A Study Of The Relationship Between Surfactant Structures And Interfacial Dilational Properties In EOR

With the developments of the theoretical model and the experimental technology, the research of the interfacial dilational rheology has become one of the research hotspots of the interfacial film properties in recent years. The study of the dilational rheology can make contribution to the more profound understanding of the microscopic structure of the interface, which is significant for elucidating the stability and demulsification mechanism of the emulsion, and may be deeply reflecting the internal law of the interfacial phenomenon as related to EOR. Moreover, the measurements of dilational properties are helpful to elucidate the mechanism responsible for lowering IFT due to the adsorption behavior of the surfactant and the interaction among surfactant molecules.In this paper, the dilatational viscoelastic properties have been investigated by means of Langmuir trough method or oscillating bubble/drop method. Two different techniques, sinusoidal oscillations and interfacial tension relaxations, have been used to study the dilational properties of the surfactant solutions and the EOR systems. The experimental results are as following:Firstly, the dilational viscoelastic properties of twenty-five types of alkyl benzene sulfonates with high purity, which were synthesized in our laboratory, were investigated by oscillating bubble/drop method and surface/interfacial tension relaxation method at air-water and decane-water interfaces. The effects of the frequency, bulk concentration, hydrophobic chain length, the degree of the branch of hydrophilic group and the position of hydrophobic chains located in the benzene ring were investigated. Interfacial tension relaxation method was employed to obtain the characteristic parameters of the micro-relaxation process. A correlation between the surfactant structure and dilational parameters has been discussed. It showed that the surfactant structure directly determines interfacial behavior. It is worth noticing that hydrophobic chains located in the different positions of the benzene show different effects on dilational properties, and leads to different behavior when the upper phase is decane. The surfactants with bi-substituted long straight meta-alkly and para-alkly show higher surface dilational parameter values, while the surfactants with long branched chain oriented para and meta of the benzene have the maximum interfacial dilational parameters.Secondly, the two representative surfactants in EOR ( multi-n-alkylbenzene sulfonates and Gemini surfactant), two typical flooding polymers (ultrahigh molecular weight polyacrylamide and hydrophobic modified polyacryamides), two kinds of organic active components ( long-chain acid and long-chain alcohol ) were selected as model compounds of EOR systems. The effects of different surfactant structure, polymer, electrolyte, long-chain acid, long-chain alcohol and diluted crude oil on the dilational properties were expounded by Langmuir through method. It was found that the surfactant may form mix-adsorption layer with polyacrylamide or form mixed complexes with hydrophobic block of hydrophobic modified polyacryamide at the interface, thus influences the interfacial dilational properties. The electrolyte can affect the viscoelastic properties of the adsorbed layer by changing the electrostatic interaction among the ionic surfactants. A small quantity of organic surface-active component may enhance the dilational modulus by forming densely packed mixed-adsorption layer with surfactant through hydrophobic interaction, while the superfluous addition of surface-active components could sharply decrease the dilational modulus mainly due to the weakening of the strong interfaction among long alkyl chains in surfactant molecules. The diluted crude oil has higher dilational parameter values due to the strong interactions existing in the active component, such as asphaltene. The surfactants increase the dilational modulus and dilational elasticity of the crude oil via forming a mixed-adsorption layer. However, the polymers weaken the strong interactions of the crude oil molecules and decrease the interfacial dilational modulus.Our results show that the measurement of interfacial dilational properties is a powerful method to probe the structure of adsorption film.