沁水盆地煤样静水压力下渗透率实验及模型分析

Experimental and model analysis of permeability of coal sample from Qinshui basin under hydrostatic pressure conditions

为研究沁水盆地煤样渗透率演化规律,构建了煤样渗透率测定的瞬态压力脉冲法实验装置,使用N2和CO2在实验室开展了3种试验条件的渗透率测定,应用Connell模型对实验结果进行分析,并讨论了模型预测值和实验值之间差别的原因。结果表明,(1)在恒定孔压变围压条件下渗透率随有效应力增大而减小;在等有效应力条件下,渗透率随孔压增大而减少;在恒定围压变孔压条件下,随孔压增大,渗透率呈先减小后变大的趋势。(2)运用Connell模型预测的恒定围压变孔压条件的渗透率值大于实验值,原因可能是由于裂隙压缩性系数和吸附应变系数存在估计误差。通过开展实验室渗透率实验和模型分析,对指导实验室内二氧化碳封存和气体驱替实验及其模拟研究具有借鉴意义。

In order to study the permeability evolution of coal sample from Qinshui basin, an experimental device based on the transient pressure pulse-decay method for measuring the permeability of coal sample is developed. Permeability measurements using N2 and CO2 are conducted under common laboratory conditions which include constant pore pressure and variable confining pressures, constant effective stress and constant confining pressure and variable pore pressures. The Connell model is used to analyze the testing data. The reasons for the difference between the model prediction and the experimental value are discussed. The results show that:(1) The permeability of coal decreased with the increase of effective stress under constant confining pressure and variable pore pressures; the permeability of coal decreased with the increase of pore pressure under equivalent effective stress; as the pore pressure increased, the permeability of coal first decreased and then increased under the condition of constant confining pressure and variable pore pressures.(2) The permeability value predicted by the Connell model for constant confining pressure and variable pore pressures is greater than the experimental value. The difference between the permeability prediction and the experimental value may be due to the estimation error of the fracture compressibility and the adsorption strain coefficient. By carrying out permeability experiments and model studies in laboratory, it is of great significance to guide the experiment and simulation researches of CO2 sequestration and gas displacement in laboratory.