A novel fully-coupled flow and geomechanics model in enhanced geothermal reservoirs

The geomechanical behavior of porous media has become increasingly important in stress-sensitive reservoirs. This paper presents a novel fully-coupled fluid flow-geomechanical model (TOUGH2-EGS). The fluid flow portion of our model is based on the general-purpose numerical simulator TOUGH2-EOS3. The geomechanical portion is developed from linear elastic theory for a thermo-poro-elastic system using the Navier equation. Fluid flow and geomechanics are fully coupled, and the integral finite-difference method is used to solve the flow and stress equations. In addition, porosity and permeability depend on effective stress and correlations describing that dependence are incorporated into the simulator. TOUGH2-EGS is verified against analytical solutions for temperature-induced deformation and pressure-induced flow and deformation. Finally the model is applied to analyze pressure and temperature changes and deformation at The Geysers geothermal field. The results demonstrate that the model can be used for field-scale reservoir simulation with fluid flow and geomechanical effects.