【作者】 袁瑞；

【导师】 李英；

【作者基本信息】 山东大学 ， 物理化学， 2013， 硕士

【摘要】 聚合物和表面活性剂是两类主要的化学驱油剂,前者通过封堵调剖降低水油流度比提高原油采收率,后者主要通过降低油水界面张力提高洗油效率提高采收率。近年来,疏水改性的聚合物由于既具有增粘效果又具有界面活性,成为备受关注的多效合一的新型化学驱油剂。本论文采用分子动力学(MD)、耗散颗粒动力学(DPD)等分子模拟方法,与动态界面张力、体相粘度、动态光散射、原子力显微镜、透射电镜等实验方法相结合,从分子水平研究了疏水改性的部分水解聚丙烯酰胺HMHPAM的分子行为和性能,考察了化学结构、环境条件等因素对聚合物分子行为与性能的影响,并提出了相关机制,为疏水改性水溶性聚合物作为高效驱油剂的分子设计和应用提供理论指导。另外,本论文还研究了烷醇酰胺非离子表面活性剂的界面行为,发现该体系不仅具有超高界面活性,并且因具有低界面电性可使驱动原油经分散和聚并发挥封堵调剖作用,因而也是多效合-的新型高效驱油剂。本文采用分子模拟方法与实验方法结合分别研究了疏水改性聚丙烯酰胺和烷醇酰胺的体相和界面分子行为和性能,并通过观察驱替过程,对两种新型驱油体系的致效机制进行了分析和比较。本论文主要分为四个部分：1.HMHPAM分子行为与构效关系研究采用耗散颗粒动力学(DPD)的方法考察了HMHPAM的浓度、聚合方式、疏水改性比例及水解程度对聚合物分子行为和溶液性质的影响。研究发现改性基团以无规形式均匀分布在分子链上的梳型结构相较于嵌段结构对HMHPAM的分子链伸展更为有利。经过疏水改性处理后,疏水基团之间疏水缔合作用的引入有利于分子链三级结构地形成,其中适当的疏水改性基团和合适的疏水改性度能使HMHPAM在溶液中形成网状结构,很大程度上增大了整个体系的流体力学尺寸。而经过水解处理后的聚合物上部分丙烯酸根基团地引入则可使聚合物分子链通过静电斥力逐渐展开,从而有效地增大了分子链的流体力学尺寸。在HMHPAM体系中,酰胺基团之间的氢键作用,疏水基团之间的疏水作用和水解基团之间的电性作用,这三种作用力共同决定着HMHPAM的性质和状态。过强的疏水缔合作用会促使聚合物分子链蜷缩,导致聚合物的水溶性降低甚至析出,而过强的电性斥力则会破坏聚合物分子链之间的三级结构使体系的粘度降低。因此在对实际应用体系进行改性处理时应根据实际体系的应用要求,结合改性的难易程度等因素,通过综合考察改性基团对聚合物溶液性质的影响,制定合成方案。在以增粘为目的烷基链长度为十六个碳的HMHPAM体系中,疏水改性基团梳型无规分布,聚合物的疏水改性度和水解度分别为2%和40%,为体系的最优状态。2.环境条件对HMHPAM分子行为和性质的影响耗散颗粒动力学模拟方法,与实验手段相结合,研究了环境pH、盐度及添加表面活性剂对HMHPAM分子行为和溶液性质的影响。研究发现,随着溶液pH增大,聚合物分子链逐渐伸展,体系的粘度逐渐升高,当pH≥8时,体系的粘度基本保持不变,因此HMHPAM的应用体系应选在偏碱性环境中更为有利。溶液中的无机盐对HMHPAM的影响也很大,聚合物溶液的粘度随着无机盐含量地增加显著下降。溶液中的无机盐不仅能够屏蔽聚合物羧酸基团之间的静电斥力,引发聚合物分子链蜷缩,而且因其水合导致的竞争吸水能力也使体系中的聚合物的水溶性下降,分子链蜷缩,这两种作用都会使聚合物溶液的粘度降低,影响聚合物的应用效果。在HMHPAM的体系中,无机盐的竞争吸水作用则是影响聚合物溶液性质的主要原因。HMHPAM体系中适量SLS地加入可以一定程度上缓解聚合物因环境变化而引起的粘度大幅降低。分子模拟结果表明,HMHPAM与SLS的相互作用位点集中在各自的疏水基团。表面活性剂在聚合物疏水基团上的聚集可以促使聚合物分子链伸展,有效地增大聚合物的水动力学半径,进而起到增粘作用,然而过量的SLS的加入则会引起聚合物三级结构地破坏从而使聚合物体系的粘度大幅降低。同时研究还发现SLS不但能使聚合物增粘,而且可以与HMHPAM在油／水界面共吸附,进而大幅度降低体系的油／水界面张力,因此适量的SLS的加入能更好地优化HMHPAM体系的体相性质和界面性质,扩大聚合物的应用范围。3.无机阳离子对HMHPAM的影响机制研究采用分子动力学与实验手段相结合,研究了Na+、Mg2+、Ca2+、Cr3+和Fe3+这5种常见的金属阳离子对聚合物粘度和溶解度的影响。研究发现其影响大小排序为Fe3+>Cr3+>>Ca2+>Mg2+>Na+。研究表明,Cr3+和Fe3+可以与HMHPAM的水解基团羧酸根以络合作用形成稳定的配合物,且此配合物不溶于水,易从体相析出。相比较于Fe3+,Cr3+的配位作用要弱一些,其在低浓度时可以作为交联剂将不同的聚合物分子链连接在一起,且保持聚合物的水溶状态,同时增加体系的粘度,而Fe3+只有降粘作用。HMHPAM在Na+、Mg2+和Ca2+存在的溶液中都保持着溶解状态,其中Ca2+可以进入羧酸根基团的第一个水合层,并与之形成稳定的离子对,研究发现Ca2+可以作为盐桥通过静电作用将不同的羧酸基连接在-起,使聚合物形成较大的聚集体。Mg2+的水合层比较致密,不易脱水,因此与羧酸根形成的离子对并不稳定,但是Mg2+的吸水能力较强,对聚合物的水溶性影响较大。Na+对聚合物的影响是最小的,其只能起到微弱的电性屏蔽作用。4.非离子型表面活性剂烷醇酰胺DDA的界面行为与超低界面张力产生机理采用分子模拟与实验结合的手段,研究了DDA的界面行为,揭示其产生超低界面张力的机理。研究发现DDA产生低界面张力的主要原因是其头基与水分子之间及头基与头基之间的强氢键作用,这种作用使表面活性剂亲水基与周围的水分子形成了较稳定且较厚的水合层,阻碍了界面层上油相和水相的接触,使原有的油-水界面,变成油-表面活性剂尾链-表面活性剂头基亲水层-水相的拟四相界面,从而使体系的界面张力大幅度降低。同时还考察了温度、盐度及pH的变化对DDA体系油/水界面张力的影响,发现界面电性对超低界面张力的产生影响很大。通过加入带电表面活性剂改变界面电性,研究结果表明,表面活性剂头基电性越强,界面电性越高,头基之间静电排斥作用越严重,界面上表面活性剂与表面活性剂之间孔隙越大,油/水直接接触区域越大,体系的界面张力越高。低电性或电中性表面活性剂因具有高界面密度,有效隔开油水层,可在不加辅助表面活性剂的情况下将界面张力将至超低。通过与离子型表面活性剂SLS和CTAB复合体系做对比,进一步验证了界面电性对界面张力的影响。5.疏水改性聚合物与低张力表面活性剂的驱油效率与致效机理本论文采用自行设计的可视物模,考察疏水改性聚合物与低电性高活性的表面活性剂体系的驱油效率,并细致观察驱替特征,发现两种新型驱油剂均可有效提高采收率,但致效机制不同。其中疏水改性聚合物不仅增加驱替体系粘度,降低原油和水的流速比,有效地缓解驱替液的窜流现象,提高体系的波及系数,还有促使油滴脱附的作用,因而可增加原油的采收率。而由表面活性剂烷醇酰胺组成的超低界面张力体系依靠超低油/水界面张力促进原油自岩石表面脱附和分散,实现对残余油的有效驱动。同时作为一种非离子型表面活性剂,烷醇酰胺在原油界面吸附形成低界面电性乳状液,易发生聚集,在高渗透带形成原油封堵层,有效防止驱油过程中的指进效应和窜流现象,因此显著提高驱油效率,一次性取得高采收率。相比较于其他驱替体系,非离子表面活性剂烷醇酰胺低张力驱替体系的驱油效率最好。更多还原

