Coupled compositional flow and geomechanics modeling of fractured shale oil reservoir with confined phase behavior

Abstract

Shale oil flow is commonly affected by the confined phase behavior, complex fracture geometries, and geomechanical effect, which are not fully considered in the conventional compositional simulators. In this study, a coupled compositional flow and geomechanics model is presented to incorporate these effects for more accurate prediction on shale oil production performance. The compositional model considering the confined phase behavior is used to model the multiphase flow in shale formations, in which the capillary pressure is introduced into the workflows of phase stability test and flash calculation. The embedded discrete fracture model (EDFM) is adopted to explicitly describe the complex fracture geometries. The deformations of hydraulic fractures and natural fractures are handled by different constitutive models. A mixed finite-volume and finite-element (FVM-FEM) scheme is used to discretize the flow and geomechanics equations, and the coupled problem is iteratively solved by the fixed-stress splitting method. Based on the proposed model, simulations are conducted on a multi-stage fractured shale reservoir to evaluate the effects of confined phase behavior, hydraulic fracture deformation, and natural fracture network on the production performance. Results show that the bubble point pressure is suppressed by the confined phase behavior effect, which leads to higher oil production. The hydraulic fracture deformation takes effect only when the hydraulic fractures cannot be treated as infinite-conductivity under poorly-propped condition. The oil production is greatly promoted with the increase of natural fracture density due to the increase of interface area between matrix and fractures.