'hree problems arise in determining flow par In fractured rocks, where the discontinuities ameters for low permeability fractured rock. The themselves may occupy areas on the order of 102 m2, first is to determine the minimum volume of rock for it is reasonable to expect REV's, if they exist, to which the permeability tensor is representative of be on the order of 104 or 105 m3. The macroperm- a larger rock mass and is amenable to a porous media eability experiment at Stripa will permit a measure method of analysis- The second problem is to deter ment of the average permeability of 105 of rock. mine this permeability tensor from field tests. The There is no assurance that this volume will be as third problem is to assign permeabilities to the large as the REVi however, the experiment, taken volumes of rock that are not directly examined in along with other small-scale testa performed at the the field. The macroperraeability experiment at same site, should provide strong indications of the btripa is an attempt to increase our understanding size and existence of the REV. The s«cond problem is to determine the permM- irregular* An assumption of undisturbed conditions bility of these large volumes from in situ test*. would not be valid. In high permeability soils or rocks, standard well tests can be run such that large volumes of the flow Another method is to define a convenient boun system are perturbed by the test in reasonable per dary surface and measure the pressure distribution iods of time. However, in low permeability rocks, on this surface. Alternatively, pressure could be standard well tests nay only affect the flow systesi measured at an array of points in space such that within a few meters of the well. Determination of an isopotential surface could be located in space* large-scale permeability values can therefor* be In an ideal, homogenous porous medium this method attempted in two ways. The first way is to synthe would prtssnt little problaa. The open interval of size large scale values fron a series of small- the piezometer would intersect a large number of scale tests done in boreholes. The sscond way is pores and grains and the pressure measured would be to create a large scale sink (or source) which will a physically averaged pressure. In a fractured perturb a large volume of the flow system, i.e., a system, however the piezometer interval may only macroscopic permeability test- intersect a few fractures. Since the direction of Small scale borehole tests will probably remain flow in these particular fractures is not neces the mainstay of hydrologic investigations since bore sarily in the direction of the average gradient as holes are the only practical means of extensively shown in Figure 2, the fractures sampled will not exploring deeply buried rocks* Therefore, reliable necessarily yield the average gradient. Without methods for predicting macroscopic permeability knowledge of the average gradient, the average or from borehole data are needed. In order to perfect equivalent permeability cannot be calculated. The such methods they will have to be checked by perform problem is equivalent to predicting the permeability ing large-scale in situ tests at the same site where of a porous medium from measurements of pressure in the borehole data has been collected. The macro only a few pores. scopic permeability test at Stripa represents a large-scale measurement that will be used to check the analysis of an extensive series of small-scale borehole tests^**'. XI. MEASURING MACROSCOPIC PERMEABILITY Any measurement of permeability must be made on a flow system with specified boundaries. The potential distribution on these boundaries as a function of time and the flux through each boundary as a function of time must be inferred or measured. Then the effective permeability can be calculated using Darcy's law. Host in situ tests cannot be con structed such that all these conditions are exactly met. Some assumptions about boundary conditions are Fig. 2. Comparison of local and average gradients, usually made in the analysis. p^ = pressure at point i. Theoretically, flow into the ventilation drift As a partial solution to the above problem, will approach steady conditions, but will never piezometers can be installed parallel to the theo actually reach equilibrium! In order to use steady retical iaopotential surfaces. These piezometers state analysis the experiment will continue for 3 to can then be open the whole width of the flow zone. 6 months or until there is no discernible change in In this case many fractures will intersect the pressure and temperature. However, both the defini piezometer and a physically averaged pressure will tion of boundary conditions and the measurement of be recorded. Two problems are presented by this flow into the drift are problems of some magnitude. arrangement* The first is that long sections of open borehole may create a significant leakage paths Theoretical Considerations in Pressure Measurement and increase the flow into the drift. This will in turn increase the measured permeability. The closer The ventilation drift can be idealized as a the open borehole is to the drift the worse this long, but finite cylindrical sink* The inner boun problem is likely to be. Another problem is that daries of this flow system are well defined. The this method of pressure measurement allows axial location of the boundary is the wall of the drift- averaging but no circumferential averaging. The The pressure on that boundary is essentially zero variability of pressure in the circumferential since the drift is kept dry. direction can be just as erratic as in the longitu dinal direction. The outer boundaries of the flow system are more difficult to characterize. Several possible The only way to ultimately insure a given set approaches can be taken. One is to assume that at of boundary conditions is to create those condi some distance from the drift the flow field ia tions artificially. This can be accomplished by undisturbed and the hydraulic potential is constant. drilling a ring of closely spaced boreholes around However, the hydrology of the region surrounding the drift and maintaining them at constant hydraulic the drift is to a large extent dominated by the head. This method may be difficult and costly to extensive Stripa nine workings. Piezoaetric pro construct, and it will not provide any information files in the vicinity of the ventilation drift are about anistropy. -39- Pressure Measurement at Strip* is equivalent to collecting about 0*050 cm per day over the floor area of the drift. At strip* 15 boreholes 30 to 40 a long have been drilled from th« ventilation drift into the One of the purposes of this experiment is to surrounding rock {Figure 1). These borehole* arc examine the utility of measuring these low flow divided into 3 groups of 5 each. Two groups (the rates by evaporating all the water into the ventila K-holes) are radial holes and ona group (tha HG tion air while Measuring the change in water vapor holes) extend from the face of the drift. Each of content between the incoming and exhaust air streams. these holes has been instrumented to monitor pres To operate successfully, the ventilation system sure, n total of 94 packers have been installed at ehouLd provide an air flow rate and temperature approximately 5 a intervals. This prevents the capable of vaporizing and carrying away all of the Ooreholes from acting as drains into the drift and influx waterl**, in addition, all parameters munt creates a 3-dimensional array of 94 zones, 90 of be steady enough to allow identification of the which are individually connected by tubing to pres equilibrium conditions* Also, the differential rel sure gages. Zones are numbered such that zone 1 in ative humidity between the air entering and leaving each hole is approximately 0 to 5 m from the drift; the experiment area must be great enough to provide zone 2 in each hole is 5 to 10 m from the drift, acceptable water vapor measurement accuracy. As a 3 and so on. point of reference, .OS m /s (100 efm) of air flow ing at normal atmospheric pressure, 20*c, and 100* 3 During the experiment air in the drift was relative humidity will transport about 50 cm of kept at ambient temperature. Pressures in the bore water vapor per minute. holes and water flow into the drift are monitored until they are quasi-steady. In further experiments For the macr©permeability experiment it is air temperature in the drift will be raised and the necessary to measure: (1) the barometric pressure; measurements repeated. (2) the air velocity in the exhaust duct? and (3) the wet and dry bulb temperatures of the incoming Between constant temperature experiments two and exhaust air streams* These measurements allow further experiments will be conducted. The first us to calculate the incoming and exhaust mass flow will be awall-scale permeability tests in which each rates of both the air and the water vapor associated zone in one or two boreholes will be drained* The with it. The difference between the incoming and flow rate from each zone will b Theoretical Considerations in Flow Measurement In most permeability tests, the water can be collected in a tube or pipe and the flow rate meas H40t rtlaln«d by air UW1 •»<- "IO-IJOOJ ured in a straight forward manner. However, in the low permeability rock of this experiment, the flow Fig. 3. Plot of heat retained versus evaporation rate into the drift is so low and the surface area rate. is so great that a significant proportion of the inflow would be lost to evaporation and the remain-* Several months were required to establish near- der would collect on the floor of the drift too equilibrium conditions in the rock temperature and slowly to measure in a reasonable amount of time* water vapor flow regimes. The experiment was ini For example, inflow to the drift of Stripa is cur tiated with a room temperature control setting as rently measured at 45 to 55 cm3 per minute which near as possible to the preexisting ambient air -40- temperature. Sotie heat was added to assure that for the water will be provided} and (3) the rock all available water is evaporated. Subsequently will be heated. As •quilibriim conditions are warmer equilibriuu room temperatures will be esta approached the third contribution would become blished to investigate the impact of that tempera negligible' The 45 ktf heater is divided into six ture upon the water influx. sections which ara separately controlled. Five sections are under manual control and one is under Flow Measurement at Stripe automatic on-offf control with feedback from a room- temperature sensor* The heater voltage is regulated A sketcn of the experimental setup waa shown to isolate it fro* the large voltage fluctuations in Figure 1. An air- and vapor-tight bulkhead ssals observed in the nine power system. off a JJ ra length of the ventilation drift. This wall consists of a structural wooden fraiue covered A 75 ram-deep trench has been cut across the with an 0.15mra thick sheet of PVC as & vapor r floor of the drift just inboard of the bulkhead. barrier, and fiberglass insulation to prevent con The trench and floor of drift are dry, therefore we densation" The vapor barrier and the structure are conclude that lateral flow through fractures in the keyed into a 20 mm deep notch on all four sides, floor of the drift is negligible* with foamed plastic sealing in the notch to prevent the loss of water through the blast damaged surface rock. A frozen-food-locker type door providea Preliminary Remits from the Ambient Temperature access through the bulkhead. Experiment Instrumentation of the 15 boreholes wee begun The general mine ventilation system delivers in June 1979 and completed in November 1979. Be about 1.4 m-Ve of fresh air to a point just outside fore fitting the holes with packers, the holes the bulkhead. The experimental ventilation system drained the surrounding rock into the drift. AJ admits a portion of this freah air into the sealed such the upgrade holes were dry and the downgrade room to pick up the water (as vapor) which flows holes were filled with water under hydrostatic into the sealed room through the surrounding rack. pressure. Ac each hole was fitted with packers the This secondary ventilation system is driven by a pressure in the hole began to rise. Example pres fan located in the exhaust duct so that a slightly sure records for R07, HG2, HG1, and R01 are shown negative pressure exists within the sealed room. in Figure 4, 5, 6, and 7 respectively. Any air leaking through the bulkhead is into the room and it is the same air as that entering through the inlet duct. In this way, the inlet wet and dry bulb measurements are representative of both the intentionally admitted air and the leakage air. The flow measuring station as well as the exhaust wet and dry bulb sensors are in the exhaust duct. These sensors sense the total air flow including leakage. The air entering the sealed room passes through, an electric duct heater. It is then distributed through an insulated duct with multiple openings along the length of the room. The air issuing from these openings is directed preferentially onto any damp spots on the rock surface (most of the water R07 z™ arrives by seeping along discrete fractures). The 6 walls of the drift are maintained in an almost-dry 5 - A condition, with fans used where necessary to provide -^-•~-~ a high air velocity over particularly damp spots. •— 3 The arrangement shown in Figure 1 will be modified - for operation at higher room temperature. The air •'—• 2 inlet duct will open directly into the room and a separate fan will recirculate room air through the heater and the distribution duct. This arrangement t will separate the flow system for heating and cir RQ1 closed culating air within the room, where high air flow rates are desired, from the flow system for room ventilation {water vapor removal), where very low flow rates are required for accurate water vapor flow measurement. Figure 4. Example pressure gage readings for R07. The climatic conditions within the room are Before instrumentation, when all the holes controlled by manually selecting a suitable air were draining freely, hole RQ1 produced about as flow rate (by adjusting a damper on the fan exhaust) much water as all the other 14 holes combined. and then adjusting the heater power as required to Earlier injection tests in R01 resulted in pressure maintain the desired air temperature in the room. responses in many of the other holes in the drift. The energy input from the heater is utilized in Consequently we instrumented R01 last and monitored three ways: (1) the sensible heat of the exhaust the response to preeBure build-up in R01 in all the air will be increasedi (2) the heat of vaporization other holes. -41- 1 i —I HG2 Zont 6 -^ =^ = Zan«5 _ ^- -f s=sJ0^y ~rP7 ~ \ / 7 ROl closed XB1.8P2-2I46 Figure 7. Example pressure gage readings for R01 The effect of closing ROt can be seen in the pressure records for R07, HG2, and in Figures 8 and 9. Figures 8 and 9 illustrate the increase in pressure experienced in the R-holes and the HG- holes. The dashed lines represent pressures meas ured on October 30, 1978; the solid lines represent pressures measured on November a, 1974. Instrumen tation and pressurization of R01 began October 31, 1 1979. The stippled area between the dashed and . . . DBH2 , solid lines shows the initial pressure increase in 0SH2 0BH2 DBH2 U>i!2 each hole due to pressurization of R01. No pres closed opened closed closed sure increase is shown for RIO because it had been 12/6 12/15 dissassentbled to fix a faulty packer. HGl was instrumented just prior to R01 and had not yet reached equilibrium when R01 was installed. Pres sure appears to decrease in zones HG33 (i.e., zone 3 in hole HG3J and RD54 because HG33 and R054 had been bled during the period October 30 to November B. The pressure declined in HG41, HG43, and HG44 with out interference. All other zones throughout the Figure b. example pressure gage readings for HG2. drift increased in pressure. DSH2. a hole parallel to the drift was also instrumented. Tn December and January this hole was reinstruraei.'-ed twice to i HGl ' 2one_4__ Y 150 r " 100 ~T/^_ 1 =° zz*^ 5 /6 1>15 12/1 12/15 1/15 f |2/l Date "' 110BH 2 DBH2 DBH2 closed closed closed] Pressure increase (stippled) in the Figure 6. Example pressure gage readings for HGl. R- holes due to instrumentation of EDI- -42- Sealing tha boreholes with packers decreased the flow into the drift from about 1000 cm3/min to 20 to 30 cm3/*dn* As th* pressure in the holes built up the flow of water into the drift increased to 45-55 c*3/stitw (The 1000 c*3/s\in represents cumulative flow from the open boreholes; after the boreholes ware closed flow was measured with the 2 X « 5 t HGI ventilation system.) This decrease in flow is much greater than was expected. In order to maintain humidity of the exhaust air at 85% we have had to lower the air flow rate to 0.5 m3/s. This air flow rate is at the lower end of the linear range of our airflow measurement system. The record of flow rate is shown in Figure 12. Erratic variation at the beginning of the record is due to changes in operation of ventilation system figure 9. cTeasure increase (stippled) in the and ongoing instrumentation of boreholes. However KG- iiolew due to instrumentation of R01. a gradual increasing trend can be discerned until late January when all the holes were instrumented. repair packer leaks. The affects of these proce The most accurate data was recorded after February dures can be seen in the pressure records for HGI 26th when the room was consistently kept dry for and HG2. The pressure record for R01 shows the almost a month* complex, dynamic buildup process in that hole. These dramatic hydraulic responses illustrate the complex nature of the fracture system at stripa* The hydrology of this rock may well be dominated by a few nigh permeability fractures* Figures 10 and 11 show che pressure distributions at the end of tne ambient teat. March 20, 19. Figure 12. Xnflow Record. Fic\ire 13 shows three separate values of con Figure 1U. Pressures in the It- holes at the end of ductivity that were calculated baaed on the assump tne ambient temperature run. tion of steady state flow and using the pressure records in (1) all zone 4's, (2) all zone 5's, and (3) all zone 6's. Thus conductivity can be plotted against the volume of rock represented by the zones 4, 5, and 6, respectively. The calculated conduc tivity is fairly stable or about 6.5 x 10~11 m/s. This may be an indication that the volume of the REV is at least as small as 5 x 104 m3, but further analysis may be needed. fry. The macropermeablllty experiment, will provide; (i) a direct, in situ measurement of the permeabil ity of 105 m3 of rock on the order of 6.5 x 10-11 m/ar (ii) a potential method for confirming the analysis of a series of small scale permeability tests performed in surface and underground bore holes; (iii) a battar understanding of the effect of open borehole zone length on pressure measure- mentr (iv! increased knowledge of the size and Figure 11. Pressures in the HG- holes at the end of existence of a representative elementary volume in the ambient temperature run. fractured rock] and (v) a basis for evaluating the -43- ventilation technique for flow aeasuzaaents in Funding for this project is administered by large-scale testing of low-parnsability rocka. the office of Nuclear Waste isolation at Battclle Memorial Institute. ' 1 ' 1 ' 1 1 1 ' 1 ' 1 ' 1 K vs rock volume - Witherspoon, p. A. and 0. Degerman, 1978. Swedish-American Cooperative Program on Radioactive Waste Storage in Mined caverns. ffi e © Program Summary. LBL-7049, SflC-01, Lawrence Berkeley Laboratory, Berkeley, - - California 94720. Witherspaon, P. A. et al, 1979. Rock mass characterization for storage of nuclear waste in granite. LflL-8570, SAC-18, - Lawrence Berkeley Laboratory, Berkeley, J l_.l 1 , 1 i 1 i 1 i 1 i 1 California 94720. Rock volume ..SLaw-aws Gale, J. E. and P. A. Witherspoon, 1979. ftn Approach to the fracture hydrology at figure 13. Permeability versus rock volume, Stripa*. Preliminary results. 1BL-7079, SAC-15, Lawrence Berkeley Laboratory, Berkeley California 94720. 111. ACKNOWLEDGMENTS KcPherson, M. j., 1979. Psychroraetry: Trias work was supported by the Assistant the measurement and study of moisture Secretary for Nuclear Energy, Office of Waste in air. Nottingham University Mining isolation of the U. s. Department of Energy Magazine, University of Nottingham, under Contract Wo. W-7405-SNG-48. United Kingdom. -44- IN SITU PERMEABILITY MEASUREMENTS FOR AN UNDERGROUND COMPRESSED AIR STORAGE PROJECT M. Voegele, R. McCain, M. Gronseth, H. Pratt Terra Tek, Inc., Salt Lake City, Utah SUMMARY water compensated CAES site. In addition to per meability, jn. situ stress was measured at several Seven injection tests were conducted to deter depths using a hydraulic fracturing technique. mine permeability as part of a site investigation for a proposed compressed air energy storage/under ground pumped hydro facility located in Maryland. This paper presents a summary of the in situ The tests were conducted in a single NX borehole permeability investigations at one CAES/UPH site. to depths of approximately 1000 meters in theSykes- Included are discussions of the fluid injection ville granitic gneiss formation. Four of the in equipment designed specifically for the project jection tests were single packer tests and were and the three distinct interpretative techniques to determine the permeability of a large section utilized. Also included is a summary of the re of the hole. The tests were performed starting near sults obtained. the top of the hole and the packers were moved down the hole for each successive test. Three straddle The underlying theme of this investigation was packer tests were performed to determine the rock dictated by time constraint and monetary consider matrix permeability of an intact zone and the aver ations. Accordingly, the field tests were performed age permeability of two fractured zones. The in as short of a period of time as was consistent interval tested during the straddle-packer tests with the quality of data required. The assumptions was 28.2 meters long. From these tests, it appears required for the adopted interpretative techniques that the rock matrix permeability is on the order justified the use of relatively short data acquisi tion times for the permeability test data. However, it must be remembered that under these conditions, bility in the fractured zones tested is on the it is only realistic to calculate the permeabili ties to within an order of magnitude. This level order of 10 cm. of calculation effort is also justified in light of the degree of confidence of the parameters which must be assumed in order to calculate the INTRODUCTION permeabilities. The typical load demand of a power generating facility tends to be cyclical with peak generation Fluid Injection Equipment required only at certain times of the day. During off-peak hours the plants operate at a much reduced An expected wide permeability range, together level of efficiency. To enable the generating with very low permeabilities led to the design of plants to operate at a higher efficiency, load a special equipment cart to handle the wide range leveling techniques, which store the extra power of flow and pressure conditions. The two major generated during off-peak hours in an easily recov design constraints were to be able to either main erable form, are currently under investigation. tain a constant injection rate or maintain a con One technique, utilizing Compressed Air Energy stant injection pressure and measure accurately Storage (CAES) together with an Underground Pumped- very small flow rates. Hydro (UPH) scheme is presently being considered for implementation near Washington, D.C. Two air-driven intensifier-type pumps operate in tandem, with positive pressure on the input side Compressed Air Energy Storage (CAES) has only of the pumps, to provide a maximum flow of approxi recently become a technique for load leveling in mately 1.8 gpm at 3000 psi. Pressure and flow on the power industry. There has to date been no the high pressure side are regulated and most of operating experience on water compensated hard rock the pump output is circulated back to the tank cavern CAES plants, but considerable development through the back pressure accumulator regulator. work has taken place and a great deal of design Fluid is drawn out of the circulation loop through experience has been gained in hydrocarbon storage an accumulator which provides a damping effect to and air storage for other applications. Water pulsations in the circulation loop. compensated CAES is a system in which the air stor age caverns are connected to the surface by a water In the constant pressure injection mode, the column, balanced by the air pressure in the storage fluid is routed directly through the flow meter cavern. The water column is then connected to a and downhole, and the injection pressure is deter surface reservoir of sufficient volume to fill the mined by the loop pressure setting. In the con underground reservoirs when the stored air is com stant rate Injection mode, fluid is routed through pletely exhausted. One of the most important design a metering valve and another back pressure regula parameters for a CAES/UPH facility 1s, of course, tor before being injected. Pressure is regulated the rock mass permeability characteristics. The to maintain a constant pressure drop across the permeability coefficient of the host rock mass metering valve regardless of downstream pressure. chosen for the site is the governing factor in de termination of the air leakage potential at a given -45- The system is closed in the sense that the The remaining question is, therefore, which vent and bypass lines return to the supply tank. value of porosity should be used in the permeabil Cumulative flow can be obtained independently of ity calculations. It should be obvious that the the flow meter by measurement of the water level more permeable portion of the mass, be it the in the supply tank. Also, the amount of fluid cracks or the inter-connected pore space, will returned when a test is vented can be determined. allow the flow of fluid more easily than the less The equipment is capable of maintaining or meas permeable portion of the mass. It therefore seems uring flows in the 0.005 to 0.3 gpm range with a likely that the porosity value of 0.015 is justifi resolution of 0.001 gpm at injection pressures as able and representative of the conditions encoun high as 6000 psi. The entire system is light and tered in the CAES/UPH boreholes. compact; it is easily portable on a small truck. The permeability values can easily be adjusted The straddle packer used for the tests was for a different value of porosity; for permeability specially designed by Lynes for hydrogeological -l? -T5 testing. Downhole pressures in the packed off in in the 10 to 10 range, equation 3 is essen terval were observed at the surface through the use tially linear. A porosity value of .5% thus would of a Lynes quartz crystal conductor wireline probe (CWL). To determine if leakage had occurred around lead to a permeability coefficient one-third of the lower packer element, a Lynes Digital Memory that for a porosity value of 1.5%. Recorder (DHR) was included in the tool string. Finally, a comment regarding the validity of the interpretive techniques themselves is in order. Interpretive Techniques Flow may be according to Darcy's Law, but the per meability may be so low such that the equations Injectivity tests were performed as part of typically used do not apply. For example, the the site investigation to provide order of magni partial differential equation: tude estimations of the permeability of sections of the CAES/UPH test well located in the Sykesville Granite Gneiss Formation. Because the formation has relatively low permeability and porosity, in jection tests using constant injection pressure is derived for radial flow from Darcy's law and „ formed the basis of the tests to determine the conservation of mass. Typically the term (aP/ar)^ permeability. is disregarded on the assumption that pressure gra dients are everywhere small and the resulting equa Discussion of Assumptions. Several of the tion is solved. For extremely low permeability, permeability coefficients were calculated on the very large pressure gradients may exist, flow may basis of an assumed value of porosity. It must be be non-laminar, and the above simplification may emphasized that the equations used to interpret not be valid. flow data are typically derived on the basis of a homogeneous medium and a radial flow regime. These At the present time there does not seem to be boundary conditions are obviously unsatisfactory agreement within the literature upon how to assess for a problem involving flow in a single fracture. this problem. One of the problems faced in this study was to de termine whether or not fracture flow was the domi nant mechanism observed at the CAES/UPH site. If Steady State Conditions. During these tests, it is clear that the flow is predominantly within the borehole was rapidly pressurized to a given the fractures, alternate interpretive equations constant pressure, measured downhole, and the flow must be found. rate required to maintain that pressure was recorded. If tne test records indicated that conditions An examination of the core from the site of relatively constant flow had been reached, an suggests that the fracture frequency has a maximum equation of the type presented by Snow (1968) was ur 1 fracture per foot. The fractures observed used to estimate the permeability. were all tight arwJ, for illustration purposes, it will be assiTiied that the average fracture width was 0.1 mm. Using a fracture spacing of 1 ft., the K= 4.778 x 10"8 ffl.1" »« l/Dw) (,) fracture porosity is seen to be less than 1 x 10~4. 4PL Allowing for a cumulative error equal to even an order of magnitude, the fracture porosity is still K • permeability, cm less than 10 . q - flow rate, gpm M = viscosity, cp The rock matrix porosity cannot be calculated AP = injection pressure, psi easily and must be estimated on the basis of repre L = interval length, ft. sentative values. Several authors have tabulated D hole diameter, in. values for crystalline rocks, (Krynine and Judd, « = 1957; Brace, 1965? or Farmer, 1968). Typical poro sity values for gneissic rocks reported range Curve Hatching for Transient Conditions. For between 1% and 2%. It is apparent that an assumed several of the tests it was not possible to reach porosity value of 1.5* is reasonable for the rock and maintain steady flow or pressure conditions. in the CAES/UPH borehole. In transient cases such as these, especially when the time of the test 1s short, the permeability coefficient 1s typically estimated using the type- curve matching technique developed by Jacob and -46- Lohman and reported 1n Earlougher (1977). This shut-in analysis, such as that proposed by Horner method was developed for a single well 1n an Infi (1967) was used to calculate the permeability nite system. coefficient. To use this method a plot of well pressure vs. log of a dimenslonless time 1s used The permeability coefficient is determined to determine a characteristic slope S. by making a log-log plot of flow and time and comparing this plot with a dimensionless type- aP curve given in Earlougher (1977), until a match (4a) point is found. The coordinates of this match a(log^) point are then used in Equation (2) to estimate the permeability. This slope is then used to determine the permeability: 4.183x10'' (2) —iTC— Bv (Mm Where: K = permeability coefficient in cm B = formation volume factor, given Where: dP = change 1n well pressure between the value 1.0 time t and t v = viscosity, cp aP = injection pressure, psi t = timeof well production, or L = interval length, ft. in this case tine since start of q = flowrate at match point of injection test to time of shut-in.hrs. type-curve matching, gpm t = time since shut-in (q0) - dimensionless flowrate at match q = flow rate in gpm point for type-curve matching v = viscosity in centipoises 5 = slope of Horner plot (note that since this is build up following injection, A relatively high degree of confidence in the slope used in calculation is actually accuracy of the fit of the data to the type curve the negative of that measured} was observed in one of the single packer tests B = formation volume factor, assumed = 1 and in two of the straddle packer tests. L = length of tested interval, ft. 2 Successive Approximations for Transient K = permeability in cm Conditions. While the injectivity tests were being run a second interpretive technique was used Four of the injectivity tests, including two to analyze those tests which did not achieve steady single packer tests and two straddle packer tests state conditions. This technique involved an had data that was of sufficient quality to inter iterative approximation to the relationship devel pret by the Horner method. In fact the shut in oped by Jacob and Lohtrra**. This relationship is data for one of the straddle packer tests was given by equation (3). almost a textbook example. 8 10 Kt P = 2.338 x 10" 3R Ln (3.459x10 )(3) •uCflV Results The results of the calculations to determine Where: AP = injection pressure, psi permeability coefficients are summarized in Table I q = flow rate, gpm and plotted in Figure 1 which also contains an v = viscosity.*, cp o abbreviated fracture log of the borehole based K = permeability, cm upon RQD and seismic velocities. The information L = interval length, ft. t = time hrs. summarized also includes test configuration ar.'. -47- an order of magnitude, than those calculated by the TABLE 1 other methods. At these low permeabilities even this discrepancy is probably acceptable considering Summary of Permeability Coefficients Determined in the assumptions and the length of the tests. The UPH/CAES Borehole Study, Sunshine, Maryland overall conclusion is that thd data from the four interpretive techniques is acceptable and consis Test 1: Hole Depth: 1279 to 3197 ft. tent. Single Picker Test Length of (fttervil: 1918. ft. The data base of in situ permeability coeffi Technique Permeability cients for crystalline rocks is limited, but it is lS s Steady state, iP • 70 psi 9 x 10" cm of interest to see how the results of this ?.tudy l3 2 Curve Matching 5 x 10" cm compare with published data. Figure 3 illustrates 3 2 Successive Approximations 5 x lo" «t a compilation of published data for in situ per Shut-In Analysis i! l meability tests in crystalline rocks. The only 2 x 10" *cra conclusion to be drawn is that the results of this -12 -15 study are in the expected range of 10 to 10 Test IB: Hole depth: 1343-3197 ft. Single Packer Test cm seen at the Savannah River Laboratory and Length of Interval: 185* ft. elsewhere for crystalline rocks at similar depths. Technique PfrmMhllitv Some investigators have proposed a decrease in permeability coefficient with depth in crystalline Successive Approximations 5 x 10"iJcmz 2 rocks (Snow, 1968 J. This may be true from the Shut-in Analysis 4 x 10"i*ca surface to a depth of approximately 100 meters. Below 100 meters there are little data and JTO trend can be quantitatively described (Figure 4). The Test 2: Hale Depth: 1790 to 3197 ft. Single Packer Test available data indicate a general 10"' - 10" cm Length of Inter/aT: 1407 ft. permeability for crystalline rocks (o depths of up to 3000 meters. This study supports that proposi Technique Permeability tion. Steady State. aP - 110 psi 6 x 10'1Jcm* Hole depth: 2606 to 3197 ft. Slmjle Packer Test Length of. Interval: 391 ft. Technique Permeability PERMEABILITY COEFFICIENT (CM') FRACTURE LOG AS INDICATED •«• Steady State, fiP - 945 psi 2-K 10"1Jcm2 LOW ROD COMMENTS I STRADDLE PACKER Test 5: Hole depth: 1691 to 1763.5 ft. Straddle Packer Test 5HT5T05E Length of intn-val: 92.5 ft. CALIPER VARIATIONS Technique Permeability I2 I• FRIABLE Steady State iP * 440 ps1 2 x 10" C3i* Steady State. flP - 470 psi Z x 10* "em* i • DISCONTINUITIES Successive Approximations 2 x IO"lscm! ls 1 DRILL BREAKS Curve Hitching 1 x 10" cm* 1 1^=' REHEALED Test 6: Hole depth: 2267 to 2359.S ft. CONTRO L ZON E • FRACTURES Straddle Packer Test Length of interval: 92.5 ft. VARIABLE Technlaue Permeability i FOLIATION Steady State, aP • 945 psi 4 x 10"lscm* Successive Approximations ,5 ••LOW VELOCITY 2 x 10" cmZ 2 ZONE Shut-in Analysis 1 x Hf'cni Figure 1 Hole de[<:H: 1832 to 1924.5 ft. Straddle Packer Test Compilation of permeability test results for Length of interval: 92.5 ft. Sykesville granite gneiss illustrating the relationship between permeability coefficient Permeability and degree of rock fracturing. Vertical lines Steady State, iP - 345 psi indicate length of test interval while hori Curve Hatching zontal width indicates error bands on the data. Successive Apcraxlnatlons 8 x lO'^cm1 Shut-in Analysis 4 x 10"' '•cm1 llote: for water at 20°C: Itr12 cm2 " ID-4 Darcy - lO-'cm/sec 15 2 7 10- cm - 10' Darcy • 10-10 cm/se: -43- auninarj^ IN SITU PERMEABILITY Seven Injection tests to determine permeabil ity coefficients were successfully completed as Hi part of the site Investigation for a proposed compressed air energy storage/underground pumped hydro facility located near Sunshine, Maryland. These tests were performed in a single deviated ih J borehole 1n the Sykesville Granite Gneiss Formation. 