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2 Geothermal Resources Council, TRANSACTIONS Vol. 7, October A SUMMARY OF WELL TESTING ACTIVITIES AT LAWRENCE BERKELEY LABORATORY, M. G. Bodvarsson and S. M. Benson Earth Sciences Division, Lawrence Berkeley Laboratory, University of California, Berkeley, California ABSTRACT This paper presents well test data collected from various geothermal fields by the geothermal group at Lawrence Berkeley Laboratory. The paper describes the type of well tests conducted, the instrumentation used and the data collected. Experience gained through interpretation of the data has helped identify problems in test procedures and interpretative methods. INTRODUCTION Since 1975 the geothermal group of the Earth Sciences Division of the Lawrence Berkeley Laboratory (LBL) has carried out extensive well testing in geothermal resources throughout the western United States and in northern Mexico (Figure 1). Data from these, injection,, variablerate, and multiplewell tests represent considerable experience in geothermal well test procedure, instrumentation, and data acquisition. Interpretation of the data has yielded many opportunities to identify and record classical reservoir engineering and geohydrologic problems. In response to the many requests LBL has received for the accumulated well test data and associated information, a report entitled "Well Test Data fram Geothermal Reservoirs ( )" (Bodvarsson and Benson, 1983) has been prepared. The report documents the reservoirs tested, the various tests conducted, and the data obtained. It also describes the techniques and instrumentation used to collect the data. The present paper summarizes that report and provides excerpts of the information it contains. GEOTHERMAL WELL TESTS The geothermal reservoirs tested to date by LBL are widely varied both geologically and hydrogeologically, and include hightemperature (30ooc), lowtemperature (6OoC), singlephase (liquid), and twophase systems. The range of boundary conditions encountered include systems that are closed, open, confined, semiconfined, faultcharged, and' fracturecontrolled. Permeabilities ranging from several allidarcies to hundreds of darcies have been calculated from the data. Negative skin values and very high positive skin values have been computed in either naturally fractured or hydraulically fractured wells. Even vary clear evidence of a nearwellbore turbulent flow regime has been detected in a fractured, liquidwater hydrothermal system 0 \, \!! I..._..! *..a.... J..I XBL The well tests conducted within each resource include, injection, and tests, and as such are varied in type, duration, and sophistication. A variety of well test instrumentation, ranging from quite simple to highly sophisticated, is used, including: gas and fluidfilled capillary tubing, quartz crystal pressure gauges, float type waterlevel gauges, wellhead and downhole temperature gauges, and other commerciallyavailable or LBLdesigned and fabricated instrumentation. Table 1 lists the well tests conducted by LBL. Available information about these tests includes: test descriptions, instrumentation used, brief results of data interpretation, the calculated hydrologic parameters, and special or unique characteristics of geothermal (or hydrologic) systems inferred from the data. The following are selected examples of well Figure 1. Location map of geothermal resources tests performed by LBL. Descriptions of other well tested by LBL. tests are given by Bodvarsson and Benson (1983). 3 97

