Geysers Field Research Articles

Two Archaeal Metagenome-Assembled Genomes from El Tatio Provide New Insights into the Crenarchaeota Phylum.

A phylogenomic and functional analysis of the first two Crenarchaeota MAGs belonging to El Tatio geysers fields in Chile is reported. A soil sample contiguous to a geothermal activity exposed lagoon of El Tatio was used for shotgun sequencing. Afterwards, contigs were binned into individual population-specific genomes data. A phylogenetic placement was carried out for both MAG 9-5TAT and MAG 47-5TAT. Then functional comparisons and metabolic reconstruction were carried out. Results showed that both MAG 9-5TAT and MAG 47-5TAT likely represent new species in the genus Thermoproteus and the genus Sulfolobus, respectively. These findings provide new insights into the phylogenetic and genomic diversity for archaea species that inhabit the El Tatio geysers field and expand the understanding of the Crenarchaeota phylum diversity.

Fault-controlled geothermal fluids of the northern Trans-Mexican Volcanic Belt: A geochemical and isotopic study of the Los Geysers field (Valley of Queretaro, Mexico)

This study focuses on the geochemical and isotopic composition of natural spring waters and gases discharging at Los Geysers thermal area (northern Trans-Mexican Volcanic Belt, TMVB) and its relations to the regional tectonic framework. Water is of Na-HCO3 type and samples were collected at temperatures ranging from 48°C to 98°C and pH from 6.8 to 9.3. Stable isotope compositions (−10.0 to −8.0‰ for δ18O and −75.6 to −69.7‰ for δD) deviate from the global and local meteoric lines suggesting fractionation by steam loss The 87Sr/86Sr values of the thermal waters range from 0.70664 to 0.70698 indicating that most of the strontium comes from the dissolution of carbonate belonging to the late Berriasian to early Valanginian in the Guanajuato conglomerate group and a minor component of less radiogenic Sr from Paleogene–Neogene volcano-sedimentary and volcanic rocks. Solute geothermometers reveal a reservoir temperature around 164°C. A mixture between air and hydrothermal CO2 composes the bubbling gases. Helium isotopes data (R/Ra=0.96–1.71) and 4He/20Ne ratios (0.53–9.41) reveal that helium is dominated by a radiogenic component with a considerable mantle-He contribution (up to 20.8%). Since there is no active volcanism at the northern TMVB, mantle-He is best explained by transport of volatiles along active faults reaching the crust-mantle boundary. The conceptual hydrogeochemical model involves a thermal aquifer at ∼1000m depth which is recharged by regional meteoric water flow, a high thermal gradient (∼153°C/km) and fast fluid upflow to the surface along discontinuities related to regional horst and graben tectonics.

Microbial Biomarker Transition in High-Altitude Sinter Mounds From El Tatio (Chile) Through Different Stages of Hydrothermal Activity.

Geothermal springs support microbial communities at elevated temperatures in an ecosystem with high preservation potential that makes them interesting analogs for early evolution of the biogeosphere. The El Tatio geysers field in the Atacama Desert has astrobiological relevance due to the unique occurrence of geothermal features with steep hydrothermal gradients in an otherwise high altitude, hyper-arid environment. We present here results of our multidisciplinary field and molecular study of biogeochemical evidence for habitability and preservation in silica sinter at El Tatio. We sampled three morphologically similar geyser mounds characterized by differences in water activity (i.e., episodic liquid water, steam, and inactive geyser lacking hydrothermal activity). Multiple approaches were employed to determine (past and present) biological signatures and dominant metabolism. Lipid biomarkers indicated relative abundance of thermophiles (dicarboxylic acids) and sulfate reducing bacteria (branched carboxylic acids) in the sinter collected from the liquid water mound; photosynthetic microorganisms such as cyanobacteria (alkanes and isoprenoids) in the steam sinter mound; and archaea (squalane and crocetane) as well as purple sulfur bacteria (cyclopropyl acids) in the dry sinter from the inactive geyser. The three sinter structures preserved biosignatures representative of primary (thermophilic) and secondary (including endoliths and environmental contaminants) microbial communities. Sequencing of environmental 16S rRNA genes and immuno-assays generally corroborated the lipid-based microbial identification. The multiplex immunoassays and the compound-specific isotopic analysis of carboxylic acids, alkanols, and alkanes indicated that the principal microbial pathway for carbon fixation in the three sinter mounds was through the Calvin cycle, with a relative larger contribution of the reductive acetyl-CoA pathway in the dry system. Other inferred metabolic traits varied from the liquid mound (iron and sulfur chemistry), to the steam mound (nitrogen cycle), to the dry mound (perchlorate reduction). The combined results revealed different stages of colonization that reflect differences in the lifetime of the mounds, where primary communities dominated the biosignatures preserved in sinters from the still active geysers (liquid and steam mounds), in contrast to the surviving metabolisms and microbial communities at the end of lifetime of the inactive geothermal mound.

