Numerical Simulation of Acid-Rock Dissolution in Porous Carbonate Reservoirs Under Different Injection Rates

Summary Calcite dissolution plays a vital role in geological, hydrological, and environmental engineering, particularly in carbon sequestration, rock weathering, and groundwater chemical evolution. When acidic fluids react with calcium carbonate minerals like calcite, they often form typical wormhole structures. Understanding the morphological evolution of dissolution channels like wormholes in carbonate rocks under acid injection is critical for optimizing applications such as acid stimulation and geological carbon sequestration. As a key factor in wormhole formation, injection rate governs whether the dissolution reaction develops into a wormhole structure either dispersed or planar-front. In this study, the widely used open-source package PorousMedia4Foam is employed to simulate fluid flow and acid-rock dissolution transport in the free flow region of porous carbonate reservoirs, taking into account the effects of acid injection rate on the formation of wormholes in both homogeneous and structurally heterogeneous porous media, as well as the formation and temporal evolution of rock wormhole structures. Results show that in homogeneous media, wormhole formation is most efficient at intermediate velocities, where reaction and transport are balanced. However, in heterogeneous media, acid fronts are significantly perturbed by structural irregularities, leading to increased branching, tortuous paths, and the loss of well-defined wormhole morphology. These findings highlight the necessity of incorporating geological heterogeneity into predictive models of reactive transport, particularly in optimizing acidizing treatments and assessing storage integrity in subsurface formations. In summary, this study provides a theoretical foundation for a deeper understanding of wormhole evolution during reactive seepage and offers valuable insights for engineering applications such as oil and gas reservoir stimulation and geological carbon sequestration.