| Low-permeability reservoirs are the most important development direction for China's current oil production.Due to the poor physical properties of the reservoir,the influence of the capillary force,and the strong Jamin's effect,the oil recovery of water flooding is only 10%to 15%.Surfactants and their combined systems are the main means of starting residual oils.Due to their higher surface activity,lower critical micelle concentration,better water solubility and stronger synergistic effects,Gemini surfactants have a good application prospect in oilfield.In this thesis,a new type of anionic-nonionic Gemini surfactant with excellent performance was synthesized by molecular design.The CTAB/GAES-1209 ultra-low interfacial tension combined flooding system was constructed.The interaction parameter of the mixed system and charge adsorption theory reveals the ultra-low interfacial tension mechanism of the combined system.The AP-P4/GAES-1209emulsion combined flooding system is developed.The relationship between the stability of emulsion and the dynamic of droplets was clarified by means of stability analyzer and rheometer,and an emulsification evaluation method for simulating stratum shear was established.The oil displacement effect of each oil displacement system was evaluated by physical simulation experiment system.The mechanism of oil displacement and the mechanism of starting and transporting residual oil were further revealed by microscopic visualization experiments.The results show that the CTAB/GAES-1209 ultra-low interfacial tension combined system can reduce the oil-water interfacial tension to 1.84×10-3 mN/m at 200mg/L,and still maintain ultra-low interfacial tension at a salinity of 1×105 mg/L.It is the most probably related to a large number of anions and cations being adsorbed onto the oil-water interface due to electrostatic attraction and the spatial structure formed by the long flexible EO chain winding.The average size of the emulsion droplet formed by the AP-P4/GAES-1209 system was 1.61?m,and the emulsion stabilization time was greater than 20 min.Emulsion stability and droplet migration rate are primarily affected by temperature and polymer concentration.There is a good correlation between emulsion stability and droplet dynamics.The simulated core shear test can form an emulsion system with uniform droplet size and good stability.The core flooding experiments showed that the oil recovery of chemical flooding can reach 6.3%17.2%after water flooding.In summary,the CTAB/GAES-1209ultra-low interfacial tension system has strong interfacial activity and moderate change of wettability,and also has a certain pressure drop increase performance.The tertiary oil recovery of the ultra-low interfacial tension system reached 14.7%in 12.2×10-3?m2permeability.The AP-P4/GAES-1209 emulsion flooding system has strong emulsifying properties and moderate interfacial tension.The tertiary oil recovery of the emulsion flooding reached 17.2%in 43.5×10-3?m2 permeability. |
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