吸附不同气体对煤岩渗透特性的影响

注CO2或者CO2/N2混合气强化煤层气开采以及进行CO2封存时,气体的吸附/解吸会影响煤岩的渗透特性。采用自行研制的煤岩三轴渗流装置进行恒定有效应力、不同气体压力条件下,煤岩吸附纯CO2,CH4,N2以及不同配比的CO2/N2混合气体对渗透特性影响的试验研究,以探讨煤岩在气体压力以及吸附作用下渗透特性的变化规律。结果表明:(1)气体组分固定的条件下,煤样渗透率随气体压力的增加呈负指数减小。(2)相同气体压力条件下,煤样吸附气体后渗透率都有不同程度的下降,且下降幅度跟吸附气体的组分有关,吸附纯CO2下降的幅度最大,吸附CH4次之,吸附N2最小;吸附CO2/N2混合气时,其中CO2组分浓度越高,煤样渗透率越低,但当N2量达到一定比例时,煤样渗透率会得到改善。(3)气体压力加卸载过程得到的煤岩渗透率–气体压力关系曲线存在滞后现象,这与气体在煤岩中的吸附/解吸曲线滞后有关,因此煤岩渗透率跟压力路径有关。试验结果对于煤矿瓦斯抽采以及CO2或烟道气注入煤层后的储层渗透率的预测与控制具有重要指导意义。

EFFECT OF DIFFERENT ADSORPTIONAL GASES ON PERMEABILITY OF COAL

Gas adsorption/desorption may influence the coal permeability after injection of CO2 or CO2/N2 mixture into unminable coalbed for enhanced coalbed methane recovery and CO2 sequestration. The laboratory experiments under constant effective stress and different gas pressures are conducted by means of self-developed triaxial gas-seepage experimental device；and the change law of permeability of coal samples under gas pressure and adsorption is discussed. The results show as follows：(1) The permeability decreases as negative exponent with the increase in gas pressure under fixed injected gas composition conditions. (2) The change in permeability of coal samples is a function of the injected gas composition. At the same pore pressure，the permeabilities of coal samples decrease after gas adsorption. The permeability reduction is the greatest for pure CO2 followed by CH4 and N2. When injecting CO2 and N2 mixtures，as the concentration of CO2 in the injected gas increases，the permeability of the coal decreases. However，as the N2 reaches a certain proportion，the permeability of coal samples will be improved. (3) The relation curves of permeability and gas pressure in loading-unloading process of gas pressure have the hysteresis phenomenon，which may be related to the gas adsorption/desorption hysteresis phenomenon in coal. Therefore，the permeability of coal is in relation to pressure path. The results have important significance for prediction and control of reservoir permeability in the process of CO2 or flue gas injection into unminable coalbed to enhance gas recovery and CO2 sequestration.