高、低阶煤孔隙结构差异性及其对甲烷吸附特性的影响研究

Research on the difference of pore structure between high and low rank coal and its influence on methane adsorption characteristics

采集沁水盆地高阶煤、二连盆地低阶煤,采用氮气、二氧化碳吸附法对煤基质纳米级吸附孔隙进行测试,分析高低阶煤的储气特征,从而确定影响高、低阶煤煤层气开发的关键因素。研究结果发现,高、低阶煤的比表面积相似,高阶煤的比表面积均值为215.33 m~2/g,可吸附甲烷49.53 cm~3/g;低阶煤的比表面积均值为212.17 m~2/g,可吸附甲烷48.96 cm~3/g。高、低阶煤储气主要为吸附气,占总储气量的99%以上,高阶煤储气主要是微孔吸附气,占总储气量的99.71%;低阶煤不同孔隙均有贡献,微孔最多,占比47.33%,其次是中孔,占比32.644%,大孔最少,占比19.69%。地层水侵入对低阶煤储气量影响大于高阶煤,平衡水条件下,高阶煤可储气量43.46 cm~3/g,低阶煤可储气量33.89 cm~3/g;受微孔特性影响,高阶煤储层储气量较高,但易储难逸,因此煤层气开采的关键问题是疏导微孔吸附气;受中、大孔及亲水性强影响,低阶煤储气量较低,且易储易散,勘察储气聚集区是低阶煤煤层气开发的首要工作。

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 m 2/g,which can store methane of 49.53 cm 3/g,while that of low-rank coal is 212.17 m 2/g,which can adsorb methane of 48.96 cm 3/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 cm 3/g,and that of low-rank coal is 33.89 cm 3/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.