双基团修饰pH敏感纳米二氧化硅材料制备及其降压增注机理研究

Nano functional materials have attracted more and more attention in oil production field for their special properties. Aiming at several technical difficulties such as fast decreasing of reservoir energy and low oil recovery, caused by soaring injection pressure and little water injection in the waterflooding stage of extra-low, ultra-low permeability reservoirs, pH-responsive bifunctional groups nano-silica materials with high efficiency are developed based on nano-silica through chemical graft modification method. In this work, the regulation of effect of group types of modified molecule, ratio and pH environment on properties of pH-responsive bifunctional groups nano-silica can be clarified through micro-channel model designed independently. Based on this, pH-responsive bifunctional groups nano-silica material and optimal modified method are developed. The adsorption behavior of pH-responsive bifunctional groups nano-silica on the pore-throat surface, oil/water interface and rock surface are studied to explore the micro-mechanism for decreasing oil/water interfacial tension, wettability alteration and flowing behavior in micro-channel. This work will lay a scientific foundation and technical support for enhanced oil recovery in extra-low, ultra-low permeability reservoirs.

纳米功能材料由于其性能特殊在石油开采领域备受关注。本项目针对特低渗超低渗油藏注水开发面临的注水压力攀升甚至“注不进去”而导致地层能量衰减快、采出程度低这一复杂技术难题，以纳米二氧化硅为基质材料，采用化学接枝改性方法，制备出高效能的双基团修饰pH敏感纳米二氧化硅材料。基于自主设计的微通道模型，采用现代分析测试方法和定量模拟实验，着重研究修饰分子基团类型、配比及pH环境对双基团修饰pH敏感纳米二氧化硅材料性质的影响作用规律，获得理想的双基团修饰pH敏感纳米二氧化硅产品和最佳修饰方法。同时，探明双基团修饰pH敏感纳米二氧化硅材料在孔喉表面、油/水界面、岩石表面吸附行为，探索其降低油/水界面张力、调控油藏润湿性的微观作用机制和微通道内的流动作用机制，进而揭示纳米二氧化硅材料的降压增注机理。为改善注水开发效果提高特低渗超低渗油藏采收率提供科学依据和新的技术支持。

纳米功能材料由于其性能特殊在石油开采领域备受关注。针对特低渗超低渗油藏注水开发面临的注水压力攀升甚至“注不进去”而导致地层能量衰减快、采出程度低的复杂技术难题，本研究以纳米二氧化硅为基质材料，采用两步法获得不同烷基和烷基酸双基团修饰的纳米二氧化硅材料，优化出最佳合成反应条件，确定了反应溶剂为DMF、纳米二氧化硅与偶联剂配比1:1、纳米二氧化硅与修饰剂配比1:1、烷基与烷基酸配比1:1、最佳修饰链长度6个碳、反应温度110℃，反应时间4 h，进而明确了最佳的修饰方法。通过先进分析和实验手段，阐明了pH值对pH敏感纳米二氧化硅材料的分散性、微观尺寸、微观形貌、表面电性、降低油水界面张力、改变润湿性、黏土防膨性、降压增注性能的影响作用规律，纳米材料在弱碱性环境下分散性好，颗粒不发生团聚，呈椭球状、粒径约为10nm左右，降低油水界面张力增强，智能调控润湿性，静态防膨率超过40%，降压率30%以上。通过研究加入纳米材料前后直微通道内的流场变化特征和孔喉表面排布特性，揭示了纳米材料在孔喉表面吸附调控壁面润湿性及粗糙度，形成疏水滑移界面层，有效降低边界层厚度，抑制黏土膨胀，增加水流通道的有效流动半径，提高流体的流动速度，从而实现降压增注的作用，为改善注水开发效果提高特低渗超低渗油藏采收率提供科学依据和新的技术支持。