预交联凝胶颗粒堵水调剖与表面活性剂驱油体系的分子动力学模拟

发布时间：2018-01-14 17:39

本文关键词：预交联凝胶颗粒堵水调剖与表面活性剂驱油体系的分子动力学模拟　出处：《山东大学》2017年博士论文　论文类型：学位论文

【摘要】：石油被称为"工业的血液",可以被炼制成汽油、煤油、柴油、润滑油等,也可以用来合成橡胶、洗涤剂、炸药、燃料等被广泛应用在人们生活的各个领域。石油作为不可再生资源,主要来源于地质开采。近年来,经过传统开采技术开采之后,油井含水量高,并且油层中剩余油的分布较为分散,多集中在水驱未能有效波及的岩石空隙。因此选择经济高效的堵水调剖剂及耐高温耐盐的驱油剂,可以更加有效的提高石油的采收率。预交联凝胶颗粒和醇醚类表面活性剂因其绿色环保,成本低廉,堵水调剖效果显著从而引起了广大科研工作者的兴趣并在探讨相关的作用机理方面进行努力研究,以期望寻找效果更加突出的化合物应用到实际采油过程中。随着研究的逐渐深入以及计算机水平的迅猛发展,采用分子动力学模拟方法在分子水平上探讨聚合物及表面活性剂堵水调剖作用显得尤为重要。与传统的实验方法相比,分子动力学模拟方法可以更加直观的观察到分子间的相互作用,从而提出合理的机理,对实验合成及开发研究具有指导性意义。本论文主要围绕预交联凝胶颗粒(Preformed particle gel,PPG))在水溶液中的溶胀、孔道中的运移行为及表面活性剂驱油过程耐盐机理进行了一系列研究:采用分子动力学模拟的方法对预交联的凝胶颗粒在水溶液中发生溶胀、在水驱压力下岩石中的运移过程、不同孔径纳米孔道中和不同表面结构的纳米孔道内表面中的运移过程及醇醚类表面活性剂十二烷基聚氧乙烯羧酸盐不同溶液中的聚集行为进行探讨,通过分析体系中不同分子间相互作用来探讨合理的作用机制,为实验合成及工业生产提供了理论指导。本论文的主要研究内容和创新成果归纳如下:(1)通过分子动力学模拟探讨研究了 PPG在遇水溶胀的过程,解释了亲水基团上中心原子水化能力不同的原因。通过不同的模拟分析,我们发现PPG溶胀主要是因为在水溶液中其侧链的亲水基团的水化作用引起的,亲水基团的中心原子带负电荷,其通过氢键和静电作用在其周围极化形成一层排列规整、有序而且紧密的水化层,并牢牢的将水分子束缚在其中。我们通过对比预交联凝胶颗粒在水溶液中溶胀前后的的回旋半径、体积和溶剂可及表面积诠释了溶胀过程。然后通过对比了 PPG两种亲水基团的三个中心原子周围水分子的弛豫时间,发现水化能力O(COO-)O(CONH2)N(CONH2),并从体系的水化层结构和氢键方面解释了-COO-上氧原子水化能力更强的原因。从空间分布函数、径向分布函数和偶极分布图进行进一步分析,发现位于-COO-周围的水分子排列更加规整有序并且紧密,而且周围形成了更多的寿命也相对较长的氢键。因此我们认为水化层内的水分子通过氢键形成的网格结构对水化层的稳定也起到了重要的作用。这些研究,对实际应用中设计合成新型的凝胶颗粒或者改进现有凝胶颗粒提供了理论基础。(2)在探讨了预交联凝胶颗粒在水溶液中的溶胀过程的基础上,采用分子动力学方法模拟研究了预交联凝胶颗粒在水驱压力下的地下岩石孔隙中的运移过程。通过分析其均方根位移、溶剂可及表面积随模拟时间的变化进一步验证了聚集体在水溶液中会发生溶胀。并发现在纳米孔道内表面形成了高度有序且结合紧密的厚度约为O.4nm的水化层。通过对体系的氢键分析发现,水分子与纳米孔内表面的Si-OH通过氢键相互作用被束缚在纳米孔内表面附近,并形成稳定的网格结构。通过计算体系中亲水基团和水分子之间的的PMF发现,H2O分子与Si-OH之间易结合难解离。从而验证了水化结构的稳定性。通过聚集体在孔道中的运移过程的模拟,发现运移过程中水驱外力需要克服PPG周围水化层内的氢键网格及PPG与纳米孔道内表面的相互作用带来的阻力,而纳米孔道内表面Si-OH与水分子间形成的水化层结构减少了预交联凝胶颗粒与纳米孔道内表面的相互作用,类似于润滑剂,从而减少了在运移过程中其需要克服的阻力。我们的模拟结果从分子水平上解释了预交联凝颗粒孔道中运移的机理,为实验数据提供了理论支持,并为实验上及三次采油堵水调剖材料选择及工业生产提供了理论指导。(3)采用分子模拟中的拉伸动力学方法,模拟了 PPG聚集体由大孔径纳米孔道中运移到小孔径纳米孔道中的过程。通过对运移过程中PPG聚集体在孔道轴向上回旋半径、均方根位移以及PPG聚集体亲水基团周围水化层内水分子数目的变化情况,我们发现在运移过程中PPG聚集体通过脱水、变形从大孔径纳米孔道运移到小孔径纳米孔道中;通过分析PPG聚集体构象能的变化及亲水基团与水化层内水分子的均力势进一步探讨了其变形脱水机制。当PPG聚集体从大孔径纳米孔道中被拉伸进入到小孔径纳米孔道中时,构象能升高,其亲水基团与水分子解离。外力拉伸PPG进入小孔径纳米孔道是需要克服亲水基团与水分子解离所需要跨越的能垒。通过我们模拟分析,从微观角度探讨了 PPG聚集体在纳米孔道运移的机制,为石油开采过程用预交联凝胶颗粒的堵水调剖机制从而提高原油开采率提供理论基础。(4)我们对PPG在不同羟基化的二氧化硅纳米孔内运移行为进行了一系列的非平衡分子动力学模拟。通过对纳米二氧化硅纳米孔内表面100%、75%和50%羟基化三种不同的体系的模拟发现羟基化程度的增加,减小了 PPG运移过程所需要施加的外力。而通过对能量的分析,我们知道纳米孔内表面附近的束缚水在PPG的运移中起到至关重要的作用。从而我们推测纳米孔内表面的化学组成和微观结构通过形成不同性质的水化层从而对PPG的运移产生了重要的影响。随着纳米孔内表面亲水性的增强,对应的水化层更加紧密,且与孔内表面更接近。通过计算界面水分子弛豫时间、扩散系数和氢键寿命对体系的动力学性质进行了分析。纳米孔内表面羟基化程度越高,则水分子弛豫时间越长,但是扩散系数和氢键寿命却相反。通过本论文的分析,我们发现不同羟基化程度的,也就是亲水性不同的纳米孔内表面会形成不同结构的水化层结构;纳米孔的表面性质通过对其周围水化层结构产生影响从而影响PPG在纳米孔道中的运移行为。(5)通过分子动力学方法研究探讨醇醚类表面活性剂与烷基类表面活性剂的耐盐性能。我们发现钙离子与表面活性剂之间形成桥联结构,降低胶束极性头之间的静电作用,从而胶束的结合更为紧致。通过分析SDC和AEC的极性头与水的径向分布函数及极性头与Na+、Ca2+之间的均力势发现AEC耐盐性能要更高,我们从分子尺度上解释了驱油性表面活性剂的耐盐机理,为实际应用中合成更加高效的驱油类表面活性剂提供了理论支持。
[Abstract]:Oil is known as "industrial blood", can be refined into gasoline, kerosene, diesel oil, lubricating oil, can also be used for synthetic rubber, detergent, explosives, fuel is widely used in various fields of people's life. The oil as a non renewable resources, mainly from geology and mining. In recent years, after the traditional mining technology for mining, oil wells with high water content, and the distribution of remaining oil in the reservoir is more dispersed, more concentrated flooding rock gap failed to effectively spread in the water. So the choice of oil displacement agent efficient water shutoff agent and high temperature and salt resistance, can effectively improve the efficiency of oil recovery. Crosslinked gel particles and ether surfactant because of its green environmental protection, low cost, water shutoff effect which aroused the interest of scientists and mechanism on related research efforts, in order to find The effect of a more prominent compound is applied to the actual production process. With the deeper research and the level of computer and the rapid development of the molecular dynamics at the molecular level of polymer and surfactant, water shutoff effect is particularly important simulation method. Compared with the traditional experimental method, molecular dynamics simulation method can be more intuitive to observe the interaction between molecules, so as to put forward a reasonable