Synthesis,Physicochemical Properties And Application Of Novel Phenyl-Containing Betaine Surfactants

With the development of reservoir exploitation,ASP flooding(alkali/surfactant/polymer)has become one of the most potential enhanced oil recovery(EOR)technologies.However,the addition of alkali will cause scale formation,pipeline corrosion,formation permeability reduction and other adverse effects.At the same time,considering the exploration and development of oil are developing towards high temperature and high salt reservoirs,it is of great significance to synthesize a new type of alkali-free,temperature resistance and salt tolerancet surfactant.In this paper,two new types of phenyl-containing betaine surfactants were designed and synthesized,and their physicochemical properties and application performance were systematically explored,providing basic data for enriching the understanding of this new phenyl-containing betaine surfactants and exploring its application in tertiary oil recovery.Firstly,two novel phenyl-containing betaine surfactants(BCB_n and BSB_n)were synthesized by Williamson etherification,Blanc chloromethylation and quaternization reaction using 2,6-dimethylphenol as raw material.The synthetic products were characterized by HPLC?¹H-NMR?¹³C-NMR and FT-ICR MS.The purity of BCB_n and BSB_n is above 95%.Secondly,the physicochemical properties of four types of betaine surfactants were systematically investigated by thermogravimetric analysis,surface properties,thermodynamic properties,micropolarity of aggregation,and morphology of micelles.The thermal stability of betaine surfactant was closely related to the types of hydrophobic and hydrophilic groups.The thermal decomposition temperatures of BCB_nand BSB_n were 197 and 245°C,respectively.The critical mecille concentration(cmc)and surface tension(?)of phenyl-containing betaine surfactants decreased significantly with the increase of carbon chain length,and their surface activity was superior to that of dodecyl betaine surfactants(ACB₁₂ and ASB₁₂).The values of p C₂₀ and cmc/C₂₀increased with the increase of carbon chain length,indicating that the long-carbon chain phenyl-containing betaine surfactants have higher efficiency in reducing the surface tension and stronger interfacial adsorption capacity.The negative values of _mand suggest that the micellization and adsorption of BCB_n and BSB_n in the bulk solution are spontaneous processes.The DLS and cryo-TEM results showed that ACB₁₂and ASB₁₂ molecules could only form micelles within the concentration range studied,however,BCB_n and BSB_n molecules spontaneously aggregated into vesicles in aqueous solution over the cmc.With the increase of surfactant concentration,the size of vesicles increased.The aggregation pattern of betaine surfactant in solution was simulated by the coarse-grained molecular dynamics method,and the simulation results were consistent with the experimental results.At the same time,the formation mechanism of vesicles was studied,and it was found that the introduction of benzene ring can increase the exposed area of hydrophobic group in solution,which is conducive to the further curling and fusion of micelles to form vesicles.Finally,the long-term thermal stability,temperature and salt resistance,static adsorption,wettability and oil displacement efficiency of betaine surfactants were systematically tested.The effects of surfactant concentration,temperature and salt concentration on interfacial tension were studied.The results showed that BCB_n(n=10,12 and 14)and BSB_n(n=10 and 12)could reach ultra-low interfacial tension with Xinjiang crude oil without adding alkali.The lowest interfacial tension(IFT_min)decreased first and then increased with the increase of temperature,and the time to reach IFT_min also decreased.The tolerance of Na Cl for BCB_n and BSB_n was more than10%,and the ultra-low interfacial tension could still be achieved when the concentration of Ca Cl₂ and Mg Cl₂ is up to 0.5%and 0.2%.At the same time,the interfacial tension of BCB₁₀ and BSB₁₀ could be maintained at the level of 10^-3 m N/m after aging at 120°C for 30 days.Therefore,series of phenyl-containing betaine surfactants had good temperature and salt resistance.BCB₁₀ and BSB₁₀ had the best wettability to paraffin film,and the lowest contact angle was 25.19°and 31.89°,respectively.The maximum adsorption capacity of phenyl-containing betaine surfactant on quartz sand was between0.6 and 0.75 mg/g.The results of core flooding experiments showed that the enhanced recovery of ACB₁₂ and ASB₁₂ slug are 3.38%and 3.2%respectively,while the recovery of BCB_n and BSB_n slug reach 4.73?6.49%due to its lower interfacial tension and better wettability.