Fully coupled dynamic hydraulic fracturing of saturated porous media based on the numerical manifold method

Accurate and efficient simulation of dynamic hydraulic fracturing of the saturated porous media has always been a pivotal topic in the oil and gas extraction. Leveraging the Numerical Manifold Method (NMM) and its inherent cutting technique, this paper proposes a fully coupled hydraulic fracturing model based on the u-p format, which incorporates the overall momentum balance and continuity conditions in both porous media and fractures. NMM approximations and the Newmark implicit algorithm are employed respectively to discretize the spatial and time domains, and the resulting system is solved based on the Newton-Raphson method. By imposing flow boundary conditions on the fracture surfaces, the present model accounts for fluid loss without introducing extra filtration coefficients. Using the Mohr-Coulomb-based LT criterion and the maximum circumferential stress criterion to determine whether crack propagation has occurred and crack propagation direction respectively, the present model is capable of simulating initiation and development of multiple cracks under hydraulic stimulations. Through modeling the KGD hydraulic fracturing, hydraulic fracturing of a pre-cracked cubic specimen and fracture interference phenomena during expansion of multiple fracture ports of a single injection well, accuracy and effectiveness of the model are validated.