纳米孔隙中水驱油两相渗吸机理与动力学特性

The length scales of slits in super-low permeability and tight oil reservoirs reach to nanometers and accordingly the traditional imbibition theories and experimental methods cannot describe the imbibition phenomena in the reservoirs with nanoslits. Therefore, it is very important to study the water-displacing-oil two-phase imbibition processes in nanoscale channels and reveal its mechanisms and dynamic characteristics. Because the length and time scales for the imbibition processes in nanoslits are both very small, the nanoscale effects, such as inertia effects and velocity slip on wall surfaces, are very pronounced. Starting from the hydrostatic equilibrium characteristics, this project studies the two-phase imbibition processes in the nanoslits with wide-range length scales by using molecular dynamics and dissipative particle dynamics simulations. The mechanisms are expected to be revealed from the aspects of imbibition mode and starting driving force etc. Then, the nanochannels are established based on the anodic aluminum oxide nanoporous membranes and the water-displacing-oil two-phase imbibition rates in nanochannels are experimentally measured. The mathematical models for the imbibition dynamics can be established by reasonably considering the viscous force and inertia force. Finally, regarding the application background of low-salinity water flooding, the regulation laws and mechanisms of ions on the imbibition processes are thoroughly investigated by using experimental measurements and molecular dynamics simulations. These results can serve as the theoretical basis for the high-efficiency production and enhanced oil recovery of super-low permeability and tight oil reservoirs. Meanwhile, they can enrich the knowledge of multiphase flow in nano-confined spaces. Overall, this project exhibits a great significance from the aspects of engineering applications and academic research.

超低渗透、致密油藏储层岩心主流吼道尺寸达到纳米级，传统的渗吸理论和实验方法都不能描述纳米孔隙岩心中的渗吸现象，必须深入研究纳米孔隙通道中水驱油两相渗吸过程的机理和动力学特性。纳米孔隙通道中渗吸过程的空间尺度和时间尺度很小，惯性作用、壁面速度滑移等纳米尺度效应凸显。本项目从静力学平衡特性出发，结合分子动力学和耗散粒子动力学模拟，研究大尺寸范围的纳米孔隙中水驱油两相渗吸过程，从渗吸模式、启动压力等角度揭示其机理；基于纳米多孔阳极氧化铝薄膜材料构建纳米孔隙通道模型，实验研究水驱油两相渗吸速率等动力学特性，合理考虑粘性力和惯性力，建立渗吸动力学的数学模型；最后以低矿化度水驱为背景，结合实验测试和分子动力学模拟，研究离子对两相渗吸过程的调控规律和机制。研究成果将为超低渗透、致密油藏的高效开发和提高采收率提供理论基础，并丰富纳米尺度受限空间内多相流动问题的理论认识，具有重要的工程应用价值和学术意义。

超低渗透、致密油藏储层岩心主流吼道尺寸达到纳米级，传统的渗吸理论和实验方法都不能描述纳米孔隙岩心中的渗吸现象，必须深入研究纳米孔隙通道中水驱油两相渗吸过程的机理和动力学特性。纳米孔隙通道中渗吸过程的空间尺度和时间尺度很小，惯性作用、壁面速度滑移等纳米尺度效应凸显。本项目基于静力学平衡特性，从分子模拟角度揭示了纳米孔隙中单相水渗吸以及水驱油两相渗吸过程的机理与动力学特性；结合实验测试技术，研究了纳米孔隙中水驱油两相渗吸速率以及离子对岩石表面油水润湿性的调控。主要研究了二氧化硅纳米通道中水的单相渗吸，提出了流动-蠕动-跳跃-钉扎输运模型来描述纳米通道水的渗吸机理，分析了动态接触角、有效粘度以及结构分离压对渗吸的影响，建立了一个修正后的Lucas-Washburn方程；分子模拟了二氧化硅纳米通道中水驱油两相渗吸过程，研究了外部驱动力、通道高度、油分子链长、壁面润湿性对渗吸的影响，获得了两相渗吸流动的基本规律，并建立了描述纳米尺度水驱油两相渗吸流动的理论模型；搭建了基于纳米多孔膜的纳米通道渗吸实验台，实现了单相及两相渗吸的精确测量；实验研究了极性、碱性、离子桥接等吸附作用下不同浓度离子对岩石表面润湿性的影响规律，并通过分子动力学模拟揭示了其微观机理。总之，本项目成果可为发展新型高效的超低渗透/致密油藏高效开采和提高原油采收率技术提供理论指导。研究结果发表SCI论文24篇，EI论文1篇，撰写英文书籍章节1篇，参加国际学术会议11次（其中大会报告1次、邀请报告1次）、国内学术会议9次（其中邀请报告2次）。本项目关于离子对岩石表面油-水润湿性调控机理的研究结果支撑了中石油勘探开发研究院发展的低矿化度提高原油采收率功能性水驱技术，长庆和吉林油田区块的岩心实验结果表明，相比于常规水驱采油，低矿化度功能性水驱的原油采收率提高13-15%，并在长庆油田超低渗透区块进行了现场试验，被评价“为认识不同原油组分在储层界面作用机理提供了重要参考”。