【Abstract】 Polymers and surfactants are widely used in EOR (Enhance Oil Recovery) as flooding agents. The high viscosity of polymer solution can reduce the mobility ratio between oil phase and water phase through plugging ability and profile control effects, and enhance the oil displacement efficiency. The surfactant can also increase the oil displacement efficiency through decreasing the oil/water interfacial tension and increasing the displacement efficiency. In recent years, the partially hydrolyzed hydrophobically modified polyacrylamide HMHPAM as a kind of new flooding agent get more and more attention, owing to its thickening effect and interfacial activity. In this thesis, the Molecule Dynamics (MD) and Dissipative Particles Dynamics (DPD) were combined with dynamic interfacial tension, viscosity, zeta potential, Dynamics Light Scattering (DLS), Atomic Force Microscopy (AFM), and Transmission Electron Microscopy (TEM) to study the properties of HMHPAM. The relationship between the conformation of HMHPAM molecular structure and its solution properties was studied at molecular level. To provide the theoretical guidance for design and applicant of HMHPAM, the influences of molecular structure and environmental conditions on HMHPAM solution were also investigated. As another new flooding agent, the alkanolamide (DDA), which has both ultra low interfacial tension and plugging ability and profile control effects, was also studied. The flooding mechanism and displacement efficiency of these two flooding agents were investigated through a flooding model.This thesis is divided into five parts:1. The relationship between molecular configuration and phase behavior of HMHPAMThe influence of the polymer concentration, polymerization process, degree of hydrolysis, and the hydrophobic modified group of HMHPAM on the polymer solution were studied by DPD simulation. It was found that the comb structure which the hydrophobic modified groups of polymer molecular chain were distributed uniformly and randomly, were better than the block copolymer. The hydrophobic modified groups of HMHPAM can help the polymer form the net-work structure, which can enlarge the hydrodynamic radius of polymer chain and increase solution viscosity seriously. The hydrolysis groups of HMHPAM can also benifit the increase of the viscosity of polymer solution, because the electrical repulsion between different hydrolysis groups can stretch the polymer chain. So in HMHPAM system, the hydrogen bond between acrylamide groups, the hydrophobic interaction between hydrophobic modified groups and the electrical repulsion between hydrolysis groups decided the phase properties of HMHPAM. The strong hydrophobic interaction can lead to polymer curl up even separate out from solution, and the strong electrical repulsion can destroy the net-work structure of polymer. For HMHPAM, the