'ft I . O*f 61 Four of the injection tests were single packer >i: * tests and were to determine the permeability of a large section of the hole. The tests were per sii ill! SI I. formed starting near the top of the hole and the packers were moved down the hole for each success ive test. s Three straddle-packer tests were performed to n% determine the rock matrix permeability of an Intact zone and the average permeability of two fractured zones. The interval tested during the straddle- packer test was 92.5 ft. long. From these tests, it appears that the rock -15 2 ,.., r-ix permeability is on the order of 10 cm or less, and that the average permeability in the -12 2 Figure 3 fractured zones tested 1s on the order of 10 cm . It is significant to note that all four of the In Compilation of in situ permeability test results terpretive techniques utilized gave results that for crystalline rocks (After Brace; 1980). agreed to within an order of magnitude for the cal culated permeability. Acknowledgements IN SITU PERMEABILITY VS. DEPTH The authors would like to express their yratitude to Acres American, Inc., the project managers and in particular, to Dr. A. S. Burgess, D Acres Consulting Services, Ltd. for his construc tive suggestions regarding interpretive techniques. Tr) IP J.!: s"° DF~D~° ' 11M*MN •wm !! UtAMI ,; TS-ii 1 ' Single | ]-)[">- o g* " !! 409*. 51nglf 0 a ji1 !"» 97So j n A P«?,r 97S* or" ;• ~ i• Slngl, D— > srsi. i' & TH» SWOT ilin- Pjtlfr °s h • ! « ! XT*? 5 Mm Da 0 qr "£ o ooo <50 50-500 >500 Figure 4 Compilation of in situ permeability test results for crystalline rocks grouped according to depth Figure 2 (After Brace, 1980). Permeability coefficients calculated for each of the seven injection tests by various interpretive techniques. -49- References 5. Horner, 0. R., "Pressure Build-Up in Wells", in, SPE Reprint Series No. 9, Pressure Analy 1. Brace, W. F., "Some New Measurements of Linear sis Methods, 1967. Compressibility of Rocks", Journal of Geophy sical Research, V. 70, n.2, p. 391-338, 1965. 6. Jacob, C, and S. Lohman, "Nonsteady Flow to a Well of Constant Drawdown in an Extensive 2. Brace, W. F., "Permeability of Crystalline and Aquifer", Trans A.G.U., V. 33, n. 4, August, Argillaceous Rocks: Status and Problems", 1952, pp. 559-569. Int'l. Journal of Rock Mechanics and Mineral Science, 1980 (in press). 7. Krynine, D.P. and W.R. Judd, "Principles of 3. Earlougher, R.C., "Advances in Well Test Anal Engineering Geology and fleo-Techniques". ysis", SPE of AIME Monograph Series, V. 5, McGraw-Hill, 1957. 1977. 8. Snow, D.T., "Rock Fracture Spacing, Openings 4. Farmer, I.W., Engineering Properties of Rocks, and Porosities", Journal Soil Mechanics and Spon, London, 1968. Foundation Engineering, ASCE 94:79-91, 1968. -50- \ CAPILLARY EFFECTS IN ROCKS OF THE EARTH; INFLUENCE ON WELL BEHAVIOR Donald L. Katz University of Michigan Ann Arbor, Michigan Water permeates the rocks of the earth. The capillary effects of water in water-gas systems in porous media frequently controls fluid movement. Oil recovery is thwarted in. good part by capillary retention of oil. Caprocks in the main are sealed by capillary retention of water in the low permeability rocks. It seems that having a view of capillary effects is basic to under standing flow at wells in low permeability zones. This paper sets forth concepts on capillary properties in the rocks of the earth which might be helpful in understanding the production of fluids from tight rocks. In underground gas storage, especially In aquifers, it became important to understand caprocks-the mechanism by which gas is held indefinitely in the earth. From studies of low permeability rocks, Interest was developed in the fluid content of all rock layers of the earth. Capillary effects which are controlling in most caprocks are very significant in fluid fL.-w in all low permeability rocks containing two phases. What has been learned from threshold pressure studies for gas displacing water may be helpful in our considerations. Quite possible the most important aspect will be the relative permeability of the non-water phase in high capillary pressures rocks approaching caprocks. Capillarity and Threshold Pressure Important milestones in understanding capillary effects were the works of Schilthuls (1938), Leverett (1941) and Rose and Bruce (1949). The concept of threshold pressure of caprocks developed for gas storage in aquifers focused -51- on low permeability rocks; Thomas, Tek and Katz (1968) and Ibrahim, Tek and Katz (1970). A host of other papers and books cover the area generally as reviewed: Katz et al. (1959); Katz and Coats (1968). Leverett presented his view of the distribution water and a gaseous phase (2) within porous media in Figure 1. A slightly revised concept to clearly portray the fact that inhibition does not give full saturation is shown in Figure 2. The connate water content on Figure 2, point A, had been discussed by Schilthuis (1) earlier. Capillary retention of liquids by cores was studied by Rose and Bruce (3), Figure 3. It may be seen that the 100% liquid saturation on drainage is in effect a threshold pressure for gas to enter a zone 100% saturated with water. Thomas* thesis (4) took up the subject of threshold pressure for rocks of cap- rock quality and was able to show the relationship between his work and the earlier treatment by Rose and Bruce as well as other Investigators, Figure 4(4). Measurement of threshold pressures at higher pressure differentials were made using apparatus illustrated by Figure 5. It was shown that water saturated rock would hold gas at 1000 psi or greater differential by capillary forces. A much more extensive study by Ibrahim, Tek and Katz (1970) provided the relation ship of threshold pressure with permeability, Figure 6. What is Caprock In the course of these studies, it seemed necessary to describe caprock. This was done by Figure 7. It is rock so low in permeability that gas below It will not penetrate the rock because the pressure differential across the inter face is less than the capillary forces holding the water. Now let us look at the spectrum of rocks, and their capillary qualities on Figure 8. The intercept at 100% water by drainage gives the capillary pressure equal to the threshold pressure. la our studies (5), a few non-porous rocks were found: anhydrite and dense limestone. They are represented by point S on Figure 8. -52- Scanning Nature of Intaraticaa At the conclusion of the AGA Studies (5), it becane clear that displacement measurements in threshold studies should be aade at the entrance to the core. Pandey (1973) at the University of Michigan took the measurements reported as Front- End Threshold Pressures (8). A limited supply of high pressure gas was admitted to the entrance to a water-saturated core and the pressure observed. In a pressure leveling technique as the interface movement stopped due to capillary forces, data of type of Figure 9 are taken. Pandey working with Nellson Rudd (1973) at Geoengineering Laboratories developed a continuous scanning technique. Non-wetting fluid is forced through a water saturated core slowly with measured front-end pressures (9). Figure 10 shows the variable nature of the pore network. A comment seems in order, the pore space Is a network of channels of variable cross section and the threshold pressure reveals the largest channels 2CJ Ceos 9) through which fluids can flow. Using the formula: Pore radius = -r one can compute the pore radius. For the shale of Figure 9 with a threshold pressure of 1000 psi differential, the pore radius is computed: radius (cm) =2x72 -4H X 1- <«ettinS> * *•" * 10~5 £Sl_£sL_ cm 1000 psi dyne - 2.1 x 10"6 cm (0.02 Micron) It would seem that such a test might be adopted as a way of characterizing rocks. Applications of Capillory and Threshold Pressure Information Whenever two phases are encountered in the earth, i.e. water and gas, or oil and water, capillary effects may control flow. Production of gas to a well bore from a low permeability rock containing mobil water is influenced by the pressure difference between the gas phase in the well and the two phase system in the rock. With water bridging the fine interstices of the rock near the well bore added pressure drop occurs. When looking at the threshold pressure-permeability correlation and recognizing that the curve continues to higher permeabilities, pressure drops of 50-100 psi may occur at the well bore. -53- In fractured low permeability rocks, a similar pressure discontinuity can well occur at the matrix-fracture interface. Consider a cavern in low permeability rock, containing fractures, with water saturated rock and gas phase in the cavern. At the matrix-cavern inter face, pressure in the water phase can be 1000 psi or more higher than that of the gas phase in the cavern. The water in a rock at a hydraulic pressure less than the threshold pressure should not flow water Into the cavern. We know little about fracture behavior in this connection but it too would have a pressure discontinuity at the cavity wall, though much lower. It would be interesting to see threshold tests on insitu fractures described with some parameter like a permeability per unit area assigning some width to the fracture zone. When fluids are stored in underground caverns, with fractures in the rock, the maximum storage pressure is generally set at the saturated rock hydraulic head. Wells Gas wells in low permeability rocks have difficulty in harvesting the gas. No first hand experience is available but waLer interference, reduction in permeability at the well bore as pressure drops, and the usual unsteady state effects of radial flow are involved. Stripper oil wells in low permeability rocks are known to flow oil to a pumped well bore at low rates over decades. Fracturing is a well known technique for providing higher permeability channels to well bores, and is not considered here. However, the behavior of fluids at the interface of matrix rock and a fracture is akin to a well bore. To make predictions of well behavior, it seems that relative permeability measurements would be very helpful when threshold pressures are used to characterize the rocks. A quick checking of the SPE literature revealed no relative permeability data below 1 millidarcy where the threshold effect begins to be consequential. -54- Reviewing Figure 8, drainage behavior, would not the step pressure occur at the well bore similar to the intercept at 1002 water saturation? Surely, If water movement accompanies gas flow, would not water bridge the pores and be the equivalent of a dynamic threshold pressure restraint on flow? Now a separate topic will be presented briefly, Where is the earth free of a moveable water phase? Gypsum-Anhydrite Seal for Salt. Michigan reef gas reservoirs have been shown to have no connate water in the upper main body of the reservoir. Dehydrated gas is injected in storage operations and remains dry upon removal. The only explanation found is chat anhydrite within the reef rock has absorbed the liquid water. The study of this phenomenon has led to an analysis of the seal for salt depositions. Salt deposits are believed to remain undissolved by a protective layer containing anhydrite which reacts with grour.d water tc form a gypsum- anhydrite seal. My experiences indicate salt deposits and maybe possibly some limestone mines are the only rocks not containing water. REFERENCES 1. Schilthuis, R.J. (1938) Connate Water in Oil and Gas Sands,Trans AIME Vol. 127, p 199. 2. Leverett, M.C. (1941) Capillary Behavior in Porous Solids,Trans AIME, Vol. 142, p 152. 3. Rose, Walter and W.A. Bruce (1949) Evaluation of the Capillary Character in Petroleum Reservoir Rock, Trans AIME, Vol. 186, p 127. 4. Thomas, L.K., D.L. Katz and M.R. Tek (1968) Threshold Pressure Phenomena in Porous Media,Trans AIME, 243, p. 174. 5. Ibrahim, M.A., M.R. Tek and D.L. Katz (1970) Threshold Pressure in Gas Storage,AGA Monograph. 6. Katz, D.L. et al. (1959) Handbook of Natural Gas Engineering, McGraw- Hill Book Co., New York. 7. Katz, D.L. and K.H. Coats (1968) Underground Storage of Fluids, Ulrioh Books, Inc., Ann Arbor, Michigan. 8. Pandey, G.N., M.R. Tek and D.L. Katz (1973) Front End Threshold Pressure Measurements, Proc. AGA Transmission Conference, p 73-T-17. 9. Rudd, N. and G.N. Pandey (1973) Threshold Pressure Profiling by Continuous Injection,SPE Preprint 4597. -55- P»r c«nl Woltr Soturol o Figure 1 Capillary Distribution of Air and Water in Unconsolidated Sand (Leverett) (2). A — Irreducible Water Saturation 8 — Residuiil Gas Saturation C — Hireshold Displacement Pressure 0 .1 3. .3 .4 .» .€ .7 WATER SATURATION, Sw Figure 2. Inhibition and Drainage Capillary Pressure Curves (5). -56- Saturation Distribution with Pressure or Height 1 ! 1 1 (5 ifiLLAIir-tllrtllVnit!' du'tviVl R|U|^ 1 1 1 1 J 1 II RES IN VOIII FORMATION 45.«« WOOMINE RANGELT WMER o.m VaisJ EL ROILE UORINO o.w b KINSELLA VIKING O.M y KAtlt 0EE»K O.W \ "*"•»« LIOUC DEVONIAN 0.14 r*f»*f r w. t*^ AUINDUM ICONSOLIHTC' 7 <).V\~ i , LEVFRETT (UNCONMLIOATI 01 0.410 L 4 Yr1 §T 11 J eu. *- 1 T T!' 1 r i i 1 \l i J , \ 1 \ 1 1 If 11 \ 1 1 V \ I1 \ i * \\ \ \ « \ _L_ s r\ * \ , .1 \\ \ V V. HI0B17ICAL tltttrtNti \ \ \> k r M N \ \ 4LUC re* »ttvt** IT ,^ N \<4 \ V Ns L^ -. ~- ^S ^ v ^v ~\ 3 ^ £•;: K »;z •*•-. i\ ^ ^ i \, :v V, ^J"^ ^ N -», v •-... £;: IV **• •.T." "'• *• "if z-^, U.I ==5 E ]/rj* trc s4j £ o.» 9 10 11 *0 IS * 40 * ) 9 t i1 0 •• fe—?t w •a 0 •* 100 , Sw WA Ten t xi*RA 1 1 :Oh Figure 3 Capillary RetentioATU n Curves tRose and Bruce) (3) -57- •io)./E, •/a. F V^K •- Datu by Wyllie 4 Rose A- Data by Rose & Bruce Q- Data by L.K. Thomas c- dynes/cm $>- fractional porosity K- darcys Mill -1 I I I I I ^7-^w ' '""HS.M.O^/5; , P8i Figure 4 Correlation of Threshold Pressure with Other Properties of Porous Media (Thomas) (4) -58- CAPILLARY TUBE FOR MEASURING WATER LEVEL INFLATED PRESSURE SEAL 51tfcSTEEL I CONTAINER— . GAS SUPPLY Figure 5 Diagram of High Pressure Core Holder for Threshold Displacement Tests (Thomas) (4) -59- -09- THRESHOLD DISPLACEMENT PRESSURE psi o 00 1 o c (J 1 * r i ....zi —i. 1 #™s 9-0 1 h=H 1 _.i/ "O ...i ; m o 1— IFF™ s 1 m Ul ] > f„ ======: CD F r l ' 1—1 —-H=m iu O '— H IH4^ W • i --i- i i > i JO o —hi *J- — -< 1 ::T: :::::: -::: .... Ln . -:^-» E__- 1 ,! •/ '» i ;i / • !i / O ==i=h==i\h EEE::: Si T- m — -. 0 M% %HKTCII m POKI (0) NATURE OF ROCK WATER SATURATION Figure 7. Nature of the Gas-Water Contact In the caprock (7). Non-lrantmitiibla Suptr Caprock > PERCENT WATER SATURATION l0° Figure 8. Variations in Capillary Pressure Behavior for Various Rocks (Ibrahim, T.k, Katz) (5). ABSTRACT RADON AS AN INDICATOR OF WELLBORE INFILTRATION RATES IN URANIFEROUS IGNEOUS ROCK P. H. Nelson and R. Rachiele Lawrence Berkeley Laboratory Berkeley, California Granitic rock at an experimental site at Stripa, Sweden is unusually high in natural radioelements f~40ppm uranium), with even higher local concentrations occurring in thin chloritic zones and fractures. Gamma-ray logs made with a borehole probe demonstrate the background level and its uniformity throughout the rock mass; spectral gamma analysis of core samples provides a quantitative estimate of the radioelement content. Groundwater seeping from these fractures into underground openings and boreholes is likewise highly anomalous in its radon content, with the groundwater activity ranging as high as one microcurie per liter. When gamma-ray logs are run in boreholes where the inflow is appreci able, the radon activity in the water, rather than the decay products in rock, dominates the gamma log. Where mixing occurs, the gamma- activity, which is proportional to the radon concentration, appears to vary in a linear fashion with the rate of water inflow. Hence, in high flow holes (above a few liters per day of inflow) the gamma ray log behaves as a crude flow log. Where mixing does not take place and where the inflow occurs at a discrete interval, a logarithmic decrease of activity alom the hole is observed, caused by the gradual decay of radon as it migratt" upward in the water column. This spatial decay can also be translatec into an influx rate. These observations indicate that the natural radioactivity in groundwater infiltrating into boreholes can be used as a method of measuring infiltration rates even where the infiltration rates are fairly low, on t.ie order of a few liters per day, providing that the groundwater carries sufficient radon. The general applicability of -64- these observations will not be known until similar observations can be made in other igneous rocks. Both the abundance of uranium and its distribution along permeable fractures are critical in providing the natural radon tracer. ABSTRACT IN-SITU PERMEABILITY TESTING OF ROCK SALT E. W. Peterson and P. L. Lagus Systems, Science and Software San Diego, California 92038 In-situ permeability tests have been conducted in the salt formation surrounding the AEC-7 borehole located at the WIPP site near Carlsbad, New Mexico. Injection tests were performed at depths of 1870 and 2270 feet using compressed air as the working fluid. Data were obtained using the Systems, Science and Software designed guarded straddle packer system capable of measuring permeabilities 5.1 miurodarcy. In each test a 100 foot length of borehole was isolated and the surrounding formation examined. The resulting data were interpreted in terms of formation permeabilities. These perr "ability values were subsequently used in various repository design studies. Complete descriptions of the instrumentation, measurement techniques, and test procedures are included herein. The analytical/ numerical methods used for data analyses, are presented and the implied permeability values discussed. Problems inherent in performing reli able reproducible quantitative microdarcy range permeabilities are identified and the resulting impact on data interpretation is discussed. This work was performed for the Sandia Laboratory, Albuquerque as a part of their research and development activities in support of waste acceptance criteria for WIPP. -66- -A- SOME CONSIDERATIONS FOR TRACER TESTS IN LOW PERMEABILITY FORMATIONS Glenn Thompson Department of Hydrology and Mater Resources University of Arizona Tucson, Arizona 85721 Tracing experiments in low permeability formations CONVERGENT-FLOW TESTS are used primarily for measurement of porosity and dispersivity. In some cases they are used for In this test type, ground water is pumped from a measuring the direction and rate of water movement. single well creating a flow system in which the Well layouts and test types are as variable as the flow lines converge on a single point—the pumping situations in which they have been applied. In well. This technique 1s useful for determining the addition a correspondingly large variety of tracers same parameters as the previous methods. A typical have been used in the past eighty years to perform well layout and the flow path of a tracer intro these tests. In order to provide some basic guide duced into the system 1s shown in Figure 5. In lines for performing tracer tests in low permeabil this technique both the dispersion and porosity ity formations, several conventional tracing measurements are aided by the observation of Lracer techniques and a listing of the most commonly used at points arranged in a line across the flow sys tracers are given below. tem, thus defining the width of the tracer plume. The principal difficulty associated with this TWO-WELL INJECTION-WITHDRAWAL TESTS method is dilution of the tracer. By comparison to the previous methods, only a small amount of tracer In this test type, water is pumped from one well can be injected because 1t 1s normally added in a and injected in a second well, thus developing the single instantaneous slug or pulse rather than maximum possible gradient between the two wells. being added continuously. Once injected, the This is the most commonly applied technique anC tracer does not leave the well as a pulse, but is has the greatest chance of success in low perme diluted out of the well at an exponentially de ability formations where wells are great distances creasing rate. The tracer is further diluted at apart or in circumstances where the probability of the pumping well when it mixes with unlabeled water tracer interception would otherwise be very low. converging there. This technique offers the advan Figure 1 shows the typica1 "' Mng design with tage over radial flow techniques of not requiring associated equipment ' filters, flow a supply of injection water; in addition, it pro meters) for a two w?' gure 2 shows the vides a more sensitive method of measuring disper theoretical flow pat is established be sion than the two-well test. tween the two wells ifw. Extended pumping. The measurement of porosity assumes that water is dis POINT DILUTION METHOD placed through the indicated flow tubes. This technique utilizes the principle that the rate The two well technique is most commonly used for of solute dilution out of a well bore is a function measurements of effective porosity and disper of the flow velocity of water around the well. The sivity although it 1s relatively insensitive to technique may be useful for determining zones of the latter. Because the tracer can be added to high or low permeability in a well that is packed the injection water for long periods of time, the off accordingly. In high permeability formations overall effect of dilution can be reduced accord the technique is useful for measuring groundwater ingly. Consequently, tracers that are detectable velocity induced by the natural gradient. Figure 6 at extremely low concentrations are not necessary shows the results of a point dilution experiment for this technique. conducted in the Conasauga Shale at Oak Ridge National Laboratory using a fluorecarbon tracer. RADIAL FLOW The tracer concentration in the well is controlled by dilution effects down to a few parts per tril Radial flow techniques can only be used where a lion, after which the concentration remains rela water supply is available for injection. This tively constant due to the rate of desorption of test requires water to be injected in a central tracer from the sides of the w<01 bore. The equa well with regular sampling taking place at obser tion for calculating the velocity is shown in the vation wells at various radial distances away from figure. The theoretical basis for the calculation the injection well. Figures 3 and 4 show what may 1s given by Drost.1 be considered a typical pattern of water movement away from the injection well. Water 1s usually OTHER FACTORS displaced in a non-symmetrical or ameboid form around the injection well. Porosity and longitu In addition to the factors influencing the choice dinal dispersivity are obtainable from this test, of test type, other conditions will have a profound although a large number of observation wells are effect on the well layout. The scale of the dis needed to obtain a meaningful estimate of porosity persion parameters measured will be a function of due to the typically irregular shape of the dis the distance between the Injection wells and the placed volume. observation wells. However, as flux distance increases, the time required to perform the test generally limited to about 1 ppm using selective increases exponentially, tracer dilution problems ion electrodes. increase, and for some tests the probability of intercepting the tracer decreases rapidly. Other Background problems also limit the utility of many more obvious factors that influence test design tracers for field use. Anions such as Br and CI are: number of holes, funds for drilling, time which are otherwise excellent tracers often have available or required to run tests to completion, backgrounds that limit their degree of dilution and manpower and equipment for pumping and moni and their range of applicability. Slight varia toring. tions in the background of a given tracer almost always lead to some confusion or ambiguity in the SELECTION OF TRACER interpretation of the results. Ideally, the first consideration in the selection A list of tracers and their important character of a tracer is the type of performance expected. istics, organized according to their general class, In particular, one may be trying to model or trace is given in Tables 1A, IB, and 1C. The list con the movement of the water itself or that of a tains only representative examples although all of solute species that is subject to some sorption. the most widely used conventional tracers are Although it is not possible to duplicate exactly named. the movement of water or most solute materials by means of tracer, some major pitfalls can be avoided by the use of the foiiuwing basic guide lines for tracer selection. Table 1. Common Groundwater Tracers in general, anions are the least sorbed solute species on natural silicate or carbonate aquifer materials. This is due largely to the fact that Characteristics the minerals tend to have negatively charged sur faces, and since anions are also negatively charged, they tend to be repealed from the simi larly charged mineral grain surfaces. Although Particulate Tracers anion exchange does take place on some clay miner al substrates, it appears to be of negligible Lycopodium spores No chemical sorption, about 50 importance in most ground water systems. Non- iim diameter, multiple tracers charged molecules (such as many organic species) possible by dying spores dif tend to be sorbod more than anions as a function ferent colors. Collected by of their polarizability.2 When exposed to a nega trapping on plankton nets fol tive charge, a dipole may be induced on the other lowed by microscope identifica wise symmetrical or neutral molecule. The tion and counting. Used almost positive pole created by the separation of charges exclusively for tracing karst makes the molecule susceptible to sorption on the conduits. negative mineral surface. Microorganisms Smaller than spores, 1 to 3 p Cations, as one would expect, are the most sorbed yeasts diameter, most useful for test solute species. These are also susceptible to coliform ing permeability of aquifer to cation exchange reactions on clays that are abun bacteria transport of organisms. Move dant in many aquifers. Figure 7 shows the results ment primarily through frac of a field tracing experiment which illustrates tures in sediment or rock. this point. Breakthrough curves of cationic, Organisms may sink or float in anionic and noncharged solutes are shown for an still water. Measured by fil observation well 2 meters from the injection well. tration followed by incubation The experiment was conducted in the Ogallala Sand and counting colonies. formation as part of an artificial recharge study 3 performed by the U.S. Geological Survey. 0.02-0.05 pin. Many types sorbed on media due to positive A variety of other factors may also influence the charge on organism. Bacterio choice of tracer. The sensitivity and ease of de phage (virus infecting E. Coli) tection are often the first considerations in shows potential as good tracer selecting a tracer because the dilution require Que to negative charge on ments of a particular tracing experiment may be a organism. Detection by cultur- primary limiting factor. Among the nonradioactive ing and cnlony counting.•* tracers, fluorocarbons offer the greatest dilution possibility having routine measurement capability in concentrations down to 1.0 part per trillion B. Nonionic Tracers 0 pg/ml) or less. Fluorescent dyes probably rate second with rapid measurement capability down to Fluorocarbons All fluoromethanes and fluoro- 0.1 part per billion \1 ng/ml) if no background CC12F2 ethanes with chlorine and/or problems exist. Aromatic organic anions are bromine substitutions. Slight CBr2F2 rapidly measurable using liquid chromatographic C2CI3F3 to moderate sorption on sili techniques in concentrations down to a few ppb. cate or carbonate material. Inorganic anions such as Cl~, Br~ and I", are etc. Strong sorption by organic Table 1. Common Groundwater Tracers - continued Table 1. COHWKHI Groundwater Tracers - continued Characteristics Characteristics B. Honianic Tracers - continued Ionic Tracers - continued materials such as coal and and in karst tracing. Used peat. Mondegradable, non 1n highly permeable sand and toxic, volatile, low solubil gravel aquifers. Detected by ity, difficult handling. fluoHmetry, 1 to 0.1 ppb. Measurement by gas chromatog raphy with electron capture Yellow dye, same as rhodamine detection. Most are detect WT but much stronger sorption able to 1 part per trillion. on aquifer materials. Aldehydes and Used in oil reservoir studies, Chelates EDTA complexes with heavy alcohols degradable, detectable at ppm E0TA-5iCr metals, or radioisotopes de level with GC. EDTA-IN tected by radiation or by post neutron activation. Some com Tritium Radioisotope of hydrogen, low plexes unstable 1n presence of HTO, CH3T sorption on most aquifer mate other cations in water. Numer rials, very restricted use in ous chelated tracers have been shallow aquifers due radiation developed and tested with vary hazard. Common use in oil ing results, mostly in oil reservoirs. T-..? = 12.3 yrs. reservoir studies. Good sensi Measurement by weak a radia tivity. tion. Thlocyanate Na, K or ammonium salts of SCN~ thiocyanate, most commonly used chemical tracer of the oil Ionic Tracers Industry. Low sorption, mea sured by colorimetry, detect Hal ides able down to 0.1 ppm. No sorption, inexpensive, high cr background in groundwater, density problems when used in Organlc anions Unlimited variety of good high concentrations, most use sodium benzoate tracers possible. Very low ful in laboratory experiments, pentafluoro- sorption, stability improved benzoic acid by fluorine substitution. Can measured by titration methods be measured with high precision or by electrical conductivity. using HPLC. Detectable in low ppb range. Very slight sorption, low nat ural background in fresh water aquifers, best general purpose groundwater tracer, measurable using selective ion electrode, practical sensitivity about REFERENCES 0.5 ppm. 1. Drost, W., 0. Klotz, A. Koch, H. Moser, F. Moderate sorption, very low Newmaier, and W. Ravert, Point dilution methods natural background, measured of investigating ground-water flow by means of by selective ion electrode, radioisotopes. Water Resources Research, V. 4, 0.5 ppm. pp. 125-146, 1968. Radioisotope t,, = 8-2 days. 2. Ciccioii, P., W. T. Cooper, P. M. Hammer and 2 J. M. Hayes, Organic solute-mineral inter Useful for short term tests, actions: A new method for the determination most common application In oil of ground water velocities. Water Resources reservoir studies. 8 and y Research, V. 16, pp. 217-223, 1980. emission. 3. Basett, R. and others, Preliminary data from a Dyes series of artificial recharge experiments at Rhodamine WT Red dye, moderate sorption, Stanton, Texas, U.S.G.S. Open file report ?'.