Hydraulic fracturing is a common method employed to increase the production of oil and gas fields. Recently, there has been increased interest in monitoring the microearthquakes induced by hydraulic fracturing as a means of obtaining data to characterize reservoir changeS induced by the injection. Two types of microearthquakes have been observed during hydraulic fracturing. Tensile events have been observed and modeled as the parting of the surfaces of a fracture. A majority of the events observed have been shear-slip events, where two sides of a fault plane slip parallel to each other but in opposite directions. The locations of the microearthquakes can be analyzed to determine regions where significant seismic energy was released, which presumably are regions where injected fluid penetrated into the rock along pre-existing fractures or zones of weakness. The spatial patterns in the locations can be analyzed to fine regions where events cluster along planes, which are interpreted to be the dominant fluid flow paths. Imaging methods can also be applied to the travel time and waveform data to obtain direct evidence for the locations of the fractures or fracture zones. 27 refs., 2 figs.

K-Ar and {sup 40}Ar/{sup 39}Ar ages from the Lathrop Wells volcanic center, Nevada, and from the Cima volcanic field, California, indicate that the recently reported 20-ka age estimate for the Lathrop Wells volcanic center is incorrect. Instead, an age of 119 {plus_minus} 11 to 141 {plus_minus} 10 ka is indicated for the Lathrop Wells volcanic center. This age corrected is concordant with the ages determined by two independent isotopic geochronometric techniques and with the stratigraphy of surficial deposits in the Yucca Mountain region. In addition, paleomagnetic data and radiometric age data indicate only two volcanic events at the Lathrop Wells volcanic center that are probably closely linked in time, not as many as five as recently reported. 32 refs., 2 figs., 2 tabs.

Flow testing and heat extraction experiments in prototype Hot Dry Rock (HDR) geothermal reservoirs have uncovered several challenges which must be addressed before commercialization of the technology is possible. Foremost among these is the creation of a reservoir which simultaneously possesses high permeability pathways and a large volume of fractured rock. The current concept of heat extraction -- a steady state circulation system with fluid pumping from the injection well to a single, low pressure production well -- may limit our ability to create heat extraction systems which meet these goals. A single injection well feeding two production wells producing fluid at moderate pressures is shown to be a potentially superior way to extract heat. Cyclic production is also demonstrated to have potential as a method for sweeping fluid through a larger volume of rock, thereby inhibiting flow channeling and increasing reservoir lifetime. 10 refs., 4 figs., 2 tabs.

Each year the Geothermal Division of the US Department of Energy conducts an in-depth review of its entire geothermal R D program. The conference serves several purposes: a status report on current R D activities, an assessment of progress and problems, a review of management issues, and a technology transfer opportunity between DOE and the US geothermal community. This year's conference, Program Review IX, was held in San Francisco on March 19--21, 1991. The theme of this review was The Geothermal Partnership -- Industry, Utilities, and Government Meeting the Challenges of the 90's.'' The importance of this partnership has increased markedly as demands for improved technology must be balanced with available research resources. By working cooperatively, the geothermal community, including industry, utilities, DOE, and other state and federal agencies, can more effectively address common research needs. The challenge currently facing the geothermal partnership is to strengthen the bonds that ultimately will enhance opportunities for future development of geothermal resources. Program Review IX consisted of eight sessions including an opening session. The seven technical sessions included presentations by the relevant field researchers covering DOE-sponsored R D in hydrothermal, hot dry rock, and geopressured energy and the progress associated with the Long …

Production system design studies often include site-specific silica scaling field experiments, conducted because the onset and rate of scaling are believed difficult to predict, particularly at relatively low levels of oversaturation such as may exist in separators, flowlines, and injection wells. However, observed scaling occurrences (Cerro Prieto, Dixie Valley, Svartsengi, Otake, Hatchobaru, Milos, experimental work) actually conform fairly well to existing theory and rate equations. It should be possible to predict low level scaling with sufficient confidence for production and injection system design and, in cases where oversaturation is allowed, to design systems with foresight to suppress or manage the scale which develops. A promising suppression technology is fluid pH reduction by mixing with non-condensible gases and/or condensate. Calculations for injection lines at Uenotai geothermal field indicate molecular deposition at rates of 0.1 to 1 mm/yr, and some potential for particle deposition at points of turbulence, which can be suppressed by an order of magnitude with about 500 ppm CO{sub 2}. Further improvements of predictive technique will benefit from more uniformity in designing experiments, reporting results, and reporting measurements of scaling in actual production systems.

