致密砂岩启动压力梯度数值的影响因素

为了分析致密砂岩启动压力梯度数值的影响因素,分别从实验设备控制方式和岩石物性参数2方面开展研究。结果表明:采用净围压模式流体恒压注入,可以降低由于实验方法不同带来的实验误差,恒围压模式下测得结果往往偏大;注入方式的不同对拟启动压力梯度数值几乎没有影响。真实启动压力梯度随含水饱和度的增加逐渐增大,达到最大值后逐渐减小,而且渗透率越高的岩心,在相同含水饱和度下的启动压力梯度越小;启动压力梯度随着可动流体饱和度、主流喉道半径增加而降低,且降低的幅度越来越小;微裂缝的存在降低了岩石启动压力梯度。基于上述分析,室内测试启动压力梯度一定要严格模拟地层条件,并按照实际地层水的矿物成分配制模拟注入水,这样测得的结果才有意义。

Influencing factors of threshold pressure gradient value for tight sandstone

In order to analyze the influence factors of threshold pressure gradient value for tight sandstone, this paper studies the experiment equipment control mode and petro-physical parameters. Result shows that the constant pressure injection fluid can reduce the experimental error caused by using different experimental methods in net confining pressure mode. Measured results under constant confining pressure are big. The different injection methods have little impact on threshold pressure gradient values. The real threshold pressure gradient increases with the increase of water saturation. After reaching the maximum, it reduces gradually. For the core with high permeability, the threshold pressure gradient at the same water saturation is small. It can reduce with the increase of movable fluid saturation and mainstream throat radius and the reducing size is smaller and smaller. The existence of microfractures reduces the threshold pressure gradient of rock. Based on the above analysis, measuring the threshold pressure gradient in the lab must be strict in simulating formation conditions, according to the mineral composition of the actual formation water, simulated water is prepared, thus the measured results have practical significance.