Modeling flow and geomechanics in fractured reservoirs

Subsurface problems are inherently challenging because they involve multiple physical processes interacting with each other. Numerical models tend to break down the system into smaller problems that are easier to solve and that could be coupled within one framework. Fractured reservoirs are especially difficult to model due to the variety of physical processes that act at different scales. These processes include (1) fracture propagation, (2) flow through fractures and through the matrix, (3) hydrocarbon phase behavior, and (4) poroelastic deformations. Modeling the interaction between these processes plays an integral role in designing many energy and environmental applications. The primary objective of this work is to construct a holistic framework that can model flow and geomechanics in fractured reservoirs using computationally efficient algorithms. The framework can handle complex multiphysics problems including: multiphase flow, mechanical deformations, the capability to stimulate new fractures or activate existing ones, and the ability to seamlessly switch between propagation and production scenarios within the same simulation study. The approach includes coupling the in-house reservoir simulator (IPARS) with a phase-field fracture propagation model. In addition to hydraulic fracturing problems, the framework can model flow and geomechanics on fixed fracture networks with dynamic aperture variations. It can also simulate multiphase flow through natural fractures using general semi-structured grids. Two numerical schemes are introduced to improve the efficiency of computations. A multirate approach is proposed to enhance the performance of the L-scheme for decoupling the phase-field and displacement equations. A domain decomposition scheme is also presented to perform space-time refinement for flow through fractured reservoirs. Local time stepping and spatial mesh refinement can be used in the vicinity of the fractures while taking large grids cells with coarse time steps everywhere else in the reservoir. This motivates space and time adaptive mesh refinement in reservoir simulations.