3 Table 1. W e l l Tests. Geothermal Production Observation Injection Reservoir Type of Test Well(s) Well(s) well(s) Test Date s Raft River Raft River Raft River RRGE 2 RRGE 2 RRGE Cerro Prieto Cerro Prieto Sus anville Susanville Susanville Klamath Falls 3830 injection product ion product ion Klamath Falls cw , 447, M50 8 M51, M90, M91 M53 LDS Church Davis, S. Pool, LDS Church WEN 1 YMCA #2 Klamath Falls cw1, cw2 Klamath Falls cw2 M101 M104, M10 Naef suzy 3, suzy 4 Naef, LLB #2 YMCA #I, Adamcheck Glen Head Parks, Adamcheck Glen Head Parks, Olson Stake, C.C. Parks, Stanke, Olson 9/12/75 9/13/75 9/30/75 10/30/75 11/ 4/75 11/ 7/75 2/13/76 2/24/76 4/ 1/76 4/12/76 2/10/77 4/13/77 7/14/77 7/18/77 7/26/77 7/30/77 8/24/77 10/ 5/77 12/ 1/77 12/ 6/77 12/16/77 12/20/77 I/ 6/78 3/29/78 4/17/78 4/21/78 5/ 2/78 5/ 4/78 1/14/78 3/30/78 5/16/78 7/24/78 7/26/78 11/29/78 12/10/78 1/ 8/79 3/ 3/82 3/ 8/82 12/ 2/79 10/24/79 10/25/79 9/29/81 9/30/81 2/ 8/82 2/12/82 CERRO PRIETO GECYPHERMU RESOURCE BAJA CALIFORNIA, MEXICO Resource Description The Cerro Prieto geothermal resource is located near Mexicali, in Baja California, Mexico. The producing field is situated in the alluvial plain of the Mexicali Valley, which is part of the seismically active Salton Trough/Gulf of California rift basin system. The field is made up of a thick sequence of essentially deltaic deposits that are discordant upon a granite and metasedimentary basement. Several major strikeslip faults have been identified within the resource. Lithologic studies indicate that several major producing intervals lie at depths of 500 to 1900 m. The resource is a liquiddominated system which shows boiling near the producing wells. Fluid temperatures in the resource range from 260 to 350OC. It is thought that secondary matrix porosity and permeability may play important roles in the hydrology of the reservoir. To date (19821, approximately 100 deep wells have been drilled into the reservoir (Fig. 2). Roughly 33 of these wells, ranging in depth from 1000 m to 2500 m, supply a steamwater mixture to the geothermal power plant, operational since April The artesian. rate of the watersteam mixture from the wells is now close to 4300 tonnes/hr. The following well tests were performed by LBL during the period January through July The tests were undertaken as part of a joint effort of LBL and Comisidn Federal de Electricidad de Mdxico (CFE) to conduct a comprehensive investigation of the entire Cerro Prieto geothermal field. [abstracted from Bermdjo M. et al., 1978; Dominguez A. et al ; Puente C. and de la Pesa, 1978; Schroeder et al., 1978; and Lyons and Van de mp,

4 ~~ ~~ ~~ ~ ~ ~~ & \ Northern region nm Bodvarsson and Benson Wells M50/M51/M90/M91 Interference Test, January 14March 30, 1978 The first test utilized four wells: M50, M51, M90 and M91. Well M101 was monitored for effects (Fig. 3 and Table 2). These wells are located approximately 1.5 km from the main producing field. The producing interval of well M91 is somewhat deeper than those of the other three wells. The producing wells were flowed at variable flowrates with overlapping intervals of 4 days to 2 weeks. Atotal of 30 days of drawdown and 15 days of recovery were observed. Pressure changes were measured in well M101 using 304 m of nitrogenfilled, 0.14 cm I.D. stainless steel tubing connected to a Paroscientific Digiquartz pressure transducer at the surface. 