A Study Of Surface Properties And Foam Properties Of Model Surfactant Systems For Foam Combination Flooding

Foam combination flooding technique is a new method in the field of enhanced oil recovery, and its pivotal question is the molecular design of surfactant. Elucidating the effects of molecular structure and the interaction between surfactant and additives on foam properties is the base of molecular design. Therefore, a study on the surface properties and foam properties of the model surfactant systems is an important research topic, which is valuable in theory and practice to design surfactants for foam combination flooding systems. In the dissertation, the surface and foam properties of a series of the model surfactants with high purity were studied. The experiments and results are as following:1) The surface tensions of fatty alcohol polyoxyethyleneether carboxylate (C_nE₃C) A series of C_nE₃C with high purity were selected as model compounds. The surface tensions of C_nE₃C aqueous solutions have been investigated by Wilhelmy plate method. The values of critical micelle concentration (cmc), surface tension at cmc (γ_cmc), efficiency in surface tension reduction (pC₂₀), saturation adsorption amount (Γ_max), standard free energy of adsorption (ΔG_mic⁰), and of micellization (ΔG_ad⁰) were obtained by thermodynamic calculation fromγ?lgc curves. It was discovered that, in aqueous solution, theΓ_max increased with the increase of hydrophobic chain length, and the effectiveness of surface tension reduction showed same tendency. Surfactant with branched hydrophobic chain has higher cmc and lowerΓ_max, while the effectiveness of surface tension reduction increased because of higher coverage of hydrophobic group.Dynamic surface tension of C_nE₃C was investigated in aqueous solution. Dynamic surface parameter and effective diffusion coefficient D_eff were obtained by use of Rosen equation and Word-Tordai equation.The dilational viscoelastic properties of C_nE₃C at water-air were investigated by means of oscillating bubble method. The dynamic dilational properties and the dependences of interfacial dilational modulus, phase angle, elasticity and viscosity on the concentrations and the frequencies were explored using method: the surface tension response to sinusoidal area variations. The result showed that the dilational viscoelastic properties of C_nE₃C are similar to the conventional surfactants.2) Foam properties of C_nE₃CThe foam properties of C_nE₃C in the aqueous solution were measured by air flowing method. The effects of the surfactant concentration, temperature, hydrophobic chain length and the degree of the branch of hydrophilic group were investigated. A correlation between the dynamic surface activity and foaming ability has been discussed. It showed that the surfactant structure directly determines the strength of liquid film and surfactants with different structure show different effects on foam properties. The dynamic surface activity determines the foaming ability when the foam formed by air flowing method.3) Foam properties and lamella life of alkyl benzene sulfonatesThe foam properties of alkyl benzene sulfonates with high purity, which were synthesized in our laboratory, were measured by air flowing method. The lamella life of alkyl benzene sulfonates were measured by electrochemical method. The effects of the surfactant concentration, temperature, and molecular structure were investigated. A correlation between the surface dilational elasticity properties and lamella life has been discussed. The result showed that branched chain and long straight ortho-alkly and meta-alkly have different effects on molecular arrangement at air/water interface, while long straight para-alkly shows little effect on it. Therefore hydrophobic chains located in the different positions of the benzene show different effects on foam properties. The dilational elasticity is the key factor which determines the lamella stability, and the lamella life shows the same change law with the dilational elasticity.4) Foam properties of compounded systemThe foam properties of C_nE₃C with different additives, such as sodium chloride, polymers, ethanol, isopropanol, 1-dodecanol, hexadecanol, alkoxyamide and sodium dodecylbenzene sulfonic acid (SDBS), were investigated. It was found that the electrolyte can affect the foam properties of the adsorbed layer by changing the electrostatic interaction among the ionic surfactants; the surfactant may form mix-adsorption layer with polyacrylamide, fatty alcohol, and alkoxyamide, thus influences the foam properties; C_nE₃C and SDBS mixture shows synergistic interaction in the following aspects: the effectiveness of forming micelle, the effectiveness and efficiency of surface tension reduction, which enhanced the lamella strength, thus the foaming ability and foam stability enhanced.