Multi-scale joint characterization of coal seam pore structure and its influence on movable fluid

Micro-pore structure affects the fluid storage and seepage in coal seams.In this paper, six samples from the Jurassic Yan'an Formation coal seam in the Shenmu area of the Ordos Basin were taken as the object of study.The pore distribution characteristics of coal seams were jointly characterized by NMR, CO₂ adsorption and N₂ adsorption at multiple scales, and the connectivity and homogeneity of microscopic pores were investigated by combining multi-scale joint characiterization with CT scanning.Results show that the micro-pores of coal are the main contributors to the specific surface area and pore volume, followed by meso-pores.There is a good uniformity in the pore size distribution of the micro-pores and meso-pores by combing NMR and adsorption, while considerable differences are found in the macro-pores.Displacement NMR and CT excel in reflecting the degree of connectivity, both of which are consistent in the characterization of connectivity.Parameters such as coordination number and seepage pore ratio can effectively reflect the degree of connectivity of the sample, whose patterns of connectivity is M6>M2>M12>M15>M10>M4.The saturation of bound water shows a satisfactory positive correlation with pore-throat ratio of coal samples.It can be seen that the pore structure has a great influence on the degree of fluid migration, which is the basis for studying and evaluating gas occurrence and seepage.