Felsic Bodies of the Coso Geothermal Field

Abstract

Virtually every production and injection well at the Coso Geothermal Field has at least five felsic dikes in the well bore. The average is ten, and wells on the East Flank portion of the geothermal field have up to 40 intrusions logged in cross section. Felsic Dikes are part of the entire well bore from 300 to 9000 feet. Average logged felsic dike thickness in cross section is thirty feet. Two high temperature signatures are located in East Flank Area and a third is located below the BLM West Area of the field, with a depth of -5000 feet below sea level. These three high temperature zones are considered to have a magmatic signature. Well bore cross sections of five wells with the depth of each felsic intrusion are graphed. Coso has 160 geothermal wells, with over 1000 individual felsic intrusion logged. The felsic dikes were a heat source at the time of emplacement.