The impact of injection on seismicity at The Geysers, California Geothermal Field

Water injection into geothermal systems has often become a required strategy to extend and sustain production of geothermal resources. To reduce a trend of declining pressures and increasing non-condensable gas concentrations in steam produced from The Geysers, operators have been injecting steam condensate, local rain and stream waters, and most recently treated wastewater piped to the field from neighboring communities. If geothermal energy is to provide a significant increase in energy in the United States (the US Department of Energy goal is 40,000 MW by 2040), injection must play a larger role in the overall strategy, i.e., enhanced geothermal systems (EGS). Presented in this paper are the results of monitoring microseismicity during an increase in injection at The Geysers field in California using data from a high-density digital microearthquake array. Although seismicity has increased due to increased injection, it has been found to be somewhat predictable, thus implying that intelligent injection control may be able to control large increases in seismicity.

The Geysers geothermal field: results from shear-wave splitting analysis in a fractured reservoir

SUMMARY Clear shear-wave splitting (SWS) is observed in 1757 high signal-to-noise ratio microearthquake seismograms recorded by two high density seismic arrays in the NW and the SE Geysers geothermal fields in California. The Geysers reservoir rocks within the study area are largely composed of lithic, low-grade metamorphism, well-fractured metagraywackes which commonly lack schistosity, warranting the general assumption that shear-wave splitting here is induced solely by stress-aligned fracturing in an otherwise isotropic medium. The high quality of observed shear-wave splitting parameters (fast shear-wave polarization directions and time delays) and the generally good data spatial coverage provide an unprecedented opportunity to demonstrate the applicability and limitations of the shear-wave splitting approach to successfully detect fracture systems in the shallow crust based on SWS field observations from a geothermal reservoir. Results from borehole stations in the NW Geysers indicate that polarization orientations range between N and N60E; while in the SE Geysers, ground surface stations show polarization directions that are generally N5E, N35E-to-N60E, N75E-to-N85E, and N20W-to-N55W. Crack orientations obtained from observed polarization orientations are in good agreement with independent field evidence, such as cracks in geological core data, tracer tests, locally mapped fractures, and the regional tectonic setting. Time delays range typically between 8 and 40 ms km −1 , indicating crack densities well within the norm of fractured reservoirs. The sizeable collection of high resolution shear-wave splitting parameters shows evidence of prevalent vertical to nearly vertical fracture patterns in The Geysers field. At some locations, however, strong variations of SWS parameters with ray azimuth and incident angle within the shear-wave window of seismic stations indicate the presence of more complex fracture patterns in the subsurface.

The Geysers-Clear Lake geothermal area, California—An updated geophysical perspective of heat sources

The Geysers-Clear Lake geothermal area encompasses a large dry-steam production area in The Geysers field and a documented high-temperature, high-pressure, water-dominated system in the area largely south of Clear Lake, which has not been developed. Both systems have been extensively studied with geophysical techniques, drilling, and geological mapping during the past 20 years. An updated view is presented of the geological/geophysical complexities of the crust in The Geysers-Clear Lake region in order to address key unanswered questions about the heat source and tectonics. Early geophysical interpretations used a gravity low centered in the area between Clear Lake and The Geysers to suggest that a large magma chamber existed at depths starting at about 7 km. This first-order assumption of a large magma chamber expressed in the gravity data was used as a guide in subsequent geophysical and geological interpretations. Drill-hole temperature evidence is strongly suggestive of a shallow, hot-intrusive body, but in this paper the complexities are documented of the geological and geophysical data sets that make it difficult to pinpoint the location of “magma” or hot, solidified intrusive material. Forward modeling, multidimensional inversions, and ideal body analysis of the gravity data, new electromagnetic sounding models, and arguments made from other geophysical data sets suggest that many of the geophysical anomalies have significant contributions from rock property and physical state variations in the upper 7 km and not from ”magma“ at greater depths. Regional tectonic and magmatic processes are analyzed to develop an updated scenario for pluton emplacement that differs substantially from earlier interpretations. In addition, a rationale is outlined for future exploration for geothermal resources in The Geysers-Clear Lake area.

