油包水型乳状液蜡分子扩散和蜡晶颗粒沉积机理研究

With the exploration of the deep-water oil fields and the construction of the sub-sea pipelines, wax deposition of waxy oil with water/oil emulsion in two-phase flow pipelines becomes a common problem. This complicated heat and mass transfer process involves phase change, diffusion, complex rheological behavior of non-Newtonian fluid, multiphase dispersion, and research on this issue is still at a preliminary stage. There are many urgent fundamental problems need to be solved before uncovering the mechanisms of molecular diffusion and particle deposition of the wax in the presence of water/oil emulsion. Significant experimental and theoretical studies are required to establish the diffusion coefficient of waxy molecules and the kinetic deposition model of water/oil emulsion. In this project, we propose to perform microscopic characterization of water/oil emulsion, and carry out experiments to investigate wax deposition with water/oil emulsion under static and dynamic conditions as well as its rheological behaviors.Through these works, we will come out with a set of parameters capable of describing the characteristics of the droplet size and distribution of the dispersed phase, and we will further quantify the relationship between the rheological behaviors and the microstructure of water/oil emulsion. In addition, the effect of the droplet size and distribution on waxy molecule diffusion in water/oil emulsion will be explored and a method for computing its diffusion coefficient will be proposed. Numerical simulations for the growth and deposition of wax particles will also be carried out to study the growth of the waxy deposition layer. Together these results will reveal the wax deposition mechanisms of water/oil emulsion in the shear flow field within the pipelines and a kinetic predictive model of the wax deposition with water/oil emulsion can be established. Accomplishing these goals will contribute significantly to the theoretical prediction and potential prevention of wax deposition. It also provides a sound basis for the pigging operation in water/oil emulsion transportation pipelines.

油包水型乳状液的蜡沉积在油气流动保障领域十分常见，它是涉及相变、扩散、非牛顿流变行为、多相分散体系等许多基础理论的复杂传热传质问题。目前，对该问题的研究处于起步阶段，揭示其蜡分子扩散及蜡晶颗粒沉积机理尚存在许多基础问题亟待解决，建立蜡分子扩散系数和蜡沉积动力学模型需要大量实验研究和理论探索。本项目拟从油包水型乳状液的微观特性研究入手，开展油包水型乳状液的静态、动态蜡沉积及非牛顿流变行为研究。提出描述油包水型乳状液分散相粒径大小和分布特征的表征参数,建立非牛顿流变行为与微观结构的量化关系；探索分散相粒径大小和分布对蜡分子扩散的影响，提出蜡分子扩散系数的计算公式；数值模拟蜡晶颗粒的生长和沉积机制及其对蜡沉积层生长的影响,探究油包水型乳状液在管流剪切流场中的蜡沉积机理，最终建立蜡沉积动力学模型，为油包水型乳状液输送管道的蜡沉积预测和结蜡防治提供理论依据。

在海底较为恶劣的环境之中，含水原油由于在泵、阀门等设备处受到剪切作用，会形成油包水乳状液。油包水乳状液流动体系由于其自身所具有的复杂性以及所处的低温和强换热环境，使得管道面临更大的蜡沉积问题。管道流动保障技术由于其在深水油气开发的核心地位，因而其重要性显得更加突出。.本项目针对油包水乳状液的微观特性、蜡分子扩散、蜡晶颗粒沉积机理、沉积层的生长、沉积物的老化、油包水乳状液的管流蜡沉积规律展开研究，建立考虑油包水乳状液微观特性的蜡沉积动力学模型，为多相混输管道的安全运行提供理论支持。项目组在合理的安排与分工之下，出色地完成了研究任务，并达到了各项指标要求，主要创新内容如下：.明确了油包水乳状液中的蜡分子扩散方式，提出了油包水乳状液蜡分子扩散系数的计算公式。首次提出并改进了近红外光谱法动力学模式测量原油析蜡点的方法，提高了原油的析蜡点测量的精确程度；明确了油包水乳状液分散相液滴对于蜡分子扩散路径的阻碍作用，提出了二维三维下蜡分子扩散路径的迂曲度的计算方法；揭示了油水界面的吸附对于界面粘度、界面剪切粘弹性以及蜡分子扩散的影响机理。.探究了管流剪切场之中油包水乳状液的蜡沉积规律，建立了考虑油包水乳状液微观特性的蜡沉积动力学模型。建立了连续相流变特性与微观特征之间的关系式；揭示了油包水乳状液沉积层的剪切剥离机理，明确了沉积层的老化特性以及变化规律。.分析了蜡晶颗粒在流场之中的受力情况，证明了剪切弥散作用对于蜡沉积没有贡献。利用数值模拟技术与分子模拟技术分析了蜡晶颗粒在流场之中的运动规律，对油流与管壁之间不存在温差条件下蜡晶颗粒的沉积情况进行了表征；对蜡晶颗粒的粘附与反弹规律进行了描述。.项目成果发表SCI与EI论文18篇，做国际会议邀请报告6次，获得化学工业联合会颁发的科技进步一等奖1项，申请专利8项，授权专利5项，培养研究生13名，研发成果具有较大的实用价值，成果丰硕，论文发表与学术交流过程活跃。