Influence of Heterogeneity on Acidizing Performance in Multi-Layered Carbonate Reservoirs

Carbonate rocks typically exhibit strong heterogeneity and multi-bedding characteristics, which exert a significant impact on acidification performance. In this study, based on the dual-scale continuum model and the open-source software FMOT, we developed an acidification simulation program suitable for multi-layered rocks, and focused on investigating the influence laws of two representative characteristics—heterogeneity intensity and interlayer permeability difference—on acidification performance. The results show that heterogeneity intensity significantly affects the development morphology of wormholes in high- and low-permeability rocks: under low-heterogeneity intensity conditions, the wormhole morphology in both layers is close to a straight line; under high-heterogeneity intensity conditions, the wormhole morphology exhibits a dendritic shape. When the interlayer permeability difference is 40 mD, the acid breakthrough times of rocks under three heterogeneity intensities (Low, Medium, High) are [476 s, 463 s, 450 s], indicating that the higher the rock heterogeneity intensity, the faster the acid breakthrough speed. In terms of porosity increment, under this condition, the porosity increments of high-permeability rocks are [0.0952, 0.0921, 0.0868], while those of low-permeability rocks are [0.0321, 0.0308, 0.0297]. It is evident that the acidizing effect of high-permeability rocks is significantly superior to that of low-permeability rocks. A further analysis of the influence of interlayer permeability difference shows that reducing the interlayer permeability difference significantly slows down the acid breakthrough speed of rocks, while weakening the acidizing effect of high-permeability rocks and enhancing that of low-permeability rocks; conversely, increasing the interlayer permeability difference accelerates the acid breakthrough of rocks, strengthens the acidizing effect of high-permeability rocks, and inhibits that of low-permeability rocks.