In the past two years, three very significant advances have been made in our understanding of the behavior and properties of Hot Dry Rock (HDR) geothermal reservoirs. First, we have determined that the rate of water loss from such deep, engineered reservoirs -- previously thought to be a major problem -- is minimal in the absence of reservoir growth, even under considerably elevated operating pressures. Second, a new method has been developed for determining the volume of hot fractured rock accessible to circulating water: i.e., the size of the HDR reservoir. This technique, after appropriate verification, will allow operators to actually quantify the size of the available thermal resource before power plant design and installation. Finally, the partitioning of reservoir fluid storage between the matrix microcracks and the network of joints has been measured at two pressure levels, one above and one below the joint opening pressure for the most favorably oriented set of joints. The observed difference in the storage partitioning above and below this threshold pressure is quite pronounced, particularly for the microcrack fraction. For any given HDR site, the measurement of this pressure-dependent storage partitioning may provide guidance as to the optimal method of reservoir production. 6 …

Mt. Pinatubo is one of several recent-age volcanoes along the west Luzon volcanic arc. A fumarole near the suminit emits gases with magmatic characteristics. Several thermal springs on the east and west flanks yield various fluid typos, including neutral chloride and bicarbonate. Three wellbores probed the Mt. Pinatubo caldera from elevations of +1230 through -1600 mRSL. Trajectories may be described as: central, crossing a boundary wall from the inside, and skirting a wall [probably] on the inside. Brine discharges indicate severe evapo-concentration effects accompanied by other phenomena. Severity of evapo-concentration indicates low fluid mobility near the wellbores. Large variations for ratios of component concentrations were observed, indicating negligible natural circulation (mixing). Implications about fluid movements and heat transfer processes are explored. Three components of steam can be quantified and all are significant: separate entry, adiabatic boiling, and boiling by rock heat.

Article highlights the contributions of American Indians during World War II, which included the efforts of individual soldiers and people groups as well as the use of land and resources on reservations for the war effort. Duane K. Hale emphasizes the underrepresentation of these activities in historical record and discusses them here.

Acid chloride corrosion of geothermal well casings, production piping and power plant equipment has resulted in costly corrosion damage, frequent curtailments of power plants and the permanent shut-in of wells in certain areas of The Geysers. Techniques have been developed to mitigate these corrosion problems, allowing continued production of steam from high chloride wells with minimal impact on production and power generation facilities.The optimization of water and caustic steam scrubbing, steam/liquid separation and process fluid chemistry has led to effective and reliable corrosion mitigation systems currently in routine use at The Geysers. When properly operated, these systems can yield steam purities equal to or greater than those encountered in areas of The Geysers where chloride corrosion is not a problem. Developments in corrosion monitoring techniques, steam sampling and analytical methodologies for trace impurities, and computer modeling of the fluid chemistry has been instrumental in the success of this technology.

Lost circulation is the loss of drilling fluid from the wellbore to fractures or pores in the rock formation. In geothermal drilling, lost circulation is often a serious problem that contributes greatly to the cost of the average geothermal well. The Lost Circulation Technology Development Program is sponsored at Sandia National Laboratories by the US Department of Energy. The goal of the program is to reduce lost circulation costs by 30--50{percent} through the development of mitigation and characterization technology. This paper describes the technical progress made in this program during the period April, 1990--March, 1991. 4 refs., 15 figs., 1 tab.

The Interstate Oil and Gas Compact Commission (IOGCC) in cooperation with US Department of Energy (DOE) has developed a workshop format to allow state regulatory officials and industry representatives the opportunity to participate in frank and open discussions on issues of environmental regulatory compliance. The purpose in providing this forum is to assist both groups in identifying the key barriers to the economic recoverability of domestic oil and gas resources while adequately protecting human health and the environment. The following topics were discussed, groundwater protection; temporarily abandoned and idle wells; effluent discharges; storm water runoff; monitoring and compliance; wetlands; naturally occurring radioactive materials; RCRA reauthorization and oil pollution prevention regulation. At the conclusion, all of the participants were asked to complete a questionnaire which critiqued the day activities. A discussion of each of the issues is made a part of this report as is a summary of the critique questionnaire which were received.

The Interstate Oil and Gas Compact Commission (IOGCC) in cooperation with US Department of Energy (DOE) has developed a workshop format to allow state regulatory officials and industry representatives the opportunity to participate in frank and open discussions on issues of environmental regulatory compliance. The purpose of providing this forum is to assist both groups in identifying the key barriers to the economic recoverability of domestic oil and gas resources while adequately protecting human health and the environment. The IOGCC and DOE staff worked with key state and industry representatives to develop a list of appropriate regulatory and industry representatives to be invited to participate. These same industry and regulatory representatives also provided a prioritized list of topics to be discussed at this workshop. After the topic leader set out the issue, views of those present were solicited. In almost every case, both the industry representatives and the regulatory personnel spoke with candor in discussing the problems. Common points of discussion for each topic were: (1) conflicting state and federal regulations; (2) conflicting regulations or permit requirements established by different state agencies; (3) increasing compliance costs; and (4) regulatory constraints that will result in ``no net growth`` in California oil …

The main objective of the DOE/GD-funded Geothermal Reservoir Technology Program at Lawrence Berkeley Laboratory is the development and testing of new and improved methods and tools needed by industry in its effort to delineate, characterize, evaluate, and exploit hydrothermal systems for geothermal energy. This paper summarizes the recent and ongoing field, laboratory, and theoretical research activities being conducted as part of the Geothermal Reservoir Technology Program. 28 refs., 4 figs.

