The numerical simulation of thermal recovery considering rock deformation in shale gas reservoir

Recently, shale gas is a hot spot of research as an unconventional resource. Advances in horizontal well drilling technology and fracturing technology have contributed to increased shale gas recovery. Different from conventional gas reservoirs, the adsorption gas content is as high as 85%, so the amount of adsorbed gas liberated from the matrix surface is very helpful for ultimately improving the recovery of shale gas. Recently, some progress has been made in the process of hydraulic fracture heating technology. The event that temperature variation promotes the release of adsorbed gas and thus enhances oil recovery has not been fully studied. In addition, during shale gas production, stress sensitivity, adsorption desorption and temperature will all have a significant effect on rock deformation, which will change the permeability of the matrix and fractures. To study the effect of thermal recovery based on coupled geomechanical effects and fluid flow. A numerical model of shale gas thermal recovery considering Knudsen diffusion, adsorption desorption and stress sensitivity was established to reflect the production process of shale gas. Moreover, discrete fracture is employed to describe hydraulic fractures and natural fractures. The influence of thermal expansion on rock deformation is considered in the geomechanical effect, and the permeability formula suitable for shale gas thermal recovery is developed. Finally, the effects of different parameters on thermal recovery were studied separately. It is obvious that heating hydraulic fractures improves the recovery of shale gas by promoting the liberate of adsorbed gas. A large amount of adsorbed gas is produced as the stimulation temperature increases. Considering the stress-sensitive permeability can more accurately reflect the change of permeability in the shale gas thermal recovery process, so as to more accurately predict the production of shale gas. The increase in recovery rate of shale gas thermal recovery depends on the stimulation temperature, bottom hole pressure, matrix heat capacity, thermal conductivity, Langmuir volume and matrix permeability. The larger the Langmuir volume and the higher the bottom hole pressure, the better the thermal recovery effect for improving shale gas recovery.