Research On The Properties Of Mixed Anionic And Cationic Surfactants Aqueous Solution And The Applications In EOR

Self-assembly of cationic/anionic surfactant mixtures in aqueous solution dependson several factors, such as Van der Waals force, hydