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Abstract: Utility of Drill-Stem Tests in Determination of the Geothermal Regime of Railroad Valley, Nye County, Nevada

Don E. French

Accurate representation of geothermal Conditions is necessary to determine generation potential of source rocks buried in Railroad Valley. Boreholes provide the best source of geothermal information, but formation temperature data must be screened for variations caused by drilling. Bottomhole temperatures from wireline logs are affected by initial formation conditions, drilling fluid that moves into the formation while drilling, and lag time between cessation of drilling fluid circulation and acquisition of logs. More accurate indicators of formation conditions are temperatures recorded during drill-stem tests, especially for tests that recovered large amounts of fluid.

Over 130 drill-stem tests were examined to establish the viability of this source of data and to determine the geothermal conditions of the Railroad Valley basin. Results indicate that 500 feet or more of fluid recovery on a test is necessary to get a temperature recorded that is not influenced by drilling perturbations. The formation temperature data collected for Railroad Valley indicate the possibility of 2 thermal regimes. A low-temperature gradient regime is probably influenced by meteoric water. The high-temperature gradient regime probably reflects the regional heat flow associated with the thin crust of the Great Basin.

AAPG Search and Discovery Article #90959©1995 AAPG Rocky Mountain Section Meeting, Reno, Nevada