| Petroleum is widely used in daily life.However,due to the low permeability of the rock formation,there is still a considerable number of residual crude oil after primary and secondary oil recovery,even some developed oil reservoirs are difficult to produce them.Based on this problem,surfactant flooding in tertiary oil recovery is an effective technique to further enhance oil recovery on the basis of water flooding.In this paper,two series of surfactants were designed and synthesized for reservoirs with low permeability,high divalent cation concentration and a reservoir temperature of 50°C.It includes a series of quaternary ammonium salt cationic surfactants LJH-1?LJH-4,and a series of di-sulfonate sodium salt anionic Gemini surfactants LJH-6?LJH-9.The structure of the synthesized surfactants was characterized by FT-IR Spectrum and ESI-Mass Spectrometry.The surface/interfacial activity,wettability and compatibility with the formation water of the synthesized surfactants were studied.The results show that LJH-3 and LJH-8 of the two series of synthesized surfactants show the best surface/interface activity and the effect of changing wettability under the conditions of distilled water.When dissolved with formation injected water?Ca Cl2 concentration is 3.772 g/L,total dissolved solids are about 80 g/L?,anionic Gemini surfactants show better compatibility than cationic surfactants.Under the condition of injected water,the interfacial tension value of LJH-6?LJH-8 decreased by an order of magnitude compared to that under distilled water,reaching on the order of 10-1 m N/m,the interfacial tension of 0.1%of LJH-8 reaches the order of 10-2 m N/m,which is 0.0163 m N/m.Under the condition of a mixed solution of Na Cl?35 g/L?and Ca Cl2?3.772 g/L?,the interfacial tension of LJH-1?LJH-4 decreased significantly.And LJH-1?LJH-3 show outstanding interfacial activities,and their interfacial tension can reach an ultra-low level of the order of 10-3 m N/m.Besides,LJH-3 with a concentration of 0.1%has the lowest interfacial tension of 2×10-4 m N/m.The salt resistance and divalent cation resistance of LJH-3with a concentration of 0.1%under distilled water were tested.When the reservoir temperature is 50°C,the concentration of divalent cation and salinity are 11 g/L and 35 g/L,the 0.1%of LJH-3 solution has the best effect to reduce the interfacial tension.A mixed solution with Na Cl concentration of 35 g/L and Ca Cl2 concentration of 9 g/L was used as simulated water.At 50°C,0.1%of LJH-3 solution with simulated water and 0.1%of LJH-8 solution with injection water were used as displacing fluids to conduct the core displacement experiments,respectively.LJH-3 and LJH-8 surfactant flooding fluids can improve oil displacement efficiency by 7.59%and 7.41%based on water flooding,respectively,and they have potential in the application of enhanced oil recovery in low permeability reservoirs. |
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