The Role of Active and Ancient Geothermal Systems in Evolution of Grant Canyon Oil Field, Railroad Valley, Nye County, Nevada
HULEN, J. B., University of Utah Research Institute, Salt Lake City, UT, LOUIS C. BORTZ, Independent Geologist, Denver, CO, and S. ROBERT BERESKIN, Terra Tek, Inc., Salt Lake City, UT
Since discovery in 1983, the Grant Canyon field has been among the most prolific oil producers (on a per-well basis) in the United States. Production through June 1990 was 12,935,630 bbl of oil, principally from two wells which in tandem have consistently yielded more than 6000 bbl of oil per day. The field is hosted by highly porous Devonian dolomite breccia loosely cemented with hydrothermal quartz. Results of fluid-inclusion and petrographic research in progress at Grant Canyon suggest that paleogeothermal and perhaps currently circulating geothermal systems may have played a major role in oil-reservoir evolution. For example, as previously reported, the breccia-cementing quartz hosts primary aqueous, aqueous/oil, and oil fluid inclusions which were trapped at about 120 degrees C ( verage homogenization temperature) and document initial oil migration and entrapment as droplets or globules dispersed in dilute (<2.2 wt. % equivalent NaCl) aqueous solutions. Additional evidence of geothermal connection is that the horst-block trap at Grant Canyon is top and side sealed by valley-fill clastic and volcanic rocks which are locally hydrothermally altered and calcite flooded. These secondary seals are enhanced by disseminated, solid asphaltic residues locally accounting for 23% (volume) of the rock. Current reservoir temperatures at Grant Canyon (120 degrees C) and the adjacent Bacon Flat field (171 degrees C) attest to vigorous contemporary geothermal activity. Based on results of our Grant Canyon work to date, we suggest that active and paleohydrothermal systems could be viable petroleum exploration targets in otherwise favorable terrain elsewhere in the Basin and Range.
AAPG Search and Discovery Article #91010©1991 AAPG Rocky Mountain Section Meeting, Billings, Montana, July 28-31, 1991 (2009)