近年来,小分子有机酸作为外源驱油剂或内源驱油剂(微生物代谢产物)提高砂岩油藏采收率的作用逐步引起关注,但具体作用机理及效果尚存争议.利用岩心驱替和润湿角、界面张力/界面扩张流变性能、Zeta电位测定等实验,探究甲酸提高原油采收率的作用机理与效果.岩心驱替实验发现:甲酸可以显著提高低孔低渗砂岩油藏采收率.随着甲酸浓度增加至15 mmol/L,原油采收率提高6.9，.润湿角测定实验发现:甲酸明显增强了砂岩表面亲水性.油滴在地层水中的润湿角为110.3°,在15 mmol/L甲酸水溶液中的润湿角为123.0°.界面张力及界面扩张流变测试结果显示:甲酸降低了油水界面张力,显著增强原油表面黏弹性.原油-地层水界面张力为27.7 mN/m,大于原油-甲酸溶液(15 mmol/L)的20.0 mN/m,原油-地层水界面弹性和黏性模量分别为11.1 mN/m和4.0 mN/m,远小于原油-甲酸溶液(15 mmol/L)的20.3 mN/m和7.9 mN/m.Zeta电位测试结果显示:甲酸和原油吸附于石英表面均能降低石英表面负电荷,但甲酸作用更明显,因此甲酸能驱替石英表面吸附的原油,甲酸吸附于原油表面增加原油表面负电荷,显著增强油滴稳定性.综上所述,甲酸促进润湿性改变与增强原油界面黏弹性协同作用,共同提高了原油采收率.

Recently,the role of organic acids as exogenous or endogenous oil displacement agents to enhance oil recovery of sandstone reservoirs has gradually attracted attention,but the specific mechanism and effect are still controversial.Regarding this,through experiment such as core displacement and contact angle,interfacial tension/interfacial expansion rheological properties and Zeta potential measurement,the mechanism and effect of formic acid in enhancing oil recovery are explored.Core displacement experiment shows that formic acid can significantly enhance oil recovery of low porosity and low permeability sandstone reservoirs.As the concentration of formic acid increases to 15 mmol/L,the oil recovery efficiency increases by 6.9，.Contact angle measurement shows that formic acid significantly enhance the hydrophilicity of sandstone surface.The contact angle of oil drops is 110.3°in formation water,and is 123.0° in formic acid aqueous solution of 15 mmol/L.Interfacial tension and interfacial expansion rheological properties measurement shows that formic acid reduces the interfacial tension,and significantly enhances the interface viscoelasticity.The interfacial tension between crude oil and formation water is 27.7 mN/m,which is greater than the 20.0 mN/m between crude oil and formic acid solution(15 mmol/L).The elastic and viscous moduli of the crude oil-formation water interface are 11.1 mN/m and 4.0 mN/m respectively,which are much smaller than the 20.3 mN/m and 7.9 mN/m of crude oil-formic acid solution(15 mmol/L)interface.The Zeta potential measurement show that the adsorption of formic acid and crude oil on the quartz surface can reduce the negative potential of quartz surface,and formic acid has a more obvious effect,so formic acid can displace the adsorbed crude oil.Meanwhile,the adsorption of formic acid on the crude oil surface increases its negative potential and significantly enhances the stability of oil droplets.To sum up,the formic acid can promote the wettability alteration and enhance the interface viscoelasticity,which works synergically to enhance oil recovery.