二氧化碳驱采出原油乳状液界面膜动力学稳定性的多尺度研究

Accompanied by the constantly promoted requests on enhancing oil recovery and reducing carbon emission, CO2 flooding has gradually been applied worldwide. There are noticeable changes in the emulsification state, emulsion stability and emulsion-breaking feature of the liquid produced by CO2 flooding, when compared with those of traditional oil production technology. Therefore, new demands are put forward to ensure the safe operation of surface gathering system. In this research project, a pressurized stirring-viscometric apparatus newly developed based on the energy dissipation principle will be first utilized to prepare crude oil emulsion at reservoir and surface transportation conditions, and uncover the impacts of CO2 pressure, temperature and oil-water ratio on the emulsibility of crude oil and stability of its emulsion. Afterwards, the changes of the interfacial film strength and anti-deformation capability by the dissolution of CO2 in crude oil emulsion will be investigated with interfacial dilational viscoelasticity as the characterization parameter. At last but not least, the dynamics mechanism of the fact that CO2 influences the aggregating state of asphaltene molecules at the crude oil/water interface will be revealed with the help of the molecular dynamics simulation method. On this basis, the phenomenological effect and its mechanism of CO2 treatment on the demulsification performance of the specific polymeric demulsifier will be extendedly probed. As a result, the multiscale study including macroscopic phenomenon, mesoscopic structure, and microscopic mechanism will be correlated and unified in this research, so the effects of CO2 dissolution on the kinetic stability of the interface in crude oil emulsion will be thoroughly clarified. The results will help to supplement the deficiency of the theoretical studies in oil-water interfacial rheology and molecular dynamics under the influence of dissolved gas, and provide technical support for the design of the surface transportation system of the produced fluid by CO2 flooding and for the optimization of the demulsification process as well.

随着国内外对油田提高采收率和减少碳排放的要求不断提升，CO2驱油技术逐渐得到推广应用。与传统采油工艺相比，CO2驱采出原油的乳化状态、乳状液稳定性、破乳特性等发生显著改变，对地面集输系统的安全运行提出新要求。本课题利用研发的基于能量耗散原理的溶气原油乳化测粘装置，分析自油藏至地面集输工况下CO2压力、温度、油水配比等对原油乳化特性和乳状液稳定性的影响；然后，以界面扩张粘弹性为表征，考察CO2在原油乳状液中的溶解对界面膜强度、抗变形能力的改变程度；最后，借助分子动力学模拟，揭示CO2影响油水界面上沥青质分子聚集状态的动力学作用机制。在此基础上，扩展研究CO2对破乳剂效果的影响及机理。本课题将宏观、介观、微观多尺度研究关联统一，全面阐述溶CO2对原油乳状液界面膜动力学稳定性的影响，有助于补充气体作用下油水界面流变学和分子动力学理论研究的缺失，同时为CO2驱采出液地面输送系统的优化提供技术支撑。

油田采出液中的油相与水相大部分以乳状液形式存在，直接影响油气集输及油水分离工艺的设计与运行。决定乳状液稳定性的关键因素为原油中的沥青质，它可以吸附在油水界面形成保护层，而沥青质的吸附特性与其缔合状态密切相关。当二氧化碳驱油技术用于提高油田采收率时，二氧化碳在油水混合体系中的溶解会显著改变乳状液的稳定性。本研究建立了一套从宏观稳定性到界面流变性直至微观膜吸附结构的多尺度评价体系，揭示了沥青质缔合程度与界面膜结构特性进而与乳状液稳定性之间的关联。分别探索了沥青质自身组成、油相中胶质与石蜡组分、不同类型流动改进剂对沥青质聚集体缔合状态的影响，建立了沥青质吸附过程完整动力学模型，从而获得各因素对油水界面吸附结构和乳状液稳定性的作用机理。设计并搭建了超临界二氧化碳处理原油装置，模拟油藏条件下二氧化碳对原油的萃取及对沥青质缔合的影响，建立了二氧化碳压力与原油乳状液稳定性降幅的关联。分别研究了带压溶二氧化碳状态及超临界二氧化碳处理后脱气条件下油水界面的力学特性与粘弹性，探究了超临界二氧化碳处理后原油流变特性变化。开发了带压溶气原油乳化测粘技术，以获取溶二氧化碳油水混合液的流变行为。分析了超临界二氧化碳处理后原油乳状液对破乳剂的感受性差异机理。总体而言，本项目将宏观、介观、微观多尺度研究关联统一，全面阐述了溶二氧化碳等各种因素对原油乳状液界面膜动力学稳定性的影响。研究成果为二氧化碳驱提高采收率技术在国内油田的推广应用，尤其是二氧化碳驱油田地面工程的工艺优化及改造，提供了重要的理论支撑和关键技术支持。同时，也有利于二氧化碳气体的重复利用及封存，减少温室气体排放。