Nuclear Magnetic Resonance Study on Microstructure and Permeability of Coals of Different Ranks

Jiajia Liu,Dan Wang,Jianmin Hu,Jianliang Gao,Gaini Jia

doi:10.1155/2020/7918510

Jiajia Liu, Dan Wang + Show 3 more

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https://doi.org/10.1155/2020/7918510

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Abstract

The microscopic pore development of most coal seams in China leads to different permeability of coal seams and different gas drainage efficiency. Representative three coal rank coal samples were selected for saturation-centrifugation observation. The microscopic pore characteristics of coal samples were measured by nuclear magnetic resonance and liquid nitrogen adsorption methods. The experimental results showed that the coal samples were subjected to saturation-centrifugation and nuclear magnetic resonance (NMR) tests. It was found that the pores of the low-rank coal (XJ-1, XJ-2) were developed at various stages, and the connectivity between the pores was good and the permeability was also good. The adsorption pores of the intermediate coal (HB-1, HB-2) and high-rank coal (ZM-1, ZM-2) were relatively developed, and the connectivity between the pores was slightly poor. The parallel coal seam samples of coals of different ranks were better than the vertical bedding. The adsorption of liquid nitrogen showed that the low-order coal had more open pores and good gas permeability; the high-order coal had more openings at one end, more ink bottles, and narrow holes, and the gas permeability was not good. Studying the micropore structure and permeability of coals of different ranks has guiding significance for mastering the law of coal seam gas storage and transportation, extracting drilling arrangements, and increasing gas drainage and reducing greenhouse effect.

Highlights

Coalbed methane is a hydrocarbon gas that is present in the coal seam and contains gas as the main component, about 80%∼90% in the adsorbed state on the surface of the coal matrix particles and 10%∼20% in the pores and cracks of the coal body
E authors of [32, 33] used T2 cutoff value to determine the boundary between the movable fluid and the bound fluid of the coal sample and distinguished the movable fluid from the bound fluid to further judge the permeability of the coal rock mass. eoretical general research suggested that the
Starting from the intersection point, the line was perpendicular to the X-axis. e value of the abscissa corresponding to this line was T2c. e T2 cutoff values of the three coal samples are significantly different

Summary

Research Article

Nuclear Magnetic Resonance Study on Microstructure and Permeability of Coals of Different Ranks. E microscopic pore characteristics of coal samples were measured by nuclear magnetic resonance and liquid nitrogen adsorption methods. E experimental results showed that the coal samples were subjected to saturation-centrifugation and nuclear magnetic resonance (NMR) tests. It was found that the pores of the low-rank coal (XJ-1, XJ-2) were developed at various stages, and the connectivity between the pores was good and the permeability was good. E adsorption of liquid nitrogen showed that the low-order coal had more open pores and good gas permeability; the high-order coal had more openings at one end, more ink bottles, and narrow holes, and the gas permeability was not good. Studying the micropore structure and permeability of coals of different ranks has guiding significance for mastering the law of coal seam gas storage and transportation, extracting drilling arrangements, and increasing gas drainage and reducing greenhouse effect

Introduction

XJ HB ZM

Signal amplitude

Cumulative porosity under

Conclusion