围压对低渗砂岩渗透率有效应力系数的影响

The effect of confining pressure on effective pressure coefficient for permeability in low-permeability sandstones

多孔岩石渗透率有效应力系数的取值至今仍没有一致的认识,影响取值的因素较为复杂.为了探索围压对低渗砂岩渗透率有效应力系数的影响,实验上采用较大的围压范围(10MPa～50MPa),选取两块低渗致密砂岩岩样,进行渗透率测试,并利用二元线性回归方法,计算了不同围压组合下的渗透率有效应力系数值,获取了该系数随围压的变化趋势.实验中,两块岩样的渗透率有效应力系数随围压的增加而减小,但各自的减小趋势略有不同.利用Bernabé和Berryman提出的模型,理论上解释了围压对渗透率有效应力系数的影响,并得到渗透率有效应力系数的下限值为岩样孔隙度.尽管渗透率有效应力系数不是一个常数,但可以表示为压差的函数,进而起到简化分析的作用.

There is still no an identical conclusion for effective pressure coefficient for permeability in porous rocks,and its value depends on many complicated factors.In this laboratory study,wide dimension of confining pressure is designed（10MPa～50MPa）to explore the effects of confining pressure on effective pressure coefficient for permeability.Two low-permeability tight sandstones are selected for testing the permeability.Effective pressure coefficients for permeability are calculated in different combination of confining pressure with the method of binary linear regression,and the variation of effective pressure coefficient for permeability with confining pressure is obtained.It shows the effective pressure coefficient for permeability decreases with the increasing of confining pressure in experiments,but there are some differences between two samples in the tendency of reduction.With Bernabé and Berryman＇s model,we explain the effect of confining pressure on effective pressure coefficient for permeability theoretically,and it shows that the lower bound of effective pressure coefficient for permeability is sample＇s porosity.Effective pressure coefficient for permeability is not a constant,but it can be expressed with differential pressure to simplify the calculation.