A FLUID FLOW MODEL OF THE COS0 GEOTHERMAL SYSTEM: DATA FROM PRODUCTION FLUIDS AND FLUID INCLUSIONS by

system at Coso. This investigation is Part of an ongoing study being perCos0 is one of several high-tempeformed through an agreement betwen rature geothermal systems associated California Energy Company and the Earth with recent volcanic activity in the Science Laboratory Division/university Basin and Range province. Within this of Utah Research Institute. fracture-dominatedsystem, temperatnres The Cos0 geothermal field is locas high as 34QnC have been measured at ated at the western edge of the Basin depths of less than 2.5 km* ('3emical and Range province on the China Lake analyses of the Production fluids show Naval weapons Center in Inyo County, CA (Fig. 1) The thermal area is assocthat steep gradients in the salinities, gas concentrations, and temperatures iated with a series of Pliocene to occur within the reservoir. Salinities Pleistocene rhyolite domes which trend and coz contents range from 1-05 * * % north-south through the Cos0 Range. TDS and 0.95 w t . % COz in the Part of the field to 0.3' w t * % Southern The geothemal system is localized and along discrete zones of fracture per0.06 w t . % C02 in the north and east. meability in the underlying crystalline Fluid data have been used metamorphic basement. Surface manifesto the and tations of the system include fumaroles temperatures of the reservoir outside and acid-sulfate springs in the norththe production zones. Homogenization ern and eastern portions of the field temperatures of the fluid inclusions at Devil's Kitchen and coso Hot Sprranged from 328" to less than 100°C. ings. Iceand clathrate-meJting temperatures To date, California Energy Company, indicate that the fluids have salinias operator for the Cog0 Geothermal in depth from 400 to 2500 m and 10 core holes ranging from 600 to 1300 m in ties UP to 1.4 equivalent w t * % NaCl and Project, has completed 66 wells ranging travels outward toward east . inclusion data can be combined to deFigure 1. Location map of the Cos0 velop a detailed hydrogeochemical model of the fracture-dominated geothermal geothermal system.