考虑滑脱效应的欠饱和煤储层渗透率模型

A Permeability Model of Undersaturated Coal Reservoir Considering Slippage Effect

在多孔介质应力-应变本构公式基础上,考虑有效应力效应、基质收缩效应、滑脱效应对煤储层渗透率的影响,建立欠饱和煤储层的渗透率动态模型,以沁水盆地某煤层气田为例,模拟储层压力从初始值降至衰竭压力过程中煤储层渗透率变化,分析模型参数敏感性。结果显示:在开发初期,欠饱和煤储层储层渗透率持续下降,储层压力下降至临界解吸压力时,渗透率降至最低点,之后渗透率开始上升;储层压力由初始值下降至临界解吸压力3.80 MPa时,渗透率下降至最低值0.186×10-3μm2,之后渗透率开始上升,当储层压力下降至2.77 MPa时,渗透率恢复至初始值,储层压力下降至衰竭压力时,渗透率上升至初始值的3.182倍;兰氏体积应变、杨氏模量及滑脱系数参数值越高,储层最终渗透率改善幅度越大,泊松比值越高,储层最终渗透率改善幅度越小;与其他参数相比,兰氏体积应变对煤储层最终渗透率改善的影响最为重要。

Based on the stress-strain constitutive equation of porous media, a permeability model of the undersaturated coal reservoir is presented considering the effective stress, matrix shrinkage and slippage effect. Using the model and parameters from the coal seam of Qinshui basin, the permeability variations of this block in the process of reservoir pressure changing from the initial value to the depletion pressure are predicted. The model parameter sensitivity is analyzed. The results indicate that at the initial stage of the undersaturated coal reservoir, the coal reservoir permeability declines until the reservoir pressure drops to the critical desorption pressure, after that the permeability rises. The simulated results show that the coal reservoir permeability in the Qinshui basin reduces to 0.186×10-3μm2 when the pressure drops to the critical desorption pressure （3.80 MPa）, then the permeability begins to rise with the pressure decline and rebounds to the initial value at 2.77 MPa, and finally at the depletion pressure 0.92 MPa, the permeability reaches to 3.182 times the initial value. Sensitivity analysis points out that the larger the value of Langmuir volume strain, Young＇s modulus and slippage coefficient, the better the improvement of the final permeability, while the Poisson ratio is just the reverse. The Langmuir volume strain is the most important influence parameter of the final permeability.