'Since there were multiple producing wells, a least squares matching routine was used in which multiple producing wells and variable flow rates can be accounted for. An excellent match of the observed and calculated data was obtained, resulting in a calculated transmissivity of 1.5 x lo6 md*ft/cp and a storativity of 2.3 x ft/psi. [abstracted from Schroeder et al., Figure 2. Well location map, Cerro Prieto geothermal resource. Table 2. M50/MSl/M9O/M91 Interference Test, January 14 March 30, WELL TEST DESCRIPTION INSTRUMENTATION ANALYSIS * Distance to (PI Pressure khh ch Classif i Fluid AP Product ion (TI Temperature md*ft/cp f t/psi cation Flow (psi) Well(s) (m) (Q) Flowrate (&/pa s (m/pa) M50 4 days (2/232/27) (Q) James method and stepwise variable weir kg/s M days (2/72/21) stepwise kg/s M90 16 days (2/163/1) stepwise kg/s M days (1/292/9) stepwise variable kg/s (Q) James method and weir box (Q) James method and weir box (Q) James method and weir box M (to M50) (PI Paros. with 304 m of 1.5 x lo6 2.3 x loo2 observation 1285 (to M51) nitrogen gasfilled (4.5 x 107) (1.1 x 106) 530 (to M;90) 0.14cm I.D. tubing 1480 (to M91) computerassisted analysis 3 99

5 401..~. 1. I I I I I I i % loo M I I 1/14/78 1/24/78 2/3/78 2/23/70 3/5/78 3AW78 3/25/78 4m78 xa Qa 2u2 Figure 3. M101 data (M50/M51/M90/M91 test). KLAMATH FALLS GEOTHERMAL RESOURCE, OREGON City Well #1 Interference Test (October 2425, 1979) The test involved pumping City Well #1 at stepwise variable rates of 16, and 43 l/s, for a total of 15 1/2 hours, while effects were monitored in the Parks, Adamcheck and Glen Head wells, 55 m8 305 m, and 430 m away, respectively (Figs. 4 and 5 and Table 3). A maximum flowrate of 43 l/s was held constant for 7 1/2 hours, during which a maximum drawdown of 33 psi was recorded in the well by electric probe. A Productivity Index (Q/AP) of 2.0 x m3/s=pa was obtained for this well. Waterlevel changes in the Adamcheck and Glen Head wells were monitored with LeupoldStevens continuousrecording waterlevel devices. A downhole Paroscientific pressure transducer was used in the Parks Well. Background data were obtained from the wells for several months prior to the test. Analyses of data indicate extremely high reservoir permeability, which is attributed to the fractured nature of the reservoir rock. [abstracted from Benson et al., 1980b and Benson, 1982bl Table 3. CW1 Interference Test, October 2425, WELL TEST DESCRIPTION INSTRUMENTATION Distance to (PI Pressure Classif i Fluid AP Production (T 1 Temperature cation Flow (psi) well(s) (m) (Q) Flowrate cw hrs 33 Parks observation st epwi se l/s (TI RTD at wellhead (Q) orifice plate and bourdon tube (PI Paros. downhole ANALYSIS * kh/v ch md* ft/cp ft/psi (m3/~a*s (m/pa) (9.9 x 106 (4.0 x possible barrier boundary ~ ~ ~~ ~ ~ ~ ~ Adamcheck observation Glen Head observation (PI L.S. waterlevel x 103 recorder (7.8 x (4.8 x lom8) possible barrier boundary (PI L.S. watearlevel x 103 recorder + (5.1 x (6.2 x 10'8) * type curve analysis t in nonartesian wells, pressure changes are recorded by measuring changes in water level in the wells 400

6 s 53.9 Parks Well CLO B U 22.4' I I I I I I ' I Glen Head Well 22.7 c E 23.0 = 0) 3! 14.3 b c p 14.6 Adamcheck Well 15.0 * E) c) m I I I I I I I I I I XBLIOI132 City Well I : 20 E n I l l n S I I I I. 10/23 10/ / xnl Figure 4. Parks well data (CW1 test). Figure 5. Glenhead/Adamcheck data (CW1 test). SUSANVILLE GEOTHERMAL RESOURCE, CALIFORNIA WEN1 Production Test (March 37, 1982) Well WEN1 was produced for five days at stepwise variable (artesian) flowrates of and 39 l/s (see Fig. 6 and Table 4). The first three rates were held constant for 12 hours each, and the third rate for 75 hours. Pressure and temperature measurements were recorded at the wellhead and dawnhole for the duration of the test and for approximately 12 hours after the well was shut in. Downhole pressure data were obtained with a Hewlett Packard quartz crystal gauge, and wellhead pressure was measured with a Paroscientific gauge. Downhole and wellhead temperatures were measured with a GearhartOwen temperature gauge, and a thermocouple, respectively. Flaw rates were measured with an orifice plate and differential pressure gauge. Semilog analysis of drawdown data indicates a reservoir transmissivity of approximately 3. 