| In recent years,chemical flooding technology has become one of the important methods to enhance crude oil recovery.Alkylbenzene sulfonates(ABS)have been widely applied in chemical flooding systems due to the advantages of wide sources,low price,and outstanding interface properties.However,as the environment for oil production becomes more and more complex,optimizing the ABS flooding system formula has become an important task in order to further enhance crude oil recovery.The key to optimizing the formula is to clarify the interaction mechanism between surfactants and crude oil.Unfortunately,it is difficult to expound the interaction mechanism between the surfactants added to the water phase and crude oil owing to the complexity of the composition of the crude oil.As the significant fraction of crude oil,resins have been the subject of many researches due to their importance in the interface behavior of crude oil/surfactant systems.However,there are few studies on the subject of resin subfractions.Therefore,this paper took the resin and its subfractions in Daqing crude oil as the research object,characterized their structure by modern physical research methods,and discussed their effects on the interface performance of ABS solutions.The main contents are as follows:1.The resin(R)extracted from Daqing crude oil was divided into five subfractions R1-R5 by precipitation method of mixed solvents.The resin and its subfractions were characterized by CHNS elemental analyzer,Fourier transform infrared spectrometer,gel permeation chromatography,synchronous fluorescence spectrometer and nuclear magnetic resonance spectrometer.The modified B-L method was employed to calculate the structural unit parameters.An average unit structure model was constructed.The dipole moments of these fractions were estimated by the Onsager method.The results showed that there were many similarities in the molecular structure of resin and its subfractions,but there were obvious differences.The molecular structure of the resin and its subfractions contained a certain amount of heteroatoms,the O content was significantly different between the fractions,the N content was also obviously different,and the difference of S content was small.There were no significant differences in the existence forms of N and S among the fractions,but there were significant differences in the existence forms of O.The molecular size order of these fractions was R1 > R2 > R3 > R > R4 > R5.The aromatic carbon ratios of R3 and R4 were higher than those of other fractions,and the aromatic ring systems presented cata condensed,while the aromatic carbon ratios of R,R1,R2,and R5 were lower,and the aromatic ring systems presented peri condensed.The average number of structural units in molecules of R1 and R2 was larger,while the average number of structural units in molecules of R,R3,R4 and R5 was smaller.The polarity order of these fractions was R1 > R2 > R > R5 > R3 > R4.2.The effects of resin and its subfractions on the DIFTs of ABS were investigated by the spinning drop method.The results showed that the effects of resin and its subfractions on DIFTs of ABS solutions are dependent on their molecular size,concentration and polarity.Resin subfractions with larger molecular size had a slight effect on DIFTs and DIFTs curves showed the “L” shape,no matter what their polarity or concentration.For resin and its subfractions with smaller molecular size,they had a significant effect on DIFTs at higher concentrations,DIFTs curves showed the “V” shape.However,the variations of minimum interfacial tension(IFTmin)were not entirely consistent with the molecular size of resin and its subfractions.The IFTmin was not only affected by molecular size but also by polarity.Resin and its subfractions with smaller molecular size and higher polarity resulted in lower IFTmin.In addition,the influence mechanisms of resin and its subfractions on DIFTs were also discussed in detail. |
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