- moderately stable, low back (in preparation). ground fluorescence, most fre quently used in surface water 4. Gerba, C. P., personal communication, Baylor College of Medicine, Houston, Texas, 5/20/80. -69- Fig, 1. Two well recirculating test. PUMPING WELL INJECTION WELL Fig. 2. Flow pattern for two-well injection-withdrawal a homogeneous isotropic aquifer. liMjec OBSERVATION RECORDING RATE WELL INJECTION WELL-\, .AND TOTALIZING J FLOW METER ..SAMPLING POINT Fig. 3. Radial flow test. Fig. 4. Radial flow test. OBSERVATION WELLS Fig. 5. Convergent flow test. —ESTIMATED INITIAL CONCENTRATION IN WELL V= velocity G= Well Diameter C'1 Inillal Concentration C- Concentration After t I * Elapsed Time s = £f feclivs Porosily \ WEEKS AFTER INJECTION Fig. 6. Point dilution experiment in Conasauga shale at Oak Ridge National Laboratory, Oak Ridge, Tennessee. -72- 0J—^-, . , , , , ,—^-, , , 0 100 200 300 400 500 600 700 800 900 1000 MINUTES Fig. 7. Radial flow tracer experiment showing the behavior of selected anionic, neutral, and cationic compounds observed at a distance of 2 meters from the injection well in the Ogallala Sand Formation at Stanton, Texas. -73- INJECTION VERSUS PRESSURE PULSE BOREHOLE TESTS IN FRACTURED CRYSTALLINE ROCKS - OBSERVATIONS AND RECENT EXPERIENCES C.B. Forster and J.E. Gale Department of Earth Sciences University of Waterloo Waterloo, Ontario,. N2L 3G1 Abstract relatively permeable zones within a low permeability framework. These zones are Previous workers have proposed the either discrete fractures, closely spaced pressure pulse test as an alternative to groups of fracture or thin porous media steady-state determination of zones. The matrix conductivities of most permeabilities in fractured crystalline crystalline cocks generally range from rocks. A field and laboratory research 10 to 10 cm/sec. The hydraulic program has been conducted to assist in conductivity of the narrow, relatively developing techniques to analyze in-situ permeable zones can be many orders of pressure pulse tests. Specifically this magnitude greater. program was aimed at i) comparing steady- state conductivity determinations to Measurement of tack mass conductivities pressure transient determinations, ii) in excess of 10" cm/sec. aro commonly assessing the eEfects of equipment carried out using steady-state injection compliance on pressure pulse test results tests (Figure 1). Unfortunately, in lower and, iii) determining the radius of conductivity rocks, an accurate flowrate influence of a transient pressure pulse measurement is difficult to achieve. test in fractured crystalline rocks. Flowrates of fractions of millilitres per hour require long test times (hours to In the laboratory, transient pressure days), sensitive measurement equipment and pulse tests and steady-state flow tests long test intervals (tens of meters) . where performed on a sample of Stripa .jOng test times increase the probability Granite core (11 cm long and 4.5 cm in of flowrate measurement errors resulting diameter) containing a single natural from temperature and pressure variations fracture parallel to and centered on the during the test. Long test intervals core axis. The test configuration reduce the capability of determining simulated a full scale borehole test permeabilities of individual fractures or cavity using borehole seals of various a small number of fractures. Thus, the compliances in a 76 mm steel tube. Test transient pressure pulse test, as results indicate a good correlation described by Brace et al (1968) , has been between steady-state and transient proposed as an alternative to steady-state conductivity determinations. Packer injection tests in fractured rocks. compliance was found to cause underestimation of sample conductivity by up to a factor of 2. With decreasing Brace et al (1968) have described the sample permeability the significance of use of the pressure pulse technique to packer compliance was found to increase. perforin permeability determinations in the laboratory. Fiaure 2 shows a schematic of the test configuration. fc test is In the field, transient pressure pulse performed by placing a rock sample between tests and steady-state flow tests were two reservoirs of fixed volume ( v^ and performed in an array of boreholes V2) • If the pressure in the upstream collared 338m below ground in a fractured reservoir (P.) is raised instantaneously crystalline rock mass. There is no the rate of 'equalization of pressures P, apparent correlation between results of and P„ in the two reservoirs is related to each test type. In order to determine the the porosity and permeability of the rock radius of influence of in-situ pressure sample. A confining pressure Pc is pulse tests in low-permeability fractured applied to the system to reproduce the rocks the volume of water in the test t state of stress expected at the point of cavity and the monitoring cavities must be sampling. Brace et al.analyzed the results the same order of magnitude as the volume of their tests by assuming that the of water in the rock mass influenced by laboratory system acts as an equivalent the test. electrical circuit containing two capacitors (equivalent to V, and V2) in Introduction series with an intervening resits tor (rock sample). The upstream reservoir Analysis of contaminant movement through with applied pulse pressure AP=P,-P2 p, is low permeablility fractured crystalline represented by a capacitor fully charged rock must be based on an understanding of at +<0 thus at t =0 the capacitor discharges the physical hydrology of such rock according to an exponential decay. Thus, masses. Fractured rock masses are the upstream reservoir pressure P. generally characterized by narrow, 'ecreases while the downstream reservoir pressure, P~ increases until both reach obtained from the relatively short the equalizaiiion pressure P-. Following pressure pulse tests in low permeability Brace et al (1968) the pressure volume rocks are expected to yield more accurate relationships can be expressed in equation rock mass conductivities than injection form by: testing in fractured crystalline rock. A method for analysis of in-situ pulse tests in fractured impermeable media has • v„> U) been proposed by Wang et al (1977) and investigated using a semi-analytical model based on solution of the diffusivity equation for different fracture configurations using appropriate rock and a = (-7) . fc- + =-) (2) water properties and boundary conditions. U0 Vl V2 However, this method is not yet amenable to analysis of the results of field tests. In order to assist in developing where the parameter a is a function of, i) techniques to interpret results of in-situ fluid visiosity, v, , and fluid pressure pulse tests, laboratory and field compressibility, g, ii) sample permeability experiments have been performed to k and cross section area A and iii) investigate the following: reservoir volumes V, and v. This relationship requires that the parameter, i) comparison of conductivities a in the governing diffusivity equation determined by steady-state conductivity tests and transient pressure pulse tests, 2 3P (3) 3X2 ii) the radius of influence of a pressure pulse test performed in fractured crystalline rocks, be equal to zero._ For a fractured sample, the parameter a contains terms which iii) the effect of variations in test include matrix fracture permeability, cavity volume (due to equipment matrix and fracture porosity, fracture compliance) on pressure pulse test stiffness, rock compressibility and jfluid results. compressibility. However, as a is assumed to equal zero Laboratory Experiments The laboratory test program was designed (4) to investigate; i) the comparison between transient annd steady-state conductivity tests and ii) the effects of packer compliance on pressure pulse tests implying that the pressure gradient is performed in a simulated field linear at all times although varying in configuration. A schematic of the test magnitude with time. equipment is shown in Figure 3. Lin (1977) used a more complete form of The test equipment consists of 3 main the same mathematical formulation, where components; upstream reservoir, downstream a ' was considered to be non zero, in a reservoir and sample cell (Figure 3). A numerical simulation of a proposed rock core ( 4.5 cm diameter and 11 cm laboratory testing program. Later, Lin long) containing a single fracture is held (1979) used this same numerical technique in the sample cell. This sample to determine rock sample permeabilities represents the dominant fracture from laboratory test data. controlling conductivity around the borehole with the sample cell exerting an A pressure pulse test performed in the hydrostatic stress on the sample which field uses the same borehole configuration would be expected at depths of as the injection test (Figure 1} and the approximately 400 to 500 m. In this pulse test pr inc iples descr ibed above. experiment the core is z sample of stripa Once a borehole cavity is sealed, a Granite containing a single natural pressure pulse is created within the test fracture parallel to and centered on the cavity by diplacement of several core axis. The downstream reservoir is milliliters of water. The decay of the simply a steel water filled tank pressure pulse is monitored by a sensitive representing the porosity of the overall pcessure transducer. The transient nature rock mass surrounding a test cavity. The of the pressure pulse test produces a test upstream reservoir was designed to time of minutes or hours which is much simulate the actual borehole cavity. A 7 less than the hours or days required for metre length of steel tube with a 76 mm injection testing of the same interval. inside diameter was used to represent the Thus, analysis of pressure decay curves borehole. Various borehole seals were -75- used to isolate a 3 metre section of the (by varying the borehole seals) causes a tube in order to represent varying degrees factor of 2 variation in conductivity. In of packer compliance. Steel plugs were addition, reasonable agreement was found used to represent the least compliant case between conductivities calculated from while standard air or water filled both steady-state and transient tests. inflatable packers represent the more However, our testing indicated that with compliant field situations. decreasing conductivity the significance of compliance effects increases. It was The test program was conducted after also found that small variations in stressing the sample through three initial temperature ( + 0.B1 C), occurring loading cycles (thus minimizing hysteretic during transient testing, can effects of stress loading and unloading on significantly affect the shape of the fracture flow characteristics). During resulting pressure decay curves. the fourth loading cycle the confining pressure was increased in a stepwise Field Experiments manner from zero to 3.4,6.9r and 13-9 MPa. At each step both steasy-state flow tes^-s The field test program was designed to and pressure pulse tests were conducted investigate i) the comparison between with similar pressure gradients across the steady-state and transient conductivity sample, (approx. 0.14 MPa). Also, at each tests and ii) the radius of influence of a step each different borehole seal was used pressure pulse test in a fractured in order to observe the effects of granite. The test program was carried out equipment compliance on the test results. in an array of boreholes collared in a drift at the 338 metre level of the Stripa Steady-state flow tests were performed Mine, (Gale and Witherspoon, 1979; Forster by applying a steady pressure gradient and Gale, 1981). The drift extends into a across the sample and monitoring the fractured granite mass with the boreholes resulting flow of water through the of interest extending beyond the end bf sample. Once steady flow and pressure the drift. The borehole array is shown in conditions were attained results were Figure 5 vith the central HG-1 borehole recorded and used in calculation of sample oriented horizontally, HG-3 and HG-4 conductivity by standard techniques, inclined downwards, HG-2 and HG-5 inclined (Forster and Gale, 1980). upwards and DBH-2 oriented horizontally. Holes HG-1 through HG-5 are 30 m in Transient pressure pulse tests were length. DBH-2 is about 75 m in length but performed by increasing the pressure in only a 30 m section was used. The dark the upstream reservoir { by displacement cylinders shown in Figure 6 represent the of several millilit\:es of water] and borehole cavities isolated using standard monitoring the resulting pressure decay. inflatable packers. Twenty-five cavities The pressure time data was recorded and were used in the test prenram, each used in calculation of sample conductivity approximately 7 litres in volume. by Brace's semi-logarithmic straight line technique. Normalized pressure P.. was Both steady-state injection tests and calculated by dividing the residual transient pressure pulse tests were pressure decay (P,-P ) by the magnitude of E performed in the isolated cavities in the original pressure pulse (4P). A plot order to compare the resulting of the log of P against time for one N conductivity determinations. Steady-state portion of the test series is shown in tests were performed by injecting water Figure 4. This test series was run at the into the cock-mass under constant pressure maximum confining pressure of P =13.8 MPa c while measuring the injection flow rate. with pressure pulse AP=0.14 MPa (A P was 1% Flow rate and pressure data obtained when of p . and pore pressure P_ = 1.4 MPa (P p p steady-state flow conditions were reached was 10% of P ). c was used to calculate the hydraulic conductivity of the rock around the test An estimated value of a for the_sample interval assuming a porous media approach. tested is in the order of 10" s/cm which Pressure pulse transient tests were is sufficiently close to zero for the performed by displacing a small volume of purposes of our analysis. Thus using a , water in a tube connected to the test the slope of a plot of log P„ against interval while monitoring the resulting time, permeability, k, can be calculated pressure increase and decay. In addition, from equation 2. Using this approach pressures were monitored during each test transient conductivity values were both in the test cavity and in several calculated (Table 1). From Figure 4 and observation cavities in order to observe Table 1 it can be seen that the least the extent, or radius of influence, of compliant configuration, the steel plug i-i th pressure pulse and steady-state seal, produces the steepest slope thus the tests. highest conductivity value while the more compliant water and air filled packers Figures 7,8,9 and 10 show normalized yielded the shallowest slopes and lowest pressure decay, P , plotted against log conductivity. From Table 1 it can also be N seen that var iat ions in packer compliance time for different test intervals. Steady-state conductivity values (calculated from injection teats, assuming produce conductivity values which porous media conditions) are shown beside underestimate the non-compliant steel plug the corresponding pressure pulse decay conductivities by up to a factor of 2. curve for each interval. Also shown in With increasing confii. ng pressure ( Figures 7,8,and 9 are the fracture logs decreasing conductivity) x.:ie significance for each test interval , (Details on the of packer compliance was found to fracture are given In Forster and Gale, 1981). increase. Significant compliance effects Figure 10, without the fracture log, is a were also found to result from summary plot of the -rurves given in temperatures variations exceeding +_ Figures 7,and 8. Tests performed in .01°C. intervals HGlrlb, HGl-3b, HG3-4, HG3-5, HG5-2 and HG5-3 (Figures 7 and 8) show field steady-state and transient tests docay curves similar in shape but having a were performed in an array of boreholes variety of decay times. Figure 9 shows collared in a granite mass 338 m below that the pressure pulse curves obtained in ground. Transient conductivities have not intervals HG3-3, HG4-4 and HG4-5 have been calculated* however steady-state significantly extended decay times. These intervals also have correspondingly low conductivities have been calculated and steady-state conductivity values. One compared qualitatively to the transient might expect that increasing decay times decay curves for each interval . There is would correspond to decreasing steady- no apparent correlation between the two state conductivities. However, as shown types of test results. This lack of in Figure 10 this trend does not appear. correlation is primarily attributed to the In fact there is a very poor correlation complex nature of the fracture system and between decay time and steady state differences between the rad-us of o ...activity . This lack of correlation influence for each test type. Observation is expected to result from a combination cavities did not respond to pressure of factors including, i) the complex pulses generated in test cavities despite nature of the fracture system, ii) nature hydraulic connection indicated by steady of test equipment (packer compliance), state testing. The minimum distance iii) differences between the volume of between cavities was 1.5 m. However, the rock mass tested by steady-state and large volume {'II) of the observation transient tests (difference in radius of cavities appears to preclude observation influence). of any pressure response resulting from a displacement of only a few millilitres of water in the test cavity. During each pressure pulse test up to s<-'Ven adjacent borehole intervals were References monitored to determine the radius of influence of a pressure pulse test. The (1) Brace, W.F., Walsh, J.B., and minimum distance between cavities was 1.5 Frangos, W.T., 1968. Permeability m ? however, throughout the test program of granite under high pressure, J. no response was obtained in any Geophys. Res. Vol. 73, No. 6, op. observation cavity. Steady-state flow 2225-2236. tests indicated a gcod connection between test cavities thus a response might have (2) Forster, C.B. and Gale, J.E,, 1980. A been expected. However comparison of the laboratory assessment of the use of volume of the test cavity (71 ) to the borehole pressure transients to volume of the pressure pulse displacement measure permeability of fractured (several millilitres) suggests rock masses. Lawrence Berkeley Lab. insufficient water was displaced in the Tech. Repor t 867 4 Un iver s i ty of test cavity to cause an observable California, Berkeley, California. response in the observation cavities. (3) Forster C, Gale J.E. 1981. A Field Conclusion Assessment of the Use of Borehole Pressure Transients to "easure the In this paper the authors have described a Permeability of Fractured Rock laboratory and field program designed Masses. Lawrence Berkeley Lab. Tech. primarily to compare steady-state Report 11829 University of conductivitly determinations to transient California, Berkeley, California. pressure pulse determinations. (4) Gale, J.E., and Witherspoon, P.A., Laboratory steady-state and transient 1979. An approach to the fracture tests were performed on a sample of Stripa hydrology at Stripa: preliminary Granite core ( 11 cm long and 4.5 cm results, Lawrence Berkeley diameter) containing a single natural Laboratory, University of California, fracture parallel to and centered on the Berkeley, California,USA. core axis. Tests performed at three different confining pressures show a good (5) Lin,W., 1977. Compressible fluid flow correlation between steady-state and through rocks of variable transient test results {Table 1). In permeability, Lawrence Livermore addition, packer compliance was found to Laboratory, University or California. -77- 6) Lin, W., 1979. Measuring the permeability Wang, J.S.Y., Narasimhan, J.N. Tseng, C.F. of Eleana Argillite from Area 17, Nevada Test and Witherspoon, P.A., 1977. Transient Site, using the transient method. Lawrence flow in tight fractures. Proceedings of In Livemore Laboratory, LJvermore, California, vitational Well-Testing Synposium, October U.S.A. 1977, Berkeley, California. Comparison of steady-state results and transient test results. Granite sample - Cycle 9k Mean K- (cn/sec)xlO Mean K Ccn/sec)xlO P Borehole Sceady Steady (MPa) Seal State Transient State Transient Steel Plug 16 74 Air Packers 16 54 l? 3.4 MPa 16 56 3.4 Air Packers 14 46 (? 5.5 MPa Water Packers @ 3.4 MPa Steel Plug 71 17 6.9 Air Packers 6.5 54 15 11 8 3.4 MPa Air Packers 55 11 ? 5.5 MPa Water Packers S 3.4 MPS Steel Plug 1.9 2.2 Air Packers 2.2 1.7 2.9 1.9 Q 3.4 MPa 13.8 Air Packers 1.4 1.5 ? 5.5 MPa Water Packers 1.1 1.1 9 5.5 MPa •A I 1 I I TY Pi P2 PI- t tPI. i r Fig. 2. Schematic of the test configuration used by Brace et al. (1968). Fig. 1. Schematic of a saddle-packer system installed in a borehole. PACKER PACKER u » r i J x x SiMUlATED BOREHOLE WITH PACKERS AND DATA AQUISmON PISTON DISPLACEMENT SCREW Fig. 3. Schematic of experimental apparatus. SINGLE FRACTURE GRANITE CYCLE NM t.6.1 s" • Pc-i3.IMPa AP-O.MHPo O 06 P^-i.«MPo flORE HOLE SEAL o STEEL PLUG • * £ 0.3 x AIR PACKERS 4 3.4 MPfl. B AIR PACKERS « 3.5MPa A WATER PACKERS « 3.HMP0. 1 1000 tZOO 1400 DECAY TIME (sac) Fig. 4. Typical plot of log of normalized pressure decay against time for a granite sample containing a single fracture. APPROXIMATE OUTLINE OF NORTH END OF VENTILATION DRIFT Fig. 5. Schematic perspective of boreholes north of the ventilation drift. APPROXIMATE OUTLINE OF NORTH END OF VENTILATION DRIFT Fig. 6. Schematic perspective of borehole installation pattern. 10* 10° TIME (seconds) Fig. 7. Plot of normalized pressure against log time for pressure pulse tests in intervals HG3-5, HG5-3 and HGl-lb. -81- 10* 10° TIME (seconds) Fig. 8. Plot of normalized pressure against log tine for pressure pulse tests in intervals HG5-2, GHl-30 and HG3-4. **-* —- •*tej; : ~> HG4-5 N"\ KssX-09 TEST -v (cm/(sec) V < 5 -H3-3B23 0.4 oa. -H4-4B23 0.5 z -H4-5C23 <0.1 \ NB. A VOLUME = 2.6cm3 for all tests 10° 102 103 10" 10s TIME (seconds) Fig. 9. Plot of normalized pressure against log time for selected pulse tests with extended decay characteristics. H1-1C23 •"—* H1-3D23 ••-• H3-4B23 « ' H3-5D23 •*-•* H5-3D23 -»—i» H5-2D23 •«— *• \ \ N.B. ALL K„VALUES IN cm/sec A VOLUME-2.6 cm3 \ ,-2K10"B O Kss«5x10-5 5BSC. 10° 10! 103 105 V'JJ"£ (seconds) Fig. 10. Sumrary plot of nonrslized pressure against 14g tijne. Curves fran figures 7 and 8. -83- ANALYSIS OF CONSTAMT-HEAD WELL TESTS IK KONPOROUS FRACTURED ROCK T. Doe and J. Renter Lawrence Berkeley Laboratory University of California Berkeley, California 94720 The constant-head injection test, also known as the pressure test or packer test, has long been Pump test a standard permeability test in geological and a) constant flaw rate , civil engineering. Most of the published data on b) annulus cross section 35.5 cm c) time given Is only to overcome the permeability of nonporous fractured rock has ' wellbore storage effect been obtained t*y such tests. In. general, the d) time limit' 7aays>f>Iminute analysis of the data from constant-head tests has been made asaum ig steady radial flow by invoking a "radius of influence". If one compares the results of steady analyses and transient flowrate analyses, the error in assuming steady flow is less than an order of magnitude for reasonable values of storativity, and this error can be mini mized through proper choice of radius of influence. Although the steady flow assumptions do not result in large errors in the calculation of is 46 cm; c)min decay 75% _ permeability, careful design of constant-head well d)mox decay 9975% tests can yield not only storativity, but also eHime limit17days qualitative information on the areal extent of >t >l minute "• permeable zones or fractures tested* Constant-head well tests have several major advantages over other well test techniques in low o) equina lent porous medium perme obi lily ' iwn I Of Infinitely long Iraclurat - permeability rock. Unlike pump tests, wellbore . linimumdecoy 10% , storage effects are virtually nonexistant. Pro elmoxlmum decoy 90% .A vided low-flow measurement apparatus is available, ilmil: 7doys»l>lminule , constant-level tests are far more rapid than slug tests and, unlike pulse tests, compliance of equip 1 example, ii • /.6 era diameter well, the loge of the ratio ot che radius of influence t the well radius only varies from 5.6 to 10.2 for rQ varying from 10m to 1000m. To account for errors due to the flow not being perfectly confined and therefore not entirely radial, several "shape factors" have been used. Hydraulic conductivity determined from shape fac tors generally employs an equation of the form K - §£ x C (3-8) where C is a diraensionless constant which varies depending on the assumed pattern of flow about the test zone. Such factors include (1) flow with potentials elliptical about the test zone (Hvorslev 1951), (2) radial flow near the well becoming spher Fig. 2 Schematic of equipme. "- used for con ical at r - b/2 (Moye, 1967), (3) empirical correc stant head injection tests. v"BL 812-8187) tions based on electrical analogues of porous media {Sharp, 1970), and (4) radial flow with the radius Constant-head tests were originally developed of influence equal to the test zone length (Snow, for damsite and other engineering investigations 1968; Ziegler, 1976). For most normal test condi by the French engineer. Lugeon (Serafim, 1968). tions, ziegler (1976) notes that the variation In Europe, hydraulic conductivity is often express between these correction factors is not greater ed in the Lugeon unit, which is equal to one liter than about 30%. per minute of flow per meter of hole length at an 2 overpressure of 10 kg/cm . Such tests are com The importance of "shape factor" corrections monly run by the Army Corps of Engineers, who have in testing of fractured non-porous rock is ques published two manualJ of injection test procedure tionable, unless the rock has a fracture spacing recommendations (Hvorslev, 1951i Ziegler, 1976). which AS small relative to the length of the packer -85- constant and the flowrate should be expected to be transient• Constant-head well test solutions have not been as widely investigated in the hydrologic or petroleum literature as constant-rate tests. Nonetheless solutions for simple geometries have been available for some time. The first hydrologic applications were made by Jacob and Lohmcn (1952) who derived type curves for transient flow in infinite aquifers and applied the results to flow- rate decline from flowing artesian wells. Hai.tush (1959) extended Jacob and Lehman's work to leaky aquifers, infinite aquifers, and aquifers with either closed or open outer boundaries. More recently, Jaiswal and Chauhan (1978} have investi gated spherical flow under constant head conditions. Extensions of constant head solutions bo include skin effects and pressure buildup after constant- head production have been made by Uraiet and Raghavan (1980) and Ehlig-Econoraidee (1979J, the former using finite differences, the latter by analytic solution. Errors in steady Flow Analysis of Constant Head PRESSURE Tests pig. 3 Hypothetical pressure-flowrate curve A pctential source of weakness in the prac for constant-head injection testa: A- laminar tice of constant-head tests is the steady flow flow, B- turbulent flow, C- fracture deformation, data analysis. First, steady flow analysis assumes (after Louis and Maini, 1970). UBL 812-8194) an infinite conductivity material at the radius of influence; and, second, it ignores groundwater seal. For tests in rocks where the fracture spac storage both due to water compressibility and to ing is large, only a few fractures will be con finite fracture or matrix stiffness. tained in any giv^n test interval, and of these only the fr^cLure with the largest aperture will Transient fiowrate solutions overcome these havt any significance, due to the cubic relation objections. Time-variable radial flow under ship of aperture to flowrate. Flow will be con constant head can be described by fined to the planes of the large-aperture fractures unless they intersect other fractures of larger aperture close to the borehole. In either case, the equipotential lines about the test zone are unlikely to follow elliptical or spherical paths, and routine application of shape factors based on such assumptions may often be in error. G(A) = constant head well test function Transient Analysis of Constant Head Test Data g = ditaensionless time S = storage coefficient The steady-state procedure of analyzing constant-head injection test data requires several Hantush (1959) gives solutions for both open and assumptions which may be difficult to quantify and closed boundaries for infinite, open, and closed nlikely to be met in nature. Among these assump boundary type curves generated from Hantush's tions are the existence of a radius of influence solutions are shown in Figure 4. and the ability to determine the time required to reach steady flow conditions. For a single fracture in a relatively imper meable rock, fracture aperture, e, determines flow Although steady-flr.w equations were standard by in the early days of hydrogeology and petroleum reservoir engineering, the recognition of the role of rock mass deformability (Theis, 1935) has made J transient analysis the basis of pump and other well (Pg/w tests since the I930's. indeed, for infinite aqui fers or fractures, steady conditions are never P = fluid density really achieved. g = gravitational acceleration V = dynamic viscosity The major difference between pump teste and constant-head injection tests is that in pump tests The flow rate into a well injected at constant the flowrate is held constant and the well test pressure should decrease rapidly upon application analysis is made on- the basis of the transient of the wellbore pressure and then decrease more change in pressure (or head! in the well. In ..-radually with increased time. If the aquifer or packer tests, the wellbore pressure is held fracture is infinite, the flowrate should never -86- •"-"-- \^ \ \ \ \ \ \ 1 \ \ \\ i i \ i \ - \ \\ 1 \1 \ \ * 1 0E-O4 I.BE-Ba l.(E Pig. 4 infinite, open, and closed boundary Fig. 5 Hypothetical transient flowrate curves B type curves for constant-head veil tests, * The error in using steady-flow analysis of well test data rather tnan the transient technique can oe quantified by preparing flowxate versus time plots for the test gecaietry and a range of hydrau lic conductivity values. The average flowrate over tne period of time flowrate date were taken, Qavi can be determined by integrating the flow over the period of time in question, i.e. talcing the total volume of fluid injected and dividing by the time, yay is the steady flowrate that would be recorded for use in steady-flow solutions. The difference between the hydraulic conductivity calculated using v;av in the steady analysis and the assumed hydrau lic conductivity in the transient flowrate curve is the error in using the steady-flow analysis. As an example of how the error in making steady-flow assumptions is calculated, consider a constant-head injection test on a 15.3 m (50 foot) section of an NX {rw = 3.6 cm) borehole. First one can construct from the type curves a family of flowrate curves for various hydraulic conductivi ties assuming a value for the storage coefficient. (Fig. 5). In civil engineering practice the steady flowrate is measured at a time when the flow appears not to change appreciably with time (a highly subjective judgment). Assuming data is taken between one and five minutes of injection. time, the volume of water injected can be taken from the area under the transient flowrate curve, uividing by the total period of test time, t, gives HYDRAULIC CONDUCTIVITY, cm/MC the steady flowrate, ^v assumed by the test operator, or . 300 Fig. 6 Ratio of actual hydraulic conductivity U(t) dt to value calculated using steady-flow assumptions Z40 / for test conditions in insert, 300-second test. 60 (XBL 812-8190). -87- Selection of a smaller radius of influence Where steady flow assumptions might prove most could have resulted in less error. Figure 7 shows useful in data analysis in very low permeability the radius of influence yielding no error for tha rocky. The lower limit of turbine flowmeter is case described above. Thus, by proper selection of about 4 ml/rain, however flowratio can be measured radius of influence, the error in calculating by use of calibrated flowtanks which give the hydraulic conductivities can be minimized. volume of water injected over a given period of time. For very low „lowrates calibrated flowtanks may not have sufficiently rapid response to allow early time determination of the transient flow rate. For such uses, hydraulic conductivity can be calculated by use of average flowrate and steady flow assumptions provided care is eiercised in choice of radius of influence. I g 10 (,,, Fig. 7 Radius of influence yielding zero error in steady state calculation for a 300 second test and test conditions in Figure 6. (XBL 812-8191) The error in use of steady flow assumptions increases with lower permeability, however, this can be compensated for either by using longer test times or smaller radii of influence. Figure B shows similar calculations of the error in steady flow calculations for two meter test zones over two hour periods. For the most extreme values of hydraulic conductivity and high values of storage, the error in calculating hydraulic conductivity Hydraulic Conductivity, cm/s is less than an order of magnitude and generally within about a factor of two or three. Fig. 8 Error in steady flow calculation in 2 mater test zone as a function of storage coeffi Discussion cient and hydraulic conductivity; 10"5 cm/s point is a 20m test, other points are for 2 hour tests. The calculation of the error in using assump (XBL 812-8192) tions of steady flowrate in constant head injection tests shows that the errors are small compared to the range of variability encountered in testing crystalline rock. Thus data which are reported in the literature for crystalline rock hydraulic con ductivity based on steady flow analysis should be considered reliable so long as reasonable valuer) of radius of influence have been used. It is not advocated here that the steady flow assumption be used routinely in testing where it may ho possible to obtain transient data. Tran sient analysis can be used for calculation of storage coefficients as well aa to study boundary effects. For example, by knowing the tine to deviation from the infinite layer type curve, one can determine the radial distances either to a boundary; or, if no deviation occurs, the radius over which the hydraulic properties are consistent, 2 the dintensionleas time (Tt/Srw ) to deviation from the infinite layer type curve is shown in Fig ure 9 as a function of r0/rw. By calculating T and S from the type curve natch the radial distance Fig. 9 Dimans toilless time to deviation from affected by the test can readily be calculated. infinite type curve as a function of distance open or closed to boundary. (XBL 812-8193) REFERENCES Banks, D.C., 1972 In situ measurements in basalt: Scrafim, J.L., 1968, Influence of interstitial Proc. aymp. of percolation through fissured watar on the behavior of rock masses in stagg, rocks. Int. Soc. Rock. Hech; Stuttgart. K and 0* Zienkiewicz (ed) Rock Mechanics in Engineering Practice, Wiley, Hew York, Davis, S.N. and Turk, L., 1964, Optimn depth of p. 55-97. wells in crystalline rocks. Groundwater 2i6-11. Sharp, J.C., 1970, Fluid flow through fissured Dick, R.C., in situ measurement of rock permeabil media; PhD thesis, Univ. of London, ity - influence of calibration error on test College• results; Assn. Eng. Geol. Bull., 12:193-212. Snow, D., 196S, A parallel plate model of fractured Bhlig-Economides, C and Raraey, H. Jr., 1979, Tran permeable media: PhD thesis Univ. Calif. - sient rate decline fox wells produced at Berkeley. constant pressure; Soc. Pet. Eng. paper 8377. , 1968 Fracture deformation and changes of Hantush, H., Nonstaady flow to flowing trails in perneability and storage upon changes in fluid leaky aquifers) Jour. Geophys. Res. v 64 no. 8. pressure: Colo. Sil. Mines Quarterly, 63: 201-244. Hvcrslev, H.J., 1951, Time lag and soil permeability in groundwater observations; U.S. Army Water , 1970, The frequency and apertures of frac ways Exp. Sta. Bulletin No. 36. tures in rock; Int. Jour. Rock Hech., and Hin. Sci.j v. 7, p. 23. Jacob, C.E. and Lehman, S., Monsteady flow to a well of constant drawdow,. in an extensive Theis, C.V., 1935, The relationship between the aquifer: Trans. Am. Geophys. Union, v. 33 lowering of the piezometric surface and the no. 4. rate and discharge of a well using groundwater storage: Trans. Am. Geophys. Union, v. 16, jaisval, C.S. and Chauhan, H.S., 1978, Transient p. 519-5 24. sperical flow to a nonpenetrating well with constant drawdown: groundwater, 16:432-436. tfraiet, A.A. and Raghavan, R. , 19B0, Unsteady flow to a well producing at a constant pressure: Louis, C. and Halni, T., 1970, Determination of in Jour. Pet. Tech. (Oct) p. 1803-1812. situ hydrsulio properties in jointed rock; Proc. 2nd Cong. Int. Soc. Rock Hech*, Belgrade Wilson, C.R., Doe, T., Long, J. and Witherspoon, P., v. 1, r,, 235-245. 1979, Permeability characterization of nearly imf.