Search

In this paper, a hydro-mechanical model for non-planar hydraulic fracture propagation in ductile formations is developed based on the Drucker-Prager plasticity theory, Biot's theory and cohesive zone model (CZM). A hybrid extended finite element method (XFEM)-finite volume method (FVM)-embedded discrete fracture model (EDFM) method is proposed for numerical implementation. The XFEM and return-mapping method are used to simulate the deformation of inelastic media with strong discontinuities. The discontinuous pressure field is modelled by the EDFM and FVM. In addition, a dual-layer iterative algorithm is proposed to solve the strong nonlinear systems by a combination of the fixed-stress iteration, Picard iteration and Newton-Raphson iterative method. Then, the accuracy and ability of the proposed model are demonstrated through several reference cases. Finally, the proposed model are applied to two numerical cases and the influences of the plastic deformation on the simultaneous propagation of multi-fractures are investigated. • A poro-elasto-plastic model for non-planar hydraulic fracture propagation in ductile formations was developed. • A hybrid XFEM-FVM-EDFM method was proposed to conduct numerical implementation. • A dual-layer iterative algorithm was constructed to solve the strong nonlinear equation systems. • The effects of rock plasticity on multi-fractures propagation in the ductile formations were investigated. [ABSTRACT FROM AUTHOR]

Rock yielding may well take place during hydraulic fracturing in deep reservoirs. The prevailing models based on the linear elastic fracture mechanics (LEFM) are incapable of describing the evolution process of hydraulic fractures accurately. In this paper, a hydro-elasto-plastic model is proposed to investigate the hydraulic fracture propagation in deep reservoirs. The Drucker–Prager plasticity model, Darcy's law, cubic law and cohesive zone model are employed to describe the plastic deformation, matrix flow, fracture flow and evolution of hydraulic fractures, respectively. Combining the embedded discrete fracture model (EDFM), extended finite element method (XFEM) and finite volume method, a hybrid numerical scheme is presented to carry out simulations. A dual-layer iterative procedure is developed based on the fixed-stress split method, Picard iterative method and Newton–Raphson iterative method. The iterative procedure is used to deal with the coupling between nonlinear deformation with fracture extension and fluid flow. The proposed model is verified against analytical solutions and other numerical simulation results. A series of numerical cases are performed to investigate the influences of rock plasticity, internal friction angle, dilatancy angle and permeability on hydraulic fracture propagation. Finally, the proposed model is extended to simulate multiple hydraulic fracture propagation. The result shows that plastic deformation can enhance the stress-shadowing effect. [ABSTRACT FROM AUTHOR]