| This paper aims to develop a flooding surfactant with good application prospects under alkalescent conditions.At present,the tertiary oil recovery technology of China is in a leading position worldwide,and the HABS alkaline ASP(alkaline,surfactant,polymer)flooding system which has been used for many years has achieved good results.However,with the increase of the oil extraction year by year,the alkaline ASP faces many problems and the alkalescent ASP flooding system has become a new direction for the oil fields in the future.A surfactant for alkalescent flooding system is developed,and simulated flooding experiments are conducted in this study.The experimental results show that the performance of the alkalescent flooding system is better than the strong alkali one which is currently used.Therefore,this research will become a significant achievement which can keep our tertiary oil recovery technology at the leading level in the world.The research process is a complete set of scientific development system,including the proposal of problems,the determination of research direction,the synthesis of surfactant,the detection of physical property,the determination of surfactant,the assessment of performance,the evaluation of simulated displacement and the study on the dynamic action mechanism of alkali.By analyzing the molecular structure of HABS firstly,2-alkoxy-5-mercaptobenzene sulfonate and alkyl diphenyl ether disulfonate(ADPODS)with similar structures are determined as research direction,and 2-alkoxy-5-nonyl benzene sulfonate with an alkoxy carbon chain number of 6,8,10 and 12 are respectively synthesized with 4-n-nonylphenol and n-alkyl bromide as raw materials.Although the interfacial properties for crude oil will be improved with the increase of the number of carbon chain,an interfacial tension of only 10-2 m N/m can be reached under alkali conditions,and an ultra-low interfacial tension of 10-3 m N/m cannot be reached even after mixing,so the alkalescent flooding ability cannot be obtained.However,the intermediate 2-alkoxy-5-mercaptobenzene sulfonic acid is a new Bronsted acid which can effectively accelerate the esterification reaction,and its alkyl carbon chain will bring a huge effect on high efficiency catalysis since an enhanced hydrophobic which is conducive to the form of microemulsion is brought by the alkyl carbon chain.In addition,a certain degree of acidity aggregation appears at the polar end,presenting a relatively high acidity.Monoalkyl diphenyl ether disulfonate,dialkyl diphenyl ether disulfonate and tetraalkyl diphenyl ether disulfonate with a 12,14,16 and 18 carbon atoms in the alkyl carbon chain are respectively synthesized with diphenyl ether and linear alpha olefin as raw materials,and the critical micelle concentration(CMC)is calculated by using conductivity.For the same molecular structure,the CMC will gradually decrease with the increase of the length of the alkyl carbon chain;for different molecular structures,the CMC of the polyalkyl carbon chain is lower than the one of the monoalkyl carbon chain,but the CMC of the dialkyl carbon chain is the lowest.Then the dissolution state of the surfactant in water is observed,and the general formula calculation,the group number method,the CMC measurement and the hydrophilic-lipophilic balance(HLB)calculation are carried out,where the HLB of monoalkyl diphenyl ether disulfonate and dialkyl diphenyl ether disulfonate can be calculated by the group number method and the HLB of tetraalkyl diphenyl ether disulfonate can be obtained by the general formula calculation.Regarding the melting point,monoalkyl diphenyl ether disulfonate will gradually go up with the increase of the length of the alkyl carbon chain,while the ones of dialkyl diphenyl ether disulfonate and tetraalkyl diphenyl ether disulfonate are the opposite.The interfacial properties for crude oil of ADPODS are mainly affected by the length of the alkyl carbon chain and the number of the carbon chain,that is,the performance will be improved with the increase of the length and number of the carbon chain.For example,the interfacial tension for crude oil of tetraalkyl diphenyl ether disulfonate with a carbon chain length of eighteen carbon atoms can reach 10-3 m N/m.In order to obtain surfactant with better performance,the molecules with the same molecular structure and different carbon chain length as well as the molecules with the same carbon chain length and different molecular structure are mixed,and it is found that the mixture of dialkyl diphenyl ether disulfonate and tetraalkyl diphenyl ether disulfonate with 18 carbon atoms in the alkyl carbon chain shows good interfacial properties for crude oil.In addition,by observing the property of the mixed surfactant with different mixing ratios,the one with a mixing molar ratio of 1:1(DT Blend)is proved to present the best interfacial properties.The interfacial tension for crude oil of DT Blend can reach 10-3 m N/m and can even be reduced to 10-4 m N/m,and moreover,an ultra-low interfacial tension over a relatively wide mixing ratio can also be achieved.According to the study on interfacial properties of DT Blend,it was found that the interfacial properties of the ASP system can be improved by the high polymer at low concentrations,and the viscosity of the polymer is highly affected by the alkali.Considering the viscosity of the ASP system and the amount of alkali used in practical applications,the polymer concentration is determined to be 0.125%.The stability of the interfacial properties of ASP system formulated with DT Blend on the 30 th,60th,110 th,and 150 th days after the mixing is observed,and the interfacial tension for crude oil on the 150 th day can still reach 10-3 m N/m,with the range of ultra-low interfacial tension mainly concentrated in the low-concentration surfactant area.DT Blend presents good interfacial properties for crude oil in different blocks in Daqing,Dagang and Shengli oil fields,all with wide range and interfacial tensions of 10-3 m N/m.Adsorption,which directly affects the consumption of surfactant and alkali,must be considered in the practical application,and Na2CO3,Na Cl,Na2SO4,polymer and re-injected sewage can effectively reduce the adsorption loss.Simulated displacement experimental plans are formulated based on the above research.Even though the amount of surfactant and alkali used in Plan 1 is significantly lower than that of Plan 2,the recovery efficiency of Plan 1 is still as high as 22.7%,which is only 7.35% lower than that of Plan 2 and is still 0.4% higher than that of HABS alkali system.Based on the unique viscosity of the polymer,different systems are prepared in a centrifuge tube to measure the change in the interfacial tension when an oil droplet passing through different systems,and to summarize the dynamic principle of alkali in ASP system.The equilibrium interfacial tension of non-petroleum sulfonate is higher than the lowest interfacial tension in the dynamic process.The ion concentration in solution will increase with the addition of alkali,and then the lowest interfacial tension is produced by the synergistic action of the added surfactant and the natural surfactant generated from the reaction of alkali and petroleum.Then the interfacial tension will increase with the natural soap entering the system from the oil-water interface.Based on the analysis of the emulsion stability,it is proved that the alkali can reduce the coalescence rate of the oil droplet in the dispersed phase of the emulsion,making the dispersed phase of the emulsion more stable. |
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