A Damage Mechanics Approach to Modeling Permeability Enhancement in Thermo-Hydro-Mechanical Simulations

Abstract

In geothermal energy production, permeability can be enhanced or inhibited over time by various multi-physics controlled processes such as chemical species dissolution and precipitation, changes in stress or pore pressure, and by temperature effects such as thermal cracking. A wide range of methods has been used to numerically simulate permeability enhancement. Models based on damage mechanics, discrete fracture mechanics, critical shear strain criteria, effective stress, and even empirical permeability multipliers have been proposed in the literature. Damage mechanics offers a way forward that encompasses micro-crack physics while allowing for a realistic description of complex fracture networks. This work seeks to apply a new damage mechanics model that includes Thermal-Hydrological-Mechanical (THM) effects in simulations of thermal cracking problems that are of significance in geothermal energy production. To this end, the damage model was implemented into a fully coupled THM finite element code. This approach allows for the macro-scale representation of complex micro-scale phenomena and offers a natural framework for the investigation of the degree of numerical coupling required for the strong feedback permeability mechanisms involved in the stimulation of permeability.