二氧化碳置换甲烷试验中渗透率变化研究

Experimental Study of Permeability on Coalbeds Methane Displacement by Carbon Dioxide

为研究煤层注CO2置换CH4过程中煤样对气体的吸附特性及渗透率变化特征,利用沁水盆地圆柱体原煤试样,在恒定体积应力（36 MPa）及不同注入压力（1~5 MPa）条件下,进行CO2置换CH4试验。结果表明：煤体对CO2的渗透率高于CH4气体;置换试验中,随注入压力的降低,煤体中CO2吸附相浓度逐渐升高,而CH4气体吸附相浓度呈相反变化趋势;在试验压降范围内,煤体对CO2、CH4气体的吸附量分别降低了48.73%、68.04%,煤体解吸CH4能力强于CO2气体。同时,在置换过程中,煤样置换渗透率受有效应力效应、基质收缩效应及滑脱效应等作用影响,其随注入压力的降低呈现先降低再增大的变化关系,且渗透率最低值出现在压力3.25 MPa时;在体积应力36 MPa条件下,注入压力下降后期渗透率相对于初期提高了17.03%。

In order to study the variation characteristics of adsorption and permeability on the displacement of CH4 by CO2injection,an experiment about the coalbed methane replacement by CO2 under given bulk stress（ 36MPa） and injection pressures（ 1~5 MPa） was carried out with cylinder raw coal specoment form Qinshui Basin,China. Based on the experiment,it is found that the permeability of coal is different for methane and carbon dioxide.The permeability for CO2 is larger than thar fot methane under the testing condition. Adsorbed phase concentration of CO2 increased with injection pressure decreasing in the displacement experiment,while adsorbed phase concentration of methane shows the opposite trend. Adsorption capacity of CO2 and CH4decreased by 48.73% and 68.04% respectively in the same pressure drop of the testing. During the displacement experiment,with comprehensive action of effective stress effect,matrix contraction effect and slippage effect,the permeability decreased at the earlier and then increased sharply during the injection pressures decreasing. And the lowest permeability appears at the 3.25 MPa. Under 36 MPa bulk stress,compared with the permeability in the initial period of injection pressures decreasing,that in late period increase by 17.03%.