Tracer technology can be successfully applied to many leak-checking and monitoring evaluations of operating systems (e.g., building HVACs), manufacturing processes and products (e.g., air conditioners), and subsurface components and systems (e.g., underground storage tanks). Perfluorocarbon tracer (PFT) technology is the most sensitive of all tracer technologies because the ambient background levels of the five (5) routinely-used PFTs are in the range of parts per 10{sup 15} parts of air (i.e., parts per quadrillion-ppq) and this technology's instrumentation can measure down to those levels. The effectiveness of this technology is achieved both in terms of cost (very little PFT need to be used) and detectability; for example, very small leaks can be rapidly detected. The PFT compounds, which are environmentally and biologically safe to use, are commercially available as are the sampling and analysis instrumentation. This presentation concerns (1) the steps being taken to commercialize this technology, (2) new applications of processes currently under study, and (3) applications in areas of use that will be particularly beneficial to the environment. 21 refs., 2 figs., 2 tabs.

The Clearlake Project is a three-party collaboration between the California Energy Commission, City of Clearlake, and Los Alamos National Laboratory. It aims to develop a deep hot, dry geothermal resource under the city. The project is funded by the Commission, and administered by the City. Technical operations are conducted by Laboratory staff and resources seconded from the Hot Dry Rock program. In addition to the normal geothermal exploration problems of predicting geological and geophysical properties of the subsurface, there are uncertainties as to what further material and environmental parameters are relevant, and how they might be measured. In addition to technical factors, policy objectives are an influence in choosing the most appropriate development scenario. 11 refs., 4 figs.

Petrologic and geochemical studies of basaltic rocks in the Yucca Mountain region are currently focused on understanding the evolution of volcanism in the Crater Flat volcanic field and the mechanisms of polycyclic volcanism at the Lathrop Wells volcanic center, the youngest center in the Crater Flat volcanic field. Geochemical and petrologic data indicate that the magma chambers which supplied the volcanic centers in Crater Flat became situated at greater crustal depths as the field evolved. Deep magma chambers may be related to a waning magma flux that was unable to sustain upper crystal magma conduits and chambers. Geochemical data from the Lathrop Wells volcanic center indicate that eruptive units identified from field and geomorphic relationships are geochemically distinct. The geochemical variations cannot be explained by fractional crystallization of a single magma batch, indicating that several magma batches were involved in the formation of the Lathrop Wells center. Considering the low magma flux in the Yucca Mountain region in the Quaternary, the probability of several magma batches erupting essentially simultaneously at Lathrop Wells in considered remote. It is more likely that the Lathrop Wells center was formed by a series of eruptions that took place over many thousands of years. The …

The Nagqu geothermal field is a single-phase, liquid-dominated system at reservoir conditions, having a high gas content. This field is located at an elevation of about 4,500 m (asl), in the vicinity of the City of Nagqu, which is one of the most important cities of Tibet.The reservoir rock is made of a highly fractured, low-permeability sedimentary sequence. During the implementation of the study described in this paper, fluid production was mainly obtained from two out of four possible productive wells. The main fault systems are located in a NE-SW and E-W directions, which seem to control fluid movement at depth. The geothermal field is restricted to a small area where hydrothermal manifestations are located. Reservoir temperature is 114 C, gas content is in the range of 0.5 to 0.6% by mass, being mainly CO{sub 2}. Reservoir transmissivity in the area of the wells is very high. Reservoir response to changes in flow rate in any of the producing wells could be detected almost immediately in the observation wells, which were distant between 300 to 900 m, depending on the production-observation well arrangement. Calcium carbonate scaling was present in all producing wells. This deposition was controlled by the CO{sub 2} …

A conceptual geologic model of the Roosevelt Hot Springs hydrothermal system was developed by a review of the available literature. The hydrothermal system consists of a meteoric recharge area in the Mineral Mountains, fluid circulation paths to depth, a heat source, and an outflow plume. A conceptual model based on the available data can be simulated in the native state using parameters that fall within observed ranges. The model temperatures, recharge rates, and fluid travel times are sensitive to the permeability in the Mineral Mountains. The simulation results suggests the presence of a magma chamber at depth as the likely heat source. A two-dimensional study of the hydrothermal system can be used to establish boundary conditions for further study of the geothermal reservoir.

