泡沫驱油中表面活性剂聚集结构的多尺度模拟

In foam flooding, zwitterionic surfactant, sulfobetaine, is far better than other types of surfactants in salt tolerance and foam stability. The experimental phenomena can be explained by the multi-scale simulations at the microscopic level. Firstly, the first principle calculation will be used to calculate the properties of surfactant in the present of cations and water molecules; secondly, all-atom molecular dynamics simulation will be used to investigate the salt tolerance of surfactant aggregates at gas/liquid interface; thirdly, one coarse grained force field will be selected to simulate the “real” bubble rupture under the direction constrain and to explore the mechanism of foam stability; finally, in the experiments the foam ability and stability of selected surfactant systems will be investigated in high salt concentrations.. This project mainly focuses on the foam flooding system, and both the theoretical and experimental methods will be used to investigate the relationship between the microscopic structure properties and macroscopic experimental phenomena. In the calculated simulations, the coarse grained model will be liked the different time and space scales from the single molecule to the molecular aggregates of surfactant. In the simulation, two issues will be solved. One is about the salt tolerance of surfactant aggregates, and the other is about the mechanism of foam stability. According to the simulated results and experimental phenomena, we hope that that the multiscale simulations can provide some theoretical guidance for the experiments in designing new surfactant with better salt tolerance and foam stability.

泡沫驱油实验中磺基甜菜碱两性离子表面活性剂耐盐、起泡和稳泡能力远强于其它类型表面活性剂，多尺度模拟计算可在微观上对此加以解释，并为后续驱油实验提供理论指导。研究内容包括：1）第一性原理计算阳离子和水分子存在下表面活性剂单体性质；2）全原子分子动力学方法模拟气液界面上的聚集结构，探讨表面活性剂耐盐实质；3）构建粗粒力场，对目标分子施加作用力，模拟“真实的”泡沫破裂过程，探讨稳定泡沫机理；4）实验研究表面活性剂在高盐浓度下的起泡和稳泡能力。. 本项目主要针对特定泡沫驱油体系，在时间和空间尺度上，结合理论和实验结果填补不同尺度模拟方法间的断层，通过粗粒化模型实现从微观到介观的粗粒化贯通，进而与实验研究相衔接。模拟中重点解决两个问题：1）表面活性剂聚集结构的耐盐实质；2）表面活性剂稳定泡沫机理。最终根据模拟结论设计耐盐、起泡和稳泡能力强的表面活性剂，为实验提供理论参照。

分子模拟作为驱油实验的有益补充，可以针对泡沫驱油、润湿翻转、稠油降粘、原油破乳等石油开采中遇到的各种问题给予分子层面上的解释，为实验中各种化学试剂的分子设计提供必要的理论参照作用。本项目采用多尺度、多种计算方法研究表面活性剂在气液、油水界面上的聚集，探讨外力情况下泡沫驱油中表面活性剂的作用及其动力学性质；在微观尺度下探究原油性质，寻找沥青质致粘的根本原因，探究不同类型表面活性剂对原油性质的影响，涉及微观尺度下的乳化和运移，为现场应用提供理论支持。. 模拟结果表明，两性离子表面活性剂、阴非离子表面活性剂在耐盐方面性质优越，受钙、镁离子的影响较小；泡沫驱油中，可以用“油桥-伸缩”机理解释原油对泡沫稳定性的影响，其关键作用在于假乳液膜的形成和表面活性剂尾链与油相的相容性；微孔表面形成的水化层对溶胀疏水聚丙烯酰胺有润滑作用，利于聚合物封堵孔喉，微孔亲水亲油性质影响驱油体系的运移；沥青质在油相中的网状聚集结构是导致稠油增粘的关键因素，表面活性剂在乳化降粘中的作用在于改变油水界面的亲水亲油性质；热力学函数熵变可以解释表面活性剂在体相、气液界面中的聚集，分子模拟可以计算表面活性剂聚集过程中的熵变数值。. 多尺度的模拟方法可以作为诸多驱油实验现象的有益补充，在分子尺度下为驱油实验中的分子设计和解释实验现象提供理论参照作用。