Modeling the Anisotropic Damaged Zone Around Hydraulic Fractures: Thermodynamic Framework and Simulation of Mechanical Tests

Abstract

We model crack propagation and damage induced by deviatoric stress around the crack tip. A new damage model is proposed to describe the damaged zone near fractures, in order to predict the mesoscale geomechanical behavior of rock during hydraulic fracturing. The process of new damage development follows a thermodynamic framework. An associated flow rule is utilized for irreversible strain rate while a non-associated flow rule is applied for damage evolution. Uniaxial tension and triaxial compression tests are simulated at the Gauss point of one element in MATLAB with the new damage model. The results illustrate the influence of anisotropic damage on stiffness degradation and residual strain development. The implementation of this new damage model in the commercial FEM software ABAQUS is undergoing. A preliminary Brazilian tension test is computed for the elastic domain using ABAQUS’ UMAT subroutine. The result agrees well with the analytic solution. The new damage model for rock matches the theoretical expectations, and shows that the proposed model can predict anisotropic damage.