An NMR-Based Method for Multiphase Methane Characterization in Coals

Sijian Zheng, Shuxun Sang, Shiqi Liu, Xin Jin, Meng Wang, Shijian Lu, Guangjun Feng, Yi Yang and Jun Hou
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Sijian Zheng: Carbon Neutrality Institute, China University of Mining and Technology, Xuzhou 221008, China
Shuxun Sang: Carbon Neutrality Institute, China University of Mining and Technology, Xuzhou 221008, China
Shiqi Liu: Carbon Neutrality Institute, China University of Mining and Technology, Xuzhou 221008, China
Xin Jin: Xi’an Research Institute, China Coal Technology and Engineering Group, Xi’an 710077, China
Meng Wang: Carbon Neutrality Institute, China University of Mining and Technology, Xuzhou 221008, China
Shijian Lu: Carbon Neutrality Institute, China University of Mining and Technology, Xuzhou 221008, China
Guangjun Feng: School of Resources and Geosciences, China University of Mining and Technology, Xuzhou 221116, China
Yi Yang: Xi’an Research Institute, China Coal Technology and Engineering Group, Xi’an 710077, China
Jun Hou: College of Civil Engineering, Anhui Jianzhu University, Hefei 230601, China

Energies, 2022, vol. 15, issue 4, 1-15

Abstract: Discriminating multiphase methane (adsorbed and free phases) in coals is crucial for evaluating the optimal gas recovery strategies of coalbed methane (CBM) reservoirs. However, the existing volumetric-based adsorption isotherm method only provides the final methane adsorption result, limiting real-time dynamic characterization of multiphase methane in the methane adsorption process. In this study, via self-designed nuclear magnetic resonance (NMR) isotherm adsorption experiments, we present a new method to evaluate the dynamic multiphase methane changes in coals. The results indicate that the T 2 distributions of methane in coals involve three different peaks, labeled as P1 ( T 2 < 8 ms), P2 ( T 2 = 20–300 ms), and P3 ( T 2 > 300 ms) peaks, corresponding to the adsorbed phase methane, free phase methane between particles, and free phase methane in the sample cell, respectively. The methane adsorption Langmuir volumes calculated from the conventional volumetric-based method qualitatively agree with those obtained from the NMR method, within an allowable limit of approximately ~6.0%. Real-time dynamic characterizations of adsorbed methane show two different adsorption rates: an initial rapid adsorption of methane followed by a long stable state. It can be concluded that the NMR technique can be applied not only for methane adsorption capacity determination, but also for dynamic monitoring of multiphase methane in different experimental situations, such as methane adsorption/desorption and CO 2 -enhanced CBM.

Keywords: low-field NMR; coal; free methane; paramagnetic mineral (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2022
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