Simulation of Refracture and Contact Mode Transitions in Tight Formations

Transitions between separation and contact modes are prevalent in rock mechanics. For stimulating tight hydrocarbon reservoirs, the transfer of hydraulic load from hydraulically loaded to in-situ cracks, removal of hydraulic load, re-fracturing, and application of cyclic loading are all examples involving contact and separation mode reversal. We propose an interfacial damage model that incorporates all contact and separation modes by combining their corresponding dynamically consistent Riemann solutions. Instead of commonly used penalty method and Lagrange multiplier approach we propose a new regularization scheme—based on the interface displacement and separation velocity jumps— that smoothens contact-separation mode transitions, remedies ill-conditioning that may arise by using penalty methods, and provides a tunable maximum penetration. In addition, we propose an aperture-based regularization approach that enables smooth transfer of hydraulic load to in-situ cracks. Numerical results, obtained by an h-adaptive spacetime discontinuous Galerkin method, demonstrate accurate modeling of contact mode transitions and intersection of cracks in hydraulic fracturing.