Modeling method and hydraulic fracture propagation for jointed rock mass using PHF-LSM method

This paper presents a coupling procedure for modeling a jointed rock mass by the level set (LS) method and for simulating hydraulic fracture propagation by a permeability-based hydraulic fracture (PHF) model. The LS functions are developed to implicitly describe the spatial distribution of joints. These functions are integrated into the PHF model to simulate the behavior for six types of joint distributions. The presented PHF model is a smeared approach that is based on a fully-coupled, pore pressure-effective stress formulation. The major assumption for the PHF model is that the permeability of the rock is assumed to be a function of the mean effective stress via a hyperbolic tangent function. By assuming that the joints are initial fractures, the hydraulic conductivity within the joints is initially different from that of the rock matrix. The numerical model results indicate that the integration of the LS method and PHF model provides a means to keep the mesh unchanged when modeling different kinds of jointed rocks and the corresponding hydraulic fracture propagation. Characteristics of hydraulic fracture in the jointed rock are also studied. We observe that one or two fracture tips can be halted by the presence of joints when the fracture zone expands in the horizontal direction. Furthermore, the direction of the fracture front can be changed by randomly distributed joints. The equivalent fracture opening, the stress path, the injection pore pressure and the propagation pore pressure are compared for different jointed rock mass.