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Title: A Reservoir Assessment of the Geysers Geothermal Field

Abstract

Big Sulphur Creek fault zone, in The Geysers Geothermal field, may be part of a deep-seated, wrench-style fault system. Hydrothermal fluid reservoir may rise through conduits beneath the five main anomalies associated with the Big Sulphur Creek wrench trend. Upon moderately dipping, fracture network. Condensed steam at the steep reservoir flank drains back to the hot water table. These flanks are defined roughly by marginally-producing geothermal wells. Field extensions are expected to be on the southeast and northwest. Some geophysical anomalies (electrical resistivity and audio-magnetotelluric) evidently are caused by the hot water geothermal field or zones of altered rocks; others (gravity, P-wave delays, and possibly electrical resistivity) probably represent the underlying heat source, a possible magma chamber; and others (microearthquake activity) may be related to the steam reservoir. A large negative gravity anomaly and a few low-resitivity anomalies suggest areas generally favorable for the presence of steam zones, but these anomalies apparently do not directly indicate the known steam reservoir. Monitoring gravity and geodetic changes with time and mapping microearthquake activity are methods that show promise for determining reservoir size, possible recharge, production lifetime, and other characteristics of the known stream field. Seismic reflection data may contribute to the efficientmore » exploitation of the field by identifying fracture zones that serve as conduits for the steam. (DJE-2005)« less

Authors:
; ; ;
Publication Date:
Research Org.:
Californina Department of Conservation, Division of Oil and Gas
Sponsoring Org.:
USDOE
OSTI Identifier:
860865
Report Number(s):
CDC-81-111
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
Geothermal Legacy

Citation Formats

Thomas, Richard P., Chapman, Rodger H., Dykstra, Herman, and Stockton, A.D. A Reservoir Assessment of the Geysers Geothermal Field. United States: N. p., 1981. Web. doi:10.2172/860865.
Thomas, Richard P., Chapman, Rodger H., Dykstra, Herman, & Stockton, A.D. A Reservoir Assessment of the Geysers Geothermal Field. United States. doi:10.2172/860865.
Thomas, Richard P., Chapman, Rodger H., Dykstra, Herman, and Stockton, A.D. Thu . "A Reservoir Assessment of the Geysers Geothermal Field". United States. doi:10.2172/860865. https://www.osti.gov/servlets/purl/860865.
@article{osti_860865,
title = {A Reservoir Assessment of the Geysers Geothermal Field},
author = {Thomas, Richard P. and Chapman, Rodger H. and Dykstra, Herman and Stockton, A.D.},
abstractNote = {Big Sulphur Creek fault zone, in The Geysers Geothermal field, may be part of a deep-seated, wrench-style fault system. Hydrothermal fluid reservoir may rise through conduits beneath the five main anomalies associated with the Big Sulphur Creek wrench trend. Upon moderately dipping, fracture network. Condensed steam at the steep reservoir flank drains back to the hot water table. These flanks are defined roughly by marginally-producing geothermal wells. Field extensions are expected to be on the southeast and northwest. Some geophysical anomalies (electrical resistivity and audio-magnetotelluric) evidently are caused by the hot water geothermal field or zones of altered rocks; others (gravity, P-wave delays, and possibly electrical resistivity) probably represent the underlying heat source, a possible magma chamber; and others (microearthquake activity) may be related to the steam reservoir. A large negative gravity anomaly and a few low-resitivity anomalies suggest areas generally favorable for the presence of steam zones, but these anomalies apparently do not directly indicate the known steam reservoir. Monitoring gravity and geodetic changes with time and mapping microearthquake activity are methods that show promise for determining reservoir size, possible recharge, production lifetime, and other characteristics of the known stream field. Seismic reflection data may contribute to the efficient exploitation of the field by identifying fracture zones that serve as conduits for the steam. (DJE-2005)},
doi = {10.2172/860865},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Thu Jan 01 00:00:00 EST 1981},
month = {Thu Jan 01 00:00:00 EST 1981}
}

Technical Report:

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  • Big Sulphur Creek fault zone, in The Geysers Geothermal field, may be part of a deep-seated, wrench-style fault system. Hydrothermal fluid in the field reservoir may rise through conduits beneath the five main anomalies associated with the Big Sulphur Creek wrench trend. Some geophysical anomalies (electrical resistivity and audio-magnetotelluric) evidently are caused by the hot water geothermal field or zones of altered rocks; others (gravity, P-wave delays, and possibly electrical resistivity) probably respresent the underlying heat source, a possible magma chamber; and others (microearthquake activity) may be related to the steam reservoir. A large negative gravity anomaly and a fewmore » low-resistivity anomalies suggest areas generally favorable for the presence of steam zones, but these anomalies apparently do not directly indicate the known steam reservoir. At the current generating capacity of 930 MWe, the estimated life of The Geysers Geothermal field reservoir is 129 years. The estimated reservoir life is 60 years for the anticipated maximum generating capacity of 2000 MWe as of 1990. Wells at The Geysers are drilled with conventional drilling fluid (mud) until the top of the steam reservoir is reached; then, they are drilled with air. Usually, mud, temperature, caliper, dual induction, and cement bond logs are run on the wells.« less
  • Discussion is presented under the following section headings: background and some technical characteristics of geothermal resources; geology and geohydrology, geophysics, and, conclusions regarding availability of geothermal energy for nonelectric uses; agricultural assessment of Lake County, site assessment for potential agricultural development, analysis of potential agricultural applications, special application of low cost geothermal energy to algae harvesting, development of an integrated agribusiness, geothermal complex in Lake County, analysis of individual enterprises, and, recommendations for subsequent work; demographic characteristics, economic condition and perspective of Lake County, economic impact of geothermal in Lake County, social and economic factors related to geothermal resource development,more » socioeconomic impact of nonelectric uses of geothermal energy, and, identification of direct heat applications of geothermal energy for Lake County based on selected interviews; cost estimate procedure, example, justification of procedure, and, typical costs and conclusions; and, recommended prefeasibility and feasibility studies related to construction of facilities for nonelectric applications of geothermal resource utilization. (JGB)« less
  • The different uses to which geothermal heat and fluids could be applied as a direct utilization of resource or as heat utilization are explored. The following aspects are covered: geotechnical assessment, agricultural and industrial applications, socioeconomic assessment, and engineering assessment. (MHR)
  • Experiment No. 6 of the Geothermal Reservoir Well Stimulation Program (GRWSP) was performed at The Geysers Field in Sonoma County, California. This well had low productivity (46,000 lb/hr), probably because it did not intersect the primary natural fracture system of the reservoir. Surrounding production wells are considered to be good wells with an average flow rate of about 100,000 lb/hr. The stimulation technique selected was an acid etching treatment (Halliburton Services' MY-T-ACID). A small water prepad was used to provide tubular cooling and fluid loss control. Following the water prepad were 500 to 750 bbl of high viscosity crosslinked gelmore » fluid and 400 to 500 bbl of a hydrofluoric-hydrochloric (HF-HCl) acid solution. The frac fluids were expected to enter only a single or limited fracture zone within the open interval. Frac rates of 20 to 40 BPM and surface pressures of 3000 psig were estimated for this treatment. During the job, however, no significant surface pressure was recorded, and all fluids flowed easily into the interval. Subsequent evaluation of the well performance showed that no noticeable stimulation had been achieved even though the frac fluids were properly injected. Temperature and gamma ray surveys along with tracer studies indicated that the frac fluids entered natural fracture channels over a 650-foot zone of the open interval, which probably prevented the staged acid etching treatment from functioning as designed.« less
  • We completed the process of identifying shear-wave splitting in the Geyser area. A total of 2700 observations were recorded with about 1700 observations from the 1988 data and about 1000 observations from 1994. Fast polarization direction map in Figure 1 shows that most of the stations in the Geyser area display consistent direction throughout the main field, between 0{degree} azimuth to 40{degree} azimuth. Some exemptions to the consistent crack alignment (fast polarization direction) can be seen in stations 9 and station 3, and also in stations 13 and 14 outside the field. Since the stations are in boreholes it ismore » possible that some of the station orientations, calculated using P-wave arrivals from located events, are erroneous. If we treat measurements of polarization direction as a statistical process, same as deep of layer measurement, we can say that in the small area of the station we have aligned cracks. Figures 2 and 3 show results of the crack density inversion assuming regional crack azimuth of 20{degree}. Almost 2400 raypaths were used to perform this tomographic inversion. There is weak dependency of the results on the regional crack direction, but the main areas of high and low crack density are the same. The changes are mainly in the size of the anomalies. Since the amplitudes of those anomalies depend mainly on the damping parameter we use in the inversion, exact regional crack direction is not a critical parameter of the inversion. The map in figure 2 and cross-sections in Figure 3 show two areas of high crack density at the top 1 km one at station 8 and the other between stations 6 and 5. At greater depth of 1 to 2 km those two area converge to one high crack density anomaly between stations 3, 4, 11, and 10.« less