Search

The effects of surfactants, namely sodium dodecylbenzenesulfonate (SDBS) and hexadecyltrimethylammonium bromide (CTAB), on the interfacial shear rheological properties of partially hydrolyzed polyacrylamide (PHPAM) and hydrophobically modified polyacrylamide (HMPAM) solutions, which are used in oilfields, were studied using a biconical method. The experimental results show that the interfacial shear complex modulus of HMPAM is significantly higher than that of PHPAM, because an interfacial net structure can be formed by HMPAM molecules through hydrophobic interactions. The SDBS and CTAB molecules can form interfacial aggregates with hydrophobic blocks of HMPAM and destroy the interfacial net structure, which results in a significant decrease in the shear modulus with increasing surfactant concentration. At the same time, the properties of the interfacial film change from viscous to elastic. At low SDBS concentrations, the mixed adsorption film formed by PHPAM and a few SDBS molecules has enhanced strength. However, SDBS molecules can displace PHPAM molecules at the interface and weaken the film at higher surfactant concentrations. The cationic surfactant CTAB neutralizes the negative charge on PHPAM, leading to partial curling of the polymer chain, which decreases the film strength. Relaxation measurements confirmed our mechanism involving destruction of the interfacial net 908 曹绪龙等:表面活性剂对驱油聚合物界面剪切流变性质的影响 No.5 1 引 言 提高石油采收率过程中,聚合物的使用能够增 大水相粘度,从而提高驱替溶液的波及效率;表面 活性剂则通过降低油水界面张力,提高微观洗油效 率. 化学复合驱兼具聚合物与表面活性剂的优势, 能够达到良好的驱油效果. 因此, 驱油聚合物与表 面活性剂间的相互作用研究,对大幅度提高石油采 收率具有较高的理论价值和实践意义. 目前,油田现场应用的驱油聚合物主要为两种 类型:部分水解聚丙烯酰胺(PHPAM)以其较好的增 粘能力和低廉的成本, 在油田得到了广泛应用, 是 化学驱提高石油采收率的重要化学剂;疏水改性聚 丙烯酰胺(HMPAM)通过分子间的疏水作用形成网 络结构, 因此能够在高温高盐油藏条件下使用, 显 示了广阔的应用前景. 驱油聚合物不仅改变了溶液的性质,也会强烈 改变油水界面的性质,从而影响提高石油采收率生 产实践中的乳化、油墙形成、采出液处理等过程, 而表面活性剂与聚合物的相互作用强烈影响体系 的应用性能.文献中关于驱油聚合物与表面活性剂 间相互作用对体相粘度、油水界面张力等的影响报 道较多, 而对于界面流变性质关注相对较少. 阳 离子表面活性剂与 PHPAM间存在静电相互作 用, 其它类型表面活性剂则与 PHPAM间相互作 用较弱; 而除静电相互作用外,各类型表面活性剂 与HMPAM间存在明显的疏水相互作用,这种疏水 相互作用强烈影响溶液中聚合物分子的网络结构, 从而影响体相粘度. 界面流变参数是界面膜特性的重要表征参数, 根据形变的不同,可分为界面扩张流变和界面剪切 流变.界面扩张流变反映的是界面及其附近微观弛 豫过程的信息;界面剪切流变研究则通过施加使界 面形状发生改变而面积不发生变化的外力,考察剪 切应力的响应,从而获得界面层结构和界面膜机械 强度的信息,是研究流体界面的有力手段.界面扩 张流变监测的是界面张力的变化,对界面膜性质的 变化更敏感, 但容易被少量高界面活性的物质干 扰, 其优势在于对界面弛豫过程的研究, 但难以直 接描述界面膜的强度;而界面剪切流变监测的是力 的变化, 直接与界面膜的机械强度相关, 与生产实 践的结合更为紧密.近年来,利用界面扩张流变的 研究手段,对于不同结构驱油聚合物与表面活性剂 的界面相互作用的认识日益加深,证实了疏水改性 聚合物与表面活性剂界面聚集体的形成.然而, 针对驱油聚合物的界面剪切流变研究十分缺乏, 仅有少量测量界面剪切粘度的文献. 在本文中, 我们系统研究了胜利油田现场用 PHPAM和HMPAM与代表性表面活性剂十二烷基 苯磺酸钠(SDBS)和十六烷基三甲基溴化铵(CTAB) 间相互作用对航空煤油-水界面剪切流变性质的影 响,研究结果有助于阐明聚合物与表面活性剂界面 相互作用以及优化化学复合驱配方. 2 实验部分 2.1 实验样品及试剂 超高分子量部分水解聚丙烯酰胺,北京恒聚化 工集团有限责任公司生产, 相对分子质量为 3.67× 10,水解度约为 21.4%,固含量为 88.4%,胜利油田 提供;疏水改性聚丙烯酰胺,北京恒聚化工集团有 限责任公司生产的 II型干粉,分子结构为疏水单体 改性的丙烯酰胺和丙烯酸的共聚物,含量约5%,相 对分子质量在2.0×10-2.2×10之间,水解度为23%, 固含量为 90%,胜利油田提供;十二烷基苯磺酸钠, 十六烷基三甲基溴化铵, 分析纯, 天津津科精细化 工研究所;航空煤油,北京化学试剂公司,经过柱提 纯,室温下与重蒸后的去离子水的界面张力约为42 mN∙m-1;实验用水为经重蒸后的去离子水,电阻率 为18 MΩ∙cm. 2.2 界面剪切流变性质原理 本文实验采用控制应变的实验方法.如图 1所 示,通过对位于界面上的转子施加一个正弦周期的 剪切扰动, 从而在样品中产生阻抗应力. 对于一个 粘弹性的界面膜,施加的应变γ由振幅γ0和角频率ω 给定,则: structure of HMPAM by the surfactant.

