A reactive-transport phase-field modelling approach of chemo-assisted cracking in saturated sandstone

Abstract

Hydraulic fracturing and acidification techniques are important approaches for deep energy recovery engineering. However, the details of the interactions and impacts between acid fluids and solid porous media remain inadequately modelled, necessitating further research in this domain. Building on this need, we present a novel approach for modelling the chemo-hydro-mechanical response in sandstone during fracture propagation which is induced by the injection of acid fluids into the reservoir. Our comprehensive framework integrates various mechanisms including acidified reactions in sandstone, reactive flow transport, pore pressure diffusion, solid deformation, mass exchanges due to chemical reactions, and fracture propagation in poroelastic media, all within the framework of the phase field approach. To accurately capture the system’s behaviour, we derive its total potential energy, taking into account factors such as poroelasticity, fracture forces acting on the fracture sides, and crack dissipation, while also integrating the mechanical–chemical degradation function into the energy derivations. The progress of chemical degradation, which we treat as a damage parameter, is characterized by mass exchanges, and these in turn manifest as changes in porosity. In order to quantify these mass exchanges, we have established a corresponding mass balance equation specifically for the minerals involved. These changes in porosity can be naturally and effectively described through the volumetric relations of the minerals situated within the solid porous media. The proposed coupled framework is verified through multiple numerical examples. Initially, we validate the model using a classical unit-slit crack example for the solid phase and discuss the predominant influences of porosity alterations on the mechanical response of solid cracking. Following this, we verify the model by injecting water/acid and compare the results with analytical solutions. Finally, a chemical benchmark is employed to calibrate the chemical reaction model and simulate acid fluid injection scenarios.