| Title | Geologic and Geophysical Study of the Orita Geothermal Field, Imperial Valley, California |
|---|---|
| Authors | Johnson, Stuart D.; Hulen, Jeffrey B.; Branch, James |
| Year | 2010 |
| Conference | Geothermal Resources Council Transactions |
| Keywords | Orita; East Brawley; Imperial Valley; Gravity; Structural model; Intrusive dates; Detachment faulting; Chaotic-seismic-reflector-doman; Brawley Fault Zone migration |
| Abstract | The Imperial Valley comprises the northern portion of the Salton Trough which is the largest geothermal province in North America. The Salton Trough hosts five geothermal developments, Cerro Prieto, Mexico (850 MW), Salton Sea (335 MW), Heber (95 MW), East Mesa (74 MW) and North Brawley (50 MW). The ultimate geothermal development of this province is likely to be more than 5,000 MW and Ram Power Corp is aggressively conducting exploration and development of projects within the US Imperial Valley portion of the province. Project targeting utilizes an in-house proprietary heat flow data base for first-pass evaluation of potential areas of interest and is followed by development of a conceptual geologic model for the origin using published tectonic and structural concepts for initial refinement of the local setting of interest. Deep exploration drilling conducted in the search for geothermal energy by petroleum companies active in the 1970 and 1980 time frame can frequently be integrated into the evaluation. Geophysical coverage on a regional scale exists for large portions of the Imperial Valley and this data is used to test the geologic model and to direct enhanced geophysical surveys including gravity, electrical and seismic techniques. The result is a refined 3-D model of the geothermal system that reconciles these diverse data sets and provides rational, tactical drilling targets. The critical elements of blending the rich geologic understanding of the Salton Trough that has evolved in the three decades post 1980 –petroleum company exploration era with historic data generated in that era is a cost effective means to schedule modern geophysical surveys to guide development drilling. Conceptual models look to target zones that are: 1) in competent rock with primary permeability, 2) ideally will have enhanced permeability developed by local faulting, 3)have temperatures consistent with supporting flash technology power generation, 4) are within commercial drilling depths and 5) ideally will be moderate to low salinity. Delineation drilling is used to confirm the reservoir characteristics and ultimately the conversion technology of choice must match the defined reservoir system. Examples from the ongoing development of the Orita project are used to illustrate the Ram Power development approach in the Imperial Valley. |