低、特低渗透砂岩气藏单相气体渗流特征实验

An experimental study on the percolation characteristics of single phase gas in low and ultra-low permeability sandstone gas reservoirs

由于低渗透、特低渗透砂岩气藏储层孔隙结构的特殊性,其单相气体的渗流特征与中高渗透储层相比存在很大的差别,有必要对其渗流特征进行研究。通过对数十块低渗透、特低渗透砂岩岩心不同驱替压力下单相气体渗流特征的实验研究,结果表明,一般情况下特低渗透砂岩储层(小于0.1×10-3μm2)的渗流特征符合克氏渗流曲线特征,但是在孔隙压力很低的情况下会表现出由于强滑脱效应而引起的非线性渗流特征;对于低渗透率储层(大于0.1×10-3μm2),气体的渗流特征在低驱替压力下符合克氏渗流曲线特征,但是在较高驱替压力下会表现出明显的高速非线性渗流特征。对于特低渗透砂岩储层而言,气体渗流一般不可能发生高速非线性流效应;而对于低渗透储层,就要考虑高速非线性效应对低渗透砂岩气藏气体渗流规律的影响。

The gas percolation characteristics of low or ultra-low permeability sandstone are greatly different from those of the medium-or high-permeability sandstone because of the peculiarity of pore structure.It is necessary to fully understand the gas percolation characteristics,so a complete gas percolation mathematical model was set up to calculate and dynamically predict the production capacity of a gas well.Dozens of low and ultra-low permeability sand core samples were tested in experiment to study the gas percolation characteristics in them.Results show that there are two obvious gas percolation characteristics.In the ultra-low permeability samples(less than 0.1 millidarcy),the percolation characteristics are fundamentally in accord with the characteristics of the Klinkenberg percolation curve,and when the pore pressure was extremely low,it shows non-linear flow characteristics caused by strong slippage effects.In the low-permeability samples(more than 0.1 millidarcy),the gas percolation characteristics are in accord with the characteristics of the Klinkenberg percolation curve in low driving pressure,however,it shows a high-speed nonlinear flow characteristic under high driving pressure.The results demonstrate that there are not in general high-speed non-linear flow effects in extremely low-permeability sandstone reservoirs,but in low permeability reservoirs,they need to be considered.