Numerical simulation and analysis of damage evolution and fracture activation in enhanced tight oil recovery using a THMD coupled model

A thermo-hydro-mechanical-damage coupled model is developed in this paper for exploring the mechanism of thermo-hydro-mechanical-damage behaviors during enhanced oil recovery. The thermo-poroelastic deformation, two-phase flow and heat transport are all solved in finite element framework. Rock damage is determined by the tensile and shear failure criterions, and the contact problem for pre-existing fractures is based on the extended finite element method and augmented Lagrangian multipliers method. Then with the numerical framework, we simulated the damage evolution, fracture activation and rock properties damage caused by the thermoporoelastic response during water injection in enhanced oil recovery. As the water injection and oil production are carried on, damage propagation and pre-existing fracture activation gradually appear around injection well. Complex fracture-damage network system and an enhanced permeability area are observed. The expansion of damage-enhanced permeability evolution to production well will greatly affect the oil recovery. And the fracture-damage network system and enhanced permeability area evolution is highly sensitive to the injection rate, injection viscosity and injection temperature difference. The simulations and discussions demonstrated that comprehensive modelling of thermo-hydro-mechanism-damage behaviors has important significance for enhanced oil recovery and other underground liquid injection engineerings.