三元复合驱微观剩余油赋存状态及形成机理

Since it has been recovered by ASP flooding, Daqing Oilfield has achieved better technical and economic effects by improving sweep efficiency and oil displacement efficiency.However,some problems existing in flooding mechanism, formation mechanism of microscopic remaining oil, and the development of oil remained in reservoir, remain to be further studied. Specifically speaking, there are few studies concerning on the displaced part of residual oil and the form of microscopic remaining oil that contributes mostly to the EOR after ASP flooding. Therefore, this project mainly studies the occurrence and distribution of the remaining oil before and after ASP flooding, the detailed classification and quantitative analysis of microscopic residual oil occurrence state in the terms of pore scale with the sealed natural cores. Using physical displacement experiments, this project analyzes the microscopic residual oil formation mechanism from the perspectives of permeability, capillary number, washing degree, changes in the light heavy component of the remaining oil in the pore and pore plugging resulting from scaling and migration of clay particles. In addition, it also focuses on the change law of microscopic remaining oil of different location and flooding stage. Furthermore, it analyzes and determines the different contributions made by different kinds of microscopic remaining oil to EOR. Finally, it provides a method to activate the microscopic remaining oil mechanism by using ASP flooding.

大庆油田三元复合驱矿场试验取得了较好的技术经济效果，三元复合体系主要通过提高波及系数和驱油效率提高原油采收率，但三元复合驱后微观剩余油赋存形态、形成机理及对剩余油的启动机制还不是十分明确，具体是动用储层中哪个部分与哪种类型的残余油，以及储层中各种类型微观剩余油对提高采收率的贡献程度等方面研究较少。因此，本项目利用密闭取心井天然岩心研究三元复合驱前后微观剩余油赋存状态及分布，对孔隙尺度微观剩余油的赋存状态进行详细分类和量化分析。结合室内物理模拟驱油实验，从渗透率、毛管数、水洗程度、孔隙中剩余油轻重组份变化以及结垢和粘土颗粒运移造成喉道堵塞等角度分析微观剩余油形成机理；并且通过研究三元复合驱在不同位置不同驱替阶段各类型微观剩余油变化规律，确定三元复合驱过程中各类型微观剩余油对提高采收率的贡献程度，明确三元复合驱启动微观剩余油机制。

本项目将荧光显微镜应用于微观剩余油的分类研究上，并使用图像软件对剩余油进行定量分析，辅以激光共聚焦原油轻重质组分的分析技术，研究毛管数对微观剩余油赋存状态的影响。.本项目对三元复合驱前后微观剩余油赋存状态进行对比分析，根据三元驱后实际情况，将普遍认可的水驱后微观剩余油的分类进行细微调整，作为三元驱后微观剩余油的分类凭证。三元驱后剩余油主要为薄膜状剩余油以及粒间吸附状剩余油。薄膜状以及其他各类剩余油的残留主要因为其存在于一些复杂的小孔道中不易被驱替。而粒间吸附状剩余油大量存在则是因为三元体系中碱对岩石颗粒的溶蚀导致新增部分粒间吸附状剩余油，使其含量上升。.通过天然岩心的室内试验对毛管数对剩余油的赋存状态进行研究。宏观上三元体系，随着毛管数的增大，其驱油效率随着增加，残余油饱和度随着降低。从微观上看，同以毛管数若存在不同的体系配比，即使驱油效率相同，但动用的残余油机理不同，程度也不同，最终微观剩余油含量也不同。合理体系配比的三元复合驱对于水驱后的角隅状，颗粒吸附状、簇状有明显的效果，但对于混相严重粒间吸附状以及孔表薄膜状效果不明显。从毛管数的角度研究则发现粘度的变化虽然不会对毛管数有明显的影响，但粘弹效应可以促使表面活性剂更充分的与角隅状接触。碱和表面活性剂的协同效应可以提高毛管数，降低宏观含油饱和度，但随着碱浓度的提升粒间吸附状不降反升，使地层情况更复杂。与粘度有效配合，表面活性剂浓度越高，毛管数越大，各种类型剩余油均能有效动用。