-armeable rank masses for nuclear waste Moye, J.G., 1967, Diamond drilling for foundation repository siting: in low flow, low perme exploration; Civil Eng. Transactions, Inst. ability measurements in largely impermeable Eng. Australia, v. CE9, p. 95-100. rocke, Proc. NEA11AEA workshop, OECD, p. 13-30. Rissler, P. 1978, Determination of water permeabil ity of jointed rock; Pub. Inst, of Fdn. Eng., Ziegler, T., 1976, Determination of rock mass per Soil Hech., Rock Hech*, and Waterways Con meability: U.S. Army Engineers Waterways struction, Auehen, Germany. Experiment Station, Tech. Report S-76-2, 85 p. -89- SOLUTE TRACER TESTS IN FRACTUREP MFMA G.E. Grisak Environment Canada National Hydrology Research Institute 562 Booth Street, Ottawa, Ontario, K1A 0E7 SUMMARY One approach to evaluating solute transport through fractured media at the 'near-Field' A single-well injection-withdrawal tracer scale 1s to attempt to determine, with tracer test design with radial satellite Instrumenta tests, the transport processes in a single dis tion is used to illustrate design calculations creet fracture. Existing analytical techniques for testing a single 100 ym fracture. Test are suited to these tests, since the conceptual durations of several days can conceivably pro model on which most tracer testing techniques vide tracer information over distances of tens were developed is that of a single, permeable of meters at realistic injection pressures. layer between parallel, relatively impermeable Calculations of the effect of matrix diffusion confining layers. There Is a clear analogy to on the test results show that only in rocks with a single, continuous, planar fracture in rela low (<0.01) matrix porosity would average tively Impermeable media. Analogies may also solute velocities be obtained comparable to be possible between layered or stratified porous those based on the design injection conditions. media systems and a set of subparallel fractures. Matrix diffusion in rocks with high matrix An analysis of flow in layered porous media is porosity would cause solute velocities to be given by Bear (1972, p.151-159) and Mercado much slower than the water velocity. It is (1967) discusses tracer spreading patterns in considered that the primary function of a con a permeability stratified porous media aquifer. servative (nonreactlve) tracer 1s to provide verification of the average velocity in a frac ture, usually calculated from hydraulic testing SINGLE FRACTURE results. Reactive and nonreactlve tracers used together can provide substantial information on Single-well injection-withdrawal tracer in situ sorption properties if used in conjunc techniques (clverglng-converg'ing flow) with tion with radial instrumentation. satellite radial Instrumentation can be used to illustrate test design and data analysis techniques in a single fracture. The type of INTRODUCTION data sought are similar to those presented by Pickens, Jackson and Inch (1980) in their dual Tracer testing techniques have occasionally tracer (reactive and nonreactive) test conducted been used in fractured media, generally with the in a confined porous media aquifer. assumption that porous media 'equivalent' para meters are applicable. (Webster, et al., 1970; The hypothetical case of a single continuous Grove and Beetem, 1971; Kreft et al., 1974; planar fracture with an aperture width 2b of Claassen and Cordes, 1975; Ivanovich and Smith, 100 urn is selected for illustration. Injection 1978; Landstr'om et al., 1978). It Is not rates 0 of 0.1 L/m1n are feasible at relatively certain however, that 'equivalent' parameters low injection pressures of about 0.035 MPa representative of a fractured media can be (Davison, 1980) which should minimize the impor derived which adequately represent the trans tance of any stress-opening of the fracture. If port processes or pathways in fractured the porosity in the fracture is assumed equal systems. Grisak et al. (1980) derived to 1.0, the water velocity V at radial distances 'representative' parameters for use 1n the r, under steady state injection conditions, can analysis of a laboratory tracer test on a large, relatively undisturbed sample of frac be calculated (Figure 1) using equation [1] tured till. The 'representative' parameters were based on the concepts of flow in sets of : 2Jlr(2b) [1] planar fractures of simple geometry. The interconnectivlty of the fracture sets was The radial distance reached by injected assumed to be represented by an effective water at any time t (Figure 2) can be calculated fracture spaaingj from which Ln effective from equation f2] fracture aperture was calculated. The ef fective aperture and spacing were then utilized rqt ,/n(2b)] [2] in numerical simulations of the laboratory tracer effluent data. Simulations of this The transit time t, or time taken for water data using an analytical solution and parameters equivalent to those used in the numerical simu to move from the Injection well to radial dis lation showed good agreement (Grisak and tances r, can be calculated by rearranging T2]. Pickens, 1980a). The assumption of zero long itudinal dispersivlty In the fracture, which Table 1 lists transit times and radial dis is used 1n the development of the analytical tances from the injection well in a 100 urn frac solution, was shown to be suitable in fitting ture at injection pressures of 0.35 and 0.035 the laboratory tracer-effluent data. MPa. Also listed for comparison are calculations for a 10 urn fracture, although pressures as Matrix Diffusion The diffusion of nonreactive and reactive solute from a fracture Into the adjacent matrix can have a considerable effect on solute trans port 1n even a low porosity matrix. A simple one dimensional analytical solutipn can be used to Illustrate the effects that matrix diffusion can have on solute transport at the scale of a single fracture tracer test with the conditions illustrated 1n Figures 1 and 2. Analytical solutions to the radial case which describe In jection/withdrawal tracer tests have not yet been developed. In order to Illustrate the effect of matrix diffusion using a constant- velocity analytical solution, a term transit velocity Vt is defined as the ratio of the radius r to the water transit time ta. The 5 10 15 transit velocity is introduced to approximate a constant velocity system. RADIAL DISTANCE lm> An analytical solution to one dimensional Figure 1 Hater velocity 1n 100 jim fracture at advectlve transport in a single fracture with radial distances r from Injection well matrix diffusion has been adapted by Grlsak and Pickens (1980) from Carl saw and Jaeger (1959) and Jost (1960). The solution for relative solute the matrix (or. ) is • (x + y) 2tP*(t-f-)]4 vt [4] with the boundary and Initial conditions Cf high as 0.35 MPa or greater may Increase the width where x distance in direction of flow of the fracture aperture. y distance into the matrix perpendicu lar to flow TABLE 1 Twt design calculations for injection- D* * matrix diffusion coefficient tracer tests. C = Input concentration (1.0) APERTURE 100 100 10 Using a transit velocity V. of 1.9 m/hr (um) 6 IHJ. RATE 1 0.1 0.01 and a matrix diffusion coefficient 0* of 10" (L/m1n) ? cm /s, breakthrough curves calculated for a RADIAL 1 hr 14 4 1.4 B'STANCE 9 distarce of 10 m are plotted on Figure 3. Matrix porosities (e ) of 0.3, 0.03 and 0.003 are used (i„) 10 hr 44 14 4 m TRANSIT 10 m 0.5 5.2 52 to illustrate porosities of shales and clays, TIKE TO welded tuffs (ignimbrltes), and crystalline (h) 20 m 2.1 21 210 rocks, respectively. The calculations show INJ. PRESS. 0.35 0.035 0.35 that, with a porous matrix such as exists in (*P»> shales, the average velocity (C*0.5C j at 10 m distance from an injection well in a 100 wm frac The velocity calculated from pressure testing ture 1s reduced to less than ^0% of the transit results requires confirmation by direct measure water velocity. The reduction in average velo ment before it can be used in solute transport city 1s due solely to solute diffusion from calculations. Results from radial instrumenta the fracture. The actual reduction may be tion can be compared to velocities calculated somewhat less pronounced in a field injection from pressure testing results and further com situation since a constant velocity Is used pared to Injection withdrawal rates and with in the calcinations. The effect of matrix dif drawal phase tracer data at the central well. fusion in trace' tests can be reduced by 1) high water velocities or large fracture aper Reactive Tracers tures, reducing the solute transported to solute stored p>tio or 2) small matrix Reactive and nonreactive tracers used porosities. simultaneously can provide substantial Informa tion regarding in situ sorption properties. The experiment presented by Pickens, Jackson and Inch (1980) illustrated that reactive tracers can yield 1n situ distribution coef 9m-.003 ficients (K.'s) which are similar to both lab oratory column and 'batch' K,'s and K.'s calcu lated by chronological mapping, over the past 20 years, of a contaminant plume created by the experimental disposal of radioactive wastes 1n the same aquifer (Jackson and Inch, 1980). The Influence of sorptlon/desorption kine tics on the reactive tracer breakthrough data are difficult to overcome in tracer tests of relatively short duration. Sorption/desorption kinetics primarily cause increased spreading about the average velocity. For analysis of field tests, sorption kinetics may perhaps be adequately treated as a dispersive mechanism and its effect incorporated into the dispersion term. REFERENCES Bear, J., Dynamics of fluids 1n porous media. Figure 3 Breakthrough curves at 10 m from American Elsevier Inc., New York, 764 p., injection well approximated with 1972. the one dimensional analytical solu tion for fracture transport and matrix Carslaw, H.S., and J.C. Jaeger, Conduction of diffusion, e = matrix porosity. Heat in Solids. 2nd Ed., Oxford University Press, London, 510 p., 1959. Dispersion in fractured media 1s a sub ject of considerable interest at present. It Claassen, H.C., and E.H. Cordes, Two-well is not clear whether longitudinal dispersion 1n recirculating tracer test in fractured a single open fracture is an important process; carbonate rock, Nevada. Hydro!nglcal however heterogeneity within a fracture plane Science Bull., XX(3), 367-382, 1975. can cause considerable uncertainty with respect to velocities and solute travel paths In any Grisak, G.E., and J.F. Pickens, An analytical tracer test In a single fracture. Anlsotropy solution for solute transport through frac within a fracture plane can be caused by a tured media with matrix diffusion. Sub number of factors, such as fracture Infilling mitted to Jour. Hydrology, 1980a. and non-planarity, which can cause the aper ture to vary in width and to range from Grisak, G.E., and J.F. Pickens. Solute transport totally open to totally closed. A discussion through fractured media: 1. The effect of of dispersion processes in a single fracture matrix diffusion. Water Resour. Res., and 1n fractured media is presented by Grisak In Press, 1980b. and Pickens (1980b). Grisak, G.E., J.F. Pickens, and J.A. Cherry, Given the uncertainties regarding the dis Solute Transport through Fractured Hedfa: persion properties of a fracture, the primary 2. column Study of Fractured Till. function of a conservative tracer should be to Water Resour. Res., In Press, 1980. provide verification of the average velocity rather than to quantify dispersion parameters. -92- Grove, D.B., and Beetem, W.A., Porosity and dis Kreft, A., A. Lenda, B. Turek, A. Zuber, and persion constant calculations for a frac K. Czauderna, Determination of effective tured carbonate aquifer using the two well porosities by the two-well pulse method. tracer method. Hater Resour. Res., 7, In: Isotope Techniques 1n Groundwater pp. 128-134, 1971. Hydrology, IAEA-SM-182/46, pp. 295-312, 1974. Ivanovich, H., and D.B. Smith, Determination of Aquifer Parameters by a Two-yell Landstrom, 0., C.E. Klock-jrs, K.E. Holmberg, Pulsed Method usiig Radioactive Tracers, and S. Hesterberg, In situ experiments on Jour. Hydrology . 36, 35-45, 1978. nuclide migration In fractured crystal line rocks. Karn-BrSnsle-Sakerhet Teknlsk Rapoort 110, English Translation, Jackson, R.E., and K.J. Inch, Hydrogeochemical 50 p., 1978. processes affecting the migration of radionuclides 1n a fluvial sand aquifer Hercado, A, The spreading pattern of injected at the Chalk River Nuclear Laboratories. water In a permeability stratified National Hydrology Research Institute, aquifer. In: Int. Assoc, of Scientific Paper No. 7, Inland Waters Directorate Hydrology, Proc. Symp. of Haifa, Publ. Scientific Series No. 104, 58 p., 1980. No. 72, 23-36, 1967. Jost, W., Diffusion in Solids* Liquids, Gases, Pickens, J.F., R.E. Jackson, and K.J. Inch, Academic Press, Hew York, N.Y., Vol. 1 Field measurement of distribution of Physical Chemistry: A SerieL of coefficients using a radial-injection Monographs, 532 p., Revised Edition, tracer test. Prepared for submission 1960. to Water Resour. Res., July 1980. -93- ABSTRACT TESTING LOW TO MODERATELY TRANSMISSIVE ZONES IN BASALT ROCKS C. D. Updegraff, K. G. Kennedy, A. A. Bakr, C. N. Culver and J. T. Kam Science Applications, Inc. Albuquerque, New Mexico Nuclear waste disposal studies are providing unique opportunities for development and assessment of different types of borehole testing methods. Recently, we completed a six month field testing program directed at determining the hydrologic characteristics of basalt rock on part of the Hanford Reservation near Richland, Washington. Well testing was conducted principally using instantaneous (pulse or slug) withdrawal or injection, crill stem and airlift pumping tests. Testing in the low to moderately transmissive rocks required up to several days and in some instances weeks to provide a complete test record for adequate evaluation. Pulse tests, where the response is shut-in, responded quickly to static conditions. They are preferred in zones with transmissivity less than about 10 ft2/sec (=10"9m2/sec). The test's >-adius of influence is generally limited to a few wellbore diameters. At dual hole sites, no pressure responses were observed at wells 100 feet apart. Pulse tests can be analyzed by 'slug' type curves similar to those by Cooper et al. (1973) and Ramey et al. (1975). More rapid responses may necessitate generation of higher dimensionless storage coefficient curves than are currently published. Pulse test results can be anomalously high or low as wellbore damage can strongly influence these short tests. Testing in tight colonnade/entablature zones will require additional input regarding fracture distribution, orientation and matrix characteristics for proper hydrologic character ization. Slug tests, where fluid movement occurs in the tubing string as a result of flow from or into the formation, is generally non- responsive in formations with transmissivity less than about -94- 10 ft /sec (=10" m /sec). They are useful in moderately transmissive zones up to about 10" ft /sec (=10" m /sec). For small storage coefficients, responses can be observed in observation wells and these data are analyzable using existing analytical solutions. Problems associated with these tests are wellfcore inertial effects and permeability changes away from the wallbore. Analysis of the recovery period of airlift, standard downhole pumping tests and drill stem-type tests data can provide the most complete and, in general, the best characterization when testing zones with transmissivities ranging from about 10" ftVsec ( = 10" m /sec) to about 10" ft /sec (=10" m /sec). The advantage of recovery tests is that the analysis can be performed adequately even if the wellbore is extensively damaged. Drill stem-type tests can also be used in low permeability horizons but require extensive flow periods prior to their buildup period. The late time data is critical to- these tests and accordingly the formation response should be allowed to return to initial or static conditions. The recovery and drill stem tests also allow evaluation of the wellbore storage effect and wellbore damage in the vicinity of the zone tested. The shape of the response curve also provides insight as to whether the media is responding as a fractured or equivalent porous media. Tracer test results indicate 1-131 can be effectively utilized in further assessment of basalt formation characteristics using a doublet well situation. -95- MEASUREMENT OF IH-SITU HYDRAULIC CONDUCTIVITY IN THE CRETACEOUS PIERRE SHALE C. E. Neuzll and J. D. Bredehoeft U.S. Geological Survey, Reston, Virginia 22092 SUMMARY the Pierre Shale is a part. Regional values obtained in this manner range from about 10 l' ra/a A receiu study of the hydrology of the to 2 x 10~9 ra/s. Cretaceous Pierre Shale utilized three techniques The hydraulic conductivities measured in situ fur measuring the hydraulic conductivity of and in the laboratory are consistent and fall "light" materials. Regional hydraulic conduc along a fairly distinct trend of decreasing con tivity was obtained from a hydrodynamlc model ductivity with increasing effective stress, or uiiiiLysIs of the aquLfer-aquitard system which depth. Regional conductivities plat distinctly includes the Pierre Shale. Laboratory values were apart from this trend and are some two to three obtaimd lrum consolidation tests on core samples. orders of magnitude larger. We believe that the In-situ values oi hydraulic conductivity were large regional conductivities reflect leakage obtained by usinv; a. borehole slug test designed through fractures or fracture zones in the shale specifically lor "tight" formations. Tlie test is which the boreholes did not penetrate. ivinJui Led by isolating a portion of the borehole Calculations based on fracture flow theory witb nut- nr two packers, abruptly pressurizing the alone cannot indicate the size and spacing of the '.hut-in portion, and recording the pressure decay fractures. However, the range of combinations of with Mm.'. The test utilizes the analytical solu fracture size an-! spacing which explain the con tion lor pressure deray as water flows Into the ductivity difference can be shown. *;uri-i. ! iny format ion. Consistent results were obtained usini: the test on thr^e successively In Situ Tests siri.il Ivr i-or Lions of a borehole in the Pierre SI-...K', A Borehole located at site "3" in figure 1 llu- in-::iiii tests and laboratory tests was tested using the modified "slug" ten: of yielded comparable values; the regional hydraulic Bredehoeft and Papadopulos.1 The borehole was i omlni-t i vi :.y was rwn LO three orders of magnitude drilled to 184 meters depth and approximately larger. Tins suggests that the lower values 13 centimeters diameter entirely In the Pierre represent inter^r.imilar hydraulic conductivity of Shale using an air drilling technique. No de i In- intact shale and the regional values represent tectable water flowed into the borehole from the let .'iid.irv permeability due to fractures. Calcu- surrounding rock. Water was added to conduct the i.ninii. based or) lractu.ro flow theory demonstrate test. that small Ir.niurts could account for the The test utilizes the solution to the coupled obs.-ived dii tvri'.u-.",. equations of ground-water flow in the surrounding rock and storage in the wellbore. The "slug" is 1 N'Ikojr' CI'I'T, a nearly instantaneous change induced fn a clused- in portion of the wellbore which is pressured by [(••cause "tight" rocks such as shales may be water. The volume of the closed-in wellbore is US.'L! !•' ••oiiiirif h.mardous waste and other assumed to be constant and the change in storage in.tier i.ils stored underground, tl is important to be and head in the wellbore Is assumed to be due .!:>:.' io measure their permeability. Very low entirely to the compressibility of the water. This ;n iiiieVu I it ii'R are difficult to measure and test is designed for low permeability formations.1 sjie. ..ii K'.lmii|uis an- required. For significant After application of the "slug" the decline In bead velrimes o! i-.ck it is also necessary to consider H in the wellbore is recorded with time and a pint tiie possible elletts oi discontinuities such as of H/H (where H Is the "slug") versus t ime 1s !r:ntiiii's which can significantly alter the gross matched with a set -)f type curves of Lbe solution. pi-riuaMUlv . 2 or near borehole hvdraulic conductivity. These to apply. Tor the purpose of plotting, tQ was tests gave consistent results for successively chosen as the moment pressurization stopped; smaller portions oi the borehole. Values for however, the flow into the shale commenced at the local hydraulic conductivity measured in this instant the pressure began to rise. Hence, the manner ranged from 10 l m/s to ? x 10 " m/s. true t in the sense of an instantaneously applied Ihe hydraulic conductivity of core samples 0 ictrLeved from two boreholes was calculated by "slug" Is ambiguous, but It would be some time analyzixb data from one dimensional consolidation before pressurlzatton ceased. As a resuLt the data tests. The hydraulic conductivity of the core points are displaced ahead by the difference (to samples measured in chis manner depends_on the actual - t chosen). Because the time scale is effective stress and ranges from 5 x 10 m/s to 2 x lO-1** m/s. logarithmic this effect is seen as a distortion of Regional hydraulic conductivity of the Pierre the data curve only In the early part of the plot. Shale was estimated usint; a digital ground-water flow model of the aquifer aquitard system of which inree tests were conducted in the borehole. Laboratory Testa A packer was set at 32 meters and the Interval from the packer to the bottom of the hole was Consolidation teflts ware conducted on samples tested. Upon completion of the first test the of the core froa boreholes at "B" and "C" in packer was lowered and reset at 64 meters and a figure 1* The tests were conducted by the U.S. portion of the original section was retested. A Army Corps of Engineers at their soil laboratory third test was conducted in the same manner with in Omaha* Nebraska. elm packer at 115 meters. The test consists of applying an instanta Since successively smaller portion! of the neous, uniaxial load to a laterally confined original 184 meter section were tested, trans- sample. Deformation Is recorded as a function mi s-sivities of three separate portions of the of time until the rate of deformation becomes borehole could then be calculated. The section of small. The process Is repeated with the load the borehole tested and the measured transmls- doubled for each repetition. sivities are shown schematically in figure 4. The The deformation of the sample with tine result is a fairly detailed picture of hydraulic depends partly on the permeability of the sample.5 .'vJucttvlty with depth at this site as measured A simple analysis of the time deformation curves Lit situ with the modified "slug" test. from the consolidation tests can be made using Terzaghi's consolidation analysis from which the Uiscussion of In-Situ Tests hydraulic conductivity can be extracted. More sophisticated analyses, such as the vlscoelastic The modified "slug" tests are internally con theory of Gibson and Lo may also be applied.6 sistent; .is successively smaller portions of the When the analysis of Gibson and Lo was applied to section were tested, successively smaller trans- consolidation data for the Pierre Shale the raiusivity values were obtained. In addition the hydraulic conductivity calculated differed from calculated conductivity consistently decreases th^L calculated with Terzaghi's analysis by only a with de.pth. few percent. Therefore, the values obtained with The modified "slug" test is not without the simpler theory of Terzaghi were used. potential sources of error.' Very small volumes Since incremental loads are applied to the of water are pumped into the borehole and allowed sample during testing it is possible to obtiin to Flaw ouL, presumably into the rock. The values of hydraulic conductivity for a range of possibility exists that sufficient leakage occurs effective stress for each sample. The effective through joints and connections in the test stress can be converted to an approximately equiv apparatus or past the packer to dominate the alent depth by assuming near hydrostatic condi pressure decay. Leakage past, the packer is par tions. Hydraulic conductivity was calculated for ticularly hard to rule out. However, if leakage effective stress loads ranging from 5 x 10s to occurs the computed conductivity will be higher 2.3 x 10 Pa which may be expected at depths of than the true conductivity of the rock. In that 50 to 2300 meters. sense the computed values can be viewed as maximum The hydraulic conductivities calculated in this manner define a fairly distinct trend There is evidence that leakage did occur in decreasing witii depth (see figure 7). the system and the calculated conductivities are too high.3 Inflation of the packer causes a small Hydraulic Conductivity of Shale Estimated with pressure rise which itself constitutes a "slug" RpRlonal Ground-Water Flow Model test. In instances where the decay of these small pressure slugs was monitored, it can be seen that The Pierre and other Cretaceous shales confine their relative decline (drop 'n U/H ) is slower three major and several minor aquifers in South Dakota (figures 5 and 6). The aquifers and than that of the higher presaure sing This aquitards interact and together form a ground-water suggests that the higher pressure differences flow system. Primarily lateral flow takes place associated with the full slug caused leakage in the aquifers and vertical leakage through the around the packer. The actual conductivity of confining beds. the rock may be lower than the values calculated. Relatively complete data on hydraulic heads Another limitation that should be recognized and transmissivity in aquifers, particularly the Is the small volume of rock involved in the test. Dakota Sandstone, are available for South Dakota. Using the solution of Lhe ground-water equation By adjusting the vertical hydraulic conductivity for a semi-iiiftnite strip with step change In head in the confining layers, including the Pierre at the boundary an estimate can be gotten for the Shale, good agreement between calculated and distance the disturbance will penetrate the rock. observed hydraulic heads can be obtained. For K = 3 x 10~13 m/s, S =• 3 x 10~5 m"1 and s For this study a numerical model of the major t = 12 hours which are representative of these aquifers and based on earlier model studies was tests, discernable changes in pore pressure will used.7 A numerical model of the shales and minor have migrated less than one half foot into the aquifers above the Dakota Sandstone was also used.7 rock from the well bore. The distance In the From these model simulations estimates ?f radial case will actually be smaller. Clearly, regional vertical conductivity in the confining only a small annulus surrounding the borehole layer above the Dakota Sandstone (here called the affects the test, and it includes the rock most "Dakota confining layer") as a whole, and in each likely to have been disturbed by drilling. of the shales individually was obtained. -97- COMPARISON OF RESULTS 2. Papadopulos, S. S,, U.S. Geol. Survey, oral coasumicstton, 1979. Results of the in-situ and laboratory testa 3. Papadopulos, S. S., U.S. Geol. Survey, oral and the model simulations are compared in figure communication, 1378. 7. Zn figure 7 the abcissa represents the 4. Bredehoeft, J. D., and Hanihaw, B. B., 1968, hydraulic conductivity and the ordinate represents On the Maintenance of anomalous fluid pres depth or the equivalent effective stress. In-situ sures, I. Thick sedimentary cs^u-nce*: Geol. tests are plotted at the mean depth of the test Soc. America Bull., v. 79, p. 1097-1106. section. Consolidation test reaults are plotted 5. Lambc, T. W., and Whitman, K. V., 1969, Soil at the mean value of two successive load Incre '• Mechanics: New York, John Wiley, 553 p. ments, The regional values are plotted at the 6. Gibson, R. E., and Lo, K. Y-, 1961, A theory arithmetic mean depth of the formation in the area of consolidation for soils exhibiting secondary modeled. compression: Norwegian Geotechnlcal Institute. As seen in figure 7 the in-situ and labora Publication No. 41. tory tests fall along a single fairly well defined 7. Heuzil, C. E., 1980, Fracture leakage in the trend of decreasing conductivity with depth. The Cretaceous Pierre Shale and Its significance regional values for the shales also decrease with for underground waste disposal: Ph.D. thesis, depth but at similar depths the regional conduc Johns Hopkins University, 150 p. tivities are two to three orders of magnitude larger than the local conductivities* These results lead to the conclusion that leakage through the shales on a regional scale occurs largely along pathways which are mare conductive than the intact shale. It is hypothe sized that the larger regional conductivities result from connecting fractures in the shales. Fracture Leakage in the Shales Throughgomg fractures can drastically affect the permeability of "tight" rocks. Fracture flow is usually approximated with the parallel plate analogy wherein flow is related to the fracture aperture* as "f - l2iTLb'J where 3 Qf is the fracture flow (L /T) .! is the hydraulic gradient (dimensionless) L is the length of the fracture normal to flow REFERENCES 1. Bredehoeft, J. D., and Papadopulos, S. S., 1960, A method for determining the hydraulic properties of tight formations: Vater Resources Research, v. 16, p. 233-238. -98- SOUTH DAKOTA Figure 1. Boreholes drilled in the Pierre shale for this study, a) location map for borehole sites A, B, C. b) cross section showing boreholes in relation to topography and Pierre shale stratigraphy. TESTED SE.CTION Figure 2. Test set up for conducting modified slug test. -99- 10* 101 10* 10» 10» TIME.INSECONOS Figure 3. Pressure decay curve and type curve match for typical modified slug; test in Pierre shale. GKOUNn SURFACF. NOT- TE5.1I1U1 T-- 3.3 "lO"'-t"o .«•/, ( 1< I.OxlO-" "Vs 4.5 K.. 1.3* IO-" r-y;, ,io-'° 'n'/s r-*.+x(o'" mv& 4-4 « 10" H-- b.5*K)"*"/s Figure 4. Results of modified slug tests in borehole at site "B." Figure 5. Schematic of major aquifers and aquitards in South Dakota (vertical dimension greatly exaggerated). Figure 6. Schematic of aquifers and aquitards over lying the Dakota aquifer (vertical dimension greatly exaggerated). [0 b 10 '- 10° MO3 IO' 0 IN SITU tiPtCIM.'SLUC.'] TESTA fcl&Mr FUlvM (LAB) TtSrt) • COKSOHDATIOM \0*l IO"3 io" io"" HrORAULIC CoNDUCnvITT Figure 7. Coaparison of regional, local, and laboratory hydraulic conductivities obtained in this study. 1 1 1 1 1 . I 1 1 . 1 • I , I , 1 s 0' 10° 10' 10s 103 10' 10s 10 10 CAHILILE I I 1 I I 1 1 I 1 I I I I I 1 1 10* 10' 10s 106 MOWRY ANP BEUE FOURCHE SAVG, IN MEIERS Figure 8. Range of SftvG (average spacing), as a function of mean aperture of fractures for the shales of the Dakota confining layer. -102- ANALYSIS OF PUMPING TESTS PERFORMED IN A HORIZONTAL RECTAr&ULAR FRACTURE D. THIERY Bureau de Recherche* GGologlques et Mlnleres Orleans - FRANCE ABSTRACT These scheaes arc interesting but they are not always adapted to real fractures mainly because The analytical solution has been derived for of anisotropy of permeability in the horizontal a constant rate uniform flux pumping test in a directions. single horizontal rectangular fracture. The solu tion is given for the drawdown at the pumped well A horizontal fracture is more likely to be and at an observation well inside or outside the elliptical than circular. In order to analyse fracture. A set of type curves which depend on drawdowns in such a fracture we derived analytical two dimensionlesr parameters has been drawn. solutions for a pumping (or injection) test in a These type curves give the dimensionless drawdown rectangular fracture which is a closer npproxima- at the pumped well versus the dimensionless time tion to an elliptical fracture. according to the shape factor of the fracture and the dimensioniess aquifer thickness. Another The drawdown has been calculated at the center set gives the average drawdown along the vertical of the fracture but also at an observation well. at an observation well versus dimensionless time depending on the dimensionless distance and the shape factor. 2. DESCRIPTION OF THE SYSTEM For both the drawdown at the pumped well The geometry of the system is defined as fol and at an observation well the solution has also low : been studied for early times and long times in the aquifer has an infinite lateral extension; order to derive approximative solutions which its characteristics are : are compared to the well known solutions in iso tropic aquifers. - constant thickness h - constant Btorage coefficient S 1. INTRODUCTION (specific storage coefficient S - S/h) - anisotropic permeability : K;:, Ky, This paper presents results which have been Kz. obtained during the research contract n° 563-78 The fracture , which is situated In the middle EGF for the Commission des Communautes Europeen- of the aquifer, has a rectangular shape with : nes. These results are described in detail , in French, in BERTRAND L., FEUGA B., NOYER M.L., - a length 2 xf THIERY D. I9801. - a width 2 yf - a negligible thickness A review of the litterature has shown that analytical solutions have been derived to deter mine the unsteady state pressure distribution 3. BOUNDARY CONDITIO INSIDE THE FRACTURE created by a well with a single flat fracture. Two types of boundary conditions may be set The available solutions are the following : inside the fracture : - a vertical finite length fracture - an infinite conductivity fracture (Gringarten et al, 1974)- - a uniform flux fra'.ture. - a horizontal finite radius circular frac a) An infinite conductivity fracture ture {Gringarten et al,1974)3 - an inclined fracture (Cinco et al,1975)1' It is a fracture which has an equivalent hy - a vertical fracture partial penetration draulic conductivity (or permeability) much higher (Raghavan et al 1976)s than the conductivity of the surrounding formation. f As a matter of fact its transmissivity (K.h pre For all these schemes (except the vertical duct) is much higher then the rock transraissivity fracture) only the pressure at the pumped well This condition is usually met in thick fractures has been computed. in a low permeability formation. The head gradient in an infinite conductivity fracture is equal to aero. -103- h «(h/ Vx^). V^TKZ (dimensionle*J thick- b) A uniform flux fracture D near. of the aquifer) The discharge from the aquifer to Che frac - time ture is performed at a uniform rate per unit area t - nTt/x-y S (relative fo the fracture of fracture. ap F area) 2 This boundary condition is probably not t_x - 4 K ht/x S (relative to the distance exactly fulfilled but, as will be shown later, to the center of the frac it is a close approximation of the infinite con Cure). ductivity boundary condition. Nota : All these notation? are consistent with The uniform flux boundary condition is very Theis's notations. interesting because it makes it possible to com pute the drawdowns analytically by the "source The shape factor F is the ratio of the length functions method" . This uethod has been descri of the fracture to its width (corrected fay the ho bed by(GRINGARTEN A.C. and RAMEY H.J. 1973)6. rizontal anisotropy factor) The source functioi associated to the rec For an horizontally isotropic aquifer : tangular fracture is obtained as the product of F - I applies to a square fracture (it is the 3 elementary source functions as shown below. shape which is the closest to the circular fractu re) F • 10 applies to a rectangular 'vacture with a length eqcal to 10 times its width. The dimensionless thickness h_ is the ratio 'r*7 of the aquifer width to the fracture extension (corrected by the vertical anisotropy factor) .The fracture extension is the geometrical mean of its length and its width. For a fully isotropic aquifer : The product is then simplified considering h_ = Q.l applies to a fracture with an exten that the thickness zf of the fracture is negligi sion equal to 10 times the thickness of the aqui ble compared to the thickness h of the aquifer- fer h_ - 10 applies to an aquifer of thickness c) Qimenslonless notations equal to 10 times the extension of the fracture. The following dimensionless variables are used : - coordinates : 4. DRAWDOWN AT THE CENTER OF THE FRACTURE Xp = x/xf The drawdown at the center of the fracture is given by the following expressions which are easy LO compute numerically : • drawdown sn - 4TTTS/Q with T - h VfcxKy " transmis- ' geometry factors F -(xf.'yf) VTTK (shape factor) - typo curvas for constant dlmensionless thic)cneii h o ...rlt,t «p(.afg2,] «T Expression (1) is easier to compute for la- i values of dimensionless time and expression (2) ir early values. The calculations have been performed for ,e following values of the geometry factors : = 0.1, 0.5, 1, 1.5, 2, 5, 10, 50. 