3 x 106 mdoft/cp (9.9 x low7 m3/pa0s). The Productivity Index (Q/AP) for this well varied with each change in flow rate, indicating nondarcy flow in the reservoir. [abstracted from Benson, 1982al CONCLUSIONS A report describing well tests conducted by LBL has been prepared (Bodvarsson and Benson, 1983). The report describes individual well tests in detail, focusing on instrumentation, well test design, and the data collected. This paper summarizes the contents of that report. Table 4. WENI Production Test, March 18, WELL TEST DESCRIPTION INSTRUMENTATION (PI Pressure Fluid AP (T 1 Temperature Classification Flow (psi 1 (Q) Flowrate ANZUJYSIS * kh/v ch md f t/cp ft/psi (m3/pa*s 1 (m/pa) WEN 1 5 days 31.5 (PI H.P. downhole 3.3 x 106 stepwise Paros at wellhead ( ) variable (TI GOO. downhole thermocouple P.I. = 4.5 x , 27, at wellhead , 2.1 x , 39 l/s (Q) orifice plate m3/s*~a t * semilog analysis t appears to be nondarcy flow in reservoir 4 01

7 Io Wellhcod pressure tpsio) I 2180 Dounhok pressure (psi01 Downhole : Flourolelgpml I. I L #..., I.,,,, & ' 20 ' 30 4: BO 90 I00 I10 I Time (hours) ImLuIZax~ Figure 6. WEN1 data (WEN1 test). ACKNOWLEDGEMENTS Bedjo M8 F. J.8 COrteZ A.8 c.8 and Arag6n A.8 A Physical and thermodynamic changes This work was supported by the Assistant Secre observed in the Cerro Prieto geothermal resertary for Conservation and Renewable Energy, Office voir. In Proceedings, First Symposium on the of Renewable Technology, Division of Geothermal and Cerro Prieto Geothermal Field, Baja California, Hydropower Technologies of the U. S. Department of Mexico. Berkeley, Lawrence Berkeley Labora Energy under Contract DEAC0376SF tory, LBL7098, pp G.0. H.P. L.S. Paros. NOMENCLATURE AND ABBREVIATIONS total compressibility reservoir thickness permeability pres sure volumetric flow rate fluid temperature porosity dynamic viscosity GearhartOwen Temperature Gauge Hewlett Packard Quartz Pressure Gauge LeupoldStevens WaterLevel Recorder Paroscientific Digiquartz Transducer REFERENCES Benson, S. M., 1982a. W e l l test data analysis from a naturally fractured liquiddominated hydrothermal system. In Proceedings of Geothermal Resources CouncilXnual ~eeting, October Berkeley, Lawrence Berkeley Laboratory, LBL Benson, S. M., 1982b. Hydrogeology of the Klamath Falls Hot Water Resource. Berkeley, Lawrence Berkeley Laboratory, LBL14793, in preparation. Benson, S. M., Goranson, C. B., and Schroeder, R. C b. Evaluation of City W e l l 1, Klamath Falls, Oregon. Berkeley, Lawrence Berkeley Laboratory, LBL10848, 9 p. Bodvarsson M., and Benson, S. M., 1983, Well Test Data from Geothermal Reservoirs ( Berkeley, Lawrence Berkeley Laboratory, LBL13295 Domfnguez A., B., Lippmann, M. J., and Bedjo M., F., Recent results of the welldrilling program at Cerro Prieto. In Proceedings Seventh Workshop on Geothermal Reservoir Engineering, Stanford University, Stanford, California, SGPTR~~, p Lyons, D. J., and van de mp# P. C., Subsurf ace geological and geophysical study of the Cerro Prieto geothermal field, Baja California, Mexico. Berkeley, Lawrence Berkeley Laboratory, LBL10540, 95 p. Puente C., I., and de la Peiia L.8 A., Geology of the Cerro Prieto geothermal field. In Proceedings, First Symposium on the Cerro Prieto Geothermal Field, Baja California, Mexico. Berkeley, Lawrence Berkeley Laboratory, LBL7098, pp SChrOeder, R. c.8 Goranson, C. B., Benson, S. M., and Lippmann, M. J., Well tests at the Cerro Prieto geothermal field. In Proceedings, First Symposium on the Cerro Prieto Geothermal Field, Baja California, Mexico. Berkeley, Lawrence Berkeley Laboratory, I&&7098, pp