Numerical analysis of fracture deformation and instability during CO2 geological sequestration using a THM-XFEM coupled model

Fracture deformation and instability during long-term CO2 geological sequestration in abandon reservoirs is simulated with a thermal-hydro-mechanical model. The two-phase in non-isothermal condition is used both in matrix and fracture, and thermoelastic and poroelastic deformation are all taken into account. The extended finite element method is employed to solve the strong discontinuity problem involving thermal-hydro-mechanical coupling. The S-W equation of state and transport equation are chosen to characterize CO2 phase change. CO2 geological sequestration in abandoned-fractured reservoir with high water-cut is discussed with a two-dimensional model. The analysis of fracture deformation shows that CO2 geological sequestration has a great effect on fracture deformation and instability. Fracture aperture, deformation and the effective fluid pressure in fracture are highly affected by the water residual saturation and injected temperature difference. The analysis of fracture instability presents that mode I mainly appears in the fracture propagation, and propagation prefers to occur in fracture near the injection wellbore. The higher CO2 phase pressure when cold CO2 injection into reservoirs with low water residual saturation can promote fracture propagation 1–2 years in advance. Fracture aperture is enhanced but fracture instability time would be delayed due to the thermal stress.