Lithologic Influences on Fracture Permeability and the Distribution of Steam in The Northwest Geysers Steam Field, Sonoma County, California
- Key words
- Exploration; USA; California; Sonoma; The Geysers; Fracture Pattern; Geologic Model; Alteration; Greywache; Faulting; Stressfield
- Location
- The Geysers, California
- Conference
- Geothermal Resources Council Transactions
- Year
- 1989
- Session
- Exploration; Fractures; Hydrothermal alteration; Hydrogeolog
- Language
- English
Abstract
A subsurface reservoir model has been constructed for the Northwest Geysers Steam Field based on the fracture patterns induced by the emplacement of intrusive rocks. The distribution of steam is not random but follow recognizable and predictable patterns influence by the different characteristics of the rocks that are encountered at reservoir depths. Graywacke appears to be the only brittle material that will propagate and maintain open fractures. In the Northwest Geysers, the intrusion of magma at depths created a fracture network generated by hydraulic fracturing that extended upwards but did not reach the surface. Subsequent fracturing related to wrench fault tectonics and subsidence above the intrusive rocks enhanced the fracture permeability.
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