二价阳离子在低盐水改变砂岩润湿性中的作用

Effect of bivalent cation on wettability alteration of sandstone by low saline water

根据岩心自渗吸实验及Zeta电位测试结果,在宏观上研究二价阳离子改变砂岩表面润湿性的机理;根据极性模拟油组分在砂岩表面吸/脱附实验和分子模拟结果,在微观上阐释二价阳离子改变砂岩表面润湿性的机理。结果表明:原油中的酸性组分和砂岩表面硅醇基团被电离而带负电,酸性组分主要通过二价阳离子架桥吸附于砂岩表面,并不能通过一价阳离子架桥吸附及范德华力吸附,砂岩表面亲水性减弱;盐水盐度降低使酸性组分、砂岩表面负电性增强,两者静电斥力增大,酸性组分脱附,导致砂岩表面亲水性增强。

The spontaneous imbibition results and zeta potential measurements macroscopically studied mechanism of wettability alteration on sandstone surface by bivalent cation.The adsorption/desorption of simulated polar oil on sandstone and molecular simulation results microscopically explained mechanism of wettability alteration on sandstone surface by bivalent cation.Results show that the acidic components of crude oil and the silanol on sandstone were ionized to be negative,and the acidic components can adsorb onto sandstone mainly by bivalent cation instead of monovalent cation,then sandstone surface changed to be less water-wet.Lower salinity can make acidic components and sandstone surface more negatively charged,and the electrostatic repulsion increased,then the acids desorbed and wettalibity of sandstone changed to be more water-wet.Therefore the effect of bivalent cation on wettability alteration of sandstone by low saline water is that the acid of crude oil can adsorb onto sandstone surface mainly by bivalent cation of formation water,when injecting low-saline water,the electrostatic repulsion between adsorbed acid and sandstone surface increases,and then acids desorp,as a result,sandstone surface changes to be more water-wet.