Geothermal energy production from hot dry rock: Operational testing at the Fenton Hill, New Mexico HDR test facility

During 1992--1993, an extended operational testing program was conducted at the Fenton Hill, NM Hot Dry Rock (HDR) test facility. Approximately 100 gpm of water was circulated for a total period of about 8 months through an artificial geothermal reservoir located about 3.5 km (11,500 ft) below the surface. Hot water was continuously returned to the surface at temperatures of 180--190{degrees}C (355--375{degrees}F). Under steady-state operating conditions, the temperature of the fluid produced from the reservoir showed no measurable decline over the span of the testing. In fact, tracer evidence indicated that access to hot rock increased as flow was directed preferentially to longer and longer pathways through the reservoir as the testing proceeded. The amount of water lost in passing through the underground reservoir also declined with time, eventually reaching levels of only about 7% of the injected volume. Operating performance data verified that significantly more energy was produced than was required to run the test facility. Geochemical measurements indicated persistently low levels of dissolved solids and gases in the circulating fluid. Because the entire system was pressurized, nothing except waste heat was released to the atmosphere during the closed-loop testing. The test program provided new information with regard to more » thermal, hydraulic, operational and environmental issues concerned with the development of HDR geothermal energy plants. The data gathered in this test will form the basis for the development of facilities to produce and market energy from HDR on a commercial scale. This paper reviews the results of the recent HDR flow testing program in detail and discusses the next steps required to move HDR technology toward full commercial application as an economic process for producing clean energy. « less