The Geysers-Clear Lake area, California; thermal waters, mineralization, volcanism, and geothermal potential

Manifestations of a major thermal anomaly in the Geysers-Clear Lake area of northern California include the late Pliocene to Holocene Clear Lake Volcanics, The Geysers geothermal field, abundant thermal springs, and epithermal mercury and gold mineralization. The epithermal mineralization and thermal springs typically occur along high-angle faults within the broad San Andreas transform fault system that forms the western boundary of the North American plate in this area. The young volcanic rocks overlie Mesozoic marine rocks of the Great Valley sequence which have been thrust above the coeval Franciscan Complex and penecontemporaneously dropped back down along low-angle detachment faults.Many of the waters of the region are nonmeteoric as defined by their isotopic signature. One type of isotopically shifted water emerges from or near Great Valley sequence rocks and is the most chloride rich. It is interpreted to be evolved connate in origin. A second type, evolved meteoric water, has moderate chloride contents, high boron contents, and high B/Cl ratios and is found locally in Franciscan rocks, notably at the Sulphur Bank mercury mine, where it probably results from near-closed-system, repeated boiling of meteoric water in host rocks that also contribute organic components to the water. At the Sulphur Bank mine fracturing of otherwise impermeable Franciscan rocks by faulting has created a localized zone of permeability in which thermal water boils repeatedly with limited venting to the surface. Boron-rich fluids were apparently present at depth in The Geysers geothermal field when intrusion of silicic magma occurred, because the concealed intrusion of felsite is surrounded by a halo of tourmaline-bearing hornfels. The volume of this poorly dated early to middle Quaternary intrusive body probably exceeds the 100 km 3 of erupted Clear Lake Volcanics. Similar intrusions may have occurred in the eastern part of the area at Wilbur Springs and the McLaughlin mine, where gold deposition and evidence of hydrothermal phenomena suggest more magmatic activity than is indicated by the small exposed bodies of early Quaternary basaltic lava. The Clear Lake Volcanics are the present locus of volcanism in the northern Coast Ranges and progressively older volcanic centers occur to the south. Geophysical data suggest that a large silicic magma body may be centered north of The Geysers steam field, providing the heat for the geothermal field.Geothermal power production has peaked at The Geysers and pressure declines indicate significant depletion of the fluid resource. The vapor-dominated field evolved from a preexisting hydrothermal system within fractured, otherwise impermeable Franciscan metamorphic rocks. A deep water table of saline fluid has been postulated to be present under the steam field, but no chloride-rich water has been found at drillable depth. We propose that recently discovered, isotopically shifted steam in the northwest Geysers area indicates the presence not of deep connate water but xather of boiled-down, boron-rich Franciscan evolved meteoric water. This water is likely to be present in limited quantities and will not provide a significant hot water resource for geothermal power production at The Geysers field or from the main Clear Lake volcanic field.

Oil and Gas Developments in West Coast in 1987

Drilling activity in the West Coast region in 1987 showed little improvement over 1986, as crude oil and gas prices remained low. A total of 208 exploratory wells were drilled, with explorationists logging 5 new-field discoveries and an overall success rate of 26%. Exploration activity in offshore California continued to decline in 1987 with only 3 new wildcats drilled and no reported discoveries. Operators meanwhile concentrated their efforts on the development of the giant Point Arguello and Point Pedernales fields and continued their efforts to obtain necessary permits to bring on-line the additional reserves discovered in the early 1980s. Exploration activity in the onshore California basins increased slightly in 1987 with 195 wells drilled compared to 189 in 1986. Explorationists scored 49 discoveries consisting of 5 new fields, 13 new pools, and 32 extensions. Drilling activity in Oregon and Washington continued to decline in 1987 with only 10 exploratory wells, 2 fewer than in 1986. Seven of these wells were completed as gas producers at Mist field in Oregon. Geothermal activity in California increased by 22% in 1987, halting the downward trend set over the past few years. Activity was again concentrated at The Geysers field with the completion of 39 new wells in 1987.

