选取不同渗透率级别的低渗和特低渗储层岩心进行水驱、二元驱油实验,研究不同驱替方式、驱替压力梯度对驱油效率的影响.实验结果表明,对于低渗透油藏,二元驱油效率高于水驱,随着压力梯度的增大,驱油效率增加,并且渗透率越低,增加幅度越明显.通过核磁共振T₂谱与恒速压汞微观孔喉测试相结合,分析岩心束缚水状态含油饱和度分布及残余油分布规律,发现较高压力梯度下二元驱替后,低渗透岩心中细微孔隙残余油较少,而高渗透岩心中较大孔隙残余油较多.

The permeability stress-sensitivity of formation rock is one of the most important research subjects in the petroleum industry and geotechnical industry. A capillary tube-pore network flow model is presented in order to explain permeability stress-sensitivity based on permeability stress-sensitivity experiments. The new model fully considers the complex connectivity among pore throats, pore structure tortuosity, different types and sizes of pore throats, and their different contribution ratios to the rock permeability. When effective stress is loaded on the low permeability rock samples, the larger pore throats, as the main flow channel, are firstly compressed smaller. Therefore, both fluid flow resistance and pore tortuosity simultaneously increase; it is the main reason that the rock permeability dramatically declines in the initial period for increasing effective stress. Since there are less large pore throats in the rock with lower permeability, those larger pore throats compressed smaller could have a greater impact on the rock permeability. Therefore, the smaller the rock initial permeability is, the stronger its stress-sensitivity is. Comparing with the experimental results for pore structure deformation, the new model is very reasonable for explaining the permeability stress-sensitivity of low permeability rock.