Effects Of Alkalis On Interfacial Tensions Of Crude Oil And Novel Betaine Solutions

During the 21st century,enhanced oil recovery?EOR?and developed new production methods have attracted fignificant notices.The chemical flooding-based tertiary oil recovery method is the most effective method.After 1956,people found that alkali added to crude oil/surfactants systems may produce ultra-low IFT and reduce oil production costs,then alkali flooding has been extensive used in oil fields for EOR.In this article,based on the performance characteristics of zwitterionic surfactants,we have systematically researched the correlative interfacial behaviors between inorganic alkali and betaine surfactants systems in the course of EOR from a new point of view.Moreover,the mechanisms responsible for IFT reduction of organic and inorganic aliali systems have been compared.The specific research and the results obtained are as followings.First,six kinds of betaines with different structures?18C?18S?22C?22S?26C and 26S?have been employed in this study.Alkali and acid has little influence on n_minin values for more oil-soluble betaines 18C?18S?22C and 22S.However,for relatively aqueous-soluble 26C and 26S,the n_minin value decreases obviously.Second,the alkali type plays a crucial role in controlling IFTs by changing the pH of solution,the stronger the alkali is,the obvious the synergism and antagonism are.For betaines with the linear alkyl chain,18C?18S?22C and 22S,the dynamic IFT curves show“V”shape.For betaines with the branched chain part,the petroleum acids and soaps adsorb competitively with betaine molecules,resulting in the increase of equilibrium IFT values.Third,the mixed adsorption between crude oil components and betaine molecules is very complicated.After adding alkali,the synergism in lowering IFT can be observed in 18C,18S,22C and 22S-crude oil systems.However,by adding alkali,the produced soaps will adsorb competitively with 26C and 26S molecules and the mixed film becomes loose,which will result in the increase of IFT.The order of the ability of alkali affecting IFT is acidic fractions>resin>asphaltene>aromatic>saturate in general.For the same crude oil fractions,the ability of alkali affecting IFT is NaOH>Na₂CO₃>NaHCO₃.Forth,According to the experimental results,organic alkali has the stronger abilities to affect the HLB of betaines.However,inorganic alkali shows the stronger ability to reduce IFT than organic alkali.The ability of organic alkali affecting HLB is DEA>EA>NaOH.Betaine surfactant can be applied to the harsh oil environment,and reduce cost.Which make it have widely used in the field of crude oil exploitation.In this article,the interfacial properties of alkali-betaine flooding system have been systematically studied,which can provide theoretical guidance for improving the efficiency of tertiary oil recovery.