Supramolecular binary vesicles were constructed by host-guest complex formation between p-sulfonatocalix[4]arene and three cationic gemini surfactants, which were identified by UV-vis, dynamic laser scattering, transmission electron microscopy, scanning electron microscopy, atomic force microscopy, and surface tension experiments. The critical aggregation concentration of gemini surfactants decreased pronouncedly by a factor of ca. 1000 owing to the complexation of p-sulfonatocalix[4]arene.

A dilute surfactant–polymer (S–P) flooding system has been designed and developed for Gudong oilfield with Shengli petroleum sulfonate (SLPS) as the primary ingredient. The dynamic behavior of the system and the interactions of the system components have been investigated through various methods, including DPD molecular modeling technology and dynamic interfacial-tension analysis. The results have shown a significant synergistic effect between sulfonate and nonionic surfactant. The interfacial tension (IFT) and its time to reach equilibrium could be dramatically decreased, suggesting a fast diffusion–adsorption characteristic of ionic surfactants as well as the high surface activity of nonionic surfactants. The S–P flooding formulation was finalized as 0.3% (w/w) SLPS + 0.1% (w/w) 1# + 0.15% polyacrylamide (PAM), in which 1#, the secondary surfactant, is able to enhance the interfacial activity of SLPS and the flooding efficiency of the system. The S–P flooding system manifests a wide range of IFT with the lowest value of 2.95 × 10 − 3 mN/m. The pilot field trial of the system has exhibited outstanding performance to improve oil production and reduce water cut since the first injection of the main slug of the S–P flooding system started in June 2004. Until July 2008, the accumulated oil-production had risen by 17.8 × 10 4 tons, with the oil-recovery increase by 6.4%. The field trial provides useful information for the further large-scale application of the SP system in Shengli oilfield.

Polymer flooding for enhanced oil recovery (EOR), especially using polyacrylamide (PAM) based systems, gradually became the largest non-Newtonian fluid process of economic significance. Yet, the mechanistic understanding lags behind. In this paper, the relations of structures — rheological properties — EOR applications were reviewed and some recent laboratory studies on associated PAM and PAM soft gels were introduced. The multi scale understanding of polymer rheology was found to be an essential factor for future developments.

The models of the nonlinear radial flow for the infinite and finite reservoirs including a quadratic gradient term were presented. The exact solution was given in real space for flow equation including quadratic gradiet term for both constant-rate and constant pressure production cases in an infinite system by using generalized Weber transform. Analytical solutions for flow equation including quadratic gradient term were also obtained by using the Hankel transform for a finite circular reservoir case. Both closed and constant pressure outer boundary conditions are considered. Moreover, both constant rate and constant pressure inner boundary conditions are considered. The difference between the nonlinear pressure solution and linear pressure solution is analyzed. The difference may be reached about 8% in the long time. The effect of the quadratic gradient term in the large time well test is considered.