1, 2, 5, 10, 50 which corresponds also to I. ,0.2 0.1, (1 02 . Two kinds of type curves have been drawn : 10* W 10* - type curves for constant shape factor F (see graph 1) Graph 2 - Drawdown at the center of a horizontal rectangular fracture For early dimensionless times the curves show a typical "one half slope" of equation ! (3) DF This equation corresponds to a vertical flow from the formation to the fracture. It does not depend on the shape factor F because there is no flow in the horizontal directions. For late dimensionless times the drawdown is a linear function of the logarithm of th« time according to the following equation : is the drawdown at time t_, This equation shows that, after a time t the variation of the drawdown does net depend on the geometrical factors F and h any more. 10** 10* 1 lO't^lO1 Graph I - Drawdown at the center of a horizontal "~ rectangular fracture It is a radial flov/ which agrees with JACOB'S The average drawdown at an observation wel1 approximation. The drawdown variation is plotted situated along the ox axis is given by the follo as a. straight Line on Keni-'ogarithmic paper but wing expression s _ J_ 1 -i Th-.'is curve can not bo recognized on log-log pap3r because of the constant s Hquation (4) ii valid after the following dimeiisionless times t corresponding to a maxi- •erf —-- dt r>> rriura ; rror of 10% : .V/T The drawdown at an observation we!I situated aloni the oy axis is given by the sumt- expression after replacing F by 1/F. Expression (r>) has been calculated numerically i 1 r>,2 J; a 218-1 for the following values of the paraiaetei s : xp = 1, 1.1, 1.2, 1.3, 1.4, 1.5, 2, 3, 10 f>.r> r>. s [ "• i. a 2.lb 4 1 , F =0.1, 0.5, 1, 2, 5, 10, r)0 5 1 ">.. (, n.ft :-M . a 2384 Two examples of type curves are drawn on graph 3 and 4. They show that for F > ! (observation 26..] ?o..i .10 2 384 1 "> wells situated along the ox axis), the curves are very close to Theis's solution (x = ">) as soon as «, HI 11! 131 2384 X> 2 even for early dimensionless times. For 1a- '_'• dimensionless tines the flow is radial and is described by equation (4) rallying JAfOB':; .ippro- ximation . Equations (It and (2J refer to the center of the fracture, but as a matter of fact, it is a clo 10' se approximation of the drawdown at any location Inside the fracture, because as it will be shown later the drawdown inside the fracture is nearly H equal everywhere. i 5. DRAWDOWN AT AN OBSERVATION HELL f difficulty arises because the drawdown field is 3 dimensionnal : the drawdown is diffe 10-1 rent at each altitude of an observation well. This difficulty has been solved considering a small diameter observation well with perforations along the whole aquifer thickness. The drawdown measured by such in obsei 'ation well is the average of the 10- drawdown along the vertical direction. This avera ge , which has been computed analytically does not depend on the dimensionless thickness h . 10 J 10"* 10- 10"" 1 *"< 10' Graph 3 ~ Drawdown at an observation well (hori zontal rectangular fracture) 06- 6. DRAHDOMN AT AN OBSERVATION HELL IN CONTACT WITH THE FHACTURE Th* average of the drawdown along the vertical hat bean computed because it doesn't depend on o any more. The calculations have been performed for various dinensionless tines. For early dinensionless times the drawdown is given by the following equations : (6) (7) The initial drawdown averaged along the verti - cal is linear with time s it is represented by a straight line of slope 1 in log-log coordinates. 1 ^-10* Graph 4 - Drawdown at an observation well Equations (6) and (7) are valid, with ,i maxi (horizontal rectangular fracture) mum error of IQt , before the following value of dlmensionless time is reached : < 1/F Equation (•!) is valid after the following DF IS) dimensionless times corresponding to a maximum error of 10 % exnression (8) shows that the linear drawdown is observed during a longer time when the shape factor is smaller i.e. when the shaoe of the frac ture is closer to a square. \ F 1 2 5 10 For late dimensionless times the variation of the drawdown is given by equation 14) . This equa 1 16.7 14.2 13.5 13.4 tion , which describes JACOB'S approximation, is valid as soon as the following dimensionless time is reached 2 11.7 11.0 10.9 10.3 5 10.3 10.2 10.1 10.1 ^vXD' 0 1 R.' ' 0.6 ! 1 ' 10 10.1 10. 10. 10. 1 1 ' 5.2 ' 5.6 ' a.l ' 13.1 ' It appears that JACOB'S approxiiuition applies 2 , 6.5 i 7.2 j 12.2 i 22.1 , as soon as the dimensionless time is greater than , abou*- 10 (as in a pumping test without any frac T T T T ture) excepted for x « 1, i.e., at the contact 5. ' H.6 1 15.2 ! 27.0 ' 53 ' of the fracture, where this minimal time is increa sed to 13 to 17. 10 i 26.4 | 29.6 , 54.7 , 105 | 50 ' 131 l 147 ' 272 ' "24 ' -107- It. appears Ui.it JACOB'S approximations is v.ili'l only after •* long (Hnensionless time (grea ter thm> I'i')) for very rectangular fractures i.e. iructutcH wits u large F shape factor. The draw coordinates relative to the center of the down inside the fracture* has been drawn for diffe fracture rent dimension less:; times on graph c>. This graph stiiiws th.it th*- 'tcvmiovm is approximative^ cons tant ni'side the f rarture. Tt moans that the erjui- v.tl Tit tr half lenqth half width Dummy variable representing time h - Aquifer thickness h ••= Aquifer limensionless thickness Pump*"i or injected discharge Drawdown (or hi?ad d,'fprcncc) jtraensionlesK drawdown Ur.tph ! Drawdown inside a horizontal rectan Permeability ili"draulic conductivity) gular fracture (average along tlio aquifer width) Trie drawdown corresponding to a pumnin^ test porjorrnivi in a ir.^inite transmissivity horizontal K^JKx Ky = Horizontal permeability rectangular fracture is then closely approximated T = Horizontal transmissivity (K.h product) by the formula that we have derived for a uniform flux horizontal rectangular fracture. S = Storaqe coefficient S = Specific storage coefficient. = S/h ?. CONCLUSION F = fracture geometry factor A new scheme has been derived for pumping •n = 1.14159 . .. tests in fractured aquifers. This scheme is cha racterized by a single horizontal flat rectangular er*== Error function fracture. exp= Exponential ^unction The drawdown has been computed at the center of the fracture and also at an observation well situated along the principal directions. Types cur ves have been drawn which makes it possible to perform pumping test analysis or to compute the drawdown corresponding to a known rectangular Fracture. °L'FERENCES 1. BERTRAND CL.), FEUGA (B.l, NOYER (M.L.), 4. CJNCO, RAMEY (H.J.), MILLER . - 1975 - Unsteady TI1IERY (D.). - 1980 - Roches chaudes haute tem state pressure distribution created by a well perature ("Hot Dry Rocks") Contribution a la with an inclined fracture. Paper SPE 5591 pre r.i^thodologie de la determination des caracte'ris- sented at SPE AIHE 50th. Annual fall technical tiques hydrauliques des milieux rocheux fractu conference wc" exhibition - (Dallas, Sept-Oct. res naturellement ou artificiellement - Commis 1975). sion des Communaut£s EuropSenneo - Contrat n° 563-78 EGF {rapport BRGM 80 SGN 029 GEG). 5. RAGHAVAN (R.), URAIET (A.), THOMAS (G.W.). 197£ 2. GRINGARTEN (A.C.), RAMEY (H.J.I. 1974 - Unstea Verfical fracture height effect on transient dy state pressure distribution created by a flow behavior. Paper SPE 6016 presented at the well with a single infinite conductivity ver SPE AIHE 51th. Annual fall technical conference tical fracture . - Soc. Pet. Eng. J. (Aug. 74) and exhibition (New-0rl6ans, Oct. 1976). 3. GRINGARTEN {A.C.J, RAMEY (H.J.). - 1974 - Uns teady state pressure distribution created by 6. GRINGARTEN (A.C.), RAMEY (H.J.). - 1973 - The a well with a single lion^ontal fra.T.i-e, par use of source and Green's functions in solving tly ;•.-•• -*r*i* .o-' . r msLiicted entry. - Socie-- unsteady flow problems in reservoirs - Soc. c.- of pr-ToiPUi' r:ig?nec:s journal - (Augubt 74) Pet. Eng. J. (0?t. 1973). -109- THERMAL ErFECTS IN WELLTESTS OF FRACTURED RESERVOIRS G.S. Bodvarsson & C.E. Tseng Lawrence Berkeley Laboratory Berkeley, California Introduction formulating the governing equations (Edw.irdr;, \9/2, Narasirahan, 1975). The set of non-linear equation;- Conventional well test analysis methods are that arises at each timeBtep ia solved by an itera usually bused upon assumptions of Isothermal fluid tive scheme and an efficient sparse solver (Huif, flow In homogeneous porous media reservoirs. Some 1977). Details of the model are given by Lippnwn:: solutions are also available for veils Intercepted et al., (1977), and Bodvarsson et al., (1979). hy singly vertical or horizontal fractures (e.g.t Cinco Ley et al.,0978), Gringarten (1971), The numerical model has been extensively Streltsova-Adams (1978)) or by highly symmetrical tested against analytical solutions for mass and fracture systems (e.g., Warren and Root (1963), heat flow. It has generally given results (Rod- Kazeml (1969)), but again they are United to varsson et al., 1980) that compare very well with isothermal conditions. In geothermal reservoirs, values given by analytical solutions. Furthermore, considerable natural temperature gradients can the code has been validated against field experi occur and it IB questionable if isothermal well ments for underground storage of hot water (Tsanp test analysis techniques can be applied to such et al., 1979). In recent years the model has been systems. Furthermore, reinjection of wastewater used successfully in studies of problems in into geothermal reservoirs creates areal temper ^eothermal reservoir engineering, well testing, ature distribution within the reservoir- aquifer thermal energy storage, and radioactive Injection testing of RGOthermal reservoirs is waste *uolation. currently being used at A number of geothermal fields (C.P,. , Krafla, Iceland; Olkaria, Kenya; Los Aztifres, Mexico; Wairafcei, New Zealand), and a rheiret ic.il basis for the analysis oi such non- isothermal tests is greatly needed. INJECTION TESTING OF WATER-DOMINATED POROUS-HEOIUH GEOTHERMAL RESERVOIRS In this paper, a numerical simulator is used During Injection tests, water of a lower to study two basic problems. The first problem temperature than the reservoir water is injected involves the analysis of injection tests of homo into the geothermal aquifer* A temperature varia geneous porous media geothermal reservoirs. Due tion will develop in the reservoir, with colder to the dependence of viscosity and density of water close to the injection, well and hotter reser water on temperature, the pressure response at voir water farther away. Tills In turn creates injection wells will be considerably different differences in density and viscosity of the fluid from the pressure transient resulting from a con within the reservoir- In our numerical model the ventional (Isothermal) pumping test. dependence of viscosity and density of the fluid on temperature is fully taken care of. The second part of this paper deals with the problem of wastewater injection into a fractured Problem and Approach geothermal reservoir. It is commonly believed that when fractures are present, the injected cold The problem considered is that of an Injection water will rapidly advance along the fractures to well fully penetrating a horizontal homogeneous wells In the production region. If true, this may Isotropic geothermal reservoir. The injected watt'r cause a drastic reduction in the amount of is at a temperature of 100JC, but the reservoir energy which could be extracted from the geothermal contains single phase water at a temperature of resource. Using a simple reservoir model with & 300 C. Actually, as will be seen later, the few major fractures,we have studied the movement of results obtained are valid for any temperature if the thermal front in the fracture relative to its appropriate correction factors are used. movement in the porous media during injection. In the numerical simulation a radial mesh Numerical Model Used (concentric circles) Is used, with fine elements close to the well covering the region with temper For this study the 3-dimenslonal simulator CCC ature variations. Farther away from the well, the (Conduction-Convection-Consolldation) , developed at mesh is made to Increase logarithmically. The t.awrence Berkeley Laboratory, was used. This reservoir is modeled as a single layer, and thus computer code solves numerically the heat and mass buoyancy forces are neglected. Figure 1 shows a flow equations for a fully sa .crated medium. It schematic picture of the model used, and the employs the Integrated Finite Difference Method parameters used in the simulation are given in (IFDH) in discretizing the saturated medium and for Table 1. -110- Oi (Ti.lOO'C) &*•> Figure 1. Model used In the study of injection Figure 2. Pressure behavior at an observation into a porous media geothermal reservoir* well (r - 2.5 in) during cold w.-.ter (100°C) injection into a 300°C geothermal reservoLr. Table 1. Parameters used in the study of injection testing of porous geothermal reservoirs* Flow rate -in- c - TMIl dr^" ™i (300 >CI \^\~^ O' T0, K0,S0 " VK,,*, 1 C^^^ *To,K,.l0 10 * 10' K)u 10' KT K>* KT KT «f Tim* (itconcfi) XILMfi-lK' Figure 3. Transient injection pressure behavior, when I00°C water is injected Into a 300°C reservoir, for different values of transmlssivity and storativity of the reservoir. Timt (ucondt) Figure 4. Injection pressure behavior, when I0O°C water is injected into a well located in a cold-spot (lower temperature region). In equation 1 the symbols used denote the following: velocity of the thermal front velocity ;>f the hydrodynamic front porosity of the formation density of the reservoir fluids heat capacity of the reservoir fluids Integrated reservoir mass heat capacity a a where p C $P*•-«- C« +• (1-$*- ") ra~n'p C , and ' p At the time when injection has Just been ter minated there is a pressure as well as a temperature gradient within the geothennal reservoir (Figure 5). If at this tine a falloff test is performed* the pressure response shown In Figure 6 would Figure 5. Schematic diagram showing reservoir result. The pressure will initially decline conditions immediately after injection. -112- at a rate corresponding to the 100 C Thela 300 C water. During the transition, the pressure solution, but later a change In slope will occur in the well actually increases. probably because of and i-he 300°C Thels curve will be followed* rapid changes In the viscosity of the water. As These results are consistent with those obtained ahown in Figure 7, the temperature of the produced by Mangold et al. , (1979). water changes from 100°C to 300°C during the transition implying • more than threefold decrease Injection - Production Test in the viscosity of the water. A case was studied where production irauedlate Discussion ly followed an injection period (that is. with res ervoir Initial conditions as shown in Figure 5)* Data from injection tests of porous media geo- The calculated pressure behavior in the well is thermal reservoirs show aeversl linear segments in shown in Figure 7. It is characterized by three a pressure-log time plot. This behavior is due to distinct straight lines. At first the pressure the dependence of fluid density and viscosity on decreases at a rate that corresponds to twice the temperature. Our results indicate that when an rate given by the Theis solution for 100 C injectlon-rest-injection procedure is employed, water. Later on the pressure decrease follows a the radius of the cold spot resulting from the slope that equals two times the slope given by first injection period may be determined. Conse Theis solution for 300°C water. The obvious quent ly an estimate of the effective porosity of reason for the doubled pressure decrease in compar the reservoir can be obtalred. ison with the Theis solution is that two Independent forces control the drawdown: the constant withdrawal rate and the initial pressure falloff condition in An injection - production test may be advan the reservoir. tageous because larger pressure changes can be observed (2 tines the rate predicted by the Theis solution). An observation of three different linear After the two double slopes, a transition segments in the data may also lead to a better occurs, after which the pressure starts declining determination of the reservoir parameters. It must at a rate corresponding to the Theis solution for be noted, however, that other factors may cause a Slop* •quoUTTiili (300*0 Figure 6. Pressure falloff after 1.2 days of injectio: 10 10 W Tim* (second*) X6L S0S-I332 Figure 7. Pressure transient behavior during a production test, immediately following 1.2 days of injection. similar break in the slope in the data shown in The mesh used for this study consists of 144 Figures 2-7; e.g., boundaries, as well as permea elements In the horizontal direction, with elements bility variation within the reservoir* One must that are fine close to the well and logarithmically therefore be quite careful when analyzing injection increasing in size away from the well. In the ver test data* Accurate knowledge of the temperature tical direction, 6 layers are used, with fine ele of the injected water and the reservoir fluids Is ments close to the fracture but larger elements essential for accurate determination of the reser away from the fracture. In the study an 8 in. voir hydraulic parameters* diameter well is used, and two alternative fracture spacings of S or 10 meters. Values of "thcr parameters used in the numerical simulations are given In Table 2. INJECTION INTO A FRACTURED GEOTHERMAL RESERVOIR The cases studied can be subdivided into 3 basic categories as shown below: The objective of the following sections of tills paper is to study the movement of the thermal 1. Injection into a fracture in an imper front In horizontal fractures relative to its meable formation movement through the porous media matrix when cold 2. Injection Into a fracture in a permeable water is injected into a fractured water-dominated formation geothermal reservoir. To date, little work has 3. Injection into a well connected to both focused on problems involving non-isothermal flow the fracture and permeable formation through fractured media, although some initial studies have been done, including Romm 1966; The following section will describe each of Bodvarsson, 1969; Kasameyer and Schroeder, 1976; these cases and the primary results obtained. Tnd n'Neill, 1978. Our present calculating can be considered as a first step to model and study the Injection Into a Fracture in an Impermeable influence of fractures on the time of cold water Formation breakthrough at the production region, when rcinjection is used. Water at .'.00°C is injected into the fracture (Figure 9) and the effect of heat conduction on the Problem and Approach movement of the thermal front is studied. Figure 10 shows the importance of thermal conduction be tween the fiacture and the rock matrix in relation The problem considered involves an injection to the movement of the thermal front within the well fully penetrating a reservoir with a number of fracture. After only 1.2 days of injection the evenly spaced infinite horizontal fractures thermal front has advanced over 80 meters when no (Figure 8). The temperature of the injected water conduction is allowed between the fracture and the is 100 C, while the temperature of the recervoir rock matrix, but only about 8 meters when a thermal water is 300 C. Again, we assume gravity effects conductivity of .1 Joules/m.sec. C is used- On to be negligible, and therefore due to symmetry the average the thermal conductivity of rock-water only half of the basic section shown In Figure 8 mixtures is about 2.0 Joules/m.sec C. In this needs to be modeled. This section consists of half simulation a thermal conductivity of .65 Joules/m. of the fracture and half of the rock matrix associ sec. C is used for the fracture elements, and ated with each fracture (note that the fractures this causes the diffusion of the thermal front are assumed evenly spaced>• shown In Figure 10. Table 2. Parameters used in the study of injection into a fractured geothermal reservoir. lock Hatrla Fracture Horizontal fracture Thermal conductivity Fracture aperture (a): 5x10r * lilL 109-7011 Fracture spaclne. (•): 5.0-10.0 Injection temperature (°C): 200.0 Figure 8. Model used in Btudy of injection into Reservoir eaaperaguce (°C): 300.0 a fractured geothermal reservoir. -114- Increasing the coefficient of thermal conduc tion b«twain the fracture and the rock aatrlx fur ther retards the movement of the theraal front •Ions the fracture. Figure 11 shows the location of the thermal front after 1.2 dayi of injection for three cases using different values of the coefficient of there*! conduction (A, - >I> 1-0, 5-0 Joules/a.sac. C). The figure also shows how increasing the theraal conductivity Increases the penetration of the therMl front into the XILKW-im surrounding formation. Figure 9. Cold water Injection into a fracture in a porous reservoir. When the emulative areal velocity of the theraal front Is plotted against the coefficient of thermal conduction, the curves in Figure 12 result. The cumulative areal velocity is calcu lated baaed upon the radial distance of the thermal front (200 C Isotherm) from the injection well at a given time. The curves show a rapid decrease in the cumulative areal velocity of the thermal front for low values of thermal conductivity, but 250 / they level off for higher values* The shape of the curves suggests that an exponential relation ship may exist between the thermal conductivity and the cumulative areal velocity of the thermal 6 200 front. E \. 1 J/«-»*C / l«0J/««-»C Another point of interest shown in Figure 11 is that the cumulative velocity of the thermal i front is time dependent, but not constant, as In ISO the case of a homogeneous porous reservoir of constant thickness. This behavior can be explained t'LZDt*. when one considers that during injection the thermal front 1B moving radially away from the well, and the effective surface area for conduc 100 ISO tOO MO tive heat transfer between the fracture and the Radial diifancs(m) rock matrix is rapidly increasing. The energy flow XILMtHM into the fracture rapidly increases and consequent ly retards the advancement of the thermal front. Figure 10. Effect of heat conduction on the O'Neill (1978) found similar retardation of the movement of the thermal front in the fracture: thermal front in the linear case, but of course temperature versus radial distance* this phenomenon is much more significant in the radial case. I'l.O !.«.1 J/m-r*C 7 ? 0.25 / 1 II ' 1.0 6 K> 19 t Radial finance (m) 1.0 to 3.0 4.0 to Thermal conductivity KU.IH-UK (J/ma-'C) Figure 11. Effect of heat conduction on the move Figure 12. Thermal front movement In the fracture: ment of the thermal front: 200°C temperature cumulative areal velocity as a function of thermal contour in r-z plane. conductivity. -115- i: i- 0 J/m*>C •• X-O.IO J/mCC • ' X« 1.0 J/m-«*C •; X« 5.0 J/mn*C F4.yure 13. Injection pressure behavior during injection into the fracture in a porous reservoir, for different values of thermal conductivity. Figure 13 shows the pressure behavior at the penetrates the rock considerably. Most of the heat injection element, during cold water injection into transfer between the rock and the fracture is by the fracture. When there is no conduction, similar convection. However, if the permeability ratio pressure behavior is observed, as in the case of a (k ) is increased to 10 , the conductive heat homogeneous porous reservoir (see last section), transfer la still very significant (Figure 15). with two distinct linear segments having slopes A comparison of two computer runs with thermal corresponding to Theis solution for the two temper conductivities of 5.0 and 2.0 Joules/m.sec. C, and atures. (In the model we assume that Parcy's law all other parameters remaining the same, shows that can be used to calculate fluid flow within the the thermal front has advanced 3 and 4 metezB fracture). However, conduction between the frac respectively, after 1.2 days of injection. ture and the rock matrix retards the movement of the front and consequently the latter linear seg ment is not observed during the simulation, although it may show up at larger times. When a large coefficient of thermal conduction is used (\ • 5.0 IOO"C I50«C Z00»C Joules/M.sec- C), the linear segment corre V * * sponding to the 300 C Theis continues at all times during the computer simulation. Injection into a Fracture in a Permeable Formation A few computations were made in order to study the movement of the thermal front when cold water was injected into a horizontal fracture in a per meable medium. The thermal conductivity of the rock matrix was fixed at 2.0 Joules/m.sec. C, but the thermal conductivity of the fracture remained at .65 Joules/m.sec. C. A fracture permeability of 1 x 10 m or 100 darcies was used for all of the cases, but the permeability of the rock matrix varied. Figure 14 shows the temperature contours in the fracture and the rock matrix after 1.2 days Radiol diitanct (m> of injection. In this run the permeability ratio between the,fracture and the rock matrix (k^) is., fixed at 10 (the permeability of the rock Is 10 or 10 md)< As the figure shows, the permeable rock allows penetration by the injected water, and con Figure 14. Isotherms after 1.2 days of injection sequently the cold water front (the 200°C isotherm) into a fracture in a porous reservoir. -116- Qi (T,«I00*C) —j- vwo*n M • 1.0 J/n-i-*C M»10 J/nrt-K T K0-IO XflL 806 -1340 Rodtal dialane* areal velocity of the thermal front decreases rap idly* almost linearly at first, then gradually levels off. The cumulative areal velocity of the thermal front in the rock increases with time until Injection into a Well Connoted to Both the it coincides with the velocity of the thermal front Fracture and the Permeable Formation in the fracture* after which the fronts advance together. The two curves for the rock shown in In thia case the fluid Is Injected both into Figure 16 represent observation points at different the fracture and the permeable formation directly distances from the fracture. At the end of the through the Injection well (Figure 16). Thus the simulation the thermal front in the rock close to thermal front moves radially away froa the well the fracture is advancing at the same rate as the both In the fracture and In the rock, although not thermal front in the fracture, but In the rock necessarily at the same rate. Two caaes are farther away from the fracture the thermal front studied: in the first one a permeability ratio still lags soz-ewhat behind. (1^) of 10 and fracture spacing of 10 meter* la used; In,the second* the permeability ratio is fixed at 10 and the fracture spacing at S meters.. In both cases* a fracture permeability of 10*~ m or 10 *d and a thermal con ductivity of 2 Joules/m.aee.°C is uaed. >,.„.,. IT& Figure 17 shows temperature contours after 1*2 days of Injection for the first case. At this tine f the thermal front (200 C te»perature contour) has advanced considerably farther in the fracture than in the porous media* over S n in the fracture* 1 2 compared to 1.5 meters in the formation. i i awe Figure 18 shows a plot of the cumulative areal *—200 »C velocity of the thermal front versus time for the first case. The lack of data far the thermal front i in the rock at early times Is dus to the space dis 1 cretization used in the study. We have defined the 4 • K »l0* thermal front as the 200 C isotherm, and at early 0 times the first rock elements hsve not cooled down Frttlvn ipwlftl • 10m sufficiently to allow accurate determination of the 1 location of the thermal front. The figure shows 5 tO 15 20 that at early times the cumulative ar*al velocity fludlal diitancs (m) of the thermal front is mors than an order of mag nitude higher in the fracture than in the formation. One must bear in mind that for i homogeneous porous radial system and a constant injection rate, the Figure 17. Isotherms after 1.2 days of injection areal velocity of the thermal front should be con into a well connected to both fracture and the stant. As the injection continues the cumulative porous formation. -117- Fracture spacing >IOm entering the fracture from the well. Figure 19 shows the location of the thernal front at different KD» 10* times during the simulation- The figure shows that X « 2.0J/ms-«C at early times the thermal front In the fracture Is well ahead of the thermal .'r*-nt in the rock. Later on, however, the thernal front in the rock starts to cctch up with the thernal front in the fract-it^ and after only 10 seconds (about 115 d.iys) the two fronts almost coincide. It is of incerest to note that after only 23 Meters from the Injection well the two fronts advance practically side by side. Summary and Discussion Time (seconds) The studies described in the last few sections can be considered as a first step to answer the key question of how fractures affect the break through time of cold water from injection wells Figure 18, Cumulative areal velocity of Lne into the production region in a geothermal field. thermal front during injection. The observation Our results indicate that when cold water is in points In the rock matrix are .10 and "i* 3 meters from the fracture. jected into horizontal fractures in impermeable rocks, heat transfer by thermal conduction between the fracture and the rock matrix retards the movement of the thermal front in the fracture considerably. Of course, the higher the coefficient of thermal conduction, the more the thermal front gets retarded, and our results indicate that there may be an exponential relationship between the V areal velocity of the front and the thermal con ductivity of the rock matrix- When cold water Is injected into a horizontal fracture in a permeable hot reservoir, the heat transfer between the fracture and the formation may become dominated by convection, dspundlng upon the permeability ratio (II) between the fracture and the rock matrix an! tne thermal conductivity of the rock. The permeable rock allows flow of cold water from the fracture into the formatior. and conse quently the cooling effects extend deep into the surrounding rock. We also studied the case of cold water injec ZO 24 tion directly from the well into both the fracture Rod la I distonce(m) and the formation. Our results indicate that al though the thermal front advances much more rapidly in the fracture than the rock at early times, the Fi.;ure 19. Isotherms after 115 days of lnjectloi thermal front in the rock eventually catches up with the one in the fracture, after which time they will advance at the same rate. The distance from che injection well to the point where the fronts will coincide depends on many factors, such The rapid decrease in the cumulative areal as the permeability ratio between the fracture and velocity of the thermal front In the fracture wich the rock matrix, the spacing and aperture of the time is due to Che continuously increasing surface fractures, and the thermal conductivity of the area, through which conductive and convective heat surrounding rock. transfer between the fracture and the formation can occur. The increase in the cumulative areal veloc Although the results presented in thia paper ity In the rock is probably due to cooling effects are quite preliminary and require further investi from the fracture. gation, they imply that in geothernial formations dominated by horizontal fractures, rapid movement ., Another calculation was made using K_ equal to of the injected water shooting through the frac 10 and fracture spacing of 5 meters* Similar tures may not accelerate the cooling of the reser results to those shown in Figure 18 were obtained, voir much. Thus, in such formations injection may although the cumulative areal velocity of the safely be used to maximize the energy recovery of thermal front in the fracture is less In this case the geothermal system, if the spacing between the at all times, due to the increased permeability of injection and the production wells is appropriately the rock and consequently relatively less water selected. Acknowledgment with both Fracture and Pore Permeability," Lawrence Uveraor* Laboratory report DCRL- The author' wish to express their $v .ude 77323. to Dr. Harcelo Ll{/pmann for critically reviewing Kaseal* H.. "Pressure transient analysis of this manuscript. They would also like to acknowl naturally fractured reservoirs with unifon*. edge Eaen Wartf for plotting the data, and Mary fracture distribution," Soc. Petr. En».. vol. Bodvarsson and Becky Sterbentz for drafting the 9, 1969, p. 451-462. figures* Tliis work was performed under the LlppMnnt M.J., Tsang, C.F., and Witherapoon, P.A., auspices of the U.S. Department of Energy, (1977). "Analysis of the Response of Geo- Division of Ceothermal Energy, under Contract thsraal Reservoirs under Injection and Pro Number W-7405-ENG-48. duction Procedures," SPE-6537, presented at the 47th Annual California Regional Meeting SPE-AZME, Bakernfield, California, April 1977. References Mangold, D.C., Tsang, C.F., Llppaann, M.J., and Hltherspoon, P.A. , (1979), ''A Study of Thermal Bodvarsson, G. (1969), "On the Temperature of Water Effects In Veil Teat Analysis," SPE-8232, Flowing through Fracturea," Journal of Geophys presented at the 54th Annual Fall Technical ical Research, vol. 74, No. 8, p. 1987-1992. Conference SPE-AIME, Las Vegas, Nevada, Bodvarsson, G.S., end Lippawnn, M.J., (i979), September 1979, Lawrence Berkeley Laboratory, "Recent Modifications of the Numerical Coda LBL-9769. CCC," in The Annual Report of the Earth Naraslahan, T.N., and Wltherspoon, P.A. (1978),"An Science Division, Lawrence Berkeley Laboratory, integrated finite difference wethod for ana LBL-10795. lyzing fluid flow in porous madia." Water Bodvarsson, G.S., and Llppnann, M.J. , (1980), "The Reaources R«s.. vol. 14, no. 2, p. 255-261. Numerical Simulator CCC," paper presented at r'Nelll, K. (1978), "The Transient Three-dimensional the Fracture Hydrology Modeling Workshop at Transport of Liquid and Heat in Fracture . Lawrence Berkeley Laboratory, Feb. 19-20, Porous Media," Ph.D. Thesis, Princeton Univer paper to be published in the proceedings of sity. the workshop* Romn, E.S. , (1966), "On One Case of Heat Transfer Cinco-Ley, H. , Samanlego, V.F., and Dominguez, In Fractured Rock," All-Union Institute for A.K., "Transient pressure behavior for a well Scientific Research and Geological Exploration with a finite conductivity vertical fracture," for Petroleum," U.S.S.R. , Preprint. Soc. Pet. Enfi. J.. Aug. 1978, 253-264. Streltsova-Adama, T-D., (1978), "Hell Hydraulics in Duff, E.S., MA28 - "A set of Fortran subroutines Heterogeneous Aquifer Formations," In Advanres for sparse unsymmetrie linear equations>" in Hydroscience» vol. 11, Academic Press, Inc. . Report AERE-R8730, Harwell/Oxfordshire, Great p. 357-42? Britain. Tsang, V.W., and Tsang, C.F., (1976), "An Analytic Edwards, A.L., "TRUMP: A computer program for Study of Geothermal Reservoir Pressure Re transient and steady-state temperature distri sponse to Cold Water Reinjection," in Tbe butions in multidimensional systems," Lawrence Proceedings of the 4th Workshop in Ceothermnl Radiation Laboratory, Llvermore, Report UCRL- Reservoir Engineering, Stanford University, 14754, Rev. 1, 1968. p. 322-331. Gringarten, A.C., "Unsteady state pressure distri Taang, C.F., Buscheck, T., and Doughty, C., (1979), bution created by a well with a single hori "Aqulftr Thermal Energy Storage; a Numerical zontal fracture, partial penetration, or re Simulation of Auburn University Field Experi stricted entry," Ph.D. Dissertation, Stanford, ments," Submitted to Water Resources Research. 