The influence of energy enhancement on the morphology of hydraulic fractures based on a fully-coupled XFEM method

Pre-fracturing energy enhancement has shown promising potential to improve stimulation performance in low-permeability reservoirs, yet its influence on subsequent hydraulic fracturing remains unclear. This study develops a fully coupled hydro-mechanical model based on the XFEM to simulate this integrated process. Both displacement and pressure fields are discretized using XFEM with appropriate enrichment functions, enabling accurate representation of fracture-induced discontinuities. A unified computational framework is established to solve the coupled hydro-mechanical response during two sequential stages: energy-enhanced injection and hydraulic fracturing. The model accuracy is validated against the classical KGD problem in permeable media. Numerical analyses are conducted to investigate stress redistribution and pore pressure evolution during energy enhancement. Parametric studies are performed to quantify the influence of injection volume, injection rate, matrix permeability, shut-in time, and fracture initiation location on fracture propagation behavior. Results show that energy enhancement elevates pore pressure and total stress, thereby reducing fluid leak-off and enhancing fracturing efficiency, though at the cost of higher injection pressure. Specifically, in a 1 mD reservoir, 30-day energy enhancement via water injection at a rate of 2.61 m³/(m·day) raises fracture propagation pressure by over 5.63 MPa compared to the non-enhanced case, while fracturing efficiency improves from 51.09% to 80.5%, and fracture length increases from 24.7 m to 50.0 m under a stimulation time of 40 s. Fracture initiation location significantly influences fracture propagation path, aperture, and symmetry. Initiating a fracture 10 m away along the minimum stress direction results in a symmetric but deflected path, with a maximum tip deviation of 3.96 m at a 50 m fracture length. In contrast, initiation along the maximum stress direction results in severely asymmetric propagation. The growth of one wing is strongly suppressed, extending only about 5 m when the total fracture length is 50 m. These findings provide critical insights for optimizing energy-enhanced fracturing treatments in unconventional reservoirs.