Numerical modeling of heat extraction in hot fractured vuggy reservoir with thermal hydraulic mechanical coupling method based on a discrete fracture-vug model

Abstract

We develop a coupled thermo-hydro-mechanical (THM) model to study the fluid flow and heat extraction processes in hot fractured vuggy reservoirs consisting of natural fracture network and vug. Fluid flow along fractures and vugs are determined according to the cubic law and Navier-Stokes equation, and an extended Beavers-Joseph-Saffman boundary condition is adopted to couple the porous media-vug interface. Heat exchange between the interface of fracture, vug and matrix are calculated based on local thermal nonequiuilibrium. We implement a fracture constitutive model to capture the variation of fracture apertures due to normal compression-induced closure and shear dislocation-induced dilation. We conduct a series of numerical experiments to systematically analyze how hydraulic properties and heat extraction parameters are affected by the combined effects of geometrical distribution and geomechanical deformation of fracture vug networks. The results show geometrical connectivity of fracture vug networks plays a critical role in dominating the thermo-hydro-mechanical processes of fractured vuggy rocks and the geomechanical deformation of fractured vuggy reservoir exerts a secondary-order influence on the response of hydraulic and thermal performance.