1971, 110 p. Warren, J.E., and Root, P.J. , (1963), "The Behavior Kasameyer, P.W., and Schroeder, R.C. (1976), of Naturally Fractured Reservoirs," J. SPE "Thermal Depletion of Geothermal Reservoir no. 3, September 1 *»63» pp. 245-255. AQUIFER RESPONSE: TO EARTH TIDES B. Y. Kanahiro and T. N. Narasinhan Earth scisnces Division, Lawrence Berkeley Laboratory University of California Berkeley, California 94720 INTRODUCTION earth tides and the response of aquifers to earth tides has been done by Helchior < 1956, 1960, 1964). The earth is, theoretically, within the gravi He reported on tidal fluctuations in deep wells in tational fields of all other celestial bodies and Turnhoux, Belgium, and a hot spring at Kiabukwa, as such is subject to tida! forces. The sun and Belgium Conyo. moon, however, because of their respective sizes and proximity account for virtually all the tidal Early discussions of the theoretical analysis forces experienced by the earth. While all of the of the response of aquifers to earth tides were earth is subject to tidal Forces, the ocean tides presented by Theis (1-39) and Pekeris (1940). in of the hydrosphere provide by far the most dramatic 1964 Hclchior presented an analysis f-r a spherical evidence of these forces at work. These same tidal cavity. A good general discussion and an analysis forces also act on the atmosphere and the litho- based on expected dilatation was presented by sphere and generate atmospheric and solid earth Bredhoeft in 1967. In 1970, Bodvarsson presented tides. These tides are of small magnitude, however, an analysis assuming a spherical cavity. Recently, and are more difficult to measure accurately. norland (1977) pr"3?' Ga H (3cos 6 - 1) , H (3cos Perhaps the earliest suggestion of the response of groundwater levels to eartn tides was made by Grablovitz in reference to periodic water- level fluctuations in a flooded coal mine in the where G is the universal gravitational constant; landlocked country of Czechoslovakia reported by a is the mean radius of the earth: Ms is the mass Klonne in 1880. tiince I860 there have been many of the sun: J^ is the mass of the moon and Q3, Q^, reports of fluctuations of a tidal nature in wells Rg, and ^ are shown in Figure 1. (Rinehart 1975) that may be attributable to aquifer response to earth tides, Young (1913) reported on tidal fluc tuations in a well near Cradock, South Africa. In The change in acceleration due to gravity is 1939, Robinson published hydrographs of several wells in New Mexico and Iowa showing tidal fluctua tions attributable to earth tides. More recently, t<3 ~ W2 George and Romberg {1951) reported on water-level fluctuations showing aquifer response to earth The radial or vertical component is tides in a well at Fort Stockton, Texas. Tidal fluctuations have even been reported in a well drilled in a water table aquifer by Richardson in Oakridge, Tennessee. More extensive work on both and the tangential or horizontal component is of accuracy of •van a quartz crystal pressure transducer. DEFORMATION OF THE EARTH "9y ~" « 0H~ if a is amumed to be much smaller then i^ or While it was not pointed out in the previous H , n±gher order terns can be neglected and discussion uf the change in acceleration due tc gravity, the earth is not a rigid body. Indeed it is in part., the deformation of the earth that causes the change in acceleration due to gravity to be no complex. It is also this deformation that ',-auass the change in pressure in the reservoir. In a gross sense this deformation may be viewed as a bulging of the earth resulting from the gravitational attraction of the moan and/or sun on the one side and centrifugal force on the other. Unfortunately the description of tne mechanics of tho situation is very complicated. In a general sense, however, it can be said that the magnitude of the dilatation at a point is determined by the change in gravitational potential that can be calculated from the positions of the sun, moon and earth and a semitheoretical model of the earth or empirically determined coefficients. The original theory of Love (1911) assumes that a spherical harmonic of second order can be used to approximate the perturbing potential. It is further assumed that the deformation of the earth induced by this perturbing potential may be expressed as the product of the harmonic and some numerical coefficient. These coefficients are Earth related to the distribution of deitities and moduli XBL 756-7S37 of rigidity in the semitheoretical earth model or figure 1- Relation of the sun and moon to a point, can be empirically estimated. Historically, they P, on the surface of the earth came to be called Love numbers and are used singu larly or in simple algebraic combinations. before discussing the effects of the earth tides on a reservoir the complex time-dependent While a considerable amount of interesting nature of the tides should be considered. While work has been done on the estimat-ion cf Love numbers the relative movements of the sun, moon and earth and the deformation of the earth, it is sufficient are indeed complicated they are to a high degree to limit the scope of this paper to the estimate of of precision periodic. For this reason the complex the total dilatation presented by Takeuchi. time-dependent nature of the gravitational tidal potential <-an be dealt with by using either Fourier analysis or a filtering scheme and invoking super position. While this can become an involved process, it will be assumed for the present that the tidal potential and the signal at the well can From this it may be seen that the perturbing ue decomposed into discrete sinusoidal components. potential may be calculated with some accuracy because the motions of the earth, sun, and moon are From the above, it might seem reasonable to reasonably well understood. The deforr-tion result assume that the change in acceleration due to ing from the perturbing potential, however, is not gravity accompanying the change in tidal potential easily determined because an earth model and Love implies a change in weight of the overburden of the numbers must be estimated. For this reason it must reservoir. This changing overburden stress may be understood that any estimations of reservoir or then cause the observed change in pore fluid aquifer characteristics based on response to earth tides will of necessity have certain unavoidable pre?-uie seen in the aquifer. This simplistic uncertainties associated with them. model, however, cannot account for the magnitude of the change in pore fluid pressure seen in even moderately deep reservoirs. There remains of course, at least in theory, the possibility of literally measuring the strain The measured amplitude of the change in gravi induced in the earth by earth tides. What would tational acceleration due to earth tides is gener be required is a very accurate measurement of ally on the order of 100 microgals. An overburden strain in six directions over a relatively large of 1,000 meters with a density of 2,650 kg/m3 would area. Since the radial component is relatively therefore imply a change in stress of only 2.65 Pa email with respect to the horizontal components, 12.7 x 10~4 m of water). This is obviously a rela however, it may be possible to use only the tively small effect that is at or beyond the range horizontal components. Given such a strain -121- measuring network at the site of a reservoir, a H • thi.r„icn*>M of the aquifer vary interesting analysis may be possible* Since the storage tera is defined with respect rut; fKuaLKM CUKS1U£K£U to the addition or removal of fluid from the reser voir, its relationship to compressibilities and l"wo types Q£ modeLs ate considered in this changes in pressure are not immediately obvious. analysis oi the response of the reservoir to To circumvent this problem for the present situa tut; earth tides described above. The first ie tion, the following definition for the storage term tnat of a confined aquifer with a single packed- is adopted* jtf well, and the second is a confined aquifer wLth a well open to the atmosphere where the S - P 9 E C (1 ,a wdtm Level is allowed to fluctuate* The first B f * f * " * v' '.asu will be considered in some detail followed uy field examples. The second case will be (Jacob, 1949). Or similarly. briefly considered in a later section* Because good data was riot XviertcSblBlLrriliS AND THE STORAGE TERM From thu pnysxcal situation of the firBt case it is apparent that the properities that may be irEtiaidted from the aquifer's response to the earth where Vj = volume of fluid and Pf « fluid pressure, tiles are related to comt--essib..! ities. In the and a , defined as : icids of nydrology and petroleum engineering, haw- «vtr, it is more cannon to deal with some type of storage ten" rather then compressibilities directly. i !iu storage term encompasses the compressibilities imt n* more convenient to use when working with tjuatiunB dealing with flow. This is because the where Vs - volume of the solid grains and majority of problems LII hydrology and petroleum o* = effective stress, i.e., the total stress unginuentig are related to the addition or removal less a percentage of the pore fluid of fluid irwn the aquifer or reservoir. Such a pressure. situation can be termed a drained problem where the addition or removal of fluid acts as the driving The above relationship, unlike the original t< tee. in contrast to this is the undrained prob- definition, does not make direct reference? to the mm wnere fluid not being injected or withdrawn. m drained or undrained nature of the problem. Uy hauier, tne driving force or load on the system is adopting this relationship in place of tho original in trie form of ai\ externally applied stress. definition it Is possible to consider the undralnod problem. in this case the magnitude of the change Historically, the first storage term to be in pore fluid pressure resulting from a load is not iiutniii'l in hydrology was tht; storage coefficient the same as the magnitude of the change in the now dltio known as the storativity. It is currently effective stress. The total quantity of fluid in detined as tne volume of water which an aquifer the aquifer or reservoir, however, must regain the rele.uies from or takes into storage per unit surface same. area ot aquifer per unit change in the component of nea.i normal to the surface (Ferris, 1962), barlier From the definitions of the fluid compres definitions of the storage coefficient expressed sibility, the coefficient of compressibility, and tne same idea, but were more restrictive in that since they were formulated in terms of aquifer thickness. Hie otiier common storage terr. used in hydrology is tne specific storage storativity. It is the stor- ativity normalized with respect to the thicknetd or tile aquifer. In petroleum engineering the stor age term -.s generally expressed as 9cH. The rela tionship between ycM and specific storativity is. Since fluid is not being added to or removed from the reservoir and the medium remains saturated, the c = total compressibility of the aquifer change in fluid volume is equal to the change in void volume. Hence, v - porosity of the aquifer »s - specific storage "j = density oE the fluid *'rou the definition of fluid compressibility £STIMATING THE WIX MODULUS The question of deciding what value should 't^t • ^(Ji-1)<",' be used for the bulk Modulus is not a simple one. It becoates a question of trying to decide what the From the effective stress law. bulk Modulus used should repress it. Should the bulk Modulus reflect the rocks miking up the aquifer or ahould it ainply be tiken ss the value obtained from the earth Model that the tidal potential is applied to? The arswer appears to be soMtwhere in between- The real earth is not v f\1-v/do- ndp concentrically homogeneous like the earth model. On the other hand the rocks making up the aquifer probably have a lower bulk modulus then the The specific storage nay then be written as Majority of the other rocks at a given depth and this might imply that the representative value of the bulk Modulus in or near the aquifer might be somewhat lower than the value that might be expected from a global p nt of view or fro-i the point of view of the earth model. =P y C f * f [' * do - ndpf J The point is that there does not appear to be any physical way to clearly determine what value larly, should be used for the bulk modulus. Xn facr., given the heterogeneities in the system, it appears d that for practical purposes it in not feasible to T "f 1 consider trying to determine explicitly what the VCH =• *C.H|t + — representative bulk modulus is, even by using suet' f do - ndp powerful methods as numerical analysis capable of The specific storage is now written in terMB handling the arbitrary geometries, while the prob of che change in pore fluid pressure which can be lem of picking a representative value for the bulk measured, the change in total stress, the porosity, modulus is a difficult one, it should l»e noted that and other coefficients which can be easily esti other similarly difficuit problems *re «ncnuuteied mated. Recall, however, that the calculations in doing the more common testa for the deturnuna' based on the change in gravitational potential tion of the hydraulic characteristics nf aquifers allow only for the estimation of the change in such as pump tests, since there is much more exper dilatation. Since this problem only deals with ience in dealing with these more common types oi changes in volume, any deviatoric portion of the test, however, the required assumptions that must- stress tensor need not be considered* The devia be made are often made in a matter of fact rashmn toric portion only gives rise to a change In shape and not subjected to much question. For exanple, IChienci, et ai. 1967). This implies that the in many pump tests it is virtually .-»rtain that trie octauedral stress, o„, defined as field conditions do not conform to the boundary "r heterogeneity conditions of the analysis b«:ij used, but experience has shown that the analysis may still be applied to arrive at satisfactory results. The reason that the results of the analysis appeal may be used. Since to be satisfactory in many cases may be be.-ause the assumptions are indeed reasonable, but in 119) other cases it may be because there is :ealty no way to independently an ive at a better estimaf and thereby bring the assumptions into question. (20) That this is sometimes true may be seen in the extremely large differences in values determ-. r^-i 121) at the same well by a longer term and a sh >rter term pump test. Of course, in the present pi ohiem a numerical quantity mu3t be estimated and since it is easy to change a numerical quantity without radically changing the analysis as would be 122) required in the case of a change in geometry there is a tendency to expect the "right" number to be chosen for each problem. Given that there is 123) justification for making somj estimate for the representative bulk modulus the question of how the bulk modulus. this estimate is to be made arises. The best estimate for the bull: modulus from the earth model Thus the ° required to evaluate the specific of Takeuchi (1950) based on the values of elastic storativity or VcH nay be estimated from the moduli presented by Bredehoeft (1967) ig 1 x 11 dilatation if the magnitude of the bulk modulus is 10 Pa. This is a rather high value being reaiistically known. The next section deals with approximately that of the ultrabasic rock, dunite. now a value for the bulk modulus can be reasonably Since aquifers are in the upper part of the trust deduced from available data. and hence usually in areas of somewhat lower bulk modulus it is reasonable to take the value of 1 x number is aqual to the racord length {2B days) to11 Pa as an upper limit* Further, since the divided by the period of the component. area being considered includes the aquifer it i« reasonable to assume that the representative value for the area would be less than this value. Values for the bulk moduli of sandstones and other common rocks are presented in table 1. As can be seen these values are almost all substantially below 1 x 101* Pa. As previously stated, however, the deformation being considered is on a large scale and the relatively low bulk modulus of the aquifer would be expected to affect, but not total ly govern the system. The beat value for the representative bulk modulus is then somewhere between these values. Since the highest values for bulk moduli of common continental rocks at depths of relatively deep aquifers is on the order of 2 x 101Q Pa to 7.5 x 10™ Pa and since the aquifer is not really at a depth where rocks approaching dunite are found it is assumed that a best estimate for the value of the represen Well record of the well at Marysville, tative bulk modulus is 5 x 10t0 Pa. Montana (XBL 811-7715) Table 1 Representative bulk moduli of a few rock types Bock type Bulk modulus Basalt''* 7.5 X 1010 Pa Dunite [T' 1.0 X 1011 Pa Granite*1' 5.5 JC 1D10 Pa Sandstone 1.7 X 1010 Pa Iron (solid)11 1.6 » 1011 Pa Fig. 3 Earth tide at the site of the well at < 'J Stacey, 1969 Marysville, Montana (XBL 811-7716) FIELD APPLICATIONS Data from two different wells were analyzed. These wells are located in East Mesa, California i.m ana Marysville, Montana. Since the overall quality of the record from the well in Montana is consid erably better than the records from the other well it will be considered first and used for illustra • .MM tive purposes* A. WELL AT MARYSVILLE, MONTANA ».tiw The Marysville well is located approximately 30 kilometers northwest of Helena, Montana. It is 2,000 meters deep with an uncased portion 0,20 vV:-v .v^sw' .«.*^ *^.^._^.*,.-.. t-£ak£i meter in diameter in a fractured granite-like, quartz porphyry. While the well is not a packed Muwxtc tweet, K off well the diameter is relatively small and as a first approximation the packed off analysis was Fig. 4 Spectrum of the well record from the well used. at Marysville, Montana (XBL 811-7717) As can be seen in Figure 2 the well record By assuming a fluid density of 1,000 kg/m3 shows periodic fluctuations that appear to corre and A fluid compressibility of 4.6 x 10-10 1/Pa spond with those of the earth tide shown in (1/PascalJ, the analysis described above may be Figure 3. Fourier analysis was applied to both applied to the amplitudes of the tidal components Accords to produce the spectrum of the well record of the well record and the tide. The results of shown in Figure 4 and the spectrum of the earth tide this analysis based on a representative bulk mod shown in Figure 5. In these figures the harmonic ulus of 5 x 1010 Pa are shown in table 2. Zt can that, forme the landward continuation of the last Pacific Rise and the Gulf of California (Iwsnberc;, 1975). The field itself is situated in essentially flat lying poorly consolidated lata Pliocene to lata Pleistocene sandstones, slltstones and claya derived from the Colorado River (Harasimhan, et al, 1977b). The reservoir itself appear* to be confined between crystalline basement rocks below and a sequence of rocki that are predominantly clay and about 2,000 feat thick on the top. The well is approximately 2,000 meters deep with a slotted section of about 250 meters. It is shut-in and monitored with a Paroscientifie quarts crystal type pressure transducer. Aside from any problems telated to the quality of the well record, there are two questions that IWHWIE HWKH. K arise in this area. The first question ia related UL 811-7111 to the abnormally high temperature that is found in all the sites studied. Since temperature Fig. 5 Spectrum of the earth tide at the site of changas the viscosity of the fluid much more than the well at Marysville, Montana the density, however, the effects on a quasi-static M2 1. 133x10-1 2.260x102 9.366x10-6 In a manner exactly the same as described for the Montana well the well record From the East Mesa S2 5.863x10-2 9.7B2x10 7.962x10"6 was submitted to Fourier analysis and compared with the predicted earth tide. The results of the ss/$ (mean - 1.14 x 10-3 1/m analysis are summarized in table 3. As car. be seen in the tables the best value of the specific stora Standard Deviation - 3.45 x. 10"6 1/m tivity over porosity for the East Mesa aquifer based on the aquifer's response to the earth tides and a bulk modulus of 5 x 10*° Pa is 5. t x 10-6 1/m. Hell At East Mesa, California Pumping tests conducted at the East Mesa Data from two geothermal walls at East Mesa, field suggest flicH values of 2.0 x 10"8 m/Pa to California were studied. The first of the two 1.1 x 10"' ra/Pa. This implies a storage coeffi wells is located about 30 kilometers east of El cient or storativity of 2.0 x 10"4 to 1.0 x 10"3. Centro, California in the Imperial Valley. If a value near the center of this range is as Lawrence Berkeley Laboratories conducted inter sumed, the most probable value based on pumping ference well tests in the area in the past few test is approximately 6.2 x 10"4. years in conjunction with the U.S. Bureau of Reclamation's invaatigation and an evaluation of The comparison of specific storativity over the site as a geothermal resource (Hitharapoon, porosity as determined from the analysis based on et al, 1976r Narasirahan, et al, 1977a; Harasimhan, the aquifer response to the earth tides and the et al, 1977b). storativity as determined from the pumping tests requires that the porosity and thickness of the The imperial Valley is part of a large sedi aquifer be known or estimated. Since in this case ment filled depression known as the Salton Trough an estimate of the thickness of th* aquifer based -1: on the geology is available the porosity can be THE PROBLEM CONSIDERED estimated and the specific 8tor*tivity over porosity compared with the pump tests' value of storativlty* As previously discussed, the quantity most Alternatively, the porosity can be calculated. A readily calculated from the earth tide is the geologically Daaeu estimate of the aquifer thick change in dilatation and from this the change in ness of 1,000 meters (Harasimhan. et al, 1977b) total stress experienced by the aquifer. The implies a porosity of twelve percent using the fluctuating water level in the open well indicates specific storativity over porosity estimate based a small though finite volume of flow. Zn a sense 1 on the bulk modulus of 5 x lO ^ pa, j^g reason the problem may be viewed as one of well bore able estimate of twelve percent for the porosity storags imposed on the earth tide esponse problem. of the aquifer indicates that the analysis of the Before attempting to treat this problem as a well record based on this theory of the aquifer's simple drained problem with sinusoidal boundary response to the earth tides gives credible results conditions, however/ two points should be made. in this case. While it is true that in the region near the well the magnitude of the change in effective stress resulting from the change in total stress is equal Table J. Kesults of the analysis of the record to the magnitude of the change in pore fluid from the well at east mesa, California pressure, there is some question as to the extent (bulk modulus of 5 x TO10 pa assumed of this area. Further, even if some kind of for the region around the aquifer) effective radius is hypothesized, the problem will not be as simple as a pumping test problem because the entire aquifer, and not just the portion inside the fictitious boundary, is being affected TIUAL aW2 &pf by the driving force* While some effort was made CUMPONSNT (x 1/gm) (Pa) (1/m) to study the possibility of an analytic solution, a complete solution was not attempted. The purpose of thin study is aimed at two things. First, it is 7 .ObuxlU-2 2..924x1 0 5.052x10~6 directed toward looking at the possible implica tions and the relative sizes of the effects of Flow 7..J62xHJ -2 4,.745x1 0 5.416X10-6 to an open well. Second, it is aimed at showing the possibility of dealing with particular field J,. /54x1U~2 1.. 102xlD 4.881x1Q~6 situations on a case by case basis. 1..704x10~ 1 5,.526x1 0 4.923x10~6 The model actually used for this study is y.,2J4x1U- 2 3. 717x10 S.035x10"6 based on an integrated finite difference scheme. The code, TERZAGI, written by T.N. Narasimhan, 1975, and based on a heat transfer code by A. (mean) = 1.14 10~5 1/m *s/w x Edwards, 1969. Since this code has been verified 7 under many diverse situations (Narasimhan, 1975) standard deviation = 2.11 x 10~ 1/m there was no need for further verification of the basic code. THIS INFLUENCE UF FLOW TO AN OPEN WELL ON MEASUHKD In view of the physical situation an axisym- AyUlFdR RESPutJiilS metric mesh with nodes logaritmically increasing in size away from the well is used. The node The original intent of this study did not representing the well is given a finite size and include the consideration of an open well and its a Binusoidal pressure generation is introduced associated complexities. Because of the poten throughout the mesh. The well bore storage in the tially large number of applications in the field, well is handled by assigning an appropriate storage nowever, it was decided that some work in this capacity to the node representing the well (see direction should be done. Since there was no Narasimhan, 1975). re idily available data for a large open well with ,od independent pump test results it was decided The mesh and configuration used for this Lnat only hypothetical cases would be studied, problem were checked in two ways. The first was before discussing the problem of flow to a well with a slug test problem. In the slug test a open to the atmosphere it is useful to consider finite volume of fluid is "instantaneously" intro what might indicate that appreciable flow is indeed duced into the well and the decline of fluid in the taking place and must be considered. Basically well is monitored. Th< results of the simulation two things would be expected* First, there would were compared to an analytic solution presented be a phase lag between the signal seen in the well by Cooper et al, 1973 with excellent matching. and the earth tide. Second, there would be an The second check was made by packing the well off. attentuation of the signal when compared to the This was done by assigning the material properties signal of a packed off flow where no flow takes of the fluid alone to the well element. The place. Since the magnitude of the phase lag and results showed that the pressure in the well was attenuation is function of the properties of the the same as that throughout the aquifer as would aquifer it is reasonable to attempt to use the be expected. response of the aquifer to the earth tides to determine these properties* The approach taken, in this somewhat preliminary study, is to explore Before discussing the numerical solution the possibility of using a numerical model to deal it should be noted that while some parameters with the inverse problem. such as the permeability and the specific stora tivity of the aquifer are chosen to reflect -126- typical field situations, other parametara such and tine conaiderations only a limited number of as the size of the wall and tha magnitude of the simulation runs ware made. driving force are choaen to ahow the effect of relatively large flow to the well. The reaulta of this study of a hypothetical problem ahould therefore not be taken to a necessarily indica tive of the effects that might be Been in a real field situation. In fact the effects of flow to an open well shown in this study are likely to De larger than that seen in the average real world field situation. Three parameters were considered in this study• They are the period of the tidal component, the permeability of the aquifer and the storativity of aquifer. While this study is of a relatively preliminary nature it does show the possibility of creating a real field situation as an inverse prob lem and some initial attempts are made at system atizing tne inverse problem into a type curve scheme, decause of space limitations only a very brief summary of the results are presented below. Further, since mest of the numerical simulations are similar in appearance, only one sample example 6 Pressure fluctuation in the well element is shown m figure 6. This example clearly shows (points) and an element distant from the well the phase lag and damping for a 24 hour tidal element {line) in the case of a well open to component in an aquifer with a permeability of the atmosphere. The period of the sinusoidal 5 x 10~'4 m? and specific storativity of generation term is 86,400 seconds (24 hours). IXBL B11-7724). When the period of the tidal component was The combinations of variables that are plotted varied the phase lag and damping increase with a to generate the type curve are. decrease of period. This is a function of the system having more time co equilibrate for the l09 longer period components. The possibility of using several components for a phase lag analysis and a [y '»] very long period component to approximate a packed where T = the transmissivity (hydraulic conductivity off well therefore arises. These possibilities times the thickness of the aquifer), r = the are considered in the type curve study presented w radius of the well, the phase lag, and oelow. The magnitude of this increase however, z = is not very large unless a relatively large diameter well is considered. PQ ~ P po its would ce expected decreasing the perme ability of the aquifer increases the phase lag where p = the amplitude of the pressure signal at dnd tne damping. The magnitude of this increase the well, po = the amplitude of the pressure signal however, is not very large unless a relatively at an infinite distance from the well. large diameter well is considered. ft sample curve for a well of 0.2 meter radius Also as might be expected, a smaller specific in an aquifer ten meters thick is shown in Figure storativity implies a more damping and phase lag. 7. The discrete points represent actual simula in terms of inven e problems it may be possible tions that were run to generate this curve. The to estimate the storativity from the very long smooth curve is based on interpolation and extrapo period component response and then only deal with lation. the permeability problem. It might be noted th.^l there is at least a Trid POSSIBILITY OF GENERATING AND USING A TYPE possibility of using this approach in the field if cuRvt; fortnightly unusually good data are available so that phase lag can be determined for the semidiur While the possibility of generating and using nal, diurnal and yearly tidal components. If the some form of type curve is always attractive in a record is good enough and sufficiently long so as situation where field application is envisioned, to determine the bimonthly tidal component it can there are a number of complicating factors in thia probably be assumed that the well equilibrates case. The primary problem is the large number of over this period. In that case the porosity and unknown variables. the thickness of the aquifer might be estimated and the storativity determined from the relation While the objective of this study is not to ship presented in the first part of this paper. generate type curves, a few attempts were made Alternatively, the well could be packed off to to survey the possibilities. Because of economic get a better estimate. This narrows the possible curves down to thoce corresponding to that study show that treating the inverse problem storativity. through numerical modeling la at least feasible for any individual situation. Further, it may be possible to simplify the inverse problem through the generation of type curves. It is not likely, however, that general type curves that are applic able to diverse situations would be practical. REFERENCES Arditty. Patricia C. and Henry J. Raraey, Jr., Response of a Closed Well-Reservoir System to Stress Induced by Earth Tides, Paper No. 7485, 53rd Annual Fall Technical Conference and exhibition, SPE of AIME, Houston, Texas, October 1-3, 1978. Bodvarsson, Gunnar, Confined fluids as strain meters, J. Geophys. Res., 75(74), 2711-2718, 1970. Bredehoeft, J. P., Response of well-aquifer systems to earth tides, J. Geophys. Res., 72(12), 3075-3087, 1967. Chapman, S., and R. S. Lindzen, Atmospheric Tides, Gordon and Breach, Hew York, 1970. Chierici, G. L., et al., The effect of over burden pressure on some petrophysical ML 796*7546 characteristics of sandstone reservoir Fiy. 7. A possible type curve for a 0.4 meter well. rocks, 7th World Petroleum Congress, Mexico Points represent numerical solutions. The City, April 1967. storativity is 1 x 1u"*3. (XBL 796-7546). Cooley, J. W. and J. W. Tukey, An Algorithm for the machine calculation of complex biJMrtAKY Atab CONCLUSIONS Fourier series. Mathematics of Computation, 19(90), 297-301, 1965. A. The Case of the Packed-off Well Cooper, Hilton H. Jr., John D., Bredehoeft, and Istavros S. Papadopulos, Response of a The problem of interpreting the response of finite-diameter well to an instantaneous aquifers to the earth tides is relatively involved charge of water, Water Resources Res., and requires a number of assumptions even in the 3(1), 263-269, 1967. case of a pached-off well. The relationships Dale, R. H., Relationship of Groundwater Tides presented in the first part of this paper are to Ocean Tides: A Digital Simulation applicable to packed-off wells and other situations Model, Ph-D. Dissertation, University of where appreciable flow to the '/fill does not exist. Hawaii, Honolulu, 150p, 1974. I'lie relationships themselves are relatively simple Edwards, Arthur L., Trump: _ A computer Program and are based on fundamental principles and reason for Transient and Steady-State Temperature able assumptions. The Camparieons of values of Distributions of Multidimensional Systems, aquifer properties determined from the response to Lawrence tivermore laboratory, Rept. earth tides and from the more standard pumping UCRL-14754, Rev. 3, September 1, 1972. testa for the two California fields are reasonably Ferris, J. G., D. B. Knowles, R. H. Brown, and good. This is especially true in view of the large R. W. Stallman, Theory of Aquifer Tests, number of assumptions that must be made in arriving Geological Survey Water-supply Paper 1536-E, at numerical values in the case of the pump teat U. S. Gov. Printing Office Washington, 1962, interpretations as well as in the case of the George, W. O. and F. W. Romberg, Tide producing interpretation of the aquifer response to earth forces and artesian pressures. Trans. Amer. tides. Geophys. Onion, 32, 369-371, 1951. Grablovitz, G., Sul fenemeno di marea osserva- B. The Case of an Open Hell tonelle miniere di Dun in Bohemia, Bull. Soc. Adriatica Sci. Naturali Trieste, 6, Having a field situation where the well is 43, 1880. open to the atmosphere makes the problem core Hamming, R. W., Numerical Methods for Scientists complicated, in this case there may be an appre and Engineers, 721p, McGraw-Hill, Hew York, ciable amount of flow to the well. This flow to 1973. the well is seen as either a phase lag bet-vain the Harrison, J. C, New Computer Programs for the signal at the well and the earth tide or as a Calculation of Earth tides. Cooperative difference in the ratio of the well signal to the Institute for Research in Environmental tide for the semidiurnal and diurnal components of Sciences, University of Colorado, Boulder, the tide. The latter is probably the better and Colorado, November, 1971. more accurate indicator of flow to the well* Klonne, F., Die periodischen schwankengen des wasserspiegels in den inundleten kohlen- schachten von Dux in der period von 8 Analyses of such situations, however, become April bis 15 September 1879, Sitzber.Kais. involved and are probably best done as case by case Akad. Wiss., 1880. studies. The numerical solutions presented in this -128- Love, A. B. H., Some Problems of Geodynanica, Ptnshart, John S«, Alterations of Flow Charac 1>i0p, Cambridge University Press* teristics within Gaothermal Areas by Tidal Cambridge, 1911. Forces, University of Colorado, CUHER 75-6, welcliior. Pi, Sur l'effet dea xtarees terreates June 1975* dana lea variation da niveau observeee dans Robinson, T. w.. Earth-tides shown by fluctua lea puita in particular at Bondage d« tions of water levels in wells in Hew Turnhout (Belgium)) Commun. Obs. Roy. Mexico and Iowa, Trana. Am. Geophva. Union, Belgigue, 108, 7-28, 1956. 