A GEOPHYSICAL APPROACH TO RESERVOIR DELINEATION IN THE GEYSERS

into regional structure in this complex and chaotic area. Regional studies of this type, however, are of limited value to reservoir investigations and it may be that the more detailed temperature gradient/heat flow studies (Frye 1976) can supply more useful information. The survey discussed here was carried out on the Rorabaugh lease in the southwest sector of The Geysers geothermal field in an area of known production, good drilling records and closely spaced data points. Initial drilling on this lease was carried out by Geothermal Resources International and the area was subsequently developed for a 55 mW power plant by Pacific Energy Corporation and their successor, Thermogenics, Inc. The study included data from several producing wells, three deep suspended wells and four shallow (250'-500') temperature gradient holes