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Description
The technology of injecting carbon dioxide into deep coal seams has the potential to enhance coalbed methane recovery. During the long-term interaction with coal seams, the impact of carbon dioxide on coal seam structures is one of the key research focuses in the field of improving coalbed methane recovery. This study uses coal samples from the Qinshui Basin in Shanxi Province as the research subjects. Based on micro-CT technology combined with Avizo software, three-dimensional digital core models of coal samples before and after the ScCO2-H2O-coal reaction were constructed to characterize the pore structure features of the Xinjing Mine coal samples. The digital cores were then integrated with the finite element software Comsol to simulate the single-phase water seepage process. On this basis, the influence of microscopic pore structure characteristics on the permeability of the core was investigated.The results show that the ScCO2-H2O-coal reaction significantly altered the pore and fracture structure of the coal samples. The porosity of the coal samples increased by 4.68 times, the pore and fracture surface area increased by 3.69 times, and the mineral content decreased by 80%. The heterogeneity of the pore structure was enhanced, while the spatial heterogeneity of mineral distribution was reduced. Based on the pore-fracture model and the pore network model, it was found that the connectivity of pores and fractures improved significantly after the treatment, with 50% of the pores having a coordination number greater than 5. Pores with radii between 90 and 100 microns contributed the most to permeability, indicating that permeability is not only related to pore radius but also to pore volume.The seepage simulation results showed that under the same pressure gradient, pore pressure gradually decreased along the flow direction, with smaller pore radii exhibiting more significant pressure changes. The presence of fractures facilitated fluid migration in a single direction but increased the complexity of seepage paths in other directions. The ScCO2-H2O-coal reaction caused significant changes in the pore structure of the coal samples, affecting pore connectivity and permeability, and exerting a major influence on fluid flow paths and properties. These findings provide important insights into the microscopic structural evolution of coal reservoirs and the mechanisms of fluid migration.
| Country | China |
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