阴离子双子表面活性剂粘弹流体提高非常规油藏采收率基础研究

The unconventional oil reservoir has become major oil resource in China, but there is still a lack of technology to improve water flooding recovery effectively. The viscoelastic surfactant flooding can overcome the shortcomings of prior art, but there are the chromatographic separation risk, high dosage and oil-water interfacial tension, and the poor heat resistance. So the constructing method,stable thickening mechanism, and oil displacement mechanism of one-component viscoelastic surfactant flooding system with low interfacial tension (IFT) at reservoir temperature are still scientific problems which need to be solved. The anionic Gemini surfactants have relatively lower adsorption loss and Critical Micelle Concentrations(CMC), higher interfacial activity and better solubility. Based on these advantages, the one-component anionic Gemini surfactant viscoelastic fluids were constructed with low interfacial tension (IFT).The relationship between molecular structure and viscosity(7s-1), viscoelasticity and interfacial activity were investigated to design the viscoelastic surfactant with low IFT, temperature tolerance and thickening ability. The viscoelastic fluids containing anionic Gemini surfactant and salt were structured by means of salt enhancing micellar structure. The effect of reservoir environment conditions（temperature,salt,pH,salinity）on the microcosmic and macroscopical properties of viscoelastic fluids were studied, and the microcosmic thickening mechanism of low IFT anionic Gemini surfactant were expounded. The oil displacement mechanism of viscoelastic fluids were researched through the tests of emulsification/ rheological property/ interfacial activity/ viscoelasticity/ wettability. All these will provide the basis for the application of temperature tolerance, low IFT and one-component viscoelastic surfactant fluids in unconventional oil reservoir.

非常规油藏已成我国主要石油开采资源，但缺乏有效提高水驱采收率技术。粘弹表面活性剂驱可克服现有技术不足，但仍存色谱分离风险，且用量及油水界面张力偏高、耐温差，因此油藏温度下，低界面张力单组份粘弹表活剂驱油体系构筑方法、稳定增稠机制及驱油机理仍是有待解决的科学问题。本项目基于阴离子双子表活剂吸附损失与临界胶束浓度低、界面活性高、水溶性好，构建单组份低界面张力低浓度阴离子双子表活剂粘弹流体，研究其分子结构与溶液粘度(7s-1)/粘弹性/界面活性间构效关系，设计低界面张力耐温增稠粘弹表活剂分子结构；借助盐对胶束结构增强作用，构建阴离子双子表活剂-盐粘弹流体，研究油藏环境条件对粘弹流体微观结构及宏观性能的影响，阐述低界面张力阴离子双子表活剂微观增稠机制；通过乳化/流变性/界面活性/粘弹性/润湿性测试、微观可视化及非均质物模驱油，阐述粘弹流体驱油机理。为耐温低界面张力单组份粘弹流体驱油应用提供依据。

非常规油藏属我国主要石油开采资源，但缺乏有效提高水驱采收率技术。粘弹表面活性剂驱虽可克服现有技术不足，其多组分易色谱分离，且用量及油水界面张力偏高、耐温差，因此油藏温度下，低界面张力单组分粘弹表面活性剂驱油体系构筑方法、稳定增稠机制及驱油机理仍有待研究。本研究以吸附损失和临界胶束浓度低、界面活性高、水溶性好的阴离子双子表面活性剂构建单组分低界面张力低浓度粘弹流体，研究其分子结构与溶液粘度(7s-1)/粘弹性/界面活性间构效关系，优化低界面张力耐温增稠粘弹表面活性剂分子结构，构建阴离子双子表面活性剂-盐粘弹流体，研究油藏环境条件对粘弹流体微观结构及宏观性能的影响，探讨低界面张力阴离子双子表面活性剂-盐粘弹流体微观增稠机制；通过微观可视化、核磁共振及非均质物模驱油，研究粘弹流体驱油机理。发现，柔性联结基羧酸盐双子表面活性剂(m=18、s=2)界面活性高、油水界面张力低(7.42×10-3mN/m)，低剪切(7s-1)增黏性(26.98mPa∙s)、粘弹性(tanδ=0.5<1)好，但耐盐(NaCl、Na2CO3)增黏性待改善；优化合成的不对称亲水头基(羧基、磺酸基)双子表面活性剂GACS416(m=16、s=4)浓度≥0.3%，具有良好的粘弹性、界面活性及增黏性，可构筑低界面张力粘弹流体；而KCl可改善GACS416溶液流变性，构筑GACS416/KCl粘弹流体(0.5%GACS416+0.3%KCl)，即使温度接近80℃，其黏度仍比水高8倍，具有流度调节和提高洗油能力(IFT≤10-2mN/m)。活性剂分子结构、浓度，KCl加量等通过影响胶束平均回转半径及胶束结构致密性而影响其增黏效果；GACS416/KCl粘弹流体对低、特低渗油藏有良好的注入性和较好的环境适应性，其最优注入参数下(0.2%、0.1ml/L、0.4PV、47.2℃)，可使均质和非均质岩心(级差3～10)水驱采收率分别提高9.58%、19.41%；其主要驱油机理是粘弹流体变形塞流全面驱替孔隙中残余油、封堵高渗通道分流启动未动用剩余油、粘弹流体/水混合驱替乳化分散残余油，夹带产出。是一种适合于低渗/特低渗、致密油藏提高水驱采收率的新技术，有明显的理论指导意义及现场应用价值。相关研究成果已用于CCUS中与CO2协同驱油，改善CO2驱效果，即将进入现场实验。