Oil and Gas Developments in West Coast in 1985

Drilling activity in the West Coast region in 1985 maintained the brisk 1984 level, the number of wells drilled decreasing by only 2%. Exploration efforts continued at the pace of the previous year with 265 exploratory wells drilled in 1985, 4 less than in 1984. Exploration offshore California continued to decline as development plans progressed for the nearly 2 billion bbl of oil discovered in recent years. Three new platforms were launched in 1985, and 13 others are planned for the Santa Maria and Santa Barbara Channel offshore areas. The Monterey Formation continued to be a hot exploration target, with 4 of the 12 exploratory wells drilled in 1985 each testing combined rates of more than 3,700 b/d of 8-16° oil. Enhanced recovery techniques for low-gravity crude are partly responsible for the success of the recent testing. Onshore California exploratory activity increased slightly, with 229 wells drilled in 1985 compared to 223 in 1984. The San Joaquin basin had the most significant find in over a decade. The Channel Exploration 63X-30 Tenneco-San Emidio was completed in Stevens sand for 2,064 BOPD and 405 MCFGD. Drilling in Oregon and Washington continued its active trend with 25 wells drilled in the 2 states in 1985, 5 more than 1984. Activity centered in Oregon's Mist field, with 16 wells resulting in 6 new pools and 1 field extension. Geothermal activity in California decreased slightly, with 62 wells drilled in 1985 compared to 76 in 1984. Activity was concentrated at The Geysers field as 3 more plants were brought on line. The Imperial Valley also saw significant activity when 3 new power plants went into operation.

Remote Control of a Geothermal Steam Pipeline

Summary Aminoil U.S.A. Inc. (AUSA) operates a pipeline delivering geothermal steam to a Geysers. Lake County, CA, power plant by means of a distributed control system. Microprocessors located in the field squire data and transmit it digitally to a control building adjacent to the power plant. From this building the shift operator monitors and controls every well in the system, regulates the delivery pressure to the geothermal power plant, and controls the condensate reinjection system. This paper discusses design, operation, and future objectives of this control system. The design covers selection of the control system, data acquisition and control requirements for individual wells, pipeline over pressure relief system control, and condensate reinjection system. The operation of the steam pipeline since power plant start-up has been very favorable. Steam delivery pressure fluctuations are controlled to less than +0.5 psi (+/-4 kPa) under normal conditions. Shift operators are capable of responding to power plant upsets (turbine trips and load reductions) in minutes, minimizing steam venting to the atmosphere. Currently the geothermal steam pipeline is manually remote operated by a shift operator. This operation has provided valuable information for conversion to an unmanned computer control operation. This proposed unmanned computer control is discussed along with our methods of approach. Introduction Our project is in the Castle Rock Springs area of The Geysers field in California, approximately 100 miles (160 km) northeast of San Francisco. The operator supplies geothermal steam to a public utility's geothermal power plant rated at 138 MW gross, 133 MW net delivered to the transmission line. Twenty-three geothermal steam wells deliver a total of approximately 2,700,000 lbm/hr (340 kg/s) of steam at rated capacity. Individual well deliverabilities range from 40,000 to 325,000 lbm/hr (5 to 41 kg/s). Approximately 5 miles (8 km) of insulated pipe is required to deliver the necessary steam flow to the power plant. Individual wellhead pipelines vary in diameter from 10 to 18 in. (25 to 46 cm), depending on steam flow capability. The wellhead pipelines feed into 24- to 30-in. (61- to 76-cm) branch lines that connect into two 36-in. (91 -cm) main steam lines with separators for condensate and particle removal. These two 36-in. (91-cm) pipelines join to form a 48-in. (122-cm) header that delivers steam to the power plant. Along the pipeline, drip legs are positioned at low points to collect condensate. These drip legs are vented to the atmosphere to remove condensate during start-up or shutdown of the pipeline. To provide electrical power for the control system. a three-point 480-V electrical distribution system parallels the pipeline. Transformers step down the line voltage to 120 Vac at the wellheads. The remote control system used to monitor and control the geothermal steam pipeline was selected primarily as a mechanical H2S-abatement method for compliance with the Lake County Air Pollution Control Dist. (LCAPCD) regulations. During power plant outages and start-up conditions, all steam is vented to the atmosphere. The LCAPCD H S-abatement requirement for an unscheduled power plant outage is given in Fig. 1, Under these conditions the vented steam rate must be limited to 35 % of full flow within 1 hour after an outage. Further reduction to 10% of full flow is required if the power plant outage is expected to be greater than 7 hours. AUSA determined that only a remote control system capable of controlling all wells in the system could accomplish this flow reduction in the short time frame required. This paper presents our control system structure, design. operation, and proposed computer control. Control System Structure A Honeywell TDC-2000 control system combined with a Honeywell 4500 computer (super station) was selected and installed. JPT P. 989^

