MICRO-SEISMICITY, FAULT STRUCTURE AND HYDRAULIC COMPARTMENTALIZATION WITHIN THE COSO GETHERMAL FIELD, CALIFORNIA

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Conference Proceedings: MICRO-SEISMICITY, FAULT STRUCTURE AND HYDRAULIC COMPARTMENTALIZATION WITHIN THE COSO GETHERMAL FIELD, CALIFORNIA

Abstract
High precision earthquake locations and subsurface velocity structure provide potential insights into fracture system geometry, fluid conduits and fluid compartmentalization critical to geothermal reservoir management. We analyze 16 years of seismicity to improve hypocentral locations and simultaneously invert for the seismic velocity structure within the Coso Geothermal Field (CGF). The CGF has been continuously operated since the 1980's and is separated into two main compartments: the main field and the east flank. These compartments are at higher temperatures than the immediate surroundings. We find that relocated seismicity in the main field is shallower than in the east flank and occurs at the same depths as the injection and production wells, while the east flank seismicity extends about 1 km below the injection and production wells and is occurring almost exclusively in regions of high temperature. In the east flank, many of the earthquakes appear to align along planar features, suggesting through-going, pre-existing faults that may act as conduits for fluid and heat transport. The seismic velocity structure is heterogeneous, with compressional wave speed (Vp) generally lower in the main field when compared to the east flank and shear wave speed (Vs) varying more significantly in the shallow portions of the reservoir. The Vp/Vs ratio appears to outline the two main compartments of the reservoir, with a narrow zone of relatively high Vp/Vs separating the main field from the east flank. In the deeper portion of the reservoir this zone becomes less prominent. Several factors influence Vp/Vs ratios in geothermal systems including temperature, fracture geometry/density, and fluid saturation or pore pressure. Comparison of the distribution of Vp/Vs ratios with a temperature model generated from well logs reveals a first-order correlation between regions of low Vp/Vs ratio and high temperature.

Authors 
Kaven, O.J.; Hickman, S.H.; Davatzes and N.C.








Published 
PROCEEDINGS, Thirty-Sixth Workshop on Geothermal Reservoir Engineering Stanford University, Stanford, California, January 31 - February 2, 2011, 1/1/2011





DOI 
Not Provided
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Citation

Kaven, O.J.; Hickman, S.H.; Davatzes, N.C.. 1/1/2011. MICRO-SEISMICITY, FAULT STRUCTURE AND HYDRAULIC COMPARTMENTALIZATION WITHIN THE COSO GETHERMAL FIELD, CALIFORNIA. Proceedings of (!) ; (!) : PROCEEDINGS, Thirty-Sixth Workshop on Geothermal Reservoir Engineering Stanford University, Stanford, California, January 31 - February 2, 2011.


Related Geothermal Exploration Activities
Activities (1)


Areas (1)
  1. Coso Geothermal Area
Regions (0)