低渗透油藏双疏型纳米流体相界面调控及渗吸驱油机理

At present, to enhance the oil recovery of the low permeability reservoir, two main methods are to alter the reservoir wettability and decrease the oil/water interfacial tension. However, there is lack of in-depth study on the hydrophobic-oleophobic wettability effect on the oil recovery in low permeability reservoirs, and the reports on the synergistic reaction mechanism of reservoir wettability and oil/water interface activation are rare. Moreover, the synergistic contribution effect of spontaneous imbibition and forced imbibition on the displacement efficiency in low permeability reservoirs remains unclear, which limits the application of EOR methods. Based on this background, we aim to combine the nano-material with the present oil recovery methods and apply a self-developed hydrophobic-oleophobic nano-silica fluid in the present study. On the basis of the results of physical simulation and property characterization with the use of high-end instruments, the self-assembly regulations of hydrophobic-oleophobic nano-silica particles at the solid-liquid interface and oil-water interface will be analyzed, the regulatory mechanisms of nano-silica self-assembly to the solid-liquid interface wettability and the oil-water interface activation will be also clarified. Additionally, we will respectively investigate the spontaneous and forced imbibition effectiveness of this kind of nano-silica fluid in low permeability cores, and quantitatively reveal the synergistic contribution of two kinds of imbibitions for oil recovery under the condition of phase interface regulation. Finally, on the basis of the above results, the micro and macro imbibition displacement mechanisms of the hydrophobic-oleophobic nano-silica fluid will be discovered. This application work will provided theoretical basis and technical support for the EOR of the low permeability reservoirs.

目前提高低渗透油藏原油采收率的主要途径是改变储层润湿性及降低油水界面张力，但“油水双疏”润湿性对低渗透油藏采收率的影响尚缺乏深入研究，有关润湿性与油水界面活性协同调控方面的研究较为欠缺。此外，低渗透油藏自发渗吸和强制渗吸之间的协同贡献机制也不明确，限制了提高采收率技术的实施。基于此，本项目拟将纳米材料与现有提高采收率方法相结合，使用自主研发的油水双疏型纳米SiO2流体开展研究。借助物理模拟、高端仪器表征等手段，分析双疏型纳米SiO2流体在液固界面和油水界面的自组装规律，明确纳米SiO2粒子自组装对液固界面润湿性和油水界面活性的调控机制。研究低渗透岩心在双疏型纳米SiO2流体中的自发渗吸与强制渗吸驱油效果，量化表征基于相界面调控作用下二者对提高原油采收率的协同贡献关系，揭示低渗透油藏中双疏型纳米SiO2流体的微宏观渗吸驱油机理，为低渗透油藏提高原油采收率提供理论依据和技术支持。

针对低渗透油藏储层物性差、注水压力高等难题，紧密结合该类油藏储层特性及开发特点，开展“双疏型纳米SiO2粒子液固界面润湿性调控机理”、“双疏型纳米SiO2粒子油水界面活性调控机理”和“低渗透油藏双疏型纳米SiO2流体微宏观渗吸驱油机理”三方面研究工作。首先，采用十八烷基三氯硅烷及非离子型烷氧基聚醚作为改性剂，合成了油水双疏型纳米SiO2粒子，构筑了油水双疏型SiO2粒子驱油体系。其次，通过界面张力、微观结构、界面润湿性等研究表明，双疏型纳米SiO2粒子可在岩石表面形成一层致密的吸附层，利用自身形貌取代岩石原有形貌，实现岩心表面的润湿性反转，在油水界面形成的吸附组装结构，将气水表面张力降至35 mN/m，将油水界面张力最低降至11 mN/m；明确了双疏型纳米SiO2粒子在岩石表面和油水界面的吸附规律，探明了不同条件下双疏型纳米SiO2粒子吸附作用对岩石壁面润湿性及油水界面活性的影响机制，揭示了双疏型纳米流体对液固界面润湿性和油水界面活性的调控机理。而后，通过岩心渗吸及驱替物理模拟研究表明，双疏型纳米SiO2流体对不同渗透率低渗透岩心的自发渗吸驱油采收率贡献值占比约60%、强制动态渗吸占比约40%；明确了不同岩石表面润湿性和不同油水界面活性条件下低渗透岩心在双疏型纳米SiO2流体中的自发渗吸和强制渗吸驱油机制，揭示了自发渗吸和强制渗吸对提高低渗岩心原油采收率的贡献程度及协同作用机制。最后，阐明了液固界面润湿性和油水界面活性对低低渗透岩心渗吸排油的影响程度，双疏型纳米SiO2流体可改善驱替液在孔吼内部的流动状况，提高剩余油和残余油驱动效率，含油饱和度由水驱末的42.76%降低至纳米流体驱末的29.12%，揭示了低渗透油藏中双疏型纳米SiO2流体的微宏观渗吸驱油机理。