Hierarchical Modeling of Hydromechanical Coupling in Fractured Shale Gas Reservoirs with Multiple Porosity Scales

The simulation of gas flow in shale formation has been a major challenge in the oil and gas industry due to related multiscale pore structure and nonlinear coupled processes such as rock deformation. In this Article, we present a new hierarchical approach for simulating hydromechanical (HM) coupling in fractured shale gas reservoirs with multiple porosity scales, which include microscale inorganic matter and organic matter (kerogen), mesoscale natural fractures, and macroscale hydraulic fractures. Specifically, an equivalent mesoscopic model is developed to represent the inorganic matter and kerogen by using the homogenization method; then, we combine this model with natural fractures and further homogenize them to form the equivalent macroscopic model. In other words, kerogen, inorganic matter, and natural fractures are represented implicitly through the equivalent continuum model, which is developed by using two-level homogenization. On the contrary, we apply the embedded discrete fracture model to explicitly consider hydraulic fractures. After that, the mimetic finite difference method and the stabilized extended finite element method are adopted for the discretization of flow and geomechanics models. Then, the HM coupling model is solved by using a sequential implicit method. Finally, we test the proposed approach by means of some numerical examples and then apply this hierarchical approach to study the effects of inorganic matter, kerogen, natural fractures, and hydraulic fractures on gas production in 3D fractured shale reservoirs.