A Multiphysics Fully-Coupled Flow and Geomechanics Simulation System with Hydraulic-Fracturing Simulation Capability

Abstract

A modular multiphysics reservoir simulation system is developed that has the capability of simulating multiphase-multicomponent-thermal flow, poro-elasto-plastic geomechanics, and hydraulic-fracture evolution. The focus of the work is on the full-physics numerical hydraulic-fracture evolution simulation capability of the multiphysics simulation system. Fracture growth computations utilize a cohesive zone model as part of the computation of fracture propagation criterion. The cohesive zone concept is developed based on energy-release rates and cohesive stresses. They capture the strain-softening behavior of deforming porous material consistent with real-life observations of poro-plastic deformation. Thus, they can be reliably used within both poro-elastic and poro-plastic geomechanics applications unlike the conventional stress-intensity-factor-based fracture propagation criterion. The partial differential equations that govern the Darcy-scale multiphase-multicomponent-thermal flow, poro-elasto-plastic geomechanics, hydraulic-fracture evolution, and laminar channel flow in the fracture are tightly coupled to each other to give rise to a numerical protocol solvable by the fully-implicit method. The ensuing nonlinear system of equations is solved by use of a novel adaptively damped Newton-Raphson method. Example fully-coupled single-phase isothermal flow, geomechanics, and hydraulic-fracture growth simulations are analyzed to demonstrate the predictive power of the simulation system. Numerical model predictions of fracture length/radius and width are validated against analytical solutions for plane-strain and ellipsoid-shaped fractures, respectively. Results indicate that the simulator is capable of modeling hydraulic-fracture evolution accurately by use of the cohesive zone model as the propagation criterion. We also simulate and explore the sensitivities around a real-life hydraulic-fracture growth problem by fully accounting for the thermal, multiphase, and compositional flow effects.