Abstract
Hydraulic fracturing is a widely used technique in oil and gas production to increase the permeability of near-well reservoir and enhance hydrocarbon recovery. Modeling hydraulic fracturing involves solving coupled multi-physics equations in a robust numerical solution scheme. We present a generalized finite element framework to simulate the propagation of fluid-driven fractures in a linear elastic medium. The fluid flow within the fracture is described by the Reynolds lubrication equation, where the classical cubic law links the fluid pressure gradient and the flow rate in the fracture plane. The GFEM framework allows fractures to propagate inside the cells, and thus finite element discretization can be non-conforming with fracture geometry. The fluid front is tracked to permit fluid lag during the simulations. A unified traction-separation law is proposed to model the mechanical behavior of the fracture faces, including contact, cohesion and interface strength softening. The traction-separation law on the fracture faces is enforced by a penalty method. The coupled nonlinear system is solved by a standard Newton-Raphson method. Several 3D numerical studies and benchmarking examples are presented to demonstrate the capability of the proposed framework in modeling fluid-driven fracture propagation.
1. INTRODUCTION
Hydraulic fracturing is a technique widely used in the oil and gas industry to enhance hydrocarbon recovery from underground reservoirs. The process often results in the initiation and growth of tensile fractures, typically driven by viscous fluid that is injected into the rock with relatively high flow rate and high pressure. After the fracture is generated, certain sand-like propping agents (also called ’proppants’) are introduced into the newlyformed fracture to prevent full closure after the fluid pressure is released. Studies on hydraulic fracturing can also be found in other geomechanical applications such as geothermal energy recovery [1], transportation of magma through earth’s crust [2], sequestration of CO2 [3], embankment dam failures [4], and induced caving in mining [5].
