CO2置换CH4试验中煤体应变及渗透率的变化

为研究煤层注CO2置换CH4过程中煤体应变及渗透率的变化特征，采用沁水煤田屯留矿3号煤层圆柱体原煤试样，在不同围压(8～20 MPa)及注入压力(1～6 MPa)条件下，进行注CO2置换煤层CH4试验。研究表明：置换试验中，煤样的轴向、径向及体积应变随有效应力的增加呈指数关系降低，随围压的增加而降低；同时随围压的增加，相同压降范围内的轴向、径向、体积应变降幅呈增大趋势；且相同围压条件下，径向应变大于轴向应变。试验同时发现，同一围压下，受有效应力效应、基质收缩效应及滑脱效应等作用影响，煤体渗透率随着有效应力的增加呈现先降低后增加的变化关系；相同有效应力条件下，渗透率随着围压的增大而减小；且在试验压力范围内，有效应力增加后期渗透率相对初期提高了8.53%~22.45%。

Variation characteristics of coal strain and permeability on coal-bed methane displacement by carbon dioxide injection

In order to study the variation characteristics of coal strain and permeability on the displacement of CH4 by CO2 injection，an experiment about the coalbed methane replacement by CO2 under given confining pressures (8-20 MPa) and injection pressures (1-6 MPa) was carried out with cylinder raw coal specimen from the No.3 coal seam，Qinshui Basin，China.With the experiment，the range of coal axial strain，radial strain and volumetric strain are 0.160%-0.011%，0.310%-0.036% and 0.780%-0.083% respectively with different confining pressures and injection pressures on the experiment.The axial strain，radial strain and volumetric strain decreases with exponential relation as the increase of effective stress，and decreases with the increase of confining pressure.The proportion of decrease of axial strain，radial strain and volumetric strain in the same pressure drop increases with the increase of confining pressure.The radial strain is larger than axial strain under the same confining pressure.During the displacement experiment，with the comprehensive action of effective stress effect，matrix contraction effect and slippage effect，the permeability decreases at the earlier stage and then increased sharply during the effective stress increase under the same confining pressure.And the permeability decreased with the confining pressure increase under the same effective stress.Under the experiment pressures，compared with the permeability in the initial period of effective stress increase，the permeability at the late period increases by 8.53%-22.45%.