2D Seismic Imaging at the Orita Geothermal Area, Imperial Valley, California

Abstract

The Orita geothermal area (OGA) is presently being explored and developed by Ram Power Incorporated (RPI) for electricity generation. It is located in the east-central portion of the fault-bounded Imperial Valley, southern California. Like in most known and producing geothermal resource areas located within this deep sedimentary basin, the surface expressions of faults are buried under thick deposits of Holocene lacustrine and deltaic sediments. Thirty-six (36) line-kilometers of two-dimensional (2D) seismic data were acquired in April 2010 primarily to image these faults as well as the gross bedding patterns of the sediments. The faults were interpreted from the final post-stack migrated sections using conventional techniques. Seismic sections in SEG-2 format were later uploaded into a seismic-to-simulation software package for clearer fault visualization, greater accuracy, and faster interpretation. Several NW-SE trending, west to southwestdipping high-angle gravity faults were delineated. This preferred fault orientation generally follows the structural trend in the Imperial Valley region. Well to fault intersection analysis and correlation showed that some of these faults were intersected by the wells drilled from 1981 to 82 and those drilled recently. These faults were found to have contributed to the higher bulk permeability of the wells, especially when they are intersected at greater depths where the sediments are slightly metamorphosed and brittle due to elevated temperature and pressure conditions.