Reservoir Evaluation Using Discharge and Injection Data from Slim Holes and Large-Diameter Production Wells at the Steamboat Hills Geothermal Field, Nevada, USA

Abstract

Slim (7 cm) coreholes and large diameter (31 cm) production and injection wells have been drilled and tested at the Steamboat Hill Geothermal Field in northwestern Nevada about 15 km south of Reno. Three slim holes were drilled, prior to production and injection well drilling, to investigate the subsurface geological conditions thermal regime, and productive characteristics of the geothermal system through injection testing. The geothermal reservoir is a shallow (150m to 825m) moderate temperature (155oC to 168oC) liquid dominated system situated in highly fractured granodiorite. Discharge and injection tests were conducted on the slim holes while running downhole pressure temperature spinner (PTS) logs. The discharge rated on the slim holes wee 3.2 kg/s, 3.5 kg/s, and 4.7 kg/s while production tests on the corresponding large diameter wells , drilled within 5m of each slim hole, gave liquid flow rates of 65 kg/s, 76 kg/s and 88 kg/s. Discharge and injection data from slim holes and production wells in the Steamboat Hills Geothermal Field indicate that it is possible to infer the relative discharge rate of production wells based on measurements from slim holes. Furthermore, the average per well cost of drilling and completing large diameter production and injection wells in the fractured granodiorite of the Steamboat Hills geothermal reservoir was more than three times that for the slim holes.