Numerical analysis of hydraulic fracture initiation and propagation in elastoplastic hydrate-bearing sediments

Hydrate-bearing sediments (HBS) exhibit pronounced plastic deformation, complicating both hydraulic fracture initiation and propagation. Conventional models typically assume purely elastic behavior and neglect energy dissipation at fracture tips, leading to significant deviations in predicted fracture responses. To address these limitations, this study developed a fluid-solid coupled numerical model within the extended finite element method (XFEM), utilizing the Mohr-Coulomb yield criterion to simulate fracture initiation and propagation in elastoplastic HBS. The model was validated against true triaxial hydraulic fracturing experiments, predicting fracture initiation pressures within 5% of measured values. Results indicate that fracture initiation is strongly controlled by localized plastic strain at fracture tips. This plastic strain acts as a primary mechanism of energy dissipation, increasing initiation pressure by up to 1.92 MPa compared with purely elastic predictions. During fracture propagation, plastic yielding leads to the development of short, wide fractures with increased opening but limited length. Increasing hydrate saturation shifts fracture propagation from ductile-dominated to brittle-dominated behavior. In addition, in-situ stress and fracturing fluid properties influence fracture initiation and propagation by influencing plastic deformation. These findings clarify the controlling role of elastoplastic behavior in fracture initiation and propagation in HBS, offering guidance for hydraulic fracturing design in marine hydrate reservoirs.