20, 656-666, 1939. Melchior, P., Die cazeitan in unterirdischen Stacey, Frank D., Physics of the Earth, 2nd ed., flussigkerten, Srdoel Kohle, 13, 312-317, 414p., John Hiley and Sons, New York, 1969. I960. Swanberg, C. A., The Mesa Geothermal Anomaly, Melchior, P., Earth tides, in Research in Imperial Valley, California* A Comparison Geophysics, vol. 2, edited by H. Odishaw, and Evaluation of Results obtained from ld3-193, Massachusetts Institute of Surface Geophysics and Deep Drilling, in Technology Press, Cambridge, Haas, 1964. Proceedings, second United Nations sympo Melchior, P., Tha Earth Tides, 458p, Pergamon sium on the Development and Use of Geother- Press, Oxford, London, 1966. mal Resources, Vol* 3, San Francisco, Morland, L. W., lairth tide effects on flows in California, Hay 20-29, 1975. horizontal permeable elastic layers con Takeuchi, H., On the earth tide of the compres nected to wells, Gaophya. J. Roy. Astro. sible earth of variable density and elas Soc,, 51(2), 371-385, 1977. ticity. Trans. An. Geophys. Union, 31, Narasimhan, T. N., A Unified Numerical Model for 361-689, 1950. Saturated-Unaaturated Groundwater Flew, Theis, C. V.( Earth tides as shown by fluctua Ph.D. Dissertation, University of California, tions of water level in artesian wells in Berkeley, February, 1975. New Mexico, Intern. Union Geodesy and Geo Narasimhan, T. N., 0. G. McEdwards and P. A. physics, Washington, D. C. -129- A DRAWDOWN AND BUILD-UP TYPE CURVE FOR INTERFERENCE TESTING H. J. Ramey, Jr. Stanford University Stanford. California ABSTRACT The main problem with single-well pressure transient tests is that distances in the reservoir Interference testing is a powerful method for are measured in units of the wellbore radius. A iu situ measurement of transmissivity, storativlty, test of an individual well can yield important in and quantitative identification of anisotropy and formation concerning the condition of the well, system boundaries. The log-log type-curve matching the formation conductivity, and drainage bound procedure can be used far analysis of Interference aries of the well. However, long periods of pro data taken during production or drawdown. Once duction are required prior to pressure build-up production is terminated, observation well pres testing for boundaries to be evident, when dis sures return toward the initial pressure. This tances are measured in units of wellbore radius. recovery, or pressure build-up, has been inter An alternate procedure is to observe pressure ef preted by differencing the extrapolated drawdown fects transmitted between two or more wells. This and measured build-up. This procedure extracts the kind of test is called an interference test. The "injection" well which causes the build-up. A new theory of interference testing was explained by type curve for both the drawdown and build-up por C.V. Theis (1935). A modern discussion of Inter tion of the test has been prepared. Application of ference testing procedures hss been presented by the new type curve shows that the older differen Earlougher (1977). There are many recent publica cing procedure may obscure detection of system tions on this important subject in both the ground boundaries. The principal of the build-up typfi water and the petroleum engineering literatures. curve may be extended to other flow problems. An example of application of interference testing to geothermal systems has been published by Chang and Ramey (1979). INTRODUCTION The initial assessment of geothermal reser One simple basis for interference test analy voirs usually has two main objectives. One is sts is the continuous line source solution. This determination of the deliverabllity from the reser model assumes that a single well is produced at a voir, and the other is estimation of the reserves, constant rate in an infinitely large slab reservoir or the economically producible amount of steam in of constant properties. The pressure effects the system. Many geothermal reservoirs are compli caured by the producing well may be observed at one cated by the fact that neither the porosity-thick or rore distant wells, which are not produced but ness product nor producible area are known, either us-id simply as pressure observation stations. The early in the life or after extended production. solution to this problem can be displayed on a One means of determining the deliverablllty is a piece of log-log coordinate paper. Figure 1 is a pressure transient test. Pressure transient tests type-curve for this problem as used commonly in can be conducted in a short period of time, and the petroleum literature. Figure 1 presents the early In the life of a geothermal development. analytical solution for the conventional line- However, estimation of steam reserves requires an source well (exponential integral solution). extended period of production with observation of mean reservoir pressure at various stages of pro duction. Material and energy balance performance (1) matching with a detectable decline in pressure -~K£)- following production is the minimum information for performance matching. Thus it is necessary to pro (2) duce a reservoir for an extended period of time \4\.2qBfx before performance matching can be accomplished (3) with acceptable risk. The dilemma is that single-well pressure tests of fairly short duration are needed to provide ac curate information on deliverability (permeability In Eqs. 2-4, English engineering units are used: thickness or transmissivity) and well condition, permeability In millidarcies, lengths in feet, while long-term production testing is required to pressures in psi, viscosity in centipoise, flow establish reserves. Fortunately, an interference rates In stock tank barrels per day, tim.. in hours, test is a type of pressure transient test that can porosity in fraction of bulk volume, formation be accomplished in a reasonable period of time, and volume factor in reservoir volumes per standard yet provide important information concerning ap volume, and total system effective compressibility parent reserves early in the life of a geothennal in reciprocal psi. development. At least two wells are required for an interference test. More than two wells is Figure 1 presents a dlmensionless pressure desirable. which is directly proportional to an observed pressure drawdown versus the ratio of a dimension!.esa tine to tht dlmenslonless distance fluid is then sufficient to sake a.i initial esti between the production and observation well squared. mate of the capacity of the system. The dimensionlesa time la directly proportional to real time, and Che dimensionlesa dls'cance i* The result obtained by this method is defin directly proportional to real distance. An impor itely preliminary, and should be checked by tant characteristic of the logarithmic scale is material-energy balance performance matching as that quantities proportions! to the plotted scale production follows. Several uncertainties have are simply displaced linearly along the scale. been identified which render the results of the Thus it is possible to graph the field data <•'}- test uncertain. The Theis line-source method de served in an Interference test as a pressure drop pends on a single-phase fluid flow model. There on the ordinate versus time on the abscissa, and may be carbon dioxide or steam caps in geothermal make a direct comparison with the analytic solution systems. In thia case, the compressibility of the represented by Fig. 1. This procedure is called system may be close to that of gas, rather than log-log type-curve matching, and has been outlined liquid. Another problen is that geothermal systems ir. detail in many references, such as Earlougher are often fractured systems. Recently, Deruyck (1977). (1980) atudied interference testing in fractured (two-porosity) systems, and Kucuk (1980) has of Once a set of field data has been matched with fered a similar study. It appears that this sort the line-source type curve, it Is possible to of system should be studied further. equate the pressure difference point with the di- mensionless pressure from the type-curve to make Both show that two-porosity system interfer quantitative calculations. In the usual case, the ence results may resemble the Theis curve for a net formation thickness (h), the flowrate (q), the homogeneous system, but the parameters which result formation volume factor (B), and the viscosity (u) from type-curve matching can be uncertain. of the produced fluid would be known. The objec tive of the pressure matchpoint would be calcula He have established the potential importance tion of the effective permeability to the flowing of an interference test '.n the early evaluation of phase (k). From the time matchpoint, it would be geothermal steam systems. Because an interference possible then to calculate the porosity-compressi test involves producing a geothermal system from bility product- In the ordinary case, the porosity an initially static condition for some time, it is would be known, and thus it would be possible to obvious that the test must eventually be termin obtain a check on the average compressibility of ated. When this happens, there is an opportunity the formation and fluid. An alternative would be to obtain additional information as pressures re to determine the in-place porosity under the as turn toward the initial state. Most discussions sumption that the average compressibility of the oi '-^terference testing deal mainly with the pres rock-fluid system were known. This step is fre sure drawdown period. But the ensuing shut-in quently done in petroleum engineering work as a period, when pressures recover toward the initial check upon porosity derived either from core analy state, can provide important information concern ses or from well logging methods. In petroleum ing drainage boundaries of the system. One dis engineering application, one frequently obtains cussion of this kind of procedure was presented by both effective permeabilities and porosities which Ramey in 1975. In general, the procedure involves agree with information known from other sources. extrapolating the initial drawdown portion of the For example, the effective permeability will fre test and differencing the pressure recovery from quently agree with that obtained from a pressure the extrapolation from the drawdown. The result buildup test on a single well, while the porosity is extraction of the effect of an injection well obtained from an interference test will frequently which caused the pressure shut-in. An example of agree with porosities obtained from core analysed. this kind of differencing is given by Ramey (1975). Fortunately, it is possible to prepare a new log- log type-curve which contains both the drawdown In the case of interference testing of geo and build-up portions of the test on a single thermal systems, analysis is often more complex. graph. In the use of the pressure matchpoint, it is often observed that the net formation thickness for the geothermal system is not known. This may be a re Pressure-Build-up Type Curves sult of the fact that the formation has not been fully penetrated by drilling, or that the system is We consider that a well is produced at con fractured and characteristics are not readily ap stant rate for a period of time, t , and then shut parent. In this case, the product of permeability in. During the initial drawdown portion, the and formation thickness is obtained, a useful quan pressures at adjacent shut-in observation wells tity for deliverability and well condition deter are represented by Fig. 1 and Eqs. 1-4. After the mination. In the case of the time raatchpoint, fre producing well is shut in, it is necessary to em quently the porosity is not known. Since the ploy the principle of superposition to generate a thickness also is not known, there is a dilemma as relationship which describes the shut-in period to the kind of useful calculation available from properly. This results in: the time matchpoint. Fortunately, Important and useful information can be obtained from the time matchpoint. The product of porosity, compressi bility, and thickness can be computed. This pro duct is sufficient to estimate the mass of geother mal fluid ir. the system per unit area. An estimate (5) of the system tirea and recovery factor far the -131- Equation 5 c*n be evaluated generally by replacing and error that data may be forced to match the the dimensionless pressures by their appropriate llnt-aourca avtn when the field data are not a good line-source values for a particular producing tine, match for the line-source solution. On the other tp, and a range of shut-in times* At* Fig. 2 pre hand, a number of other field cases have been found sents such a graph. The format Is similar to which appear to provide reasonably good matches Pig. 1, except the pressure build-up lines are with the new drawdown-build-up type curve shown in shown as a family of curves dropping below the Fig. 2. line-source solution) each displaying the parameter of dlinensionless producing time divided by the dl- ACKNOWLEDGMENT mensionless distance squared. This work was conducted at Stanford University Figure 2 is the general solution for both under DOE Grant # LBL Subcontract # 1673500. pressure drawdown and pressure build-up measured at a shut-in observation well caused by a well pro REFERENCES ducing at a constant rate for time, tp. Obviously, a single type-curve match between field data and 1. Chang, C.R.Y., and Raraey, H.J., Jr.; "Well Fig. 2 can be made with the match Involving both Interference Test in the Chlngshui Geothermal the prod tion and the build-up data. Field," Eroc., Fifth Workshop on Geotheraal Engineering, Stanford University, Dec. 12-14, Field Example 1978, 71. In 1975 Ramey presented several sets of pres 2. Deruyck, B.G.: "Intelference Well Test Analysis sure drawdown and build-up interference data. We for a Naturally Fractured Reservoir," MS re will select one example from this reference for port, Stanford universiry, June 1980. purposes of discussion. The example will be the production of well 5-D with an interference effect 3. Earlougher, R.C.: Advances in Well Test Anal measured to, well 1-E, 700 ft away from well 5-D. ysis, Society of Petroleum Engineers of AIME This test actually involved injection rather than Monograph No. 5 (1977). production, but the principle is the same. The injection into well 5-D caused a pressure rise in 4. Kucuk, F.: "Transient Flow in Naturally Frac 1-E, and after shut-in, the pressure rise declined, tured Reservoirs and Its Application to Devon approaching the initial pressure at an extended ian Gas Shales," paper SPE So. 9397, presented period of shut-in. at the 55th Annual Fall Meeting, SPE of AIME, Dallas, Texas, Sept. 21-24, 1980. The details of the field example will not be given completely here. The results for well 1-E 5. Theis, C.V.: "The Relation Between the Lowering were selected by Ramey in 1975 to illustrate the of the Piezometric Surface and the Rate and principle of differencing pressure build-up data to Duration of Discharge of a Well Using Ground extract the effect of the well causing the shut-in. water Storage." Trans., AGU (1935), 16, 519. As found In this study, well 1-E appeared to provide a reasonable match with the line-source solution for 6. Ramey, II.J., Jr.: "Interference Analysis for both the drawdown and pressure build-up data. (See Anisotropic Formations—A Case History," Jour. Ventzel, 1942, for rate change differencing.) Pet. Tech. {Oct. 1975), 1290, Table 1 provides the field data for the exam 7. Wenzel, L.K.: "Methods for Determining Per ple interference fall-off test at well 1-E. Fig. 3 meability of Water Bearing Materials," Geol. is a log-log type curve of both the drawdown and Survey Water Supply Paper 887, US Government build-up pressure drops as a function of the total Printing Office, Washington, 1942, 93. test time. This sort of field data graph can be matched directly with the new drawdown-build-up line-source type-curve presented in Fig. 2. Fig, 4 TABLE 1—FIELD EXAMPLE INTERFERENCE FALL OFF Is an Illustration of the kind of match that can be Well 1-E obtained between the well 1-E example and the new drawdown-build-up type curve. In the match shown Total Time. •U AA in Fig. 4, the same matchpoint found by Ramey in (hours)' (rwurs) Ipsi)'* 1975 has been maintained. It is evident by com 27.5 3 paring the field data with the new type-curve that 47 5 although the drawdown portion matches the line- 72 11 95 13 source reasonably well, the build-up portion of the 115 14 16 curve after shut-in does not appear to match the 125 24 16 computed buildup curves in Fig. 2 ideally. This 142 41 13 192 91 10 may represent an indies on of some sort of bound 215 1H 10 ary effect becoming evident during the build-up 2-10 139 6 portion of the test. 295 194 5.8 •itif^Si;USUSJ.'S r On the other hand, in the 1975 publication by Ramey, the differencing procedure was used to analyze the pressure build-up portion of the test. q » 115 b/d r - 700 ft The build-up portion ws=r found to match the line- B - 1 res b/Stb h = 25 ft source solution reasonaM i well. We suspect that U • 1 cp t = 101 hrs the differencing procedure involves enough trial -132- Fig. 1—The Continuous Line-Source Solution Type Curve Vfl,W Fig. 2—Draudovn and Buildup Interference Test for a Line Source Well Fig. 3—Field Data Graph for Well 1-E -133- Fig. 4—Type-Curve Match for Well 1-E *f 'Aplt.Atl &?-r \%t~ P S ^-Aplt)-Ap ACTUAL DATA O Fig. 5—Field Example Interference Falloff Analysis, Well 1-E ABSTRACT MULTIPLE PRESSURE MEASUREMENTS AND WATER SAMPLES IN SMALL DIAMETER DRILL HOLES S. D. Patton and W. H. Black Westbay Instruments, Ltd. West Vancouver, B.C., Canada Three different types of hydrologic testing in drill holes are noted: 1) packer testing during drilling, 2) packer testing after drilling, and 3) testing and monitoring in permanent casing systems. The Profiler is an example of the first type and MP and CPI casing systems are examples of the third type. The paper describes the development of the Profiler and casing systems which are compatible with wireline drill holes from 60 to 100 mm (2-3/4 to 4") in diameter. Field installation of the casing systems and methods of obtaining pressure measurements and water samples are described. These techniques include floating the casing into the hole, inflation of packers, backfilling, decontamination pumping using pumping ports, and the use of probes for water sampling and pressure measurements. Test results from the Profiler and from MP casing installations are presented in the form of diagrams of depth vs. pressure head with depths ranging from 30 to 820 m (100 to 2700 ft). Pressure measurements and pressurized water samples have been obtained from as many as 18 p->rts in the same drill hole. The paper concludes with a discussion of the advantages and disadvantages of the three types of hydraulic testing in drill holes. -135- ]^^ PRESSURE MEASUREMENTS IN LOW PERMEABILITY. FORMATIONS A. F. Veneruso and T. D, McConneil Sandia National Laboratories Albuquerque, NM 87185 ABSTRACT This paper examines the performance countered in deep exploration drL1ling, requirements and identifies candidate hot dry rock geothermal, and fluid waste hardware implementations for pressure in disposal. In these tight formations, per strumentation that is needed to provide meabilities of less than one microdarcy well test data in low permeability forma are typical, whereas, in oil and in geo- tions. Low permeability values are typi thermal formations the permeability is cally defined to be less than I microd&rcy usually greater than one millidarcy. and are usually encountered in hard rock Groundwater flow in tight formations has formations, such as granite, that are of been shown to be dominated by flow through interest in hot dry rock geothermal, deep fractures rather than through the forma exploration drilling, and fluid waste dis tion's intrinsic permeability.1 In these posal. Groundwater flow in these "tight" cases we cannot use Darcy' s law or the formations has been shown to be dominated usual dimensionless coefficients tc esti by flow-through fractures rather than mate the scale factors and dynamic re through the formation's intrinsic permea sponses necessary to properly select and bility. In these cases, we cannot use the operate wellbore pressure instruments. familiar form of Darcy'a law or the usual Also, research into low permeability for dimensionless coefficients to estimate the mations may require certain improvements expected scale factors and dynamic re to be made in pressure instrument perfor sponses necessary to properly BPlect and mance. Each of these issues is explored set up th2 wellbore pressure instrument. in the following paragraphs. First, as a This paper shows that the expected instru basis for comparison, a quick review will ment responses can be estimated using some be made of pressure measurement \.n moder recent work by Wang, Narasimhan, and ate permeability formations, then the be Witherspoon. This paper further describes havior of low permeability formations will t-Yie minimum electronic capability that the be examined, and finally the key perf or- downhole pressure instrument must have in mance characteristics of four candidate orde*" to provide the required measurement pressure instruments will be reviewed. resolution, dynamic range, and transient response. Three specific hardware imple mentations are presented based on the fol PRESSURE INSTRUMENTS FOR MODERATELY PERME lowing transducers: a quartz resonator, a ABLE FORMATIONS capacitance gauge, and a resistance strain gauge. The mathematical model describing the flow of fluid in a moderately permeable INTRODUCTION formation is described by the well-known diffusivity equation2: Reliable measurements from downhole pressure instruments are essential to pro »2P=i|| CI) vide the reservoir engineer with suffi cient data to analyze a reservoir's per formance and project future production where < is the diffusivity. In radial co under various modes of operation. Down- ordinates. Equation 1 is usually expressed hole pressure data is also essential in as determining the condition of production and injection wells and their associated formations. In recognition of the impor i^| + i i£ = i *p (2) tance of pressure measurement to well testing, a significant body of knowledge dr r jr < at has been developed to assist both instru mentation and reservior engineers with the where design, operation, and interpretation of this instrumentation. However, as new well testing regimes are encountered, it is important to reexamine the basic as and k = formation permeability (m*1} sumptions and interpretations made con cerning pressure instruments to avoid in 9 = formation porosity (dimension- correct analyses and conclusions. less) As the focus of thiB symposium demon & = fluid compressibility (m sz kg-1) strates, there is keen interest in low permeability formations such as those en u » fluid viscosity (kg m-1 s-i) -136- The following steady-state radial pressure pulse* PN» Figures 2 and 3 (taken flow equation2 completes this simple from Reference 3 show the response to model: pulse testing with a normslited ordinate pressuret 2ukh Ipe-Pw> (4) p Bu actu>l ' ln(re/rw) PNCt) (7) ^applied and a dimensionless wellbor* leaking capa formation thickness (m) city factor, u, that is proportiona 1 to the ratio of the wellbore fracture contact B format ion volume area to the wellbore test volume, or equivalently factor (dimens ionless) r = radius into the formation (m) 2 Fracture Width e Wellbore's Test Length (8) r = radius of we11bore (m) (or distance between packers) p = pressure at radius r Note that because of the low permea 0 (kg n.-'.-*) bilities (usually less than 1 microdarcy) in these tight formations, the pressure p = pressure in well- time history is characterized by extremely bore [kg m"ls~'i ) large ranges of test time and smaller res olution values when compared to the usual q = flow rate (n3s-M pressure testing in moderate permeability formations. In general, the specifica Equations 2, 3, and 4 are typically tions required here are every bit as used by instrumentation and reservior en stringent, if not more so, than those re gineers to design well tests and to deter quired for pressure instruments in moder mine the types of pressure gauges required ate permeability formations. To obtain and the setup of those gauges in terms of useful data, such as given in Figures 2 the maximum pressure anticipated, the res and 3, the pressure instrument must be olution and the time response require appropriately specifiedr the key parame ments. For example. Chapter 13 of Refer ters of interest are given in Table 1. ence 2 presents numerous exercises in which typical oil field values for the In this context, accuracy or measure above parameters are used to determine the ment precision is defined as the maximum instrument's performance requirements. value of the uncertainty in pressure mea Figure 1 is taken from Reference 2 to in surement over the entire ful1 scale range dicate a typical pressure-time response in of the instrument. Resolution or measure a constant flow rate test. ment sensitivity is defined as the small est (worst case) detectable change in the pressure measurement over the instrument's PRESSURE INSTRUMENTS FOR LOW PERMEABILITY range. As an example, assume an instru FORMATIONS ment with the following ratings: Groundwater flow in tight formations 100 si has been shown to be dominated by fracture p»»« = ° p flow rather than flow through the forma tion's intrinsic permeability. In these circumstances, Equations 1, 2, and 3 are = + 1% of full scale reading modified through the use of an equivalent permeability* that is related to the frac tures present. As an example for the ide al case of a single horizontal fracture. Equation 2 is written with Suppose a particular measurement is ob tained of p 832. Then the actual pressure is:mea s Pactual = 832 ± (irj0x l000) Psi v = (Fracture Width)-* ,,, 12 -832+10 psi Reference 2 gives an excellent analysis of and, if a subsequent change in pressure pressure transient response to pulse pack takes place, ws can be certain the mea er testing in a low permeability, fracture sured change is detectable if it is great dominated formation. For a given applied er than p = x l00 ai m l p-i Figur• 4 shows the basic element of re8 ^rm ° P i the generic types of pressure instruments) the resistance strain gauge* the capaci Added to the characteristics listed tance type transducer, and the two quartz in Table 1 is the need to establish the crystal transducers. The HP instrument1* instrument's measurement stability over operates on the principal that a quartz time and over temperature. Measurement crystal resonator's natural frequency can drift with time is an important specifica be changed by applying stress. Two types tion because, as shown in Figures 2 and 3, 6 of resonators are in common use, the shear test times can easily range out to 10 mode of crystal resonator used in the HP seconds (11.6 days). Testing can be done gauge, and the transverse mode used in a at shorter intervals but only at the ex gauge built by Paroscientific.b The ad pense of ••equiring greater measurement vertised performance characteristics of resolution. the HP and Paros gauges are given in Table 3 along with representative strain and Measurement drift with temperature ia capacitance gauges. another important specification tht is of ten overlooked. In formations of inter est, temperatures can range up to 300*C. Figure S indicates the activities However, for typical instruments, tempera that are underway at Sandia to upgrade ture sensitivities can range from +^ 0.01 these transducers for geothermal and geo- psi/'C to 1 psi/*C. pressure applications; Figures 6 through 8 summarize the key elements of those pro If a measurement resolution of ^ 0.1 jects. psi is desired then it becomes important to also specify the temperature stability As an example of some specific design of the instrument—especially if wellbore and development factors, we will briefly temperatures are expected to vary during review our activity in the quartz trans the test . Often it is not sufficient to ducer area. Over the past 2 year3, con know only the instrument's temperature. siderable work has been done6-6 at Sandia As we shal1 discuss later, even small tem to understand the temperature and pressure perature gradients on an instrument can t-shavior of quartz-resonator-type pressure result in dramatic errors in measurement. transducers so that they may be applied to geothermal logging. INSTRUMENT SPECIFICATION GOALS Ideally, the crystal's resonant fre Table 1 lists a set of pressure in quency should be sensitive to pressure or strument specifications that are propose. 1 stress and independent of temperature. as design goals for measurement in tight Unfortunately, temperature has a very formations. The preceeding analytical re large effect. Figure 9 shows a family of sults were used along with a range of ex curves of frequency versus temperature for pected reservoir conditions (i.e., 10~B < various crystallographic rotations of the u < 10"3) to provide measurements that common AT-cut crystal. As can be seen, would satisfy the interpretation made in most of the curves have one or two points Reference 3. Commercially available pres where the slope is zero. For a particular sure transducer specifications are listed crystal, this point is referred to as the in Table 2 (from Reference 2). turning point, and, if the crysta 1 were operated very close to this temperature, Inspection of Table 2 indicates that very small frequency deviations could be none of the transducers currently avail achieved for a small change in tempera able satisfies all the requirements put ture. forth in Table 1. Some may satisfy one requirement or another but none of the commercial instrument's advertised speci Figure 10 shows an AT-cut which has fications even address all of the needs. been rotated beyond the limit of Figure 9 Accuracy has not been called out as such to achieve a turning point at 275'C. This because it is not a prime consideration in curvc is contrasted with the rotated X- that i t can be determined by the instru cut, showing the significantly reduced ment 's stability, resolution* and correc temperature effect of this new cut. tion for nonlinearities. In practice, to achieve the required There will be specific instances resolution, it is necessary to have two where a particular instrument will satisfy closely matched crystals, one of which is the immediate needs - For instance, an used to provide a reference frequency to interference test at a moderate tempera compensate for temperature. Even so, Fig ture would not have any relatively abrupt ure 11 shows that for good pressure reso temperature changes and the Hewlett lution the two crystals must be within a Packard1* (HP) model 2811-P. pressure gauge few millidegrees of each other or must system combined with a temperature probe both be within a few degrees of the turn would meet the requirements. ing point. -138- Figure 12 displays the requirement! 3. Wang, J. S. Y., T. N. Narasimhan, C. and approaches being taken by our project F. Tsang, and P. A. Witherspoon, "Transi to incorporate the above knowledge into ent Flow in Tight Fractures," Invitational the technology applicable to quartz pres Weil-Tsating Symposium Proceedings, LBL- sure instruments. 7027, UC66, TID-4500-R66, Lawrence Berke ley Laboratory, October 19-21, 1977. CONCLUSIONS 4. Ksrrer, H. E.r and J. Leach, "A Quartz The pressure time history of well Resonator Pressure Transducer," IEEE tests in low permeability formations is Trans. Ind. Elec. and Control Instr. characterized by extremely large ranges of IECI-16, p. 44 (1669). test time. This requires more stringent instrument resolution and stability than 5. Paros, J., "Digital Pressure Transduc the usual pressure testing in moderate ers ," Measurements and Data, Issue 56, permeability formations. It is also im Vol. 10, No. 2, March - April 1976. portant to consider the temperature gradi ent sensitivity of the instrument; even 6. Eernisse, E. P., "Quartz Resonator small temperature gradients in a well test can result in dramatic errors in measure Pressure Gauges: Design and Fabrication ment . Technology," SAND78-2264, Sandia Labora tories, January 1974. None of the pressure transducers cur 7. Eernisse, E. P., "Rotated X-Cut Quartz rently available satisfies all the re Resonators for High Temperature Applica quirements for the entire range of well tion," Proc. 32rd Annual Symposium on Fre testing expected in low permeability for quency Control, 1978. mations . Some transducers may satisfy some of the requirements, but none of the 8. Eernissee, E. P. "Temperature Depen commercial instruments' advertised speci dence of the Force Frequency Effect for fications even address all of the needs. the Rotated x-Cut., Proc. 33rd Annual Sym For example, in cases where there are no posium on Frequency Control, 1979" abrupt temperature changes, the HP model 2811-B quartz resonator pressure gauge combined witli a temperature probe meets most of the performance requirements. However, this instrument has exhibited large errors in the presence of even mod- e-fc temperature gradients. Table 1. Pressure instrument requirements Usinq the measurement needs identi fied by reservoir engineers and an under for low permeability reservoirs. standing of the function and performance limitations of existing pressure instru Pmax i 7S0° P3i ments, a development project is described that is directed toward correcting the technical deficiencies. The existing in struments are being upgraded with more • RESPONSE SPEED stable components such as a rotated X-cut quartz crystal for the resonator-type gauges; special electronics are being de signed to improve the stability and output • RESOLUTION signal strength of strain gauge pressure sensors; and improved materials and design configurations are being investigated to upgrade the capacitor- Lype pressure in • TEMPERATURE strument. REFERENCES • TEMP. STABILITY \^f^\ 1 O.Dl ^ 1. Brace, W. F., J. B. Walsh, and W. T. Frangos, "Permeability of Granite Under • TEMP. GRADIENT High Pressure" J. Geophysical Research 73, erap/r | 1 ' '•C/sec No. 6, pp. 2225-2236; 196S. 2. Earlougher, R. C. "Advances in Well • TIME STABILITY Test Analysis," Monograph Vol. 5, Society of Petroleum Engineers, New York and Dal las, 1977. -139- Table 2. Down-hole pressure gauges (from Earlougher, "Advances in Well Test Analysis") Section I: Self-ContainedvVirefine Gauges tMaximu m Maximum Approximate Ma"imv*n Sensitivity Accuracy. Approximate Service Type Time Chart Size. Pressure' Percent of Percent of OD Length' Temperature' Pressure Oow.i Hole' P « r Gauge Ipso Full Scale Full Scale (in 1 (in.) (*F) Element* (hours) lin) Amerada RPG-3 25.000 0.05 0.2 1.25 77 650 B 360 2> < 5 Amerada RPO-4 25.000 0.056 0.2 1 76 650 B 144 1.8 >< 5 Amerada RPG-5 20.000 0.05 0.25 1 5 20 450 B 120 2' <5 Kuster KPG 25.000 0.05 0.2 1.25 66 700 B 360 2> c 5 KuMW K-2 20.000 0.05 0.25 1 41 500 L 120 2i < 3 KuslerK-3 20.000 0.042 0.25 125 43 500 B 120 2.4: < 4 Kuster K-4 12.000 0.067 025 0 75 42 450 B •*2 1.5x 25 Leutert Precision Subsurface Pressure Recorder 6.400 0005 0.025 1 25 139 300 P 360 98> < 3.1 Leulert Precision Subsurface Pressure Recorder 10.000 0.005 0.025 1 42 139 300 P 360 9.8 x 3 1 Sperry-Sun Precision Subsurface Gauge 16.000 0.005 0.05 1 5 108 300 B 672' 23) • 7 1 Section 2. Permanently installed, Surrace-flecoro'ingGauges Maximum Maximum Sensitivity. Accuracy. Approximate Service Type Pressure' Percent of Percent of OD Length* Temperature Pressure Type Type Gauge (psi) Full Scale Full Scale (in) (in.) fF) Element* Signa 1' Conductor* Amerada EPG-512' 10.000 0.002 0.02 1 25 13 300 D F S Amerada SPG-3 25.000 0.04 0.2 1.25 49 350 B R s Flopetrol 10.000 0.001 0.06 1.42 29 257 S F s Lynes Pressure Sentry MK-9PES 10.000 0.2 0.2 1 5 33 300 B B S Maihak SG-2 5.700 0 1 10 3.54 11.54 17o D F s Maihak SG-5 5,700 0.1 1.0 165 B43 176 D F s Sperry-Sun Permagauge 10.000 0.005 O.05 1.66 120 or 240 no max u G T BJCentn'itt-PHD System10 3.500 3" N/A" N/A" B C P Section 3. ffefr.j •'able Surface-Recording Gauges Maximum Maximum Sensitivity. Accuracy. Approximate Service Type Pressure1 Percent of Percent ol 00 Length' Temperature Pressure Type Type Gauge (psi) Full Scale Full Scale (in.) tin.) fFI Element* Signa 1' Conductor* AmeradaEPG-512* 10,000 0.002 0.02 125 13 300 0 F s Amerada SPG-3 25.000 0.04 0.2 1 25 49 350 B R s Flopetrol" 10.000 0.001 0.06 1.42 29 257 S F s Hewlett Packard HP2811B 12,000 0.00009" 0.025" 1.44 39 302 Q F s Kuster PSR 5.000 0.04 0.02 1.38 36 212 a F s Lynes Sentry MK-9PES 10,000 0.2 0.2 1.5 13 300 e B s Maihak SG-3 5,700 0.1 1.0 176 0 F s Sperry-Sun Surface Recording 15.000 0.006 0.05 1.5 72 300 B D s •GirlergaLageifiieavailaBle - rwenCtorMminliiimpli«bY>nclirtion*nlhistaeie r^t»»*e*'Om.nlofrh»lion Juptfiefl 6y the nMniifatlurei arK^mer Wu<(H ^i(*i*d <0 tW'tliab-e r.