HYDROLOGIC PROPERTIES OF THE DIXIE VALLEY, NEVADA, GEOTHERMAL RESERVOIR FROM WELL-TEST ANALYSES

Abstract

Temperature, pressure, and spinner (TPS) logs have been recorded in several wells from the Dixie Valley Geothermal Reservoir in west central Nevada. A variety of well-test analyses has been performed with
these data to quantify the hydrologic properties of this fault-dominated geothermal resource. Four complementary analytical techniques were employed, their individual application depending upon availability and quality of data and validity of scientific assumptions. In some instances,
redundancy in methodologies was used to decouple interrelated terms. The methods were (1) step drawdown, variable-discharge test; (2) recovery
analysis; (3) damped-oscillation response; and (4) injection test. To date, TPS logs from five wells have been examined and results fall into two distinct categories. Productive, economically viable wells have permeability-thickness values on the order of 105 millidarcy-meter (mD-m) and storativities of about 10-3. Low-productivity wells, sometimes
located only a few kilometers from their permeable counterparts, are artesian and display a sharp reduction in permeability-thickness to about 101 mD-m with storativities on the order of 10-4. These results
demonstrate that the hydrologic characteristics of this liquid-dominated geothermal system exhibit a significant spatial variability along the range-
bounding normal fault that forms the predominant aquifer. A large-scale, coherent model of the Dixie Valley Geothermal Reservoir will require an
understanding of the nature of this heterogeneity and the parameters that control it.