基于吸附势理论的深部煤储层吸附气量研究

Amount of adsorbed gas in deep coal reservoir based on adsorption potential theory

为了揭示深部煤储层煤吸附特性,量化表征煤储层吸附气量,以鄂尔多斯盆地东缘石炭—二叠系煤为研究对象,通过高温高压条件下煤的等温吸附实验研究,从煤级、温度及压力的角度解读高温高压条件下煤吸附特征。基于吸附势理论,建立了不同煤级煤的吸附特征曲线及吸附气量预测模型。应用预测模型对临兴地区石炭系8+9号煤层吸附气量进行了计算,结果表明:深部煤储层吸附气量受煤级、压力、温度的综合控制,煤级在0.77%~2.18%,即气煤—贫煤阶段,煤级和压力对煤吸附能力显示正效应、温度起负效应,且随着压力增大温度的负效应更为显著。不同煤级对应的煤吸附甲烷特征曲线不同,煤级越高则吸附势随吸附空间增大而减小的速度越缓慢。计算的绝对吸附量为19.6~31.1 cm^3/g,含气饱和度为37.8%~78.8%。

In order to reveal the deep coal reservoir adsorption characteristics of coal and the quantitative characterization on the amount of adsorbed gas of coalbed methane,this paper studied the coal samples of carboniferous-permian in eastern Ordos Basin and analyzed the methane isothermal adsorption experiments of high temperatures and pressures of coal samples.An interpretation of the adsorption characteristics was made under high temperatures and pressures from the geological factors including coal rank,temperature and pressure. The curves of coal adsorption characteristic and the prediction model of amount of adsorbed gas with different coal ranks were established based on the adsorption potential theory.Meanwhile,a case study on the amount of adsorbed gas of the No.8＋9 coal seam in Linxing area was analyzed based on this model.The results show that the adsorption characteristics of deep coal reservoir are comprehensively influenced by temperature,pressure and coal rank.When the coal rank is between 0.77% and 2.18%,which is from gas coal to poor coal,the coal rank and pressure show a positive effect on adsorption ability,but temperature has a negative effect. In addition,the negative effect is more significant with the pressure increases. Different coal ranks have different curves of coal adsorption characteristic.The higher of coal rank,the slower of rate at which the adsorption potential decreases as the adsorption space increases. The calculation of the amount of absolute adsorbed is between 19.6 cm3/g and 31.1 cm-3/g,and the gas saturation is between 37.8% and 78.8% in the study area.