Investigation on Key Parameters of N 2 Injection to Enhance Coal Seam Gas Drainage (N 2 -ECGD)

Xin Yang, Gongda Wang, Mingqi Ni, Longyong Shu, Haoran Gong and Zhie Wang
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Xin Yang: School of Civil and Resources Engineering, University of Science and Technology Beijing, Beijing 100083, China
Gongda Wang: School of Civil and Resources Engineering, University of Science and Technology Beijing, Beijing 100083, China
Mingqi Ni: School of Civil and Resources Engineering, University of Science and Technology Beijing, Beijing 100083, China
Longyong Shu: Mine Safety Technology Branch, China Coal Research Institute, Beijing 100013, China
Haoran Gong: Beijing Key Laboratory for Precise Mining of Intergrown Energy and Resources, China University of Mining and Technology, Beijing 100083, China
Zhie Wang: School of Management Engineering, Capital University of Economics and Business Beijing, Beijing 100083, China

Energies, 2022, vol. 15, issue 14, 1-15

Abstract: Practice shows that CO 2 /N 2 -ECBM is an effective technology to enhance coalbed methane. However, there are few field tests in which the technology is applied to enhance the gas drainage in underground coal mines, and the effect is uncertain. In this study, firstly, the reasons for the decrease of gas drainage efficiency in the exhaustion period were analyzed based on the theory of fluid mechanics. Secondly, the mechanism of N 2 injection to enhance coal seam gas drainage (N 2 -ECGD) was discussed: with the gradual decrease of gas pressure in the drainage process, coal seam gas enters a low-pressure state, the driving force of flow is insufficient, and the drainage enters the exhaustion period. The nitrogen injection technology has triple effects of “promoting flow”, “increasing permeability” and “replacing”. Thirdly, the numerical simulations of the nitrogen pressure on drainage effect were carried out based on the fully coupled model. The results show that the higher the nitrogen pressure, the greater the displacement effect between injection and drainage boreholes, the larger the effective range. Finally, a field test of N 2 -ECGD was carried out in the Liu Zhuang coal mine in Huainan Coalfield, China. The results show that N 2 injection can significantly enhance the gas flow rate and CH 4 flow rate in the drainage boreholes, and the coal seam gas content decreased 39.73% during N 2 injection, which is about 2.6–3.3 times that of the conventional drainage. The research results provide an important guidance for promoting the application of N 2 -ECGD in underground coal mines.

Keywords: coal; coal seam gas; gas drainage; nitrogen injection drainage; injection pressure (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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