A Hydro-Chemo-Mechanical Coupled Phase-Field Model for Acid Fracturing Simulation in Carbonate Reservoirs

A comprehensive understanding of acid dissolution patterns and their effects on fracture propagation remains limited. To address this gap, we present a hydro-chemo-mechanical coupled variational phase-field model for simulating acid fracturing in carbonate reservoirs. Fluid flow is governed by Darcy’s law in the matrix and the Poiseuille–Reynolds equations in fractures, while a two-scale acid transport model captures dissolution-induced porosity changes. The key innovations of this study include making Young’s modulus a function of porosity, thereby capturing the evolving mechanical response of the rock, and eliminating the need for additional weighting functions by employing a phase-field variable to regularize both matrix-fracture flow and acid transport. Numerical results indicate that acid fracturing reduces the initiation pressure and forms wider but shorter fractures. Furthermore, heterogeneities induce complex wormhole channels and irregular pressure distributions. Three-dimensional simulations reveal that the acid dissolution region exhibits an irregular, ellipsoidal shape. These wormholes alter the dissolution geometry and pattern, leading to an uneven structure around the fracture. This work provides a unified framework for more accurately predicting and optimizing acid fracturing in carbonate reservoirs.