\[hough •* I** Own careK;,.-, HsernbiM-| this latte nether the author not 5PEA1ME an gum rut* accuracy O' the oil* luppnta Th* reacei inouir] contact tl"* manufaclortjr 'v wtO*'Ci B*»n* »*uw could nol MotJMmedhy the Julhw 1 Normally elements arej.jirjtHe m several rangn with [hclaa*3l K*ngabout Ota MOo* Olo 1 OOOpSi 7 Length mir v»r depending on soot tcntigural-On. value n appro*.matt normal length without weight w: I torn 3 Nri-.-.ijii». (ernptutjubort which gauge cannot bcuted noim*»iirtumi(fnptfjiuit;to' nwmii diibrHtan * S • Bouruontube 0 - Drephragm G - Gil chambiH win transducer al surface P —SotM.ngpmen 0 - Oscilietmg auarti cr-rital S — Strain gauge 5 T.m(depenOiontiociicn«er> C toe m not ma iif tome in M*t<*i'angei iian.ngat looat abou'3noui 6 Clock •* electronic without mechanical (.niiage to «co«H< 7 8 —Bmarr signal C - Current D - Of.HH f — Frequency C— Gas column tosurfac e R — RMntance 8 P — Normal Bow*' cable lor puma no special conductor S — Sin|Vt-condiJCtor armored cable, found re I urn T - V„-.« -00 steel tubing 9 Alio Hewlett Packard GRC Paros CEC Quartz Capacitive Quartz Pressure Pressure Pres/Temp Pressure Strain Specification Tool Tool Gage Cage Max Pressure (psi) 11,000 10,000 5,000 10,000 Accuracy (±%) .025® .05 -- © Resolution (+?) .0001 .01 -- © Hysteresis f, non- repeatability (+%) .004 .02 0.02 0.25 Operating Range (°F) 32 to 302 32 to 300 -65 to 225 75 to 400 (calibrated) (compensated) Thermal Shift («/°F) © 0.005© .004 0.02 Sensitivity to Thermal Shift Rate (l/°F/min) -- .0075 © Requires that temperature is known to ± 1.8°F © Hysteresis and nonrepeatability include accuracy and resolution @ Thermal shift is corrected to obtain indicated accuracy » 600 T—ri i|—i—r-rr|—r O i 500 S Ul 400 £ S 300 ffi U 0.oo £ 200 nraadypp ! Til i iiil 10"2 10"1 1 10 10-2 INJECTION TIME, t, HR Figure 1. Calculated injectivity pressure response for Example 13.2 in Ref. 2. 0.9 £• 3 DIMENSIONLESS TIME TDF= —j, a (2b) T (from Wang et. al. LBL) Figure 2. Type curves at early time for a finite fracture volume (from Earlougher, Ref.2) -142- 1.0 = 0.S = 0.2. ^^t-.. •» 0.5 0.5. 1.0 1.0' , 0.5 6 a= ID- ' 2.0 a = 10* 2.0- 2b = lOjim 2b= 1pm 5.0 50'. bM =0 3 r | r = r 0.0 F 10 102 103 104 10s 106 t (sec) CLOSED FRACTURE BOUNDRY 1.0 a = 10-6\ 2b= ^^im \ • 2 b = 10fim\ - 0.5 M| = 0 \ • V V " if. = 0.2—% »F=0.2—% V«, 0.5-JJL • V« 0.5-*. "" 1.0-* 2.0% 2.0-m ,00 5.0-^ 0.0 1 10 10* 103 104 105 10 t (sec) OPEN FRACTURE BOUNDRY VF/VW = FRACTURE-WELLBORE VOLUME 2b S FKA^TURE WIDTH a = DIMENSIONLESS LEAKING CAPACITY Figure 3. Normalized pressure decays (from Wang et al., Ref. 3). RESISTIVE STRAIN GAUGE-Resistor bridge pattern on diaphragm changed by deflection. (CEC) Ap CAPACITIVE TRANSDUCER- Capacitance changed by deflection of diaphragm. till! Ill I (GRC) Ap P SHEAR MODE QUARTZ RESONATOR-Stress in quartz causes resonant frequency shift — Af (H.P.) I AP TRANSVERSE MODE QUARTZ RESONATOR-Stress in vibrating element causes change of frequency Af P P (PAROS) ^ .------=--- AP Figure 4. Types of gauges in common use. -144- • GEOTHERMAL - 7500 PSI, 275°C, ± ,01 PSI 1. DEVELOP QUARTZ CRYSTAL GAGE SIMILAR TO H.P. 2. JOINT PROGRAM TO HARDEN COMMERCIAL CAPACITIVE OR STRAIN GAGE TOOL. (LESS RESOLUTION) 3. ADD HIGH TEMPERATURE BOURDON TUBE GAGE TO EXISTING GEOTHERMAL TEMPERATURE TOOL CIRCUITRY. (LOW RESOLUTION) • GEOPRESSURE - 20,000 PSI, 200°C, * 0. 1 PSI 1. DEVELOP CIRCUITRY FOR STRAIN GAGE TOOL ON JOINT PROGRAM WITH LBL. 2. JOINT DEVELOPMENT PROGRAM WITH A MANUFACTURER TO HARDEN THEIR EXISTING CAPACITIVE GAGE TOOL. 3. MODIFY EXISTING H.P. PRESSURE TOOL FOR OPERATION IN THIS ENVIRONMENT, Figure 5. Sandia/DOE pressure instrumentation program. -145- OBJECTIVE - TO DEVELOP AN ACCURATE, MEDIUM RESOLUTION LOGGING TOOL FOR USE IN GEOPRESSURE WELLS UP TO 20,000 PSI AND 200°C CAPABILITIES - ACCURACY OF t 5 PS! RESOLUTION OF + 0,1 PSI (OVER PERIOD OF 5 DAYS) APPROACH - ADAPT A COMMERCIALLY AVAILABLE STRAIN GAUGE TRANSDUCER TO SPECIAL 200°C CIRCUITRY Figure 6. Geopressure logging tool using a strain gauge pressure transducer. -146- •STRAIN GAGE TRANSDUCER - BELL & HOWELL, CEC DIVISION STRAIN GAGE MODEL 1000, HAVING SPUTTERED GAGE PATTERNS. A SPECIAL GAGE WILL BE REQUIRED FOR 20,000 PSI. •CIRCUITRY - SPECIALLY DESIGNED VCO AND CHOPPfcR-STABILIZED DC AMPLIFIER CIRCUITS ARE BEING DESIGNED EMPLOYING HARRIS 2600 HIGH TEMPERATURE OPERATIONAL AMPLIFIERS, THESE CIRCUITS WILL BE COMPATIBLE WITH THE NEW HARRIS 300°C OP AMP NOW UNDER DEVELOPMENT. • READOUT - TEMPERATURE, PRESSURE, AND FLOW WILL BE MULTIPLEXED AND SURFACE INSTRUMENTATION WILL BE USED FOR TEMPERATURE, CORRECTED PRESSURE, AND FLOW INDICATION. • PARTICIPANTS - LBL: TOOL HARDWARE, TESTING AND RESERVOIR ENGINEERING SUPPORT SANDIA: ELECTRONIC DEVELOPMENT, FABRICATION, AND TEST SUPPORT Figure 7. Geopressure and pressure instrumentation development at Sandia. -147- OBJECTIVE - TO ENHANCE THE CAPABILITIES OF A STANDARD COMMERCIAL PRESSURE TOOL TO SATISFY THE GEOPRESSURE ENVIRONMENT OF 20,000 PSI AND 200°C, CAPABILITIES - ACCURACY OF + 2 PSI RESOLUTION OF + 0,05 PSI (OVER PERIOD OF 5 DAYS) APPROACH - TO APPLY SANDIA AND COMMERCIAL TECHNOLOGY, AS APPLICABLE, TO EXTEND THE APPROPRIATE CAPABILITIES. THIS WORK IS BEING DONE AS A JOINT DEVELOPMENT EFFORT WITH THE MANUFACTURER. Figure 8. Geopressure logging tool using a capacitive diaphragm transducer. -148- -140-120-100-80 -60 -40 -20 0 20 40 60 80 100 120 140 AT °C Figure 9. Frequency-temperature curves of AT-cut crystal. -149- 0.5 0.0 1 » -1.0 > o z in 2 -1.5 or -2.0 -2.5 J 1 I J I I I I I L 0.0 50.0 100.0 150.0 200.0 250.0 300.0 TEMPERATURE <°C) Figure 10. Measured frequency versus temperature characteristics for the rotated X-cut (The typical AT-cut chosen for a 275°C turning point is shown for comparison). -150- 100 AT=1.0°C I z OJ 2 i- 3 8 Ul in 0) ESTIMATED LIMIT DUE TO AGING EFFECTS 0.001 SO 100 150 200 250 300 TEMPERATURE OF TRANSDUCER (°C) Figure 11. Estimated pressure resolution versus temperature for rotated X-cut crystals. -151- REQUIREMENT - MINIMIZE FREQUENCY SHIFT DUE TO TEMPERATURE. 1. FREQUENCY SHIFT OF CRYSTAL RESONATORS MUST BE MINIMIZED 2. OVERALL THERMAL INTERACTIONS MUST BE MINIMIZED 3. OSCILLATOR CIRCUITS MUST BE VERY STABLE 4. TURNING POINT OF CRYSTAL MUST BE INDEPENDENT OF PRESSURE APPROACH 1. SELECT CRYSTALLOGRAPHIC AXIS TO MINIMIZE FIRST AND SECOND DERIVATIVES OF FREQ. VS. TEMP. CHARACTERISTIC AT 275°C 2. USE TWO IDENTICAL CRYSTALS, COUPLE THEM THERMALLY FOR TRACKING, AND ENCLOSE IN TEMPERATURE CONTROLLED OVEN 3. USE PIERCE TYPE OSCILLATOR CIRCUIT WITH AUTOMATIC GAIN CONTROL AND ENCLOSE IN OVEN 4. INVESTIGATE CONFIGURATIONAL CHANGES TO MINIMIZE SHIFT OF TURNING POINT CAUSED BY PRESSURE Figure 12. Quartz crystal transducer development program. -152- IHQTRUMEHTATIOII FOR DETERMINING ROCK MASS PERMEABILITY BY hTDRO-PNEUMATIC PRESSURE TESTING W. 0. Miller U. 5. Army Engineer Waterways Experiment Station Vicksburg, Mississippi The Waterways Experiment Station (WES) has a interfaced transducers is functioning. Additional research project underway which has the goals of ly, this capability provides the ability to verify 'ieveloping better analytical techniques for inter pressure measurements by changing transducers while acting and evaluating rock mass permeability as a test is in progress. The electronic components u> ii as determining tnd describing the phenomena of the unit are protected from the testing environ that control the flow of water through a rock mass. ment with a waterproof housing and 0-ring seals. As: a by-product of this investigation, new and im proved instrumentation has been developed for use To reduce friction losses in the test section in the fiuld of pressure testing. at high flow rates, stainlers steel, wire-wrapped, keystone-slotted well screen is used in lieu of per The requirements for accurate measurements of forated pipe. For RX boreholes, the test section rock mass permeability in low-permeability environ screens currently being used are 1-3/h inch in di ments are precision, repeatability, and reliability. ameter and have a So. 80 slot, i.e. 0.080-inch slot At the initiation of this study, a detailed review width-. -»f existing pressure test equipment was made, and m: a result, new instrumentation was developed "by To facilitate the control and monitoring :-i* 'rIK'.l whi^-h eliminates many problems noted in earlier any pressure test, various uphole systems haw boon systems. Some of the problems which were noted in designed and assembled. Constant pressuie t*-s*.r art- existing systems were the unreliability of el^ctron- controlled with a specially fabricated procure reg i" transducers in thx- testing environment; the in- ulating by-pans valve. Figure 3. The flow rate is ubiJity tr, verify or cross-check downliole pressure monitored with flow meter manifolds, Figure -J, en— measurements; a difficulty in n&intaining or assur pable of measuring water flow rates from 0.0i '.c ing a posit ive packer tc test section differential 250 gpm, and air flow rates from 0.15 to 7^0 cfir.. pressure; and very lonfi packer inflation and defla If constant flow tests are conducted, they are r*on- tion timer, ir, deep borings. The time required for trolleO w'+h a specially designed automated fi-.v inflation ami deflation ranged bet.._en 15 and 20 control valve. Figure 5, which monitors the flow meter output and maintains the desired flow ra*» rninutei: in deep borings (1500 to 2000 feet) when a with a regulating valve. mifply of .-ompressed air on the surface was used for packer inflation. It was also noted that per forated pipe was frequently used in the test sec An uphole control system, Figure 6, ha:: bef-i. tions which constituted a source of excessive fric designed and constructed to monitor test data ami tion losaea if high flov rates were attained. operate the downhole control unit. Control and monitoring of the downhole electronics is accom In order to eliminate the problems encountered plished with a single, multiconductor, vaterprcuf with existing pressure test equipment, a downhole signal transmission cable, Figure 7. A programmable control unit. Figures 1 and 2, was designed for con data acquisition system, Figure 8, has been inter ducting tests in NX boreholes. The unit maintains faced with the uphole control system to provide •< it preset, minimum differential pressure between the permanent record of test data. Data which arc packers and the test section, and controls infla- currently monitored and recorded at a test veil are tion and deflation of the packers. The packer re test section pressure, pressure beneath the test sponse to inflation and deflation commands is section, pressure above the test section, packer greatly increased in deep borings since the control pressure, line pressure on the ground surface, ar.d unit is located downhole, and inflation is accom flow rate. The data acquisition system, however, plished with the testing fluid (which is normally has expansion capabilities for reading up tc 1000 either water or air). For increased flexibility, data points (either strain gage or analog signals). the control unit was designed with the capacity for With the above monitoring capacity, a complete operating as either a single- or double-packer sys three-dimensional array of piezometers may be in tem by the use of simple ground surface control stalled around a pressure test well for the purpose commands. of describing the pressure bulb generated. Since data reduction techniques in pressure testing arc Within the control unit four transducers (rated a function of the assui-*d flow pattern from the from 0 to 3000 psi) are used to measure packer pres well, a knowledge of the pressure bulb generated by sure, test section pressure, and the pressures above a test is very useful. and below the packers. Redundancy was designed into the system by interfacing three of the dovnhole Various components of the pressure testing pressure sensing points (above packer, test section, system have been tested individually. The auto and below packer) through a nine-way valve to three mated flow control valve, flow meters, and data transducers. In the event of a transducer failure acquisition system, along with transducers designed during testing, a critical pressure sensing point specifically for water level measurements, have can be moved to another transducer with simple been field tested in a series of field pumping :.ests ground surface controls. With such flexibility, a and have proven to be very successful to date. test can be continued as long as one of the three The downhole control unit and the uphole control -153- system have been tested extensively In the labora data, which provide a better understanding of the tory. One field iest, Figure g, has been conducted phenomena which control the movement of voter (or to date with the complete pressure testing system. air) through rock masses. All components checked out satisfactorily in the testing environment. Initial pressure tests (water and air) will be The entire system is ready for field applica conducted at well-defined or geologically predict tion, with the following exceptions. Prior to per able sites. Rock coring as well as borehole forming an air pressure test, thermocouples must logging will be conducted nt each site to accurate be installed in the downhole control unit for ly deJiermine the geologic features and fissure measuring fluid temperature in the test section as characteristics which could control flow through well as in the flow meter manifold to measure up- the rock mass. In the interim, a modeling effort hole fluid temperature. All the necessary moni is heing initiated which will identify and delin toring and recording provisions have been included eate the relative contribution of the various in the existing instrumentation for temperature geologic features which control the overall per measurements and installation of the sensors is the meability. If the model studies reveal flows only remaining requirement. which are significantly different than the usual assumption of flow in continuous porous media, a The equipment and instrumentation which have discontinuum approach to data reduction will be made. The end product would be formulas which been developed provide the accuracy and reliability better reflect the boundary conditions and provide required for an evaluation of pressure testing data a means of possibly integrating geologic and and techniques. The primary emphasis of future pressure test data for a more accurate evaluation vork will be directed toward developing interpre of the permeability. tative techniques, using pressure test and geologic Fig. 1. Downhole control unit with packers and screen. -154- Fig. 4. Flow meter manifold with pressure regulator. CONTROL SECTION DETAIL Fig. 2. Downhole control unit schematic. FLOU KANirOUl PRESSURE REGULATING BY-PASS VALVE Fig. 5. Automated flow control valve with Fig. 3. Pressure regulating by-pass valve schematic. flow meters and instrumentation. -155- Fig. 6. Uphole control system for hydro-pneumatic Fig. 8. Uphole control system, data acquisition pressure test equipment. system, and 50-channel expansion unit. Fig. 7. Signal transmission cable. Fig. 9. Sinp.le-packer pressure test data. -156- ABSTRACT FRACTURE CHARACTERIZATION IN CRYSTALLINE ROCK WITH THE BOREHOLE TELEVIEWER Mark D. Zoback Office of Earthquake Studies U. S. Geological Survey Henlo Park, California The borehole televiewer is an ultrasonic device originally developed by Mobil Oil Corp. to map the smoothness of well bores and casing. Planar fractures that intersect uncased boreholes are easily detected with the tool and as the tool contains a fluxgate magneto meter, it is straight-forward in reconstructing the strikes and dips of the fractures. Results are reported from studies that have been done in eight wells drilled into granitic rocks. Six of the wells are in California; the depth of these wells is about 250 m. In South Carolina data are available from two wells approximately 1.1 km deep. The following generalizations characterize the data: 1) Although moderate decreases in fracture density with depth are observed, this effect is not dramatic, even in the deeper wells. 2) In some cases a predominant fracture trend persists over the entire depth range of the well; in other cases distinct fracture sets are limited to a particular depth range. 3) Correlation between the televiewer and sonic velocity logs is generally good; zones of dense fracturing have much lower velocity and a progressive decrease in fracture density with depth correlates with a moderate increase in velocity. In some zones of little apparent fracturing, however, low velocities are sometimes observed suggesting the presence of microfractures or undetected fractures. -157- ABSTRACT DOWNHOLE DOUBLE PACKER INSTRUMENTATION WITH HIGH PRESSURE RESOLUTION CAPABILITY AND IMMEDIATE SURFACE MONITORING ABOVE, BELOW AND IN THE STRADDLED INTERVAL K. G. Kennedy, W. Miller and R. R. Phillips Science Applications, Inc. Albuquerque, New Mexico Surface monitoring of transient and static test data is essential for effective utilization of high cost downhole testing instrumen tation. Science Applications, Inc. (SAI) and Lynes, Inc. have developed design and testing methods for allowing this type of monitoring. We recently tested basalt rocks to depths of about 1500 m (4500 feet) on a project funded by Rockwell Hanford Operations in Richland, Washington. The downhole instrumentation consists of a modified version of the Lynes 'Treat and Test Tool' Packer Assembly, integrated with a sensor carrier located just above the top packer that contains three quartz pressure transducers ported above, below and into the straddled interval. A shut-in tool is located above the carrier; it is closed to prevent disturbing the formation pressure when the tool is run into the well. Downhole multiplexing of the frequency signals allows rapid transmission of both pressure and temperature data to surface proces sing equipment, where it is printed, displayed, recorded and plotted, utilizing Hewlett-Packard microprocessing equipment. The 0 to 5000 psi quartz pressure tranducers have a demonstrated resolution of ^0.01 psi and an accuracy of about +2.5 psi. The water-inflatable rubber packers provide excellent borehole sealing capability using a packer inflation pressure typically 1500 psi above the downhole pressure. The inflation procedure, however, can create a 'squeeze' or overpressure in the interval between the packers. This is undesirable in testing low permeability zones and can create extensive inte>prQtation problems and delays. -158- The instrumentation package is particularly well suited to conduct instantaneous pulse or slug tests and drill stem-type tests. Incor porating a shut-in tool just above the packer and downhole electronics assembly allows much more versatility in testing than would an open conduit connecting the formation with the surface. When testing in open hole conditions with multilayered aquifers, additional packers installed below and above the double packer system would be an improvement in the method for documenting fluid movement in the rock around the packers. -159- LIST OF PARTICIPANTS AAMODT, Lee ARELLANO, Victor M. Los Alamos National Laboratory Interior Internado Palmira P. 0. Box 1663 Apartado Posta 475 Los Alamos, New Mexico 87544 Cuernavaca, Morelos (505) 667-5048 MEXICO ABOU-SAYED, Ahmed BANKS, Don Ten-aTpk, Inc. Waterways Experiment Station University Research Park P. 0. Box 631 420 Wakara Way Vicksburg, Mississippi 39180 Salt Lake City, Utah 84108 (601) 634-2630 (801) 582-2220 FTS 542-630 AGARWAL, Ram G. BASLER, James A. Amoco Production Co. U.S. Geological Survey P. 0. Box 591 Water Resources Division Tulsa, Oklahoma 505 Marquette N.W. (918) 664-3042 P. 0. Box 26659 Albuquerque, New Mexico 87125 AHMED, Usman (505) 766-2810 TerraTek, Inc. FTS 474-2246 University Research Park 420 Wakara Way BENSON, Sally Salt Lake City, Utah 84108 Lawrence Berkeley Laboratory (801) 582-2220 Bldg. 90/1106 1 Cyclotron Road ALLMAN, David W. Berkeley, California 94720 University of Idaho (415) 486-5875 209 Taylor, #13 FTS 451-5875 Moscow, Idaho 83843 (209) 882-7977 BENTLEY, Michael E. Bureau of Economic Geology ALMEN, Karl-Erik University of Texas Geological Survey of Sweden Box X, University Station Sveriges geologiska undersokning Austin, Texas 78712 Vretgrand 18 (512) 471-1534 S-753 22 Uppsala SWEDEN BLACK, John H. 018/15 56 40 Institute of Geological Sciences Building 151 ANDERSON, Merlin Harwell Laboratory Halliburton Services Didcot, Oxon 905 Alice ENGLAND P. 0. Box 1431 0235 24141 x 2232 Duncan, Oklahoma 73533 (405) 251-3137 BLACK, Bill (W.H.) Westbay Instruments Ltd. ANDERSON, Terry 0. 265 - 25th Street Halliburton Services West Vancouver, B.C. P. 0. Box 1431 Canada V3L 4G2 Duncan, Oklahoma 73533 (604) 926-8541 (405) 251-3271 -160- BLUM, Justin COHEN, Lewis Woodward-Clyde Consultants Lawrence Berkeley Laboratory #3 Embarcadero Center, Ste. 700 Bldg. 90/1106 San Francisco, California 94111 1 Cyclotron Road (415) 956-7070 Berkeley, California 94720 (415) 486-6457 BijDVARSSON, Gudmundur FTS 451-6457 Lawrence Berkeley Laboratory Bldg. 90/1024D CORDOBA, Francisco 1 Cyclotron Road Interior Internado Palmira Berkeley, California 94720 Apartado Posta 475 (415) 486-5350 Cuernavaca, Morelos FTS 451-5350 MEXICO BODVARSSON, Mary COTNER, Gene Lawrence Berkeley Laboratory CER Corporation Bldg. 90/1024D P. 0. Box 15090 1 Cyclotron Road Las Vegas, Nevada 89114 Berkeley, California 94720 (702) 735-7136 (415) 486-5350 FTS 451-5350 DERBY, James A. Halliburton Services BRANAGAN, Paul P. 0. Box 1431 CER Corporation Duncan, Oklahoma 73533 4,7/0 S. Maryland Parkway (415) 251-3271 Las Vegas, Nevada 89109 (202) 735-7136 DOE, Thomas Lawrence Berkeley Laboratory BRIGHAM, William E. Bldg. 90/1106 Stanford University 1 Cyclotron Road Petroleum Engineering Dept. Berkeley, California 94720 Stanford, California 94305 (415) 486-67,78 (415) 497-1774 FTS 451-677B '• BURNS, Floyd L. FARRELL, Clifford Batelle Bechtel Incorporated Office of Nuclear Waste Isolatiu 50 Beale Street 505 King Avenue San Francisco, California Columbus, Ohio 43201 (415) 764-5655 CARLSSON, Leif FILBEY, Gil Geological Survey of Sweden Go Wireline Services Sveriges geologiska undersBkning 2730 Gundry Vretgrand 18 Long Beach, California 90805 S-753 22 Uppsala (213) 426-6559 SWEDEN 018/15 56 40 GALE, John E. Dept. of Earth Sciences CHRISTENSEN, Chris University of Waterloo Nuclear Waste Experimental Programs Waterloo, Ontario Division 4512 N2L 3G1 Sandia Laboratories (519) 885-1211, ext. 3464 Albuquerque, New Mexico 87185 (505) 264-9930 -161- GILMAN, Jeffrey A. HAWS, Jerr Woodward-Clyde Consultants Oil Recovery Department #3 Embarcadero Center Research Division San Francisco, California 94111 Marathon Oil Company (415) 956-7070, ext. 437 7400 South Broadway P. 0. Box 269 GORANSON, Colin Littleton, Colorado 80160 Lawrence Berkeley Laboratory (303) 794-2601 Bldg. 90/1024A 1 Cyclotron Road HERRGOTT, John G. Berkeley, California 94720 Hewlett Packard (415) 486-6657 690 East Middlefield Road FTS 451-6657 Mountain View, California 94042 (415) 969-0880 GOYAL, Keshav P. Lawrence Berkeley Laboratory HORNE, Roland N. Bldg. 90/1024D Dept. of Petroleum Engineering 1 Cyclotron Road Stanford University Berkeley, California 94720 Stanford, California 94305 (415) 486-5400 (415) 497-9595 FTS 451-f100 HSIEH, Chin-Hang GRAHAM, David L. Conoco, Inc. University of Idaho 125 Roadrunner Drive Rt. 4, Box 291-A #20 Ponca City, Oklahoma 74601 Moscow, Idaho 83813 (405) 765-8905 (208) 885-7977 HSIEH, Paul GRISAK, Gerry University of Arizona Environment Canada Dept. of Hydrology 502 Booth Street Tucson, Arizona 85719 Ottawa (602) 626-3131 Ontario, Canada K1V 8H2 HSU, Sungnan (613) 995-4020 Halliburton Services Drawer 1431 GUVANASEN, Varuttama Duncan, Oklahoma 73533 Lawrence Berkeley Laboratory (405) 251-3350 Bldg. 90/1106 1 Cyclotron Road IGLESIAS, Eduardo R. Berkeley, California 94720 Lawrence Berkeley Laboratory (415) 486-6001 Bldg. 90/1024G FTS 451-6001 1 Cyclotron Road Berkeley, California 94720 HANSON, Jonathan (415) 486-5943 Lawrence Livermore Laboratory FTS 451-5943 Box 808, L-220 Livermore, California 94530 IRVINE, Jeffrey (415) 422-6509 Lawrence Berkeley Laboratory Bldg. 90/1106 HARRISON, Roger 1 Cyclotron Road Eureka Energy Berkeley, California 94720 215 Market Street (415) 486-6789 San Francisco, California 94106 FTS 451-6789 -162- JAMESON, I. LEE, Pat Enthalpy Inc. Gartner Lee Associates Ltd. 320 College Ave., Ste. 305 Toronto Buttonville Airport Santa Rosa, California 95401 Markham (707) 54C-6429 Ontario Canada L3P 3J9 (416) 297-4600 KAM, James T. Science Applications Inc. LICHTNER, Peter 200 Lomas N.W., Ste 600 Lawrence Berkeley Laboratory Albuquerque, New Mexico 87102 Bldg. 90/1140 (505) 247-0381 1 Cyclotron Road Berkeley, California 94720 KANEHIRO, Brian (415) 486-5298 Lawrence Berkeley Laboratory FTS 451-5298 Bldg. 90/1106 1 Cyclotron Road LIPPMANN, Marcelo Berkeley, California 94720 Lawrence Berkeley Laboratory (415) 486-4717 Bldg. 90/1012E FTS 451-4717 1 Cyclotron Road Berkeley, California 94720 KATZ, Donald L. (415) 486-5035 University of Michigan FTS 451-5035 Ann Arbor, Michigan 48104 LONG, Jane KEENEY, Ronald C. Lawrence Berkeley Laboratory Radian Corporation Bldg. 90/1106 8500 Shoal Creek • 1 Cyclotron Road Austin, Texas 78'\ Berkeley, California 94720 (512) 454-4797 (415) 486-6697 FTS 451-6697 KENNEDY, Keith G. Science Applications, Inc. LUNDY, Don 200 Lomas N.W., Ste. 600 Brown and Caldwell Albuquerque, New Mexico 87102 Consulting Engineers (505) 247-0381 1501 N. Broadway Walnut Creek, California 94596 KIHARA, Deane University of Hawaii McEDWARDS, Donald G. 2540 Dole Street Harding Lawson Associate Honolulu, Hawaii 96822 7655 Redwood Boulevard (808) 948-7167 P. 0. Box 578 Novato, Calfornia 94747 KING, M. S. (415) 892-0821 Engineering Geoscience University of California MAEDER, Paul F. Berkeley, California 94720 Brown University (415) 642-3157 Providence, Rhode Island 07912 (401) 863-7655 KUNZMAN, William J. Marathon Oil Company 7400 South Broadway Littleton, Colorado 80160 (303) 794-2601 MANGOLD, Donald C. MILLER, H. 0. "Yogi" Lawrence Berkeley Laboratory U.S. Army Engineers Bldg. 90/1024F Waterways Experiment Station 1 Cyclotron Road P. 0. Box 631 Berkeley, California 94720 Vicksburg, Mississippi 39180 (415) 486-6459 (601) 634-2117 FTS 451-6459 MOLLY, Martin W. MEHRAN, Mohsen U.S. Department of Energy Lawrence Berkeley Laboratory Division of Geothermal Energy Bldg. 90K San Francisco Operations Office 1 Cyclotron Road 1333 Broadway Berkeley, California 947?" Oakland, California 94612 (415) 486-5655 (415) 273-7943 FTS 536-7943 MERCER, Jerry H. U.S. Geological Survey MOUNT, Russell Water Resources Division Hydro-Search, Inc. 505 Marquette N.w. 333 Flint Street P. 0. Box 26659 Reno, Nevada 89501 Albuquerque, New Mexico 87125 (702) 322-4173 (505) 766-2810 FTS 474-2246 NARASIMHAN, T. N. Lawrence Berkeley Laboratory MEYER, Charles F. Bldg. 90/10120 G. E. TEMPO 1 Cyclotron Road P. 0. Drawer QQ. Berkeley, California 94720 Santa Barbara, California 93102 (415) 486-5655 (805) 965-0551 FTW 451-5655 MILLER, Billy R. NELSON, Phillip Lynes, Inc. Lawrence Berkeley Laboratory P. 0. Box 12486 Bldg. 90/1070 Houston, Texas 77017 1 Cyclotron Rocd (713) 790-9132 Berkeley, California 94720 (415) 486-6758 MILLER, Constance W. FTS 451-6758 Lawrence Berkeley Laboratory Bldg. 90/1042 NEUMAN, Shlomo P. 1 Cyclotron Road University of Arizona Berkeley, California 94720 7632 Calle Cabo (415) 486-6454 Tucson, Arizona 85715 FTS 451-6454 (602) 885-3482 MILLER, Frank G. O'BRIEN, Maura Stanford University Lawrence Berkeley Laboratory Petroleum Engineering Dept. Bldg. 90/1042 Stanford, California 94305 1 Cyclotron Road (415) 497-2938 Berkeley, California 94720 (415) 486-4745 FTS 451-4745 -164- OLSON, Karl R. PELKA, Walter Lawrence Berkeley Laboratory RWTH Aachen Bldg. 90/1106 Elsass-Str. 88 1 Cyclotron Road D-5100 Aachen Berkeley, California 94720 West Germany MIS) -86-6129 FTS 451-6129 PETERSON, Ed Systems, Science & Software O'SULLIVAN, M. J. 3398 Carmel Mountain Road Lawrence Berkeley Laboratory San Diego, California 92038 Bldg. 90/1024C (714) 453-0060 1 Cyclotron Road Berkeley, California 94720 PHILIP, John F. (415) 486-6452 Lawrence Berkeley Laboratory FTS 451-6452 Bldg. 90/1012A 1 Cyclotron Road PALEN, Walter A. Berkeley, California 94720 University of California (415) 486-6468 Bldg. 90/1024D FTS 451-6468 Berkeley, California 94720 (415) 486-5350 P0P1ELAK, Roman FTS 451-5350 D'Appolonia Consulting Engineers, Inc. PALMA, Julio Cesar P. 0. Box 22417 Institute Nacional Elect. (I.N.D.E.t 7400 south Alton Court San Jose Villa Nueva, Guatemala Denver, Colorado 80222 Guatemala, C.A. (303) 771-3464 460 712 ext. 19 PRATT, Howard R. PAPADOPULOS, Stavros S. TerraTek S. S. Papadopulos & Associates University Research Park 8216 Scotch Bend Way 420 Wakara Way Potomac, Maryland 20854 Salt Lake City, Utah 84108 (301) 983-9119 (801) 582-2220 PATTON, Frank PRUESS, Karsten Westbay Instruments Ltd. Lawrence Berkeley Laboratory #2-265 - 25th Street Bldg. 90/1042E West Vancouver, B.C. 1 Cyclotron Road Canada V7V 4H9 Berkeley, California 94720 (604) 926-8541 (415) 486-6106 FTS 451-6106 PAULSSON, Bj'drn Lawrence Berkeley Laboratory RACHIELE, Richard Bldg. 90/1070 Lawrence Berkeley Laboratory 1 Cyclotron Road Bldg. 90/1106 Berkeley, California 94720 1 Cyclotron Road (415) 486-6789 Berkeley, California 94720 FTS 451-6789 (415) 486-6789 FTS 451-6789 -165- RAMF?, J. H. SANYAL, Subir K. Stanford University Stanford University Petroleum Engineering Dept. Stanford, California 94305 Stanford, California 94305 (415) 497-0691 (415) 497-1774 SAREM, A. M. Sam RAPIER, Pascal M. Union Science & Technology Division Lawrence Berkeley Laboratory Union Oil Company of California Bldg. 90/1070G 376 South Valencia Avenue 1 Cyclotron Road Brea, California 92621 Berkeley, California 94720 (714) 528-7201 (415) 486-4708 FTS 451-4708 SCHLEMHER, A. E. Texas Eastern Corporation REDA, Daniel C. P. 0. Box 2521 Sandia Laboratories Houston, Texas 77001 9508 Admiral Nimitz N.E. (713) 759-5466 Albuquerque, New Mexico 87111 (505) 844-4916 SCHROEDER, Ron C. Lawrence Berkeley Laboratory REMER, Janet Bldg. 90/1012C Lawrence Berkeley Laboratory 1 Cyclotron Road Bldg. 90/1070 Berkeley, California 94720 1 Cyclotron Road (415) 486-5560 Berkeley, California 94720 FTS 451-5560 (415) 486-4450 FTS 451-4450 SCHWARZ, Werner J. Lawrence Berkeley Laboratory ROGERS, Leah Bldg. 90/1070 Lawrence Livermore Laboratory 1 Cyclotron Road East Avenue Berkeley, California 94720 Livermore, California 94550 (415) 486-4706 (415) 422-3538 FTS 451-4706 ROGERS, Leo A. SEKI, Arthur Institute of Gas Technology Hawaii Natural Energy Institute 3424 South State Street University of Hawaii at Manoa Chicago, Illinois 60616 2540 Dole Street (312) 567-5292 Honolulu, Hawaii 96822 (808) 948-8890 ROCKAR, Evelyn M. Institute of Gas Technology SIMPSON, E. S. 3424 South State Street University of Arizona ITT Center Department of Hydrology Chicago, Illinois 60616 Tucson, Arizona 85721 (312) 567-5825 (602) 626-1855 SAARI, Kari SMITH, Donald A. University of California University of Idaho 440 Davis Hall 849 Kennett Avenue Berkeley, California 94720 Moscow, Idaho 83843 (415) 642-6557 (208) 882-0792 -166- SPANE, Frank A., Jr. THOMPSON, Glenn Rockwell Hanford Operations University of Arizona P. 0. Box 800 Oept. of Hydrology Richland, Washington 99352 Tucson, Arizona 85721 (509) 942-2615 (602) 626-4208 STEPHENSON, Dale E. THUR, William O'Appolonia Consulting Engineers, Lawrence Berkeley Laboratory Inc. Bldg. 90/1070 2340 Alamo S.E., Ste. 306 1 Cyclotron Road Albuquerque, New Mexico 87112 Berkeley, California 94720 (505) 842-0835 (415) 486-4381 FTS 451-4381 STERBENTZ, Rebecca Lawrence Berkeley Laboratory TSANG, Chin Fu 31dg. 90K Lawrence Berkeley Laboratory 1 Cyclotron Road Bldg. 90/10UH Berkeley, California 94720 1 Cyclotron Road (415) 486-6696 Berkeley, California 94720 FTS 451-6C96 (415) 486-5782 FTS 451-5782 STONE, Randolph Lawrence Livermore Laboratory UPDEGRAFF, C. David P. 0. Box 808 Science Applications Livermore, California 94550 200 Lomas Bldv. N.W. (415) 422-6499 Albuquerque, New Mexico 87112 (505) 247-0381 STRISOWER, Beverly Lawrence Berkeley Laboratory VECHIL, Jack Bldg. 90/1046 Go Wireline Services 1 Cyclotron Road 5024 Airport Drive Berkeley, California 94720 Bakersfield, California 93308 (415) 486-6658 (805) 399-9541 FTS 451-6658 VENERUSO, A. F. STROMOAHL, A. W. Sandia Laboratories Lawrence Berkeley Laboratory P. 0. Box 5800 Bldg. 90/1070 Albuquerque, New Mexico 87185 1 Cyclotron Road (505) 844-9162 Berkeley, California 94720 (415) 486-6708 VON BRIESEN, Roy FTS 451-6708 Johns Hopkins University Johns Hopkins Road TEILMAN, Maren Laurel, Maryland 20810 IECO (301) 953-7100 180 Howard Street San Francisco, California 94105 VONDER HAAR, Stephen (415) 442-7300 Lawrence Berkeley Laboratory Bldg. 90/1024D TH1ERY, Dominique P. I Cyclotron Road BRGH Berkeley, California 94720 BP 6009 Orleans (415) 486-5350 France 45018 FTS 451-5350 -167- WANG, Joseph S. Y. YU, Kwang Lawrence Berkeley Laboratory Johns Hopkins University applied Bldg. 90/1012G Physics Lab. 1 Cyclotron Road 1 Johns Hopkins Road Berkeley, California 94720 Laurel, HD 20910 (415) 486-6753 (301) 953-7100 FTS 451-6753 YUEN, Paul WITHERSPOON, Paul A. University of Hawaii Lawrence Berkeley Laboratory Hwaiii Natural Energy Institute Bldg. 90/1106 2540 Dole Street 1 Cyclotron Road Honolulu, Hawaii 96822 Berkeley, California 94720 (808) 948-8890 (415) 486-5082 FTS 451-5082 ZAIS, Or. Elliot J. Elliot Zais S. Associates, Inc. WOLLENBERG, Harold 7915 N.W. Siskin Drive Lawrence Berkeley Laboratory Corvallis, Oregon 97330 Bldg. 90/1046 (503) 757-9795 1 Cyclotron Road Berkeley, California 94720 ZOBACK, Hark (415) 486-5344 U. S. Geological Survey FTS 451-5344 345 Middlefield Rd. Menlo Park, California 94025 YANES-MORENO, Alberto Apartado Postal 475 Cuernavaca Mor. MEXICO -168- NAME INDEX C = Committee A = Author Ch = Chairman L. Aamodt - A 11 R. Agarwal -A 2 K. E. Almen - A 15 A. Bakr - A 94 D. Banks -A 3 W. Black - A 135 G. S. Bodvarsson - A 110 J. Bredehoeft - A 96 I. Carlson - A 15 C. Culver - A 94 S. N. Davis - A 1 A. 0. OuBois - A 38 T. Doe - Ch, A, C iv, vi, vii, 84 C. Forster - A 74 J. Sale - Ch, A iv, 74 G. Grisak - A 90 ;'. Hanson - A 15 J. Kam - A 94 B. Kanehiro - A 120 D. Katz - A 51 K. Kennedy - A 94, i58 J. C. Long - A 38 R. McCain - A 45 T. D. MrConnell - A 136 W. MilTe. - A 158 W. 0. Miller - A 153 T. N. Narasimhan - C, A vii, 120 P. Nelson - A 64 C. Neuzil - A 96 S. PapadO|.ulos - Ch iv F. Patton - A 135 -169- r E. Peterson - A 66 H. Pratt - A 45 R. Rachiele - A 64 H. Ramey Jr. - A 130 J. Remer - A 84 L. A. Rogers - A 14 R. C. Schroeder - Ch, C iii, vii W. J. Schwarz - A, C vi, vii D. P. Theiry - A 103 G. Thompson - A 67 C. F. Tsang - A 110 D. Updegraff - A 94 M. Voegele - A 45 A. F. Veneruso - A 136 C. R. Wilson - A 38 P. A. Witherspoon - C, A vii, 38 M. Zoback - A 157 U.3.GP011981:7B9-009/5718 -170-