Pore Structure Characteristics of Carbonate Rocks and Their Influence on Permeability

The formation of heterogeneous pore structures is primarily influenced by the depositional environment and diagenetic processes. The inhomogeneity of carbonate media leads to the development of microfractures and dissolution pore structures, which significantly contribute to the permeability of the aquifer. In this study, various theories and methods, including geological, hydrodynamic, fractal geometry, threshold segmentation, three-dimensional reconstruction, and pore network extraction methods are integrated. Focusing on the karst Baotu Spring area in northern China, representative carbonate rock samples from the Jinan Spring area were selected. Using computed tomography (CT) scanning technology, these core samples were digitally reconstructed, allowing for an in-depth analysis of the spatial structural characteristics of the pores, fractures, and dissolution pores. Additionally, on the basis of the Navier-Stokes equations, the fluid flow process within the pore structure of carbonate rocks was simulated, and the effective permeability was determined. In this study, the impact of pore characteristic parameters on permeability were explored. The results reveal that the total porosities of the carbonate rocks range from 0.89% to 10.35%, with effective porosities varying between 0.6% and 6.12%. The surface porosities of the samples exhibit significant variability, with the pore structure showing strong inhomogeneity and high permeability. Correlation analyses of key parameterssuch as the porosity, fractal dimension, equivalent diameter, and aspect ratioindicate that the pore shape, structural complexity, and size are crucial factors affecting permeability. Porosity is positively correlated with permeability, with variations in permeability being smaller at lower porosities. The fractal dimension has a nonlinear relationship with porosity: at low porosities, the pore structure is simpler and poorly connected, whereas at higher porosities, the pore count increases, the structure becomes more complex, and the connectivity improves, thereby increasing permeability. Comprehensive analysis suggests that the geometric complexity and structural inhomogeneity of pores are key factors controlling the permeability of carbonate rocks.