Use of Hydrogen Peroxide To Abate Hydrogen Sulfide in Geothermal Operations

Summary Environmental restrictions on hydrogen sulfide emissions from geothermal operations in the Geysers high-pressure steam field in northern California has led to the development of hydrogen-peroxide-based abatement processes. One process involves the spray injection of hydrogen peroxide and sodium hydroxide into escaping steam during well drilling operations. Other processes involve peroxide treatment of steam condensate in power plants. High sulfide abatement levels have been achieved with these processes. Introduction Geothermal resources, whether vapor or liquid dominated, usually contain hydrogen sulfide. Some representative sulfide values' for operational geothermal fields are given in Table 1. Hydrogen sulfide possesses an objectional odor even at concentrations below 0.5 cm3/m3 (0.5 ppm). At 10 cm3/m3 (ppm), eye irritation occurs, and respiratory tract irritation occurs at 50 to 100 cm3/m3 (ppm). Loss of consciousness and death can occur at concentrations of 500 cm3/m3 (ppm) or more.The expanding development of the Geysers field has led to environmental restrictions limiting the amount of hydrogen sulfide that may be emitted during well drilling, stacking, and power generation.As other geothermal fields are developed (e.g., in the Imperial Valley, CA, New Mexico, Nevada, and the U.S. gulf coast), similar restrictions could be imposed if hydrogen sulfide levels prove high enough to exceed present or future ambient or emission standards.The wellknown use of hydrogen peroxide for sulfide destruction in municipal and industrial wastewater treatment fields stimulated the investigation of hydrogen peroxide for treating geothermal steam and fluids.The investigation led to the successful oxidation of hydrogen sulfide during the drilling of steam wells. This was accomplished by the injection of hydrogen peroxide and sodium hydroxide into the steam, using separate spray nozzles. The process presently is used as required by well drillers in the Geysers field. In a second part of the investigation, on a laboratory scale, hydrogen sulfide in steam condensate from a Geysers field geothermal power plant was oxidized with hydrogen peroxide. In this process, trace amounts of iron salts or excess hydrogen peroxide were used to reduce the reaction time to put it within the required limits. The process was modified by Pacific Gas and Electric Co. to improve sulfide removal in its geothermal power plants. Description of Geothermal Processes Well Drilling The hydrogen-peroxide/sodium-hydroxide injections are started when the drill bit penetrates the steam reservoir. Thereafter, the injections continue for about 16 days, the time required to complete the well. This is termed the air drilling phase. Steam production increases from zero at the beginning of the air drilling phase to essentially full capacity of the well at the time of completion. Hydrogen sulfide is a normal constituent of the steam and is released to the atmosphere during the air drilling phase after flowing through a blooie line (a steel pipe) leading to an atmospheric separator (Fig. 1). This is used to suppress noise and remove particulates. Power Generation Seven to 12 wells are used to supply the 454 000 kg/h (1 million lbm/hr) of steam for each 55-MW turbine. JPT P. 914^

