鄂尔多斯盆地延长组致密砂岩油藏低盐度水驱作用规律

Low-salinity waterflooding laws in the tight sandstone oil reservoirs of Yanchang Formation in Ordos Basin

目前低盐度水驱研究主要集中于中高渗透、高黏土质量浓度的砂岩油藏,是否适用于致密砂岩油藏有待于深入研究。基于这种情况,以鄂尔多斯盆地致密油藏岩心和原油为研究对象,利用岩心驱替实验、润湿角测定实验、界面张力以及界面扩张流变测定实验开展致密砂岩油藏低盐度水驱作用规律研究。实验结果表明:低盐度水驱适用于致密砂岩油藏,调整注入水离子组成改变岩石表面润湿性以及油水相互作用,即可实现采收率的提高;其中,降低Ca^(2+)质量浓度或增加SO_(2)质量浓度可促进极性原油组分脱离岩石表面,增强岩石表面水湿性;与此同时,降低Ca^(2+)质量浓度或增加SO_(2)质量浓度可促进极性原油组分在油水界面的吸附,降低界面张力并增强界面黏弹性;降低Ca^(2+)质量浓度或增加SO_(2)质量浓度对提高采收率有较好效果。研究成果为低盐度水驱在致密砂岩油藏中的应用提供了理论参考。

By now, the study on low-salinity waterflooding is mainly focused on the sandstone oil reservoirs with medium-high permeability and high clay content. Whether it is applicable for the tight oil reservoirs needs further study. On this basis, taking the cores and crude oil from the tight oil reservoirs in Ordos Basin as the research objects, the laws of low-salinity waterflooding in tight sandstone reservoirs are studied with the help of core flooding experiment, wetting angle measurement, interfacial tension and interfacial dilation rheology determining experiments. The experiments shows that the low-salinity waterflooding is applicable for tight sandstone oil reservoirs as adjusting the ionic composition of injected water can change the rock surface wettability and the oil-water interaction, so as to enhance the oil recovery;Herein, the decrease of Ca^(2+) mass concentration or the increase of SO_(2) mass concentration can both promote the polar crude oil components desorbed from the rock surface and enhance the water wettability of the rock surface;Meanwhile, the decrease of Ca^(2+) mass concentration or the increase of SO_(2) mass concentration can accelerate the adsorption of the polar crude oil components on the oil-water interface, reduce the interfacial tension and enhance the interfacial viscoelasticity;Decreasing the mass concentration of Ca^(2+) or increasing the mass concentration of SO_(2) has a better effect on enhancing the oil recovery.These study achievements provide the theoretical references for the application of low-salinity water drive in tight sandstone oil reservoirs.