The enhanced geothermal system is applied to develop the hot dry rock geothermal resource. The hot dry rock is dry and impermeable rock, like granite, in the depth of 3000~6000 meters; and its temperature is as high as 200 °C. The energy of the hot dry rock is extracted to generate geothermal electricity. The extraction is through the technology of the enhanced geothermal system. In the enhanced geothermal system, two wells, the injection well and production well, are built to create a circulation loop to cycle fluid. The geothermal energy between two wells is extracted by the circulating fluid in fractures. Those fractures are created through hydraulic fracturing treatment. Hence, hydraulic fracturing is the key technology to achieve geothermal energy in the enhanced geothermal system. In this paper, the hydraulic fracturing in enhanced geothermal system was studied in the laboratory through high temperature true-triaxial hydraulic fracturing test system. The test system could provide 30 MPa in-situ stress, 100 MPa injection pressure, and up to 250°C at temperature to simulate the actual reservoir condition. The granite outcrops were selected from the hot dry rock geothermal field in China. In addition, based on experimental data, a thermal-hydraulic-mechanical coupling model was developed to simulate fracture propagation in the high temperature hot dry rock geothermal reservoir.

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