开发过程中煤储层渗透率动态变化特征

Dynamic variation character of coal bed methane reservoir permeability during depletion

为了摸清开发过程中煤储层渗透率动态变化特征,分析了影响煤储层渗透率动态变化的3种效应,引用了P&M渗透率模型,并以沁水煤层气田二叠系山西组3号煤储层为例,模拟了储层压力从初始值降至衰竭压力整个过程中煤储层渗透率的变化.结果显示:渗透率先减小后增大;压力降至临界解吸压力3.8 MPa,渗透率衰减少了34%,降至最低值;继续降压至2.5 MPa,渗透率回弹至初始水平;降压至衰竭压力0.7 MPa时,渗透率增至初始渗透率的2.8倍,预示该区块有较好的产气条件和前景.并通过敏感性分析得出,杨氏模量越大,基质收缩效果越显著,含气饱和度越高,越有利于改善煤储层渗透率.并据此提出2条建议:①在进行煤层气区块优选时,应加入"动态渗透率"这个关键参数,这样可能会发现"先天"条件差而开发中后期物性易得到改善、开发潜力较大的区块;②以渗透率动态变化特征为依据,不断调整和优化排水降压幅度和节奏.

Based on three effects influencing of dynamic variations, using P ＆ M model and parameters form number 3 coal seam of Qinshui basin, the permeability variations of this block were predicted. The results indicate that permeability declines first and then ascendes： when pressure drops to desorption pressure （3.8 MPa）, permeabili- ty decreases to 66% of initial value; after then the permeability begines to increase, reboundes to initial value at 2. 5 MPa; at the end pressure 0. 7 MPa, the permeability reaches to 2. 8 times of initial value, which reveales good depletion prospect of this CBM field. Also sensitivity analysis pointes that higher Young＇ s modulus, more obvious matrix shrinkage is and higher gas saturation is favour of permeability improvement. Finally, two suggestions were proposed： （1） Add the ＂dynamic permeability＂ to the parameters for selecting favorable CBM block, avoiding missing some potential blocks. （2） Adjust and optimize the depletion method, according to the variation characters.