mechanism, has guiding significance to the experimental synthesis of research and development. This thesis mainly focuses on the pre crosslinked gel particles (Preformed particle gel, PPG)) swelling in aqueous solution, migration behavior and surface active agent in the pore of the oil displacement process carried out a series of study on the mechanism of salt tolerance by molecular dynamics simulation method of pre crosslinked gel particle swelling in aqueous solution, in the rock under pressure in water flooding The migration process, discusses the aggregation behavior of nano pore with different pore sizes and different surface structure of nano pore surface in the migration process and the ether surfactant twelve alkyl polyoxyethylene ether carboxylate in different solutions, through different molecular interaction analysis system to study the mechanism of action of reasonable, provides a theoretical guidance for industrial production and experimental synthesis. The main research contents and innovative achievements are summarized as follows: (1) by molecular dynamics simulations to investigate the process of PPG in water swelling, explains why in the heart of atomic hydrophilic hydration ability different. Through simulation analysis of different, we found that PPG is mainly due to the hydration swelling the hydrophilic side chains in aqueous solution by the central atom of negatively charged hydrophilic groups, through hydrogen bonding and electrostatic interaction in the surrounding polarization The formation of a layer of ordered, orderly and close the water layer, and firmly bound water molecules in them. We compared crosslinked gel particles in aqueous solution before and after the swelling of the radius of gyration, and the volume of the solvent accessible surface area. And then through the interpretation of the swelling process of the ratio of water molecules around PPG two a hydrophilic group three atom relaxation time, found that the hydration ability of O (COO-) O (CONH2) N (CONH2), and from the system of the hydration layer structure and hydrogen bond reason -COO- oxygen atom hydration ability. From the spatial distribution function, radial distribution function and dipole distribution map for further analysis, found that the water molecules located around -COO- more orderly and closely, but also formed around the more life is relatively long. So we think that the hydrogen bonding of water molecules in the hydration layer by means of hydrogen bond network Stable lattice structure on the hydration layer also plays an important role. The research on the practical application of the design and synthesis of novel gel particles or provides a theoretical basis for improving the existing gel particles. (2) based on the swelling process of crosslinked gel particles in aqueous solution on the crosslinked gel particles in the transport process of underground water flooding rock pore pressure under the simulated by molecular dynamics method. Through the analysis of the mean square displacement, solvent changes and surface area with the simulation time to further validate the aggregates will occur in aqueous solution. The swelling and found in the nanopores formed on the surface of highly ordered and combined close the thickness of O.4nm hydration layer. Based on the system of hydrogen bond analysis found that water molecules and nano hole Si-OH through hydrogen bonding interactions trapped near the surface in nanopores, and The formation of grid structure. Through the calculation of the PMF system between hydrophilic group and water molecule found between H2O molecules and Si-OH combined with difficult to verify the stability of the water dissociation structure. Through the simulation of transport process in the pores of the aggregates, found the water flooding forces need to bring overcome interaction around PPG hydration layer of hydrogen bonds within the grid and PPG and nanopores surface resistance during the process of migration, and the formation of nano pore surface and Si-OH between water molecules in the hydration layer structure reduces the precrosslinking interaction of gel particles with nano pore surfaces, similar