A fast simulation method for hydraulic-fracture-network generation in fractured rock based on fully coupled XFEM

In considering the rapid decrease of stress away from the crack tip, a fast simulation method based on fully coupled XFEM is proposed to handle the low efficiency and poor convergence in simulating the generation of complex fracture networks. The weak forms of governing equations are discretized by the XFEM approximation of displacement field and FEM approximation of one-dimensional pressure field. The Newton-Raphson method is then adopted to solve the resulting fully coupled u-p discretization equations. After the validation of the numerical model by the propagation of a single fracture and interaction between hydraulic fracture and natural fracture, several numerical cases are adopted to illustrate the superiority of the proposed model in computational efficiency. The influence of several key factors on the propagation of hydraulic fracture in a formation containing regularly and randomly distributed natural fractures is investigated. Numerical results show that the orientation has the greatest influence on the pattern of the hydraulic-fracture network in formation with regularly distributed natural fractures. Higher natural fracture density, lower differential stress, and interface strength can contribute to the higher injection pressure, the longer total length of shear fracture, and the more complex fracture network.