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Fifty Years of Power Generation at the Geysers Geothermal Field, California – the Lessons Learned

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Fifty Years of Power Generation at the Geysers Geothermal Field, California – the Lessons Learned PROCEEDINGS, Thirty-Sixth Workshop on Geothermal Reservoir Engineering Stanford University, Stanford, California, January 31 - February 2, 2011 SGP-TR-191 FIFTY YEARS OF POWER GENERATION AT THE GEYSERS GEOTHERMAL FIELD, CALIFORNIA – THE LESSONS LEARNED Subir K. Sanyal1 and Steven L. Enedy2 1GeothermEx, Inc. Richmond, California 94806, USA E-mail: [email protected] 2Calpine Corporation Middletown, CA 95461, USA E-mail: [email protected] ABSTRACT INTRODUCTION This paper analyzes the fifty-year history of The Geysers geothermal field in California has been commercial power generation at The Geysers supplying commercial electric power continuously geothermal field in California as six distinct and for the last half century (1960 to present). Only two consecutive periods (1960-1969, 1969-1979, 1979- other geothermal fields in the world have had a 1986, 1986-1995, 1995-1998, 1998-2004 and 2004- longer history of power generation, namely, 2010) reflecting the intricate interrelationship Lardarello in Italy (continuously producing since between the prevailing socio-economic forces, field 1948) and Wairakei in New Zealand (continuously development and management practices, and producing since 1958). Since the 1970s, the level of consequent reservoir response. It is shown that this power generation at The Geysers has been field has proven to be by far the largest source of consistently higher than at either Lardarello or commercial geothermal power tapped to date in the Wairakei, or at any other geothermal field in the world, and its history presents a singularly pioneering world. As discussed below, The Geysers field is case of ingenious field management in the face of expected to be capable of supplying several hundred unpredictable socio-economic forces and challenging megawatts of power even another five decades from reservoir behavior. The most important innovation in now, when the field will have completed a century of this regard has been the augmentation of injection commercial power generation. This long production into the reservoir by piping in treated municipal history and the high level of power generation makes effluents from long distances outside the field. this field unique in the geothermal world. It is shown that (a) this field by now has produced BACKGROUND electricity equivalent to a 1,033 MW plant producing at 90% capacity factor over a typical project life of The Geysers is a steam field, that is, it produces 30 years; and (b) innovations in field management saturated steam rather than water or a steam-water have led to a 33% higher generation level today than mixture. Furthermore, this field represents an forecast two decades ago. This paper also attempts to essentially closed system rather than the usual forecast the future of this field. We believe the situation of an open geothermal system receiving present generation capacity of about 850 MW will natural recharge of hot or cold water from outside the have declined to about 700 MW over the next two reservoir. Steam fields are relatively rare, there being decades, taking into account the planned addition of only half a dozen commercially exploited steam at least 100 MW new capacity in the near future. A fields in the world compared to the numerous century since its exploitation began, this field would geothermal fields producing hot water or two-phase still be exploited by continued injection into the fluids (steam-water mixture). Figure 1 shows a map relatively pressure depleted reservoir, or possibly of this field showing the boundary of the known topping the yet-unexploited ultra-high temperature steam production area, the locations of the power zones known to exist below the exploited system. plants and the “unit area” dedicated to each power Finally, we point out the lessons learned by the plant. This field is the largest geothermal field in the geothermal industry from the history of this unique world in terms of the areal extent (at least 100 square field. kilometers) and has more than 400 active wells at 1 present. There are 18 operating power plants, steam production between 1960 and 1987, when it generating about 850 MW at present in this field. peaked at 10 billion kg per month, equivalent to about 1,600 MW (net). The installed generation Figure 2 presents the historical production and capacity in this field peaked at about 2,000 MW (net) injection data from the field during the past five