Abstract
CO2 enhanced coalbed methane (CO2-ECBM) technology has been recognized as one of the most important technologies to enhance the recovery of CBM. However, due to the complex pore structure and strong heterogeneity of coal rocks, the industry still lacks a unified understanding of the adsorption mechanism of CH4 and CO2. In this study, three models of different coal rank were established based on realistic coal macromolecules. The grand canonical Monte Carlo (GCMC) method and equilibrium molecular dynamics (EMD) method were used to study the adsorption mechanism of CH4 and CO2 gas molecules. Then the occurrence characteristics of the two gas molecules in coal nanopores were analyzed. By analyzing the two-dimensional (2D) cloud maps of the density distribution of a total of 96 sets of CH4 and CO2 schemes, the non-uniformity of the gas adsorption behavior in the nanopores of coal can be observed. The results show that CH4 is mainly adsorbed as a mono-layer in coal nanopores; occurrence of gas within the nanopores, there are high-density adsorption layer region and bulk region; density ratios are negatively correlated with both pressure and pore size; the reduction of the pore size will help to improve the gas storage capacity in the nanopores. Cylindrical nanopore models representing different coal ranks and pore sizes were constructed that embody the complex amorphous structure and strong heterogeneity surface properties within the coal nanopores. The research in this paper can enrich the theory of CBM accumulation and provide theoretical guidance for highly efficient development of CBM.
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Acknowledgments
This work was supported by the National Science and Technology Major Project of China (2016ZX05044-004-002). Computer time for this study was provided by the HP High Performance Computing Cluster of the State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation at Southwest Petroleum University.
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Li, Y., Lu, Lz., Yang, Zz., Wang, Hh., Liu, Zb. (2022). Simulation Study on the Occurrence Characteristics of CH4 and CO2 in Coal Nanopores. In: Lin, J. (eds) Proceedings of the International Field Exploration and Development Conference 2021. IFEDC 2021. Springer Series in Geomechanics and Geoengineering. Springer, Singapore. https://doi.org/10.1007/978-981-19-2149-0_279
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