渗流介质对渗透率测试结果的影响

Effect of Different Types of Seepage Fluid on Permeability

分别利用氮气与氦气,采用不同的驱替压差对不同渗透率级别的特低渗岩心进行渗透率测试,并且分析了不同渗流介质的滑脱效应对渗透率测试结果的影响。实验结果表明:利用氦气和氮气测试岩石渗透率,均存在滑脱效应;相同孔隙压力下利用氦气测得的渗透率均大于氮气测得的渗透率,二者之间具有较为明显的差别,岩心孔隙压力越小,两种气体测试的渗透率差别越大,这表明在低压测试渗透率时,氦气由于分子直径较小,自由程大,引起的滑脱效应对渗透率的贡献较大;岩心渗透率越低,渗透率受滑脱效应的影响越显著。

Permeability is a crucial parameter to evaluate the ultra-low permeability reservoir. The permeability of ultra-low permeability core samples was tested by using both nitrogen and helium. The factors affecting permeability were analyzed, including fluid types, displacement pressure, slippage effect, and their interaction. The research indicates that slippage effect exists, when the permeability is tested by either nitrogen or helium, however, there are differences in the results. With the same displacement pressure, the permeability tested by helium is bigger than that tested by nitrogen, and the differences are even more significant for the lower pore pressure. It is indicated that when helium at low pore pressure is used for the test, the slippage effect makes a bigger contribution to the permeability, since the diameter of helium molecules are smaller, and the molecular free length is longer. Slippage effect is stronger, especially for the lower permeability core samples.