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• 1. [Image] Geological and Geophysical Analysis of Coso Geothermal Exploration Hole No. 1 (CGEH-1), Coso Hot Springs KGRA, California

  	The Coso Geothermal Exploration Hole number one (CGEH-1) was drilled in the Coso Hot Springs KGRA, California from September 2 to December 2, 1977. Chip samples were collected at ten foot intervals and ...
  	Citation × Citation Citation Abstract Copy Title: Geological and Geophysical Analysis of Coso Geothermal Exploration Hole No. 1 (CGEH-1), Coso Hot Springs KGRA, California Author: Galbraith, R.M. Year: 1978 The Coso Geothermal Exploration Hole number one (CGEH-1) was drilled in the Coso Hot Springs KGRA, California from September 2 to December 2, 1977. Chip samples were collected at ten foot intervals and extensive geophysical logging surveys were conducted to document the geologic character of the geothermal system as penetrated by CGEH-1. The major rock units encountered include a mafic metamorphic sequence and a leucogranite which intruded the metamorphic rocks. Only weak hydrothermal alteration was noted in these rocks. Drillhole surveys and drilling rate data indicate that the geothermal system is structurally controlled and that the drillhole itself was strongly influenced by structural zones. Water chemistry indicates that this geothermal resource is a hot-water rather than a vapor-dominated system. Several geophysical logs were employed to characterize the drillhole geology. The natural gamma and neutron porosity logs indicate gross rock type and the acoustic logs indicate fractured rock and potentially permeable zones. A series of temperature logs run as a function of time during and after the completion of Drilling were most Useful in delineating the zones of maximum heat flux. Convective heat flow and temperatures greater than 350/sup 0/F appear to occur only along an open fracture system encountered between depths of 1850 and 2775 feet. Temperature logs indicate a negative thermal gradient below 3000 feet Title: Geological and Geophysical Analysis of Coso Geothermal Exploration Hole No. 1 (CGEH-1), Coso Hot Springs KGRA, California Author: Galbraith, R.M. Year: 1978 The Coso Geothermal Exploration Hole number one (CGEH-1) was drilled in the Coso Hot Springs KGRA, California from September 2 to December 2, 1977. Chip samples were collected at ten foot intervals and extensive geophysical logging surveys were conducted to document the geologic character of the geothermal system as penetrated by CGEH-1. The major rock units encountered include a mafic metamorphic sequence and a leucogranite which intruded the metamorphic rocks. Only weak hydrothermal alteration was noted in these rocks. Drillhole surveys and drilling rate data indicate that the geothermal system is structurally controlled and that the drillhole itself was strongly influenced by structural zones. Water chemistry indicates that this geothermal resource is a hot-water rather than a vapor-dominated system. Several geophysical logs were employed to characterize the drillhole geology. The natural gamma and neutron porosity logs indicate gross rock type and the acoustic logs indicate fractured rock and potentially permeable zones. A series of temperature logs run as a function of time during and after the completion of Drilling were most Useful in delineating the zones of maximum heat flux. Convective heat flow and temperatures greater than 350/sup 0/F appear to occur only along an open fracture system encountered between depths of 1850 and 2775 feet. Temperature logs indicate a negative thermal gradient below 3000 feet Close

• 2. [Image] Geological and Geophysical Study of the Origin of the Warm Springs in Bath County, Virginia. Final Report, June 1, 1975--April 30, 1976

  	The results of heat flow determinations and a reconnaissance dipole electrical resistivity survey in Bath County are described. A geologic map was compiled based on published maps and supported by reconnaissance ...
  	Citation × Citation Citation Abstract Copy Title: Geological and Geophysical Study of the Origin of the Warm Springs in Bath County, Virginia. Final Report, June 1, 1975--April 30, 1976 Author: Costain, J.K. Year: 1976 The results of heat flow determinations and a reconnaissance dipole electrical resistivity survey in Bath County are described. A geologic map was compiled based on published maps and supported by reconnaissance geologic mapping in areas where published maps were not available. A regional bipole--dipole electrical resistivity survey was made in order to detect the presence of resistivity lows that might be associated with a geothermal system at depth. A single hole was drilled to a depth of approximately 300 m (approx. 1000 feet) to obtain a heat flow value that is representative of the area. The data were used to attempt to arrive at a model that unambiguously explains the origin of the thermal springs Title: Geological and Geophysical Study of the Origin of the Warm Springs in Bath County, Virginia. Final Report, June 1, 1975--April 30, 1976 Author: Costain, J.K. Year: 1976 The results of heat flow determinations and a reconnaissance dipole electrical resistivity survey in Bath County are described. A geologic map was compiled based on published maps and supported by reconnaissance geologic mapping in areas where published maps were not available. A regional bipole--dipole electrical resistivity survey was made in order to detect the presence of resistivity lows that might be associated with a geothermal system at depth. A single hole was drilled to a depth of approximately 300 m (approx. 1000 feet) to obtain a heat flow value that is representative of the area. The data were used to attempt to arrive at a model that unambiguously explains the origin of the thermal springs Close

• 3. [Image] Downhole Electrical Detection of Hydraulic Fractures in GT-2 and EE-1

