压力变化对裂缝性致密砂岩储层气体渗透率的影响

The Effect of Pressure Variation on Gas Permeability in Fractured Tight Sandstone Reservoir

裂缝性致密砂岩气的渗透率随环境压力的改变而发生动态变化,直接影响气藏的开采。为研究裂缝性致密砂岩储层气体渗透率的变化机理,选取了塔里木盆地库车坳陷典型裂缝性致密砂岩样品,在固定围压、内压、有效应力三种条件下,运用非稳态法进行测量氦气渗透率的实验,并基于滑脱效应和有效应力的分析,探讨了二者对裂缝性致密砂岩气渗透率变化的耦合控制作用。结果表明,在裂缝性致密砂岩储层中:(1)固定围压时,在内压增加的过程中,有效应力与滑脱效应互相竞争,开始阶段滑脱效应占主导,达到气体渗透率低值点后,有效应力占主导;(2)固定内压时,有效应力对渗透率的影响占优势;(3)固定有效应力时,渗透率只受滑脱效应的影响;(4)内压与绝对渗透率损失系数、有效应力与滑脱因子都呈现正相关关系;(5)有效应力由大到小变化,对孔隙结构的破坏不可逆,渗透率损失大。该项研究对进一步认识裂缝性致密砂岩储层气体渗透率变化机理具有理论参考意义。

The gas permeability of fractured tight sandstone dynamically changed with the variety environmental pressure,which directly affects the exploitation of gas reservoirs.In order to study the change mechanism of gas permeability in fractured tight sandstone reservoir,typical fractured tight sandstone samples from the Kuqa depression in Tarim Basin were selected and the unsteady state method was used to carry out the experiment of measuring the permeability of helium under three conditions-fixed confining pressure,fixed internal pressure and fixed effective stress.Furthermore,the couple controlling factors of gas permeability change were investigated by comprehensively analyzing the effect of slippage and the effective stress on gas permeability.The results show that,in the fractured sandstone reservoir:①fixed the confining pressure,the slippage effect significantly at the beginning and the effective stress is dominant when the gas permeability has hit bottom;②fixed the internal pressure,the advantage on permeability lay with the effective stress;③fixed the effective stress,the permeability is only affected by the slippage effect;④there is a positive correlation between the internal pressure and the absolute permeability loss coefficient,so does the effective stress and slippage factor;⑤as the effective stress was descending,the damage to the pore structure is irreversible and the permeability loss can t be ignored.It is concluded that the study has theoretical reference significance for further understanding the gas permeability change mechanism in fractured tight sandstone reservoirs.