CO2注入对煤储层应力应变与渗透率影响的实验研究

以沁水盆地成庄矿煤样为研究对象，利用实验室自主研发的CO₂注入与煤层气强化开采实验模拟装置进行不同有效应力和CO₂吸附压力下的煤岩渗透率测试。实验结果表明，煤岩的裂隙压缩系数受到CO₂吸附的影响，初始状态下、亚临界CO₂吸附和超临界CO₂吸附煤样裂隙压缩系数分别为0.066、0.086和0.089。引起裂隙压缩系数改变的原因主要有两方面:CO₂和煤中矿物反应提高了煤基质的不连续性；CO₂软化了煤基质同时降低了煤岩的力学性质。利用考虑吸附应变以及内部膨胀系数的渗透率模型对实测渗透率进行拟合，发现有效应力和内部膨胀系数成正比。CO₂吸附压力和有效应力的增大均提高了煤岩的内部膨胀系数，这影响了煤岩孔裂隙的开度，降低了煤储层的渗透率，并最终降低CO₂在煤储层中的可注性。 

Experimental study of the influences of CO2 injection on stress-strain and permeability of coal reservoir

Based on the coal samples of Chengzhuang coal mine in Qinshui basin, the permeability tests under various effective stresses and CO₂ adsorption pressures of coal were conducted by using the independent-developed experimental simulation device for CO₂ injection and enhanced coalbed methane recovery. The results indicate that the fracture compressibility of coal is affected by CO₂ adsorption, the fracture compressibility coefficients of coal under initial state, subcritical CO₂ adsorption and supercritical CO₂ adsorption are 0.066, 0.086 and 0.089. Two reasons are concluded as:the reaction of CO₂ and minerals in coal improves the internal discontinuity of coal matrix; CO₂ softens the coal matrix and reduces its elastic modulus. The fitting results of measured permeability by adopting the permeability model considering adsorption swelling strain and internal swelling coefficient show that the effective stress is proportional to the internal swelling coefficient. CO₂ adsorption effect blocks some pores and fractures, effective stress not only compress fracture structure but also advances the internal swelling coefficient. The combination of the two effects reduces the injectivity of CO₂ into coal seam, especially for injecting high pressure CO₂ into coal reservoirs with high effective stress.