Linking TOUGH2 and ABAQUS to Model Permeability Enhancement Using a Damage Mechanics Approach

Abstract

In geothermal energy production, permeability can be enhanced or inhibited over time by various multiphysics 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. Previous damage models do not account for the reversible nature of permeability enhancement. During injection, permeability may increase, but during shut-in time, permeability may decrease again. This work seeks to develop a reversible permeability enhancement methodology that is applicable to cyclic injection scenarios for geothermal energy production. Our damage model was implemented in coupled Thermo-Hydro-Mechanical (THM) simulations using AUTOUGH2, the University of Auckland’s version of TOUGH2, coupled with the solid mechanics code, ABAQUS. This work offers a step forward and a flexible framework for the modeling of injection-induced damage and permeability enhancement.