鄂尔多斯盆地长7段页岩油渗吸驱油现象初探

鄂尔多斯盆地长7段陆相页岩油储层孔渗小，连通性差，通过单纯的水驱作用难以采出，盆地页岩油的开发主要通过大规模体积压裂增加油水置换面积进而增加采收率。开发实践与室内实验证明，储层流体与井筒流体之间存在渗吸置换现象，且通过油水渗吸置换采出的页岩油占比为15%~40%，为页岩油的有效开发提供了新的思路。通过岩心外边界敞开实验，对比不同渗透率岩心的吸水排油能力，定量研究孔隙半径、界面张力、岩心渗透率等因素对渗吸置换有效性的影响。实验显示，小于10 μm的孔隙中采出的原油占渗吸采油量的56%~80%；当界面张力为1.18 mN/m时，页岩油储层的渗吸采收率最大；在界面张力较小（小于2 mN/m）时，渗透率与渗吸采收率成正比关系，而当界面张力大于4 mN/m时，渗透率与渗吸采收率没有明显的相关性。

Preliminary study on imbibition and oil displacement of Chang 7 shale oil in Ordos Basin

Chang 7 Member shale oil reservoir in Ordos Basin， China is continental and shows characteristics of low porosity and permeability with poor reservoir connectivity. Oil displacement efficiency of this type is low， because water breaks through underground during water flooding. Shale oil in the basin has been developed by large-scale fracturing to increase water-oil contact thus to improve oil recovery rate. Oil recovered by water imbibition was proved to be effective， and both development practices and indoor experiments showed that shale oil recovered by water imbibition accounts for 15%-40% of the total， providing a new method for oil displacement in shale oil reservoir. In this study， open-boundary core system was used to quantitatively study the impacts of pore radius， interfacial tension and permeability on oil recovery by water imbibition underground. Indoor experiments showed that shale oil produced from pores with radius less than 10μm accounts for 56%-80% of the total； shale oil recovered by water imbibition peaks when interfacial tension is 1.18 mN/m； core permeability is positively correlated with imbibition recovery when interfacial tension is less than 2 mN/m， while the two are not significantly correlated when interfacial tension is higher than 4mN/m.