| Abstract |
Low-temperature sedimentary geothermal resources are widespread in the continental regions of the Earth’s crust. They are quite different in nature from the geothermal resources associated with volcanic systems or tectonically active regions of the crust. Their management during long-term utilization also requires somewhat different emphasis than that of the conventional geothermal resources. More examples of sedimentary resources, which have been utilized heavily for direct applications, can be found in China. More than 3500 geothermal wells had been drilled in China by 2010, most of them in sedimentary geothermal systems. Two Chinese sedimentary geothermal systems, the Xianyang system in Shaanxi and the Xiongxian system in Hebei Province have been assessed by lumped parameter pressure response modelling and volumetric calculations. They are of quite contrasting nature, the Xianyang system being a porous-type sandstone system and the Xiongxian system being a fissured-karst carbonate rock system. Xianyang lies in Wei River sedimentary basin in the center of China. The average permeability-thickness of the Xianyang reservoir is estimated to range from 2 to 7 Darcy-m through the lumped parameter modelling. The Xianyang sandstone reservoir appears to approach a closed reservoir in nature. The volume of geothermal fluid stored underground in the Xianyang territory is estimated to be 59•109 m3 and recoverable heat to be 13•1018 J. Xiongxian lies in the North China Basin at about 110 km and 100 km from Beijing and Tianjin, respectively. Large scale reinjection started in Xiongxian in 2009. The internal permeability-thickness of the Jixian reservoir in Xiongxian is estimated to be up to 95 Darcy-m, and the external permeability over 14 Darcy-m, according to the lumped parameter modelling conducted. The potential of the Jixian reservoir is rather promising for future exploitation, partly because reinjection should be easy. The pressure response of the Jixian reservoir is comparable to that of an open reservoir. The volume of geothermal fluid stored in the Jixian reservoir, in the Xiongxian territory, is estimated to equal 9.6•109 m3 and the recoverable heat to be 2.5•1018 J. The lumped parameter models for the respective systems are used to calculate reservoir pressure predictions for different future production scenarios. |