  	Electrical geophysical methods including mise a la masse and self-potential (SP) for determination of hydraulic fracture characteristics were used at the hot dry rock geothermal project. Electrical and ...
  	Citation × Citation Citation Abstract Copy Title: Downhole Electrical Detection of Hydraulic Fractures in GT-2 and EE-1 Author: Kintzinger, P.R. Year: 1977 Electrical geophysical methods including mise a la masse and self-potential (SP) for determination of hydraulic fracture characteristics were used at the hot dry rock geothermal project. Electrical and induction logs indicated that the resistivity contrast between the granite and 200/sup 0/C water at the 2926-m (9600-ft) depth is a factor of 1000 or more. Thus the water in a hydraulic fracture, formed to connect two adjacent deep holes, is a good conductor compared to the confining granite. Mise a la masse-type measurements were made to help determine the characteristics for hydraulic fractures formed in each of the two geothermal holes GT-2 and EE-1. Once a hydraulic fracture has been formed, mise a la masse effects are obtained both with the fracture pressurized above hydrostatic and when depressurized to hydrostatic. This indicates that once the fracture has been created, enough natural propping exists that a conductive zone persists even when the fracture is deflated. A fracture was formed in a 18-m (60-ft) zone immediately below 1957 m (6420 ft) in EE-1. Later a set of SP logs was run in this zone with no pressure, with pressure building, with pressure decreasing, and again with the fracture depressurized. Results show that during times of change of parameters in hydraulically fractured regions in the hole, natural SP logging helps to determine the position of the fracture. However, after a fracture has come to equilibrium with fluid parameters such as temperature, pressure, salinity, and pH, an effect of the fracture may not be evident. Self-potential logs provide an excellent method for locating the bottom of steel casing that has been set in the hole Title: Downhole Electrical Detection of Hydraulic Fractures in GT-2 and EE-1 Author: Kintzinger, P.R. Year: 1977 Electrical geophysical methods including mise a la masse and self-potential (SP) for determination of hydraulic fracture characteristics were used at the hot dry rock geothermal project. Electrical and induction logs indicated that the resistivity contrast between the granite and 200/sup 0/C water at the 2926-m (9600-ft) depth is a factor of 1000 or more. Thus the water in a hydraulic fracture, formed to connect two adjacent deep holes, is a good conductor compared to the confining granite. Mise a la masse-type measurements were made to help determine the characteristics for hydraulic fractures formed in each of the two geothermal holes GT-2 and EE-1. Once a hydraulic fracture has been formed, mise a la masse effects are obtained both with the fracture pressurized above hydrostatic and when depressurized to hydrostatic. This indicates that once the fracture has been created, enough natural propping exists that a conductive zone persists even when the fracture is deflated. A fracture was formed in a 18-m (60-ft) zone immediately below 1957 m (6420 ft) in EE-1. Later a set of SP logs was run in this zone with no pressure, with pressure building, with pressure decreasing, and again with the fracture depressurized. Results show that during times of change of parameters in hydraulically fractured regions in the hole, natural SP logging helps to determine the position of the fracture. However, after a fracture has come to equilibrium with fluid parameters such as temperature, pressure, salinity, and pH, an effect of the fracture may not be evident. Self-potential logs provide an excellent method for locating the bottom of steel casing that has been set in the hole Close

• 4. [Image] Dipole-Dipole Resistivity Survey of a Portion of the Coso Hot Springs KGRA, Inyo County, California

  	A detailed electrical resistivity survey of 54 line-km was completed at the Coso Hot Springs KGRA in September 1977. This survey has defined a bedrock resistivity low at least 4 sq mi (10 sq km) in extent ...
  	Citation × Citation Citation Abstract Copy Title: Dipole-Dipole Resistivity Survey of a Portion of the Coso Hot Springs KGRA, Inyo County, California Author: Fox, R.C. Year: 1978 A detailed electrical resistivity survey of 54 line-km was completed at the Coso Hot Springs KGRA in September 1977. This survey has defined a bedrock resistivity low at least 4 sq mi (10 sq km) in extent associated with the geothermal system at Coso. The boundaries of this low are generally well defined to the north and west but not as well to the south where an approximate southern limit has been determined. The bedrock resistivity low merges with an observed resistivity low over gravel fill east of Coso Hot Springs. A complex horizontal and vertical resistivity structure of the surveyed area has been defined which precludes the use of layered-earth or two-dimensional interpretive models for much of the surveyed area. In general the survey data indicate that a 10 to 20 ohm-meter zone extends from near surface to a depth greater than 750 meters within the geothermal system. This zone is bordered to the north and west by bedrock resistivities greater than 200 ohm-meters and to the south by bedrock resistivities greater than 50 ohm-meters. A combination of observed increases in: (1) fracture density (higher permeability), (2) alteration (high clay content), and (3) temperatures (higher dissolved solid content of ground water) within the bedrock low explain its presence Title: Dipole-Dipole Resistivity Survey of a Portion of the Coso Hot Springs KGRA, Inyo County, California Author: Fox, R.C. Year: 1978 A detailed electrical resistivity survey of 54 line-km was completed at the Coso Hot Springs KGRA in September 1977. This survey has defined a bedrock resistivity low at least 4 sq mi (10 sq km) in extent associated with the geothermal system at Coso. The boundaries of this low are generally well defined to the north and west but not as well to the south where an approximate southern limit has been determined. The bedrock resistivity low merges with an observed resistivity low over gravel fill east of Coso Hot Springs. A complex horizontal and vertical resistivity structure of the surveyed area has been defined which precludes the use of layered-earth or two-dimensional interpretive models for much of the surveyed area. In general the survey data indicate that a 10 to 20 ohm-meter zone extends from near surface to a depth greater than 750 meters within the geothermal system. This zone is bordered to the north and west by bedrock resistivities greater than 200 ohm-meters and to the south by bedrock resistivities greater than 50 ohm-meters. A combination of observed increases in: (1) fracture density (higher permeability), (2) alteration (high clay content), and (3) temperatures (higher dissolved solid content of ground water) within the bedrock low explain its presence Close