Propagation of toughness-dominated fluid-driven fractures in reactive porous media

Abstract

Fluid-driven open-mode fractures in porous media are the result of multiple physical processes governed by fluid properties, porous media properties, geometrical fracture properties, and fluid injection parameters. For example, a propagating open-mode fracture in which most work is spent on creating new fracture surface rather than on moving fluid through the fracture is said to be in a “toughness-dominated” regime. However, other multiphysical phenomena such as thermal dilation and mineral-dissolution can also affect fracture propagation. This study focuses on the facilitation of fracture propagation in toughness-dominated regime by weakening of the rock at the fracture tip by injection of a reactive fluid that causes mineral dissolution. We explore this coupled problem through numerical simulation using a finite element method (FEM) formulation based on the phase-field approach in order to solve equations for fluid flow, poroelasticity, linear elastic fracture mechanics and reactive transport. We couple mechanics and reactive fluid flow by assuming that fracture toughness decreases due to increases in rock porosity caused by mineral dissolution. The numerical simulation results show that acid injection and mineral dissolution (1) lower fracture breakdown pressure and (2) can bridge a transition from toughness-dominated to viscosity-dominated fracture propagation at constant injection pressure. Our results demonstrate that acid injection can change fracture propagation regimes and enable new phenomena that are not possible in unreactive porous media. The understanding of fracture propagation patterns and geometry manipulation is critical for safe and effective use of reactive fluids in the subsurface, such as in hydraulic fracturing, harnessing of deep geothermal energy, and carbon geological sequestration applications.