超低渗透油藏的岩石界面油水活化和驱油机理研究

At present, for the oil reservoirs with ultra-low permeability, a traditional oil displacement technology to enhance oil recovery is to reduce the oil/water interfacial tension resulting in the depressurization and augmented injection. However, the produced effect is not good. For these reservoirs, the pore throats are very tiny, the films of water and oil are thick, and the injection pressures are high. Therefore, we will seek to obviously decrease the thicknesses of absorbed water and oil for rock surface by changing from the liquid wettability to the intermediate wettability, which results in increasing the relative permeabilities of oil and water. We will synthesize the novel hybrid surfactants containing fluorocarbon and hydrocarbon chains and sulfonate anion in this project. The mechanisms on micellization thermodynamics, the micellar structures and their match-relationship with pore structures, the interfacial activation on rock, and the migration of residual oil will be studied for these novel surfactants. In this project, we try to obtain the novel fluorinated surfactants that present the multiple properties of oil-flooding materials, and the mechanisms on the migration of the novel surfactants in the pore throats will be investigated. These surfactants can not only modify the wettability of rock but also reduce dramatically the oil-water interfacial tension. The other aim is to solve the present-day problem that the reported fluorinated surfactants can only reduce the oil/water interfacial tension to about 1.5 mN/m, but can not reduce the interfacial tension to a low value (0.01 mN/m order of magnitude). This will provide the theoretical and experimental basis for the effective exploration of ultralow-permeability oil reservoirs.

目前对于超低渗透油藏提高采收率的途径通常是通过降低油水界面张力，而达到降压增注的目的，但效果有限，本项目针对超低渗透油藏的孔喉半径小，岩石界面油水膜厚，注水压力很高的特征，拟改变岩石的液润湿为中间润湿，显著削弱岩石界面的吸附油水膜，以提高油水相对渗透率。研制含氟碳链和碳氢链的阴离子双链氟表面活性剂(新型活性剂)，研究它们的胶束化热力学、胶束结构及与储层孔隙结构的匹配性，研究它们在岩石界面使油水活化的机理，使孔隙中残余油驱替的规律。项目旨在获得这些新型活性剂在超低渗孔喉中的运移规律，期望新型活性剂能作为多功能驱油剂，不仅能改变岩石润湿性，活化岩石界面的液膜，还能显著降低油水界面张力，并且还期望解决氟活性剂能使油水界面张力降低到约1.5 mN/m，难于降低到0.01 mN/m数量级的难题。项目的完成将为超低渗透油藏的更有效开发提供理论基础和实验依据。

目前，在超低渗透砂岩油藏的活性水驱油技术中，常用的磺酸盐类碳氢表面活性剂在不加碱时，油水界面张力（IFT）属低界面张力(10^-1 mN/m)，使得毛细管压力的降低有限；其使砂岩更亲水，砂岩表面的水膜厚度增加，反而使得水相渗透率降低。而且与含氟活性剂相比，其耐温性能更差。含氟活性剂既憎水又憎油，能增强砂岩的水相非润湿性以及原油的流动性，但其油水界面张力高（5-15 mN/m），这使毛管压力的降低和原油的乳化受到限制，而且品种少，价格高，耐盐性较弱。因此，本项目针对超低渗透砂岩油藏的开发，研制了含氟碳链和含碳氢链的3个系列磺酸盐型双链杂化含氟活性剂，包括HFS、PFVB和GFD系列，研究了它们的溶液性能、与碳氢活性剂的复合机理、在砂岩表面的动、静态吸附机理、胶束化热力学机理、驱油机理等。这些活性剂均在常压下一步或2步法合成，易于工业化，30℃时临界胶束浓度（CMC）低至0.343 mmol/L,温度升高，CMC更低;溶解性好，Krafft点均低于0℃；耐盐高于50000mg/L；耐温高于90℃；新型含氟活性剂浓度为0.1 g/L的盐水溶液能使油相和水相在砂岩表面达到中间润湿（接触角θ为90º-95º）；活性剂总浓度0.23 g/L的新型含氟活性剂复合体系盐水溶液（30 g/LNaCl）的IFT能低至0.07 mN/m，且水相在玻璃表面的接触角（θ）达到72º（纯净水的θ为48º），当NaCl浓度为60 g/L时，该复合体系的IFT低至0.005 mN/m，θ为72.27º。PFVB的驱油性能最好，其驱替的溶液浓度并不是越高越好，存在最佳值，为0.03 g/L, 此时，水相渗透率增幅为54%，采收率提高幅度为8%，其复合体系的驱油性能更好。在30℃~ 55℃范围内，新型含氟活性剂的胶束化的标准摩尔吉布斯函数变低于−36.20 kJ/mol，其胶束形成的自发性强于碳氢活性剂，而且主要是熵驱动过程；胶束直径主要约为30 nm，胶束结构能与孔隙结构很好地的匹配。研究发现，在超低渗透砂岩油藏驱油中，活性剂的岩石水相非润湿性对驱油的贡献明显超过了油水界面活性的贡献。