Effects of Supercritical CO2 on the Pore Structure Complexity of High-Rank Coal with Water Participation and the Implications for CO2 ECBM

Xicong Ma; Yi Du; Changqing Fu; Huihuang Fang; Haonan Wei; Zhejun Pan; Shuxun Sang; Junying Zhang

doi:10.1021/acsomega.3c01486

Effects of Supercritical CO₂ on the Pore Structure Complexity of High-Rank Coal with Water Participation and the Implications for CO₂ ECBM

ACS Omega. 2023 May 19;8(21):18964-18980. doi: 10.1021/acsomega.3c01486. eCollection 2023 May 30.

Authors

Xicong Ma¹, Yi Du^{1

2}, Changqing Fu³, Huihuang Fang⁴, Haonan Wei¹, Zhejun Pan⁵, Shuxun Sang⁶, Junying Zhang²

Affiliations

¹ National and Local Joint Engineering Research Center for Carbon Capture Utilization and Sequestration & State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi'an 710069, China.
² State Key Laboratory of Coal Combustion, School of Energy and Power Engineering, Huazhong University of Science & Technology, Wuhan 430074, China.
³ College of Geology and Environment, Xi'an University of Science & Technology, Xi'an 710054, China.
⁴ School of Earth and Environment, Anhui University of Science and Technology, Huainan, Anhui 232001, China.
⁵ Key Laboratory of Continental Shale Hydrocarbon Accumulation and Efficient Development, Ministry of Education, Northeast Petroleum University, Daqing 163318, China.
⁶ Jiangsu Key Laboratory of Coal-based Greenhouse Gas Control and Utilization, China University of Mining and Technology, Xuzhou, Jiangsu 221008, China.

Abstract

To reveal how mineral changes affect a coal pore structure in the presence of water, an autoclave was used to carry out the supercritical CO₂ (ScCO₂)-H₂O-coal interaction process. To reveal the changes in pore complexity, mercury intrusion capillary pressure (MICP), low-pressure nitrogen adsorption, CO₂ adsorption, and field emission scanning electron microscopy (FESEM) experiments were combined with fractal theory. The experimental data of MICP show that the MICP data are meaningful only for the pore fractal dimension with pore sizes >150 nm. Therefore, the pores were classified into the classes >150, 2-150, and <2 nm. The results show that the pore volume and specific surface area of the coal increased significantly after the reaction. ScCO₂-H₂O can cause the formation of many new pores and fractures in the coal. The presence of H₂O may increase the potential for the injection of CO₂ into the coal seam. The complete dissolution of calcite surfaces caused a significant increase in the pore volume and specific surface area of the pores >150 nm. The morphologies of these pores are controlled by the morphologies of the complete dissolution carbonate particles. The pore morphologies were relatively uniform, and the fractal dimensions decreased. However, the incomplete dissolution of calcite leads to irregular variations in the morphologies for the pores in the 2-150 nm pore size range. The pore morphologies that are produced by incompletely dissolved calcite particles are more complex, which increases the fractal dimensions after the reaction. The fractal dimensions of the pores <2 nm decreased after the reaction, indicating that the newly generated micropores were more uniform and had regular pore morphologies.