A Cohesive-Zone Model for Simulating Hydraulic-Fracture Evolution within a Fully Coupled Flow/Geomechanics-Simulation System

Abstract

Summary 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 hydraulic-fracture-evolution-simulation capability of the multiphysics simulation system. Fracture-growth computations use a cohesive-zone model as part of the computation of fracture-propagation criterion. The cohesive-zone concept is developed using 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 (PDEs) 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 simulation system 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.