Gas Flow Coupled To Elastoplastic Geomechanics For Shale Gas Reservoir

Fluid production from shale gas formations has increased significantly,Stimulation and hydraulic fracturing are critical in making these systems productive,and hence it is important to understand the behavior of the reservoir.When modeling fractured reservoirs using discrete fracture network representation,the geomechanical effects are expected to have a significant impact on important reservoir characteristics.It has become more accepted that fracture growth,particularly in naturally fractured reservoirs with extremely low permeability.A coupled flow and geomechanics model considers flow physics and rock physics simultaneously by coupling different types of partial differential equations through primary variables.A number of coupled flow and geomechanics simulation have been applied to describe fluid flow in porous media but the majority of these coupled flow and geomechanics simulation have limited capabilities in modeling single phase flow and geomechanical deformation in a homogeneous and fractured reservoir To solve these challenging problems,COMSOL software capable of performing coupled fluid flow and geomechanical modelling and simulating.In this study a partial differential equations derived for fluid flow and geomechanics and implemented to the COMSOL 3.5a for simulation of flow and rock deformation in a homogeneous and/or fractured reservoir system.Mixed finite element formulation derived that satisfies local mass conservation and provides a more accurate estimation of the velocity solution in the fluid flow equations.Continuous Galerkin formulation used to solve the geomechanics equation.These formulations allowed to use unstructured meshes,a fulltensor permeability,and elastic stiffness.Mohr-Coulomb failure criterion employed to the simulator to evaluate potential areas of shear failure in the rock.In this work numerical simulations performed on coupled flow and geomechanics for fractured reservoirs,From numerical tests,indicate that the production of gas causes redistribution of the effective stress fields,increasing the effective shear stress and resulting in plasticity,Shear failure occurs not only near the fracture tips but also away from the primary fractures,which indicates the generation of secondary fractures.From various numerical tests,shear failure is enhanced by a large pressure drop at the production well,Young's modulus and low frictional and dilation angles.These complicated physics for stress-sensitive reservoirs cannot properly be done by the uncoupled or flow only simulation,and thus,tightly coupled flow and geomechanical model are highly recommended to the shale gas reservoir during gas production.