in 1989. Subsequently, steam production and power decades. Figure 2 shows the monthly production generation in the field declined continuously for the (uppermost plot) and monthly injection (middle plot) next 7 to 9 years, reaching stability after 1995. in billion kg, and the percent of the produced mass Between 1995 and present both steam production and injected each month (lowermost plot) as a function of power generation have seen relatively modest time. declines with time. 1969 1979 1986 1995 2.5 1998 2004 1 2 345 6 7 2.0 63.1 billion kg per / year 1.5 kg) 12 13.9 billion (10 kg / year 1.0 31.1 billion kg / year 0.5 Cumulative Production, Injection and depletion 0.0 Figure 1: Location of power plants and unit areas at 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 The Geysers geothermal field. Figure 3: Cumulative production, injection and depletion data for The Geysers. 1969 1979 1986 1995 1998 2004 12 10 1969 1979 1986 1995 1998 2004 8 100 1600 6 4 123 4 5 6 7 (billion kg) 2 Monthly Production 80 1280 0 8 1 2 3 4 5 6 7 Generation 6 60 960 4 (billion kg) 2 otl Injection Monthly 640 40 Generation (MW) 0 Depletion 140 Depletion(billionkg) n 120 o i t c u 100 d o 20 320 r 80 P o t 60 n Ratio, % o i t 40 c e j n 20 I 0 0 0 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 Figure 2: Historical production and injection data Figure 4: Annual depletion data for The Geysers. for The Geysers. Figure 5 presents the monthly steam production rate As attempted in this paper, the fifty-year history of (thousand kg/month) from the field (on log scale) the field can be best described as seven distinct versus time to establish the productivity decline trend periods of 3 to 10 years’ duration both in terms of in the field since 1987. Figure 6 presents a similar field and well behavior as well as the prevailing plot of the steam production rate in kilopounds per socio-economic forces; these periods are indicated in hour (on log scale) versus time since 1980 for a Figure 2. typical well (GDC-12) to illustrate the changes in the productivity decline trend of individual wells. Figure 3 presents the cumulative production, injection and depletion (that is, production minus injection) history of this field (in trillion kg), while Figure 4 shows the annual steam depletion (billion kg) and the power capacity (MW) versus time. Figures 2 and 4 show that this field had increasing 2 1995 1998 2004 1x107 9x106 D = 4.8% per year 8x106 D=2.9%peryear 7x106 D=2%peryear 6x106 5x106 4x106 3x106 456 7 2x106 Steam Production Rate (1,000 kg/month) 1x106 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005 2007 2009 2011 Figure 5: Total steam production rate from The Geysers field versus time. Figure 7: Crude oil and Natural Gas Prices. 1979 2 1969 1986 1995 1998 2004 1986 1995 1000 1998 2004 1 2 345 6 7 3 4567 1 D = 4.2% per year ) h p k ( e t a D = 1.2% per year R 0 n o i t 100 c u d o r P m a e t Inflation Rate / Interrest Rate Rate / Interrest Rate Inflation S -1 -2 10 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 Years Ye ar Figure 6: Steam production rate of well GDC-12 Figure 8: History of U.S. inflation rate to interest versus time. rate ratio. We believe the long history of this field exemplifies the intricate inter-relationship between the socio- economic forces at play, field development and management practices, and consequent reservoir response. Therefore, in Figures 7 through 9 we present the histories of some indicators of the prevailing socio-economic forces in the United States over the last half century. Figure 7 shows the history of crude oil and natural gas prices, Figure 8 presents the history of the ratio of inflation rate to interest rate, and Figure 9 presents the history of two leading stock market indicators (Dow Jones Industrial Average and Standard & Poor 500). We will refer to the field behavior trends shown in Figures 2 through 5, an individual well behavior trend shown in Figure 6, and the trends in the socio-economic forces shown in Figure 9: Leading stock market indicators. Figures 7 through 9, in the remainder of this paper. In light of the above-discussed background, we analyze below the history of this field through each THE FLEDGLING YEARS (PERIOD 1) of the seven successive periods. Electric power generation started at The Geysers with the installation of a 12 MW (gross) plant in 1960. During Period 1 (1960-1969), the installed capacity grew very slowly to above 100 MW (Figures 2 and 4). During this period the produced steam was 3 vented to the atmosphere, the steam condensate was developer's bank loan for a geothermal project could disposed of at the surface and there was no injection.
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