A hydro-thermo-mechanical numerical model for HDR geothermal reservoir evaluation

A two-dimensional numerical model of coupled fluid flow, heat transfer and rock mechanics in naturally fractured rock is developed. The model is applicable to assessments of hot dry rock (HDR) geothermal reservoir characterisation experiments, and to the study of hydraulic stimulations and the heat extraction potential of HDR reservoirs. Modelling assumptions are based on the characteristics of the experimental HDR reservoir in the Carnmenellis granite in Cornwall, S. W. England. In particular, the model assumes that fluid flow is horizontal and is confined to the most hydraulically conductive fractures in two orthogonal and vertical fracture sets. The mathematical model representing the hydro-mechanical interactions that are induced during reservoir creation is described. Furthermore, the solution method for calculating thermally induced stresses and strains in the reservoir due to heat extraction is discussed. The resultant numerical model, HOTGRID, is used to investigate the effects of stress perturbations on the fluid flow distribution in an HDR geothermal reservoir.