A conceptual geologic model of the Roosevelt Hot Springs hydrothermal system was developed by a review of the available literature. The hydrothermal system consists of a meteoric recharge area in the Mineral Mountains, fluid circulation paths to depth, a heat source, and an outflow plume. A conceptual model based on the available data can be simulated in the native state using parameters that fall within observed ranges. The model temperatures, recharge rates, and fluid travel times are sensitive to the permeability in the Mineral Mountains. The simulation results suggests the presence of a magma chamber at depth as the likely heat source. A two-dimensional study of the hydrothermal system can be used to establish boundary conditions for further study of the geothermal reservoir. 33 refs., 9 figs.

Injection of atmospheric air mixed with cold water has been occurring since 1982 at the Los Azufres geothermal field. Several chemical and thermodynamical evidences show that air injection into this fractured hydrothermal system could be considered as a long term natural tracer test. Nitrogen and Argon separated from the air mixture migrate, under the action of the induced injection-extraction gradient, from reinjection sectors to production zones following preferential paths closely related to high permeability conduits. A coarse numerical estimation of the average permeability tensor existing at Tejamaniles, the southern sector, explains the unsuccessful recovery of the artificial tracer tests performed in past years: the anisotropic nature of the fractured volcanic rock would demand considerably quantities of tracer in order to be detected at the producing wells, especially when fluid extraction was low. At the same time concentrations of calcium, cesium, chloride, potassium, rubidium and sodium, are increasing in the liquid produced by the oldest wells of this field's sector.

A new approach to the analysis of x-ray absorption fine structure (XAFS) data is presented. It is based on the use of radial distribution functions directly calculated from a single-particle ion hamiltonian containing model potentials. The starting point of this approach is the statistical average of the XAFS for an atomic pair. This average can be computed using a radial distribution function (RDF), which can be expressed in terms of the eigenvalues and wavefunctions associated with the model potential. The pair potential describing the ionic motion is then expressed in terms of parameters that are determined by fitting this statistical average to the experimental XAFS spectrum. This approach allow the use of XAFS as a tool for mapping near-neighbor interatomic potentials, and allows the treatment of systems which exhibit strongly anharmonic potentials which can be treated by perturbative methods. Using this method we have analyzed the high temperature behavior of the oxygen contributions to the Fe K-edge XAFS in the ferrosilicate minerals andradite (Ca{sub 3}Fe{sub 2}Si{sub 3}O{sub 12}) and magnesiowustite (Mg{sub 0.9}Fe{sub 0.1}O). Using a temperature dependent anharmonic correction derived from these model compounds, we have found evidence for a local structural change in the Fe-O coordination environment upon melting …

Fundamental research related to organic geochemistry, fluid-rock interactions, and the processes by which fluids migrate through basins has long been a part of the U.S. Department of Energy Geosciences program. Objectives of this program were to emphasize those principles and processes which would be applicable to a wide range of problems associated with petroleum discovery, occurrence and extraction, waste disposal of all kinds, and environmental management. To gain a better understanding of the progress being made in understanding basinal fluids, their geochemistry and movement, and related research, and to enhance communication and interaction between principal investigators and DOE and other Federal program managers interested in this topic, this workshop was organized by the School of Geology and Geophysics and held in Norman, Oklahoma in November, 1991.

The principal objective of this symposium is to review the available information on fractured/faulted terrains in terms of a coherent hydrogeologic model of ground-water fluid flow and transport, particularly as it pertains to the Yucca Mountain region. This review addresses the influence and significance of fractures on ground-water flow and the transport of conservative-species solutes within the context of the hydrogeologic setting of the Yucca Mountain area. The relations between fluid flow and fractured or faulted host rock are examined integrally from information on geologic, seismologic, hydrologic, and geomechanical properties of the system. The development of new hydrogeologic approaches that incorporate information from this integrated database are contrasted with more standard approaches toward understanding flow in fractured reservoirs. Ground-water flow in both the unsaturated zone and the saturated zone are considered. The application of various models of flow is addressed, examples include porous-media equivalent and discontinuum fracture-network models. Data and interpretations from the Yucca Mountain area are presented to establish a context for information exchange. The symposium includes discussions relevant to technical considerations for characterizing the Yucca Mountain area hydrogeology. On the basis of these discussions, CASY has compiled this document in order to formally summarize the proceedings and communicate …

Vapor-dominated geothermal systems are proposed to originate by downward extension (by the ''heat pipe'' mechanism) into hot dry fractured rock above a large cooling igneous intrusion. High temperature zones found by drilling are shallow parts of the original hot dry rock where the penetration of the vapor reservoir was limited, and hot dry rock may extend under much of these reservoirs. An earlier hot water geothermal system may have formed during an early phase of the heating episode.