应力环境对煤岩吸附变形和渗透率的影响试验研究
Experimental study on influence of stress environment on coal-rock adsorption deformation and permeability
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摘要: 注入CO2增强煤层气开发过程中，煤储层渗透率的变化受有效应力变化、气体吸附/解吸引起的煤基质膨胀/收缩和气体滑脱效应耦合作用影响；为此，采用稳态法进行CH4、CO2渗流试验，研究不同应力环境下煤的吸附应变和气体滑脱效应对CH4、CO2渗流过程的影响。试验结果表明：相同应力环境下煤吸附CO2产生的最大吸附应变为CH4的1.01~2.39倍，使得CH4在为煤中渗透率始终高于CO2；同时随着埋深增加，外部应力增大，吸附应变减小；低应力环境下渗透率随气体压力减小呈“V”字形变化，随着外部应力增大，渗透率与气体压力呈负指数相关；此外，外部应力增大还将强化气体滑脱效应影响，使其更早的主导渗透率的演化。Abstract: In the process of injecting CO2 to enhance coalbed methane development, the change of coal reservoir permeability is affected by the coupling of effective stress change, coal matrix swell/shrinkage caused by gas adsorption/desorption, and gas slippage effect. Therefore, the steady-state method is used to conduct CH4 and CO2 seepage experiments to study the influence of coal adsorption strain and gas slippage effect on the CH4 and CO2 seepage process under different stress environments. The results show that the maximum adsorption strain produced by coal adsorbing CO2 under the same stress environment is 1.01 to 2.39 times of CH4, making the permeability of CH4 in coal always higher than CO2 . At the same time, as the buried depth increases, the external stress increases, the adsorbed strain decreases. In a low-stress environment, the permeability changes in a V shape with the decrease of the gas pressure, with the external stress increases, the permeability and the gas pressure are negatively related. In addition, the increase of external stress will strengthen the influence of gas slippage effect, making it dominate the evolution of permeability earlier.
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