A three-dimensional transient model for EGS subsurface thermo-hydraulic process

Understanding the subsurface thermo-hydraulic process in enhanced or engineered geothermal systems (EGS) is crucial to the efficiency of heat extraction and the sustainable utilization of geothermal reservoir. We present in detail a three-dimensional transient model for the study of subsurface thermo-hydraulic process during EGS heat extraction and demonstrate its capability through test simulations. Since this model considers the actual existence of local thermal non-equilibrium between rock matrix and fluid flowing in the porous heat reservoir during EGS heat extraction, the model results shed light on the local heat exchange in the reservoir. One other salient feature of this model is its capability of simulating the complete subsurface thermo-hydraulic process during EGS heat extraction, not only the thermo-flow in the reservoir and well boreholes, but also the heat conduction or transport in rocks enclosing the reservoir. The results obtained from the test simulations, though the considered reservoir is imaginary and homogeneously fractured, corroborate the capability and validity of the present model. Moreover, the model results from the specially designed triplet well EGS case indicate its superior heat extraction performance.