Overview of Geothermal Energy Developments: ABSTRACT

Exploration for geothermal resources includes evaluation of the volcanic history, regional geology and hydrology, geochemistry of hot springs, and use of selected geophysical methods to determine temperature, heat flow, and structure of prospective areas. Geothermal energy is primarily used for electric power generation. At the Geysers field in northern California, geothermal energy has proved to be a viable, mechanically reliable, and environmentally acceptable resource. The field competes economically with alternative forms of power generation such as oil, gas, nuclear, and hydroelectric. The Geysers field is an example of a vapor-dominated geothermal reservoir. The field produces 630 Mw, with a total capacity estimated to be about 2,000 Mw. It is the only geothermal field used to generate significant quantities of electricity in the United States. Other areas experiencing active development are the Imperial Valley of California, Baca area of New Mexico, and Roosevelt area of Utah. Overall, plans have been announced for nine power plants at seven sites, with a total generating capacity of 300 Mw. The new areas are all liquid-dominated systems. The Department of Energy estimates that 15,000 to 20,000 Mw of geothermal power can be developed in the western United States in the next 2 decades. With improved exploration, drilling, and utilization technology, it has been estimated that several times this amount of power can be developed, provided that delays due to environmental and legal/institutional issues can be resolved. End_of_Article - Last_Page 761------------

Geysers Field Trip

The Geology and Geophysics of the Geysers Geothermal Area Field Trip on Sunday preceding the 1978 Fall Meeting was full. The bus trip to the area 70 miles north of San Francisco featured detailed discussion of the geology of the area, glimpses of differing strata in road cuts, and a useful summary/handout on the Geysers area.The AGU bus was met by two representatives of the Union Oil Company, which operates numerous generating plants on the geothermal steam. The Union representatives provided everyone with copies of a July 31, 1978, Fortune article detailing Union's continuing geothermal development plans. Currently drilling the Imperial Valley and the Los Alamos area, Union is western states.

Reservoir performance of the Geysers Field

The Geysers Field, located in Northern California, has an installed generating capacity of 502 MWe. Total withdrawal rate is approximately 8-5 million lb/h of steam from 95 wells. Four new generating plants are currently under construction, which will bring the installed capacity to 908 MWe by 1979. The reservoir rock consists of naturally fractured graywacke, a very competent rock with low interstitial porosity and permeability. The reservoir contains dry steam with an initial pressure of approximately 514 psia at sea level datum. Static pressure gradient is that of saturated steam to the total depths of wells drilled to date. The initial development at The Geysers Field occurred in an area which has two shallow dry steam anomalies. Recent studies have shown that the steam in these anomalies is being fed through fractures connecting them with the deeper regional fracture system. Development of the regional system has created two distinct pressure sinks. The larger of the two pressure sinks is in the oldest and most developed portion of the field. This sink has grown larger with the addition of new production capacity. There is no pressure interference between the two sinks, but pressure interference between wells in a given pressure sink is very rapid. Pressure behavior at observation wells in these sinks resembles an ideal single-phase system with constant pressure boundaries. The expansion of the field has been the result of continued exploratory drilling and testing of new step-out wells. Based on the successful exploratory wells drilled to date, it is estimated that the generating capacity of The Geysers could reach 1800 MW by the mid-1980s.

