低渗透孔隙中油水两相渗流的微流体学机理研究

The unconventional oil reservoirs are characterized by the phenomenon of low permeability. The microfluidic mechanisms of oil-water two-phase flow in low-permeability pores are relevant to the efficient development of the unconventional oil reservoirs. The flow passages are generally micron-scale channels with pore-throat geometry in low-permeability oil reservoirs. This project is proposed to investigate the microfluidic mechanisms of oil-water two-phase flow in the low-permeability microchannels with structured pore-throat geometry. The microchannels will be manufactured by micro etching technique. The microscopic technology will be employed to observe the behavior of oil-water flow in the low-permeability microchannels. The measurement technology of micro multiphase flow, combined with numerical simulation, will be applied to study the microfluidic oil-water two-phase flow in the microchannels. The interaction between wettability and surface tension, to which significant attention will be paid, probably has remarkable impact on the regimes of microfluidic oil-water flow. The viscous resistance of oil-water mixture and the deformation resistance of oil droplet will be measured and quantitatively analyzed. The primary components of energy dissipation will be determined for the oil-water two-phase flow in the low-permeability microchannels. How the low Reynolds number, surface force and micro-scale geometry influence the microfluidic oil-water flow will be revealed. The key scientific issues such as deformation resistance and dynamic relaxation will be resolved for oil droplets. The dependence of relative permeability on viscous resistance, droplet deformation resistance and flow regime will be discovered for the oil-water flow in low-permeability pore. The droplet-based flow theory will be advanced by this project in the cross fields of microfluidic multiphase flow and flow in porous media. New insights will be presented for the microfluidic mechanisms of oil-water two-phase flow in low-permeability porous media. The findings here will provide scientific support to the enhanced recovery of unconventional low-permeability oil reservoirs.

低渗透现象是非常规油藏的重要特征之一，低渗透孔隙中油水两相渗流的微流体学机理关系到非常规低渗透油藏的高效开发。本课题针对低渗透孔隙中孔道与喉道的特征几何尺度，应用微蚀刻技术、显微摄像技术、微尺度多相流测试技术以及可捕捉相界面的两相流数值模拟方法，研究微米级尺度的油水两相微流动及其影响因素，量化分析粘性阻力、油滴变形阻力等力学因素在微流动阻力中的权重，确定低渗透过程的主要能量耗散环节；重点解决壁面润湿性与油水界面张力的交互作用如何影响油水两相微流动的相态，以及油滴在微米级喉道处的变形阻力、动力学弛豫等关键科学问题；将宏观渗流参数与微流动参数相联系，探索相对渗透率与微流动相态、粘性阻力、油滴变形阻力等微流动参数的基本关系。研究成果可以对低渗透孔隙中油水两相渗流的相态机理与可变形颗粒动力学机理提出新见解，在多相微流体学与渗流力学的交叉领域提出新理论，为非常规低渗透油藏的高效开发提供科学依据。

低渗透现象是非常规油藏的重要特征，低渗透介质的渗流通道是带有孔喉结构的微通道，其中油水两相渗流的微流体学机理对低渗透油藏的高效开发有重要意义。本项目采用微尺度多相流测试技术和数值模拟方法，研究油水两相的微流动与渗流，设计并建立了拥有专利技术的试验装置，采用微流体技术加工了不同尺寸、带有孔-喉结构的微通道，采用差压比较法测量了微通道中油水两相的阻力特性，采用显微摄像技术观测了油水两相的微观流型。将微流动与岩心渗流进行了对比，发现微通道中的孔-喉结构是油水两相渗流存在启动压力梯度的主要微观因素，揭示了低渗透孔隙启动压力梯度等宏观渗流现象的微观机理。应用多相微流体学理论对微流动相态的影响因素进行了量化分析，揭示了雷诺数、泊肃叶数、润湿性、界面张力以及微尺度等参数对油水两相微流动的影响效果，研究结果为解决壁面润湿性与油水界面张力的交互作用如何影响油水两相的微流动相态等关键科学问题提供了实验依据。研究了喉道间距对油水两相微流动的影响以及油滴在喉道处的变形阻力，提出了微喉道局部阻力损失预测模型，揭示了低渗透孔隙中油水两相渗流的微流动相态机理和可变形颗粒动力学机理。对20微米至200微米范围的微通道，在不同接触角条件下采用数值模拟方法研究了油段塞的流动过程，发现了润湿性不仅影响油段塞的形状以及流型，还能促进两相微流动的减阻；若油接触角小于30度，此时壁面润湿性为强亲油性，致使油段塞消失而形成附壁油膜，段塞流转变为环状流。将达西渗流定律与两相流分相模型相结合，建立了油水两相渗流单元模型。通常认为油水两相的相对渗透率之和小于1，而本项目的实验结果和渗流单元模型都表明，油水两相的相对渗透率之和在某些条件下可以大于1，该结论是对传统理论的突破，也是对渗流问题的新认识。本项目已获得的研究成果在微流体学与渗流力学的交叉领域提供了新知识和新见解，对非常规低渗透油藏的高效开发有重要的科学意义。