油酸改性纳米TiO2的制备及其驱油性能评价

Preparation and Oil Displacement Properties of Oleic Acid-modified Nano-TiO2

纳米颗粒驱油技术在低渗油藏有较好的驱油效果,但纳米颗粒作为驱油剂在水溶液中的团聚并堵塞地层小孔隙的问题,一直未得到很好的解决。本文使用低成本的油酸对纳米TiO2进行表面改性,采用红外光谱分析仪、扫描电镜和Zeta电位分析仪分析了改性纳米TiO2的结构和形貌。并通过低渗透岩心模拟驱油实验优选合理的驱油体系。研究表明,使用油酸对纳米TiO2表面进行改性,当反应物摩尔比为1∶1,在60℃条件下反应4h时,改性得到的纳米TiO2在水溶液中稳定性最好。红外光谱测定证明了油酸基团成功接枝到纳米TiO2表面。改性后的纳米TiO2颗粒分散稳定性得到大幅提升,粒径的测试结果显示纳米TiO2在水溶液中的平均粒径为246.7nm。质量分数为0.05%的改性前后的纳米TiO2体系在亲水载玻片表面的接触角分别29.95o、81.44o,油水界面张力值分别为0.475和0.74mN/m,说明改性TiO2颗粒提高采收率的机理依然是主要依靠改变岩石润湿性和降低油水界面张力两方面。对于渗透率范围在9×10^-3数12×10^-3μm^2的低渗油藏,合理注入体系为0.1%改性纳米TiO2+0.05%OP-10,注入体积为0.3PV,提高采收率达到15%。纳米TiO2溶液不仅能降低注入水的压力,而且能提高低渗透油藏的采收率。

Nanoparticle flooding technology has a good oil displacement effect in low permeability reservoirs,but the problem of nanoparticles agglomeration in aqueous solution and blocking small pores in the formation has not been well solved. Low-cost oleic acid is used herein to surface modification of nano-TiO2 for reducing the agglomeration of nanoparticles,and the oil displacement system was optimized through low-permeability core simulation flooding experiment. The results showed that when the molar ratio of oleic acid to nano-TiO2 was 1∶1 and reacted at 60℃ for 4 h,the obtained modified nano-TiO2 had the longest stabilized dispersion time in aqueous solution. Infrared spectroscopy confirmed that the oleic acid group was successfully grafted onto the surface of nano-TiO2. SEM and Zeta potential indicated that the dispersibility and stability of the modified nano-TiO2 particles was greatly improved. The particle size test results showed that the average particle size of nano-TiO2 in aqueous solution was 246.7 nm. the contact angle of unmodified nano-TiO2 and modified nano-TiO2 system with mass fracion of 0.05% on the surface of hydrophilic slide was 29.95o and 81.44o,respectively,and the interfacial tension value was 0.475 and 0.74 mN/m,respectively,which explained the mechanism of enhancing oil recovery of the modified nano-TiO2 was still mainly relying on changing rock wettability and reducing oil-water interfacial tension. As for the low peameability reservoir with peameability of 9×10^-3-12×10^-3 μm^2,the reasonable injection parameters of the displacement system was 0.1% modified nano-TiO2 + 0.05% OP-10,and the reasonable injection volume was 0.3 PV,at this time,the enhanced oil recovery reached up to 15%. The nano-TiO2 solution could not only reduce the pressure of the injected water,but also improve the recovery rate of low-permeability core.