Two-Phase, Two-Dimensional Simulation of a Geothermal Reservoir

Abstract A numerical mathematical model for simulating production from a two-phase geothermal reservoir production from a two-phase geothermal reservoir was developed and tested. The model was a two-dimensional areal or cross-sectional unsteadystate description of the flow of mass and heat within an anisotropic, heterogeneous, porous medium containing a single-component, two-phase fluid. Flow in the production well was. taken to be one dimensional and steady state, using an approximate representation of a two-phase mixture. A totally implicit solution scheme was used. The simulator was used to investigate the effects of various levels of porosity, permeability, and initial pressure and liquid-phase saturation distributions on production. The numerical simulator was tested for a wide variety of conditions and was found to be stable for large time steps. Based on the numerical results, the behavior of a two-phase geothermal reservoir was classified into three types, depending on the initial liquid saturation. It was found that superheated regions formed more readily in reservoirs of low porosity and permeability. Introduction A geothermal system occurs as a heat anomaly that can be explained as follows. The earth's interior is hotter than its surface. This difference produces a temperature gradient that, in turn, produces a temperature gradient that, in turn, provides a measure of the heat flow rate. The provides a measure of the heat flow rate. The average heat flux for the earth is 1.5 mu cal/sq cm-sec. A geothermal system involves a flux that is 1 1/2 to 5 times higher than the average. Consequently, a geothermal system occurs as an anomaly in terms of heat flow. A high heat flux, along with surface seeps, is indicative of a geothermal system. Since the main mode of heat transfer within a geothermal fluid reservoir is convection, the reservoir itself is called a hydrothermal convention system. Hydrothermal convection systems have been classified into two types based on the physical state of the dominant pressure-controlling physical state of the dominant pressure-controlling phase: hot-water systems and vapor-dominated phase: hot-water systems and vapor-dominated system. In hot-water systems, fluids exist within the reservoir mostly in the liquid state and generally produce from 70 to 90 percent of their total mass as water at the surface. Vapor-dominated systems generally produce dry to superheated steam, and fluids exist within the reservoir mostly in the vapor state, Surface manifestations will usually take the form of fumaroles, mud pots, mud volcanoes, turbid pools, and acid-leached ground. Only three known areas exist as this type of system. These are the Geysers field in California, the Larderello field in Italy, and the Matsukawa field in Japan. The pressures of vapor-dominated systems are below hydrostatic. Also, the initial pressures and temperatures in vapor-dominated systems are very close to the temperature and pressure relating to the maximum enthalpy of saturated steam - 236 degrees C and 31.8 kg/sq cm. An explanation for this behavior has been given by James and by White et al. Reservoir engineering principles have been used to study production aspects of geothermal systems only during the last decade. In that time, relatively few models have been developed that simulate the production from a geothermal reservoir containing production from a geothermal reservoir containing both a liquid and a vapor phase. In fact, only three models have assumed the presence of a two-phase Hudd within a geothermal presence of a two-phase Hudd within a geothermal reservoir. One of these models, developed by Donaldson, was a steady-state, one-dimensional description of two-phase flow within porous media, but did not simulate production. The other two models, those of Whiting and Ramey and of Brigham and Morrow, were lumped-parameter formulations. Thus, objective of this paper is to develop a model that simulates production from a two-phase geothermal reservoir in greater detail than has been done previously. SPEJ P. 171

The Reich case: Economic implications of depletion allowances

The Reich case was tried in the 1969 Tax Court of the United States and the Court held that geothermal steam is a gas and is an exhaustible resource at The Geysers field. Accordingly, all geothermal steam producers are now entitled to deduct as current expense the intangible costs of developing and drilling geothermal steam wells and all producers who can demonstrate that their geothermal steam resource is depletable are entitled to what is now a 22 percent depletion allowance. The key expert witness in the case was Dr. Henry J. Ramey, Jr. and a summary is presented of his monograph which was submitted as evidence. His conclusion, based on a reservoir engineering analysis, was that the geothermal resource at the Big Geysers area had, as of 1968, a 20 to 46 years of productive life remaining. In the economics portion of the paper, it is demonstrated that the corporate income tax discriminates against risky and capital-intensive industries such as oil and gas and geothermal. The central economic argument in favor of percentage depletion allowances and expensing privileges is that these provisions remove the discriminatory bias of corporate income taxes. The economic consequences of depletion allowances are 1. — a short- and long-run increase in production; 2. — a short- and long-run increase in investment in renewal-exploration, discovery, and development; 3. — lower prices; 4. — a ratio of reserves to output—the Life Index—which tends to be constant; 5. — a short-run increase in profits which encourages the entry of new firms and a long-run situation in which average rates of return are again equalized across industries.