optimal hydrolysis degree and hydrophobic degree were40%and2%, respectively.2. The Influence of Environment Conditions on the Properties of HMHPAMThe influences of pH, salinity and additive agent (sodium dodecyl sulfonate (SLS)) on the properties of HMHPAM by dissipative particle dynamics (DPD) simulation combined with viscometer and AFM observations (Atomic Force Microscopy) were studied. The effects of electrical shielding effect and water absorbing ability of salts and pH on the behavior of HMHPAM molecules were investigated through changing the interaction parameter between different beads. The conformation variation of polymer chain described by root-mean-square (RMS) end-to-end distance and simulation snapshot was compared with the change of solution viscosity. The hydrolyzed groups of HMHPAM were existed in the form of acrylic acid in acidic solution and acrylic acid anion in alkaline solution. The electrostatic repulsion between different acrylic acid anion groups can stretch the polymer chain and increase the solution viscosity, which resulted in the higher viscosity of HMHPAM solution in environment with pH>8. It was found that, the water absorbing effect of salts was the main reason seriously reduced the viscosity of HMHPAM solution, while the influence of electrical shielding of salts was not obvious. The added SLS can influence the interfacial activity and bulk phase thickening property of HMHPAM. HMHPAM can be absorbed onto the oil/water interface and reduce the oil/water interfacial tension of system. The added SLS reduced the interfacial tension obviously, which help to broaden the potential application of HMHPAM. In the HMHPAM solution, the SLS can enter the hydrophobic domains of polymer chain through hydrophobic interaction, which can enlarge the molecular chain of polymer and increase the system viscosity.3. The influence of inorganic cations on HMHPAMThe effects of Na+, Mg2+, Ca2+, Cr3+and Fe3+ions on the HMHPAM solutions was explored using the MD simulations and experimental methods. It was found that the influence of multivalent cations on the property of HMHPAM was not rely on the water absorbing ability of cations, but the direct interaction between the cations and polymer. The influence degree of cations on HMHPAM solution was Fe3+>Cr3+>>Ca2+>Mg2+>Na+. The Cr3+and Fe3+both have coordination interaction with acrylic anion groups and there would be about three acrylic anions groups bound with Cr3+or Fe3+. But the interaction degree of Cr3+or Fe3+with HMHPAM in solutions were found to be different, therefore their influence on properties of HMHPAM were dissimilar, trace amount of Cr3+can be regarded as cross-linker and increase the systems’ viscosity, but the Fe3+can only decreased the viscosity of polymer solution. The hydration ability of Mg2+was bigger than Ca2+, but Ca2+have more strong influence on capacities of polymer solution, which was reordered to the classical Hofmeister series. It was found that the hydration shell