Coupled Thermal-Hydro-Mechanical Modelling And Simulation Of Fluid Flow In Enhanced Geothermal System

Enhanced Geothermal System(EGS)generates an artificial geothermal reservoir by hydraulic fracturing which provides a pathway for heat transmission through the fractures by circulating cold water to the hot dry rock and extract heat energy.The process involves complex process of Thermal-Hydro-Mechanical(THM)coupling.This work presents a numerical approach to simulate and analyze heat extraction process in an EGS reservoir.The reservoir is considered as fractured porous media comprising of rock matrix blocks,hydraulic fracture and natural fracture networks.STARS from Computer Modeling Group(CMG),a commercial thermal simulator is used in this work for numerical modeling.The reservoir performance in this work is investigated in terms of thermal evolution and reservoir hydraulics.Geomechanical coupling is done by considering stress dependent permeability in both matrix and fractures;and the effect of stress dependent permeability in fractures is more profound than in matrix,because the fractures are the main pathway for the flowing fluid in the reservoir.Sensitivity analysis allow us to determine parameters that has significant impact on produced energy rate.Sensitivity analysis of main parameters controlling the outlet temperature of EGS are also studied in this work,these parameters includes well spacing,main fracture half length,main fracture conductivity,secondary fractures length,natural fractures density,injection rate,injection temperature,reservoir permeability and reservoir porosity.The results were such that;Coupling stress dependent permeability when modeling for enhanced geothermal system has a significant impact on fracture conductivity.Since the fractures are the main pathway of flowing fluid in EGS,stress dependent permeability effect may be considered only in fractures when modeling.Furthermore,fracture halflength,fracture conductivity,injection rate,matrix porosity,matrix permeability and well spacing while injection temperature,natural fracture density and secondary fracture length have less impact on produced energy rate.