Geologic Setting of the Potential EGS Site at the Gonghe Basin, China: Suitability for Research and Demonstration of Hot Dry Rock Geothermal Energy Development

Abstract

Hot dry rocks (HDR) are increasingly explored now in China, and the Gonghe Basin in the northeastern edge of the Qinghai-Tibetan Plateau is regarded as the first potential demonstration site to exploit the HDR geothermal energy. Four wells were drilled in the Gonghe Basin, which revealed a highest temperature of 236oC at a depth of 3705 m. Downhole temperature logs indicate that the geothermal gradient in the hot granite is 71.4oC/km, with a mean heat flow of 119.3 mW/m2. Seismic, magnetotelluric and electrical prospecting in the Gonghe Basin indicates the NW-SE striking faults within the depth of 15-35 km allowing the heat transport from the cooling magma chamber in the depth of 8-32 km to the shallow zones, overlain by caprocks composed by the Quaternary lacustrine sediments with the thickness of 0.7-1.6 km. It is estimated that the hot dry rocks cover an area of over 3,000 km2 in the depth of 3-5 km, representing exploitable geothermal resources with the amount of 13.66 EJ. Since the geologic settings of the Gonghe Basin are comparable to that of several enhanced geothermal systems carried out in crystalline basement, e.g. the Cooper Basin in Australia, and the Milford FORGE in the USA, the methods of reservoir permeability enhancement and long-term monitoring in these fields can be important references for future EGS demonstration in the Gonghe Basin, China.