Numerical simulation and analysis of thermo-hydro-mechanical behaviors of hydraulic fracturing in naturally fractured formation using a THM-XFEM coupling model

Activation and propagation of natural crack during hydraulic fracturing make an essential contribution to the reservoir stimulation. For the sake of figuring out the impact of thermo-poroelastic deformation in multi-field coupling on natural crack activation, a thermo-hydro-mechanical coupled model is developed in this paper. The thermo-poroelastic deformation and non-isothermal fluid flow in fractured media are all taken into account, and the contact problem for natural crack surfaces are solved by the augmented lagrangian multiplier method. Then the extended finite element method is adopted for the discretization of the coupled model. The developed model is verified against the analytical models of fracture propagation, heat transfer and crack loaded in shear. Sensitive analysis is conducted using the numerical model. Numerical results show that the key factors affecting interaction pattern between hydraulic fracture and natural crack are the geomechanical parameters while thermal effect only contribute to natural crack activation. Thermal stress can lead to an increase in fracture aperture but a reduction in fluid pressure in fracture, and the high reservoir temperature and coefficient of thermal expansion will aggravate this. Besides, the non orthogonal intersection angle will cause an asymmetric distribution of fluid pressure and aperture in activated natural crack.