非连续油相在多孔介质中的启动与运移机理研究

As the reservoir enters the high water-cut stage, the residual oil gradually transforms from continuous phase to discontinuous phase. When the discontinuous oil phase migrates in the pores of the porous media, there is a starting phenomenon, and the pressure drop in the pore is much higher than the calculation value of Darcy's law. At present, the traditional reservoir engineering method and pore network micro-flow simulation are difficult to accurately describe this phenomenon, so the mechanism of discontinuous oil phase flow in porous media is still unclear, and the accuracy of remaining oil development dynamic optimization and capacity prediction is facing major challenges. By computational fluid mechanics and flow experiments, the starting process of oil droplets in the pore level channel will be simulated, and the control factors and the influence laws will be analyzed. Then the critical conditions of the discontinuous oil phase in different cross sections will be obtained. The simulation of oil drops flow in variable diameter pore will be carried out, and a mathematical representation model will be established to reflect the starting and migration of discontinuous oil phase in the pore. Based on that, through 3D Micro-Continuum model, the simulation method for the starting and migration of discontinuous oil phase in porous media will be set up, the influence of discontinuous oil phase starting on porous media seepage will be explored, and the theory of multiphase flow in porous media will be developed and perfected. The study will provide an important theoretical support for the prediction accuracy of the development of residual oil in high water-bearing reservoirs, and promotes the scientific and effective development of the residual oil in high-water-bearing oilfields in China.

随着油藏进入高含水阶段，剩余油逐渐由连续相转化为非连续相。非连续油相在多孔介质孔隙内运移时存在启动现象，孔隙内压力降远远高于达西定律计算值，目前传统的油藏工程方法和孔隙网络微观流动模拟难以准确描述这一现象，使得多孔介质内非连续油相流动机理尚不清楚，剩余油开发动态优化和产能预测的准确性面临重大挑战。本课题拟利用微流动实验和计算流体力学方法，模拟孔隙级微通道内滞留油滴启动过程，得到不同截面孔隙内非连续油相启动临界条件；进而开展变径孔隙中油滴运移模拟，建立非连续油相在孔隙内启动与运移的数学表征模型；在此基础上，通过三维微观连续介质模型内流动模拟研究，建立非连续油相在多孔介质中的启动与运移模拟方法，阐明非连续油相启动对于多孔介质渗流的影响规律，完善并发展多孔介质中的多相流动理论，为高含水油藏剩余油开发的预测准确性提供理论支撑，促进我国高含水油田剩余油科学、有效的开发。

经过长时间注水开发，以大庆、胜利为代表的老油田已经进入高含水开发阶段，储层多孔介质中剩余油逐渐由连续相转化为非连续相。根据实验结果，非连续油相在孔隙内运移时存在启动现象，启动过程中非连续油相所受到的阻力远高于达西定律计算值，从而阻碍非连续油相在多孔介质内的运移。该现象使得油水两相渗流机理非常复杂，传统的油藏工程方法以及油藏数值模拟方法目前难以准确描述启动过程中的压力变化规律，非连续油相的启动和运移特征未能真正体现在多孔介质渗流理论中。为了揭示多孔介质内非连续油相的启动与运移机理，研究非连续油相在圆形截面孔隙内的启动现象，分析了不同长度非连续油相和多个非连续相存在下，孔隙内的压力降变化规律，提出了等效粘度模型，揭示了孔隙内非连续油相启动时压力降变化的原因：毛管力压差的消失和水膜包裹油滴的等效粘度降低；对于非圆形截面孔隙，提出单角毛细管模型，推导了不同截面形状下孔隙内油水两相的分布规律，在此基础上，利用计算流体力学方法，研究了非圆形截面孔隙内非连续油相的运移机理，发现非圆形截面孔隙内非连续油相运移时存在临界速度，速度小于临界速度时非连续油相无法脱离孔隙内壁，孔隙内为非达西流动，该现象是多孔介质启动压力梯度和非达西流动的微观愿意。本研究旨在揭示多孔介质内非连续油相的运移机理，完善并发展多孔介质中的多相流动理论，为高含水油藏高效开发和预测提供理论指导。