Research on the difference of pore structure between high and low rank coal and its influence on methane adsorption characteristics
High-rank coal in the Qinshui Basin and low-rank coal in the Erlian Basin are collected to test the nano-scale adsorption pores of coal matrix by nitrogen and carbon dioxide adsorption methods,and analyze the gas storage characteristics of different coal ranks,so as to determine the key factors affecting the CBM development of high and low-rank coal.The study results have showed that the specific surface area of high and low-rank coals is similar.The average specific surface area of high-rank coal is 215.33 m2/g,which can store methane of 49.53 cm3/g,while that of low-rank coal is 212.17 m2/g,which can adsorb methane of 48.96 cm3/g.High and low-rank coal gas storage is mainly adsorbed gas,accounting for more than 99％of the total gas storage.The gas storage of high-rank coal is mainly microporous adsorbed gas,accounting for 99.71％of the total gas storage,and different pores contribute to the gas storage of low-rank coal,with the most micropores accounting for 47.33％,followed by mesopores accounting for 32.644％,and the least macropores accounting for 19.69％.The effect of formation water intrusion on the gas storage capacity of low-rank coal is greater than that of high-rank coal.Under the condition of equilibrium water,the gas storage capacity of high-rank coal is 43.46 cm3/g,and that of low-rank coal is 33.89 cm3/g.Due to the influence of microporous characteristics,high-rank coal reservoirs have high gas capacity,but it is easy to store and difficult to escape.On the basis,the key issue in CBM development is to divert microporous adsorbed gas.Due to the influence of mesopores,macropores and strong hydrophilicity,low-rank coal has low gas storage capacity and is easy to store and disperse.Exploring gas storage and accumulation areas is the primary task for the development of low rank CBM.
high rank coallow rank coalpore structuregas adsorption methodspecific surface areagas storageCBM development
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