Fault-dominated geothermal reservoirs
Geothermal fields in three geologic provinces of the western US are being developed utilizing major fault systems as the primary reservoirs: Heber, California, in the Salton Trough rift basin; Beowawe, Nevada, in the northern Basin and Range; and Roosevelt Hot Springs, Utah, at the eastern boundary of the Basin and Range. Geologic definition of the fault system controlling the thermal water plume was complicated in each case by lateral flow of thermal waters in shallow aquifers and by skewing of the rising thermal water plume by regional meteoric water movement. Spacing of development wells in faults is determined by permeability as measured during well testing. Parallel strands of faults within a zone may not be in good pressure communication even though tied to the same ultimate source of geothermal fluids at depth. The final size of development is determined by the area of the fault that is permeable and carrying waters of commercial temperatures. The key elements of the Heber geothermal field are: impermeable capping clays at 1000 to 2000 ft, a shallow matrix permeability reservoir in deltaic sandstones from 2000 to 4500 ft, and a major north-northeast-trending normal fault carrying thermal through highly indurated sediments below 4500 ft. The normal fault controlling the system is a tensional structure formed in an area subject to dextral shear bounded by northwest-trending strike-slip faults. Thermal waters rise at temperatures greater than 390/sup 0/F (199/sup 0/C) from south to north in the normal fault. Outflow into permeable sandstones above depths of 4500 ft is spread to the north-northwest by regional ground-water flow. These structural and hydrodynamic features were defined by dipmeter data, core analysis, porosity logs, temperature data, lost circulation zones encountered during drilling, and production zones identified on spinner surveys.
- Research Organization:
- Chevron Resources Co., San Francisco, CA
- OSTI ID:
- 6247649
- Report Number(s):
- CONF-870606-
- Journal Information:
- AAPG (Am. Assoc. Pet. Geol.) Bull.; (United States), Vol. 71:5; Conference: American Association of Petroleum Geologists annual meeting, Los Angeles, CA, USA, 7 Jun 1987
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
GEOTHERMAL FIELDS
RESERVOIR ROCK
GEOLOGIC FAULTS
GEOTHERMAL FLUIDS
NEVADA
PERMEABILITY
POROSITY
RIFT ZONES
SANDSTONES
SEDIMENTARY BASINS
UTAH
FEDERAL REGION IX
FEDERAL REGION VIII
FLUIDS
GEOLOGIC FRACTURES
GEOLOGIC STRUCTURES
NORTH AMERICA
ROCKS
SEDIMENTARY ROCKS
USA
150201* - Geology & Hydrology of Geothermal Systems- USA- (-1989)