含表面活性剂的两相驱替微观渗流机理及模型研究

Two-phase displacement is a fundamental process in water flood oil recovery, and is also widely found in engineering applications such as geological carbon sequestration and remediation of groundwater contamination. In the water flood, the addition of surfactants has gradually become a promising way to enhance oil recovery and has received considerable attention, as it can not only decrease the interfacial tension between oil and water, but also modify the wettability of solid surfaces. In the presence of surfactants, the multiphase flow behavior in porous media is significantly different from that in the surfactant-free case. To date, the mechanisms of two-phase displacement with surfactants in porous media are still poorly understood, greatly hindering the development of surfactant flooding technology. In this project, a hybrid method will be proposed to simulate two-phase flows with the capabilities for soluble surfactants, contact-line motion, and handling three-dimensional complex geometries, in which the lattice Boltzmann color model and the finite element method are used to solve the immiscible two-phase flow and the surfactant transport, respectively. The hybrid method will then be used to systematically study the two-phase displacement with surfactants in porous media, fully revealing the effect of the flow, fluid properties and pore structure, as well as the surfactant properties and concentration on the displacement process. Based on the numerical results, along with those from micromodel experiments, an optimal match between surfactant properties and pore structure will finally be established to maximize the oil recovery. This research will provide theoretical foundation for optimizing the selection of surfactants and improving the technology of oil extraction.

两相驱替是注水采油中的一个基本过程，也广泛存在于二氧化碳的地质封存、地下水污染的治理等工程应用。注水采油中，添加表面活性剂既能降低油水间的界面张力，又能改变壁面的润湿性，已成为提高原油采收率的有效手段并受到广泛关注。多孔介质内含表面活性剂的多相流动特性与干净界面情况存在显著差异，对含表面活性剂两相驱替渗流机理认知的不足已严重制约了表面活性剂驱采油技术的发展。本项目通过格子玻尔兹曼颜色模型求解互不相溶的两相流动、有限元法求解表面活性剂浓度，建立适合于三维复杂几何边界、含可溶表面活性剂和运动接触线的两相流动混合计算方法；基于此，对多孔介质内含表面活性剂的两相驱替过程进行系统深入的数值研究，全面揭示表面活性剂的属性和浓度在各流动、物性、几何参数下对驱替过程的影响规律；结合微模型实验研究，提炼表面活性剂属性与孔隙结构在提高采收率方面的最佳匹配原则，为表面活性剂的优化选型，改进开采技术提供理论基础。

表面活性剂驱主要依靠降低油水界面张力和改变壁面润湿性等机理提高微观洗油效率，最终大幅度提高原油采收率。数值建模含表面活性剂的多相渗流极具挑战，不仅需要考虑表面活性剂对流扩散、界面聚集及表面吸附等物理化学作用进行多场耦合，而且需要重新推导考虑表面活性剂影响的壁面润湿边界条件。由于建模和算法实施的复杂性，含表面活性剂的多相渗流模拟鲜见文献报道，亟需革新含表面活性剂的多相流计算模型和润湿边界条件，深化表面活性剂驱渗流规律研究。.本项目基于LBM颜色梯度模型求解流体流动、有限差分法求解扩散界面形式的表面活性剂界面浓度和体相浓度控制方程，并采用Langmuir状态方程实现速度和浓度场的耦合，建立了含可溶表面活性剂的多相流模拟方法。根据杨氏方程和Langmuir状态方程建立接触角与表面活性剂界面浓度之间的函数关系，基于“预估-校正”思想实施动态接触角，发展出含表面活性剂影响的润湿边界条件。以此为基础，构筑了含表面活性剂的多相渗流模拟体系。获得了库塔流中不同粘度比条件下表面活性剂对液滴破裂临界毛细数的影响规律，揭示了表面活性剂增加液滴变形、提升液滴运动的作用机理。开展了多孔介质微模型内自吸过程模拟，深刻剖析了微模型内Lucas-Washburn公式失效与几何突变引起的毛细阀阻力之间的联系；推导了微模型内自吸过程的预测公式，并通过LBM模拟和微模型实验证实了其完美预测能力，突破了Lucas-Washburn公式描述微模型内自吸的局限性。开展了真实岩石数字岩心内表面活性剂驱渗流模拟，揭示了不同流体饱和度和粘性比条件下表面活性剂对流体分布、相对渗透率以及比界面长度的影响规律，绘制了系列相对渗透率曲线，为实现向油藏尺度模拟跨越提供了重要的本构关系。.项目执行过程中共发表学术论文36篇，其中SCI论文35篇，授权发明专利2项，登记软著3项，培养从事相关工作的研究生6名，超额完成项目预期研究成果。基于项目研究成果开发了高性能多相渗流模拟软件，已被多家研究机构及企事业单位用于微观渗流机制及驱油机理研究，有效促进了提高采收率技术及渗流理论的进步。