Earth Sciences Division Berkeley Lab
Annual Report 2000–2001
Energy Resources Program
NON-CONDENSABLE GASES: TRACERS FOR RESERVOIR PROCESSES IN VAPOR-DOMINATED GEOTHERMAL SYSTEMS Alfred Truesdell and Marcelo Lippmann Contact: Marcelo Lippmann, 510/486-5035, mjlippmann@lbl.gov
RESEARCH OBJECTIVES
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At The Geysers field, 75 miles (120 km) north of San changes over time in steam temperatures and steam fractions Francisco, California, the largest known vapor-dominated geot(from individual wells) shows that steam from wells in the hermal system in the world, injection of water back into the center of the NCPA field originates from fairly uniform condireservoir began with commercial exploitation in 1960. This injections produced by injection. In contrast, steam from wells in tion, consisting of steam condensate and available surface water, peripheral areas originates from progressively drier reservoir was limited to 30% of the mass extracted. In late 1997, in the zones, which may return to near-original conditions depending steam field operated by the Northern California Power Agency on the characteristics of the injection operations. (NCPA), the amount of injection essentially doubled when lake Contours of total non-condensable gases show that changes water and treated waste water from in the location and amount of liquid the South East Geysers Effluent injected have been very effective in C-1 C-7 C-4 P-5 399000 H-2 P-2 P-9 F-5 C-5 C-11 H-1 P-6 Pipeline were delivered to the limiting gas concentrations in the C-2 C-6 C-9 Q-5 Q-6 Q-8 Q-7 F-7 C-8 Q-9 N-5 F-6 H-3 N-1 P-8 398000 F-2 F-1 -1 southern part of the system. steam produced by most of the F-3 N-4 N-6 Q-4 Q-1 N-2 0 H-5 150 D-1 A-1 -1 N-3 Q-3 B-5 P-4 397000 The purpose of this work is to NCPA wells. A-4 B-4 P-7 -5 Y-5 Y-2 Y-1 A-5 500 update studies of steam chemistry to D-6 D-7 1000 B-3 1000 396000 B-6 J-2 SIGNIFICANCE OF J-3 A-6 D-2 B-2 E-4 reflect changes resulting from the E-2 A-3 1500 D-8 1000 00 Y-3 395000 20 E-3 E-6 E-1 FINDINGS J-6 -6 increased liquid injection, to test the Y-4 -4 1992 0 E-5 J-4 J-5 250 applicability of geochemical analysis This study confirms the useful1790000 1792000 1794000 1796000 1798000 1800000 to steam fields with a relative high ness of non-condensable gases to 399000 P-9 P-2 C-1 C-7 C-4 H-2 H-1 F-5 C-5 P-5 P-6 Q-5 Q-6 Q-8 C-8 F-6 C-6 C-9 rate of injection, and to evaluate the identify reservoir processes in Q-7 Q-9 H-3 F-2 F-7 C-2 N-5 P-8 N-1 398000 Q-4 F-3 use of non-condensable gases to vapor-dominated geothermal sysN-2 N-4 N-6 Q-1 -1 H-5 F-4 N-3 397000 Q-3 P-4 D-1 -1 identify reservoir processes. tems, particularly in The Geysers A-1 -1 P-7 B-5 A-4 A-5 Y-1 D-7 15 B-4 Y-2 field. Variations of gas ratios in the 00 00 20 396000 10 A-6 B-3 00 D-6 D-2 J-2 APPROACH B-2 E-4 produced steam explain processes J-3 E-2 A-3 D-8 Y-3 395000 E-3 E-1 Y-4 -4 1997 J-4 J-6 -6 resulting from large-scale producThe methodology used in this 1500 E-6 E-5 1790000 1792000 1794000 1796000 1798000 1800000 tion and from an increasing amount study is different from that of earlier C-11 C-1 C-7 C-4 Q-5 399000 H-2 H-1 of injected liquid. It also illustrates work, which was based on oxygen P-9 P-2 P-5 F-5 C-5 Q-2 P-6 F-7C-8F-6 N-5 C-9 Q-8 Q-7 Q-9 F-2 Q-6 F-1 H-3 that changes in the source (i.e., and hydrogen isotopes. This method P-8 C-2 C-6 N-1 398000 Q-1 N-2 N-4 F-4 F-3 Q-4 1500 H-5 N-6 chemical characteristics) of the is no longer effective because N-3 397000 D-1 Q-3 P-4 A-4 A-5 injectate are useful in detecting the increased injection of creek and lake B-4 P-7 A-1 B-5 Y-2 Y-1 D-7 15 Y-5 20 00 B-6 396000 D-6 00 various phenomena occurring in the water and treated waste water has B-3 0 A-6 0 D-2 J-2 5 B-2 E-4 A-3 E-2 J-3 reservoir. lessened the isotopic contrast between Y-3 3000 D-8 395000 2000 E-3 E-6 E-1 Y-4 J-4 E-5 J-5 reservoir steam and injectate. RELATED PUBLICATIONS 1790000 1792000 1794000 1796000 1798000 1800000 We use D’Amore’s (1991) gas geothermometer grids and changes D'Amore, F., and A.H. Truesdell, Figure 1. NCPA Geysers steam field. Contours of total in total gas contents in the steam to Calculation of geothermal reservoir non-condensable gas in the produced steam (in ppmv) construct time-series diagrams for temperatures and steam fraction for 1992, 1997, and 2000. Injection wells in use are individual NCPA wells over their from gas compositions, Geoshown as solid circles. entire production histories. Instead of thermal Resources Council Transdescribing the grid diagram behavior actions 9(I), pp. 305–310, 1985. of each well, the behaviors are divided into types and interD'Amore, F., 1991, Gas geochemistry as a link between geotpreted according to their patterns. The distribution—over space hermal exploration and exploitation, in Application of and time—of non-condensable gases in the produced steam was Geochemistry in Geothermal Reservoir Development, edited also analyzed. by F.D'Amore, UNITAR/UNDP, Rome, pp. 93–117, 1991. Truesdell, A., B. Smith, S. Enedy, and M. Lippmann, Recent ACCOMPLISHMENTS geochemical tracing of injection-related reservoir processes in the NCPA Geysers field, Geothermal Resources Council Grid diagrams for nearly 70 NCPA wells were drawn by a Transactions 25, 2001. computer program using the equations given in D’Amore and Truesdell (1985). The wells have been in production from the midACKNOWLEDGMENTS to-late-1980s to 2000 (later data were not available). Four types of grid diagrams were recognized (linear, hairpin, This work was supported by the Assistant Secretary for Energy cluster, and random) by Truesdell et al. (2001). In addition, contour Efficiency and Renewable Energy, Office of Power figures showing the distribution of total non-condensable gas in Technologies, Office of Wind and Geothermal the NCPA field were developed for different years (e.g., Figure 1). Technologies, of the U.S. Department of Energy The application of gas geochemistry to detect and monitor under contract No. DE-AC03-76SF00098. 00 25 00 30
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