Geothermal Potential of Southwestern United States: ABSTRACT

The area comprises the states of California, Nevada, Utah, Colorado, New Mexico, and Arizona, and includes the following geologic provinces: the Colorado Plateau, Basin and Range, Sierra Nevada and Southern California batholiths, Great Valley and Coast Ranges of California. This area is considered favorable for geothermal prospecting because of the presence of many hot springs, Tertiary and especially Quaternary volcanism, and faulting of both block and rift type. The Geysers field, the largest geothermal field in the world as well as the only commercially producing End_Page 1444------------------------------ field in the United States, is in the northern Coast Ranges of California about 75 mi north of San Francisco. In the Salton Sea area of the Imperial Valley, California, large flows of steam and geothermal fluids have been obtained, currently uneconomic because of high-mineral content. Twenty miles south of the Mexican border in the same basin, the Cerro Prieto geothermal field produces 75 megawatts and appears to be capable of supplying energy for considerably more power. In the Valles Caldera, near Los Alamos, New Mexico, discovery of a new field has been indicated by recent exploratory drilling. Flows of hot water and flashed steam have been recorded in several areas in Nevada, none of which have proved commercial. Exploration for geothermal resources is in the early stage of activity. A total of 149 exploratory wells has been drilled in 55 different areas. Many of these wells were shallow and not adequately tested. It is too early to predict what the success ratio will be until deeper and more conclusive tests are drilled. To January 1974, exploration has been hampered by the unavailability of public lands, which cover well over half of the prospective territory. Leasing activity during the last few years, coupled with geologic and geophysical work by private industry, and successful utilization of 150 to 225°C waters by the heat-exchange method, suggest that there will be an extensive exploration-drilling program in the next few years that should shed much light on the amount of geothermal reserves present in the southwestern United States and how significant a part this form of energy will play in our total energy picture. End_of_Article - Last_Page 1445------------

Geothermal Energy: ABSTRACT

Geothermal energy is used mostly for electric power generation with a current worldwide installed capacity of about 1,000 Mw. This is equivalent to one nuclear power plant . The only geothermal area in the world completely developed by private enterprise is at The Geysers in northern California, where it has proved to be a viable, mechanically sound, and economic resource, competing with alternative forms of power generation, such as oil, gas, nuclear, and hydro in the Pacific Gas and Electric system. The Geysers field produced 300 Mw and is estimated to have a potential production in excess of 1,000 Mw. The National Petroleum Council estimates that by 1985 about 15,000 Mw of geothermal power can be developed in the western United States. With improved exploration, drilling, and utilization technology, and modification of certain institutional barriers, it has been estimated that geothermal power may be of the order of 75,000 Mw by the year 2000. End_of_Article - Last_Page 798------------

Worldwide Development of Geothermal Industry: ABSTRACT

The total installed capacity of geothermal generating plants in the world today is approximately 630 megawatts (MW), distributed among the following five countries: Italy 340; New Zealand, 190; USA, 50; USSR, 30; and Japan, 20. Approximately half of this present capacity has been installed during the last 10 yr and the success of these installations is stimulating worldwide interest in geothermal energy. Exploration projects are now underway in Mexico, El Salvador, Chile, Turkey, Kenya, China (Taiwan), and the Philippines. Although approximately 30 thermal areas have been drilled in the western United States during the past 10 yr, only two are undergoing active development. The Geysers field in northern California accounts for all the geothermal power production in the United States, and the Salton Sea field in southern California is being developed for the extraction of sodium and calcium chlorides from geothermal brines. The principal incentives for development of geothermal power are: (a) lack of more conventional sources in the market area, and (b) competitive economic position of geothermal power even where other sources are available. Geothermal sources generate low-cost, base-load power even at capacities under 100 MW, making them particularly advantageous in market areas where power demands are still low. Low steam pressures make it necessary to use small generating units, i.e., on the order of 25-50 MW, but total capacities of several hundred megawatts can be expected from a single steam field. All the thermal areas now under investigation share a common regional geologic setting: the areas are located in orogenic zones, where late Tertiary or Quaternary volcanism has taken place. Tectonically the regions are characterized by vertical movements, both uplift and subsidence, which have taken place on normal faults. The geometry of fault-block movement appears to be an important factor in controlling the location of shallow igneous intrusions which are believed to be the source of heat for the high-temperature thermal systems now being exploited for power generation. End_of_Article - Last_Page 564------------

The self-sealing geothermal field

The self-sealing geothermal field