to the lubricant, thus reducing the need to overcome in the migration process resistance. Our simulation results explain the molecular mechanism of precrosslinking PQRTICLES migration channels, provides theoretical support for the experimental data, and for the three time and oil blocking Water industrial production and section material selection provides a theoretical guidance. (3) the tensile dynamic method of molecular simulation, simulation of the PPG aggregates by a large aperture in nanometer channel migration to small aperture in nanometer channel. Based on the migration process of PPG aggregates in the axial channel cyclotron radius, RMS displacement and PPG aggregates of hydrophilic hydration layer around the number of water molecules changes, we found that during the migration process of PPG aggregates by dehydration, deformation from large aperture nano pore migration to small pore size in nanometer channel; both hydrophilic and hydrophobic forces and through the analysis of the PPG aggregates conformation can the layer of water molecules to further explore the potential the deformation mechanism of dehydration. When PPG aggregates from large aperture nano pore is stretched into a small aperture in nanometer channel, conformational energy increased, the hydrophilic group and water molecule from solution PPG. The force stretching into the small aperture nanopores are needed to overcome the hydrophilic group and water molecule dissociation required across the barrier. Through our simulation analysis, discusses the mechanism of PPG aggregates in nano pore migration from the microscopic point of view, for the oil extraction process with water shutoff mechanism of pre crosslinked gel particles to improve and provide a theoretical basis for crude oil extraction rate. (4) we conducted a series of non-equilibrium molecular dynamics simulation on the migration behavior of PPG in different hydroxylated silica nanopores. The nano silica nano hole in the surface of the 100%, 75% and 50% simulated hydroxylation of three different systems were found to increase the degree of hydroxylation, reduced by PPG the migration processes needed for the applied force. Through analysis of energy, we know that the bound water near the surface of the nano hole plays a crucial role in PPG migration. Thus We speculate that the chemical composition and microstructure of nano hole surface by forming a hydration layer with different properties and migration of PPG had a significant impact. With the increase of nano hole surface hydrophilic, hydration layer corresponds more closely, and the hole inner surface closer. By calculating the interfacial water molecule relaxation the time dynamics of diffusion coefficient and hydrogen bond lifetime of system is analyzed. The higher the nanoporous surface hydroxylation degree, water molecular relaxation time is longer, but the diffusion coefficient and the hydrogen bond lifetime is the opposite. Through the analysis, we found that different degree of hydroxylation, which is hydrophilic nano hole the inner surface will form a different structure of the hydration layer structure; surface properties of nano hole through the hydration layer around the structure so as to influence the effect of migration behavior of PPG in nanopores. (5) by molecular The kinetic method study of ether surfactant and salt resistant properties of alkyl base surfactants. We found that the bridge structure is formed between calcium ion and surfactant micelles decrease the electrostatic interaction between the polar head, which combined with the micelles is more compact. The polar head and the water analysis of SDC and AEC in the radial direction the distribution function and the polar head and Na+, were found between the Ca2+ potential of AEC in salt tolerance to higher performance, we explained the mechanism of salt tolerance oil flooding surfactants from the molecular scale, for the practical application in the synthesis of more efficient oil displacement surfactant provides a theoretical support.

【学位授予单位】：山东大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TE39

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