Intermediate Depth Drilling and Geophysical Logging Results at Superstition Mountain, Naval Air Facility El Centro, California

Abstract

The US Navy Geothermal Program Office (GPO) is conducting geothermal energy exploration adjacent to Superstition Mountain in western Imperial Valley, at the Naval Air Facility, El Centro (NAFEC), CA. Exploration activities conducted by GPO over the past few years indicates that a thermal anomaly appears to coincide with an active transtensional right stepover occurring between the parallel northwest trending Superstition Mountain fault and the Superstition Hills fault to the north. Based on the earlier shallow drilling, detailed geologic mapping, seismogenic fault mapping and stress analysis, and a variety of geophysical surveys, including gravity and magnetic, selfpotential electrical and magneto-telluric, two moderate depth test holes completed in December 2008, and a third test hole, NAFEC-3, completed in November 2010, further confirmed the existence of a moderate temperature anomaly with temperatures reaching 255°F (124°C) at less than 3500 feet (1067m). The thermal anomaly coincided with hydrothermal alteration within the granodiorites intersected by the test hole. Fracture and stress field analysis has been conducted through the total length of the hole. Geophysical logs, including UBI, Sonic, Resistivity, Gamma Ray, Borehole Caliper, and Temperature, were acquired through the entire length of NAFEC-3 and have been used in conjunction with the drilling log. Additional geological studies are in process for NAFEC-3, in combination with two other nearby test holes, NAFEC-1 and NAFEC-2, including a Fluid Inclusion Stratigraphy (FIS) study and a petrographic and hydrothermal alteration study.