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.

Efficient coalbed methane (CBM) recovery combined with carbon dioxide (CO₂) sequestration is a promising strategy for sustainable energy production and greenhouse gas mitigation. However, the molecular mechanisms controlling pressure-dependent CH₄ displacement by CO₂ in coal nanopores remain insufficiently understood. In this study, molecular dynamics simulations were conducted to investigate CO₂-driven CH₄ recovery in a slit-pore coal model under driving pressures of 15, 20, and 25 Mpa. The simulations quantitatively captured the competitive adsorption, diffusion, and migration behaviors of CH₄, CO₂, and water, providing insights into how pressure influences enhanced coalbed methane (ECBM) recovery at the nanoscale. The results show that as the pressure increases from 15 to 25 Mpa, the mean residence time of CH₄ on the coal surface decreases from 0.0104 ns to 0.0087 ns (a 16% reduction), reflecting accelerated molecular mobility. The CH₄–CO₂ radial distribution function peak height rises from 2.20 to 3.67, indicating strengthened competitive adsorption and interaction between the two gases. Correspondingly, the number of CO₂ molecules entering the CH₄ region grows from 214 to 268, demonstrating higher invasion efficiency at elevated pressures. These quantitative findings illustrate a clear shift from capillary-controlled desorption at low pressure to pressure-driven convection at higher pressures. The results provide molecular-level evidence for optimizing CO₂ injection pressure to improve CBM recovery efficiency and CO₂ storage capacity.

Carbonate reservoirs are typically characterized by well-developed natural fractures, and complex fracture-network geometries can significantly affect the effectiveness and efficiency of acidizing. In this study, a numerical simulation program for acidizing reactive transport in fractured carbonate reservoirs was developed based on a dual-continuum theory coupled with an Embedded Discrete Fracture Model. By decoupling complex fracture characteristics, we systematically investigated the controlling mechanisms of fracture dip angle and feature length ratio (FLR) on wormhole evolution and acidizing efficiency. The results show that fractures with small dip angles favor the development of the main wormhole trunk, whereas fractures with large dip angles redirect wormhole growth and promote the formation of complex branches. Under low FLR conditions, wormhole propagation is primarily governed by matrix heterogeneity, while a higher FLR markedly enhances the influence of fracture dip angle on overall wormhole development. The response of acid breakthrough volume (${\mathrm{PV}}_{\mathrm{BT}}$) to dip angle is strongly regulated by FLR. When FLR < 0.2, ${\mathrm{PV}}_{\mathrm{BT}}$ first increases and then decreases with dip angle, reaching a maximum at 45°, whereas for FLR > 0.2, ${\mathrm{PV}}_{\mathrm{BT}}$ increases approximately linearly with dip angle, indicating a substantial reduction in breakthrough efficiency. This study provides a theoretical basis for optimizing acidizing treatments in heterogeneous fractured carbonate reservoirs.