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Minerals 2018, 8(3), 117; https://doi.org/10.3390/min8030117

Experimental Study of CO2-Water-Mineral Interactions and Their Influence on the Permeability of Coking Coal and Implications for CO2-ECBM

1
Development and Research Center of China Geological Survey, Beijing 100037, China
2
School of Energy Resources, China University of Geosciences, Beijing 100083, China
3
School of Energy Science and Engineering, Henan Polytechnic University, Jiaozuo 454000, China
4
College of Geoscience and Surveying Engineering, China University of Mining & Technology, Beijing 100083, China
5
Department of Chemical and Petroleum Engineering, University of Calgary, Calgary, AB T2N 1N4, Canada
*
Author to whom correspondence should be addressed.
Received: 18 January 2018 / Revised: 6 March 2018 / Accepted: 14 March 2018 / Published: 19 March 2018
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Abstract

Coal permeability is one of the most critical parameters affecting gas flow behavior during coalbed methane (CBM) production. However, little research has been conducted on how permeability evolves after CO2 injection in coking coal. Hence, examining possible chemical interactions between coal minerals, water, and injected CO2 can be very helpful to better characterize coking coal. In this study, coking coal specimens obtained from the Malan and Tunlan mines located in the Gujiao block of the Qinshui basin were treated with water and CO2 to achieve a better understanding of their dissolution kinetics, pore structure, and permeability. It was found that the relative carbonate mineral content decreases with time, while the relative clay mineral content increases after the reaction with CO2 and water. Scanning electron microscopy (SEM) confirmed these mineral alteration phenomena. Carbonate minerals (calcite, dolomite) dissolve faster than clay minerals (montmorillonite, illite and kaolinite). In particular, the dissolution rates of Ca2+ in carbonate minerals increases with decreasing temperature (25–45 °C) and pH (4.3–6.3), and the dissolution rate of Ca2+ ions in the calcite reaction solution is higher than that in the dolomite solution. In addition, the results of low-pressure nitrogen adsorption analysis showed that CO2 injection can enlarge smaller size pores into larger size pores and change the overall pore size distribution. Therefore, CO2 injection can increase the porosity of coal beds and ultimately their permeability, which in turn facilitates CBM production. View Full-Text
Keywords: CO2 injection; ion dissolution; reaction kinetics; pore structure; coal permeability CO2 injection; ion dissolution; reaction kinetics; pore structure; coal permeability
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Guo, H.; Ni, X.; Wang, Y.; Du, X.; Yu, T.; Feng, R. Experimental Study of CO2-Water-Mineral Interactions and Their Influence on the Permeability of Coking Coal and Implications for CO2-ECBM. Minerals 2018, 8, 117.

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