油水乳状液流场压降与剪切能的关联及其对化学破乳机制的影响

During oilfield development, crude oil is mainly produced as emulsion with different stability degrees, and the existence of various shear flow fields is determined by the dynamics of petroleum production system. These external shearing actions directly affect the thermodynamics and dynamics stability of oil-water emulsion system in the process of its formation and destruction. In chemical demulsification, selection of the best injection points during oilfield practices still remains a very challenging task for both operators and chemical vendors. In the gathering & transportation of oil-water emulsion, product of shearing force, shearing area and distance of the flow will constitute the shear work. .Therefore, shearing energy is introduced in this project, the energy responsible for dispersion of one phase of the liquid into the other as the fluid flows through the pipe is dependent on the turbulence available in the pipe. In the flow field, with the constant conditions such as oil-water emulsion system property, temperature and aging time, shearing action will be the dominant factor of oil-water emulsion formation, emulsifying degree and emulsion stability. So, the emulsion point is the area with high shearing energy. Alternatively, in the process of demulsification of petroleum production system, the strong turbulent point with high shearing energy is also the area where chemical demulsifier mixed most sufficient, due to the turbulence and shear will accelerate the chemical demulsifier molecule diffusion and adsorption on the oil-water interface and increase the times and intensity of impact effect among water droplets. Based on the analysis of shear history of oil-water two-phase system in formation pores, wellbore perforations, tubings, christmastrees and surface flowlines, relational model of oil-water emulsion flow field pressure drop and shearing energy in different points is established, using shearing energy to quantitatively describe the contribution of macroscopic flow pressure drop on shearing action. According to the simulation experiments, oil-water emulsion behavior of the shearing energy variation in two-phase flow is identified, effect of different shearing energy on chemical demulsification efficiency is studied and action mechanism of demulsifier in oil-water interface of different shear flow fields is explained. Then the shearing energy is used to analyze and establish the method system of chemical demulsifier option and injection points optimization during petroleum production..Determination of injection points could combat lots of operational and economical problems such as over-treating and re-emulsification. Unnecessary high budgets for demulsifier chemicals will be reduced in field, theoretical basis of crude oil chemical demulsification technology application and development will be extended. In the meanwhile, the surface and subsurface integrated approach in oilfield development will be further improved.

油田开发过程中，原油大部分以各种不同稳定程度的乳化液形式采出，且其采输系统本身的动态性决定了各类不同剪切流场的存在，所带来这些外部剪切作用直接影响着油水乳化液体系在形成及破坏过程中的热力学与动力学稳定性。本项目基于对原油/水两相体系在近井地带地层孔隙和射孔井眼、垂直油管、井口油嘴及集输管道内的剪切历史分析，拟引入剪切能来定量描述其宏观流动压降对剪切作用的贡献，建立不同节点区域油水乳状液流场压降与剪切能的关系模型；通过模拟实验，辨识考虑两相流动过程中剪切能变化的油水乳化行为，研究剪切能差异对化学破乳效能的影响，多尺度解释破乳剂在不同剪切流场中油水界面的作用机制，进而运用剪切能分析并构建原油采输过程中化学破乳剂选择及注入节点优化的方法体系，拓展原油化学破乳技术应用与发展的理论基础，同时进一步丰富油田开发地下地面一体化的理论方法。

针对油水乳状液流场压降对剪切作用的影响及所带来油水乳化液体系在形成与破坏过程中的热力学和动力学稳定性差异问题，以原油采输系统为背景，引入剪切能概念，将原油乳化体系微观“剪切变形”和宏观“流动压降”构建有效联系，建立了考虑气液比影响下定量描述流场压降对剪切作用贡献的理论模型，并给出了模型的求解与应用方法。研究分散相液滴的变形度和取向角特征参数变化，建立了剪切能和界面Gibbs自由能的关系模型，并发现剪切能是体现油水混合物体系动能对乳化过程中界面Gibbs自由能贡献的一种有效形式。明确了剪切能影响下的连续相、分散相相间作用机制和协同规律，其中，剪切能与油水乳化行为呈正相关关系，剪切能升高，油水乳化行为加剧、乳化稳定性增强。与此同时，紊流和剪切会加速化学破乳剂分子在油水界面的扩散、吸附，促进成膜破裂，增加水珠间发生碰撞、聚并的数量和强度，且该机制在原油采输系统中更占优，诱使化学破乳剂在高剪切能节点或其上游投加，能够发挥更佳的破乳效能，同时还可防止二次乳化，从而构建了一套可为油田助剂注入方案设计、工程建设及现场应用提供科学理论依据的化学破乳剂最佳注入节点位置优化方法。