Gas desorption mechanism of difficult to drain coal: experimental study based on pore-particle size coupling effect

Abstract

In this paper, the control mechanism of pore structure and particle size distribution on gas desorption behavior is revealed through pore fracture structure characterization, isothermal pressure desorption test and field gas extractable quantity investigation. (1) When the gas pressure is lower than 0.3 MPa, the particle size of the coal sample and the gas desorption show an abnormal relationship. Although the desorption rate of the small particle size coal sample is fast and the desorption amount is large, the residual gas content is higher, and the residual amount is reversed at the 0.3 MPa pressure point. When the pressure drops below 0.2 MPa, the non-extractable amount of coal samples with two particle sizes exceeds 3 m3/t.(2) The difference in gas adsorption and desorption characteristics of coal samples with different particle sizes is due to pore structure : specific surface area dominates adsorption capacity (5 mm particle size coal sample has stronger adsorption capacity), while pore distribution regulates desorption efficiency-macropores promote initial desorption rate (20 mm particle size coal sample has slow initial desorption rate), micropore volume determines residual gas content under relatively low pressure conditions (5 mm particle size coal sample has high residual gas content), and mesopores affect desorption continuity through equilibrium diffusion resistance.