of Ca2+was loose and dehydrated easily which made it interact with acrylic anions directly. The Ca2+can form stable dipolar pair with different acrylic anions though strong electrostatic attraction and leads to the forming of big aggregations of polymer. While the dense hydration layer adhered to Mg2+strongly which made the Mg2+only enter the second hydration shell of acrylic anions and the formed Mg2+-HMHPAM dipolar pair was unstable, so the influence of Ca2+on the viscosity of HMHPAM solution was bigger than the Mg2+4. The interfacial property of DDAThe MD simulation and experimental methods were combined to study the interfacial behavior of DDA. It was found that the mechanism of DDA systems getting ultra low interfacial tension was ascribed to the strong hydrogen bond between the head groups of DDA and water molecules, form thick hydrated layer with water. The formed hydrated layer can be regarded as a barrier stopping the oil phase from directly contacting with water phase, which turns oil/water interface into oil/hydrophobic tail of DDA/hydrated layer of head group/water interface, and reduces the interfacial tension significantly. In addition, the interfacial charge has a great influence on the oil/water interfacial tension of DDA system. For the DDA solution, the added ionic surfactants introduced charge into the oil/water interface. The higher charge of surfactant head group always means the stronger electrostatic repulsion between each other, and the oil/water interface can contain some macropores with no surfactants covering. In the macropores domains, the water molecules and oil molecules contact directly and the interfacial tension increases seriously. So it can be concluded that the interface with low or zero charge would be beneficial for getting the ultra interfacial tension system. The mechnism was testified in the SLS/CTAB system.5. The oil displacement efficiency of the two types of new flooding agentThe flooding efficiency of hydrophobically modified polymer and non-ionic surfactant DDA system were studied by a sample flooding model. It was found that both of these two systems can increase the displacement efficiency, while the mechanisms were different. The HMHPAM solution has high viscosity, which can reduce the mobility ratio between oil phase and water phase, relief the crossflow effect of displacement fluid and increase the oil displacement efficiency. While the low interfacial tension of DDA system can promote desorption and dispersion of crude oil from rock surface, and increase the oil displacement efficiency as a result. In addition, as a kind of non-ionic surfactant, the DDA can lead to the dispersive crude oil aggregate again. The aggregated crude oil drops can be regarded as blocking agent which can prevent the fingering effect and crossflow effect of the displacement fluid in the process of oil displacement. Compared with other flooding agents, the non-ionic surfactant DDA has the best oil displacement efficiency.更多还原