Hydraulic fracturing (HF) is extensively employed in deep underground engineering to enhance rock mass permeability and improve resource extraction efficiency. However, the widespread presence of natural fracture (NF) in subsurface formations significantly alters HF propagation paths, leading to complex fracture geometries that are difficult to predict accurately. Traditional numerical approaches, particularly the conventional eXtended Finite Element Method (XFEM), encounter limitations in simulating intersecting fractures due to element-wise propagation constraints, which may cause unrealistic fracture deflection or failure of HF–NF intersection. To address this challenge, this study proposes an innovative “crack merging” strategy within the XFEM framework, enabling hydraulically induced fractures to merge with pre-existing NFs and propagate along their tips without mesh reconstruction. A two-dimensional coupled hydro-mechanical numerical model is established, incorporating a cohesive zone damage formulation, the maximum principal stress criterion for crack initiation, and the Benzeggagh–Kenane (B–K) energy-based fracture evolution law. The fracturing fluid is modeled as an incompressible Newtonian fluid, and NFs are assumed to be open, frictionless, and non-penetrable by HFs. Model validity is verified through comparison with laboratory experimental results.
Chen et al. (2026) studied this question.