基于纳米-微米孔喉网络模型的润湿性动态变化条件下致密油基质渗吸规律研究

Imbibition is of great importance to enhance tight oil recovery, and using surfactant to change the matrix wettability for improving oil displacement effect of imbibition is one of the most promising methods of enhancing tight oil recovery. However, nanopores are widely developed in the matrix of tight oil reservoir, and matrix pores have the characteristic of Nano-micro multiscale distribution. The imbibition mechanism in Nano-micro pore throat under wettability dynamic change is complex and not clear. Starting with the characteristic of Nano-micro pore throat and based on the multiscale digital rock built through multi-resolution CT scanning, this project will construct the physical model of Nano-micro pore throat network multiscale imbibition. According to the different imbibition mechanism in nanopores and micropores, the imbibition dynamic functions will be established respectively, and applied in the multiscale imbibition physical model to couple trans-scale imbibition. The process of surfactant solution imbibition in the Nano-micro pore throat network will be simulated and the influencing mechanism of dynamic changing wettability on imbibition path and imbibition rate will be researched, and imbibition law in Nano-micro pore throat network will be revealed. Combining indoor experiments of core imbibition, the imbibition dynamic model of matrix of tight oil reservoir will be established, and the imbibition law and key influencing factors will be clarified. The research achievements of this project will be useful for exploiting the potentialities of oil production with imbibition, and promoting the tight oil development.

渗吸作用对提高致密油采收率意义重大，通过表面活性剂改变基质的润湿性从而提高渗吸驱油效果是目前最有潜力的提高致密油采收率方法之一。但致密油基质纳米孔隙广泛发育，且孔隙具有纳米-微米多尺度分布的特征，润湿性动态变化条件下微纳米孔喉渗吸机理复杂且尚不明确。本项目从微纳米孔喉特征入手，基于多精度CT扫描建立的多尺度数字岩心，构建纳米-微米孔喉网络多尺度渗吸物理模型，针对纳米孔隙和微米孔隙渗吸机理的不同，分别建立相应的渗吸动力学方程，并利用孔喉网络渗吸物理模型进行跨尺度渗吸流动耦合，模拟表面活性剂溶液在纳米-微米孔喉网络中的多尺度渗吸过程，研究润湿性动态变化对渗吸路径与渗吸速度的影响机制，揭示纳米-微米孔喉网络渗吸规律，并结合室内岩心渗吸实验，构建润湿性动态变化条件下的渗吸动力学模型，明确致密油基质的渗吸规律及其影响因素。本项目的研究成果将有助于充分挖掘渗吸驱油潜力，促进致密油的有效开发。

我国致密油资源储量巨大，经济有效开发致密油资源对保障国家能源安全具有重要意义。致密油藏微纳米孔喉广泛发育，开发困难，充分发挥渗吸驱油作用对提高致密油采收率意义重大。首先，本项目综合利用铸体薄片、FE-SEM、高压压汞、恒速压汞、核磁共振、微纳米多尺度CT扫描等测试方法明确了致密油藏微纳米孔隙结构与流体分布特征，形成了一套致密油藏复杂孔隙结构与油藏物性表征方法；其次，基于致密油藏微纳米孔隙分形特征，构建致密油基质数字岩心等效分形介质模型，考虑固-液边界层效应与气体滑脱效应，分别构建了致密油藏表观液体渗透率模型、低速非达西渗流模型和表观气体渗透率模型，推导了拟启动压力梯度与滑脱系数表达式，可以有效表征致密油藏非线性渗流规律；继而，开展致密岩心在地层水与表面活性剂溶液中的自发渗吸实验，明确了表面活性剂类型与浓度、界面张力、润湿性、地层水矿化度等对渗吸驱油速率与采收率影响；最后，推导了润湿性不变与润湿性动态变化条件下油水两相自发渗吸非线性动力学方程，基于致密油基质微纳米孔隙结构特征，建立岩心尺度渗吸数学模型，明确了润湿性、界面张力、孔隙结构分布、重力、粘滞力对渗吸驱油速度的影响。依托本项目共发表论文21篇（其中SCI检索论文16篇），申请发明专利7项，培养研究生7名。本项目研究成果为致密油藏复杂孔隙结构表征、非线性渗流规律和自发渗吸提高采收率提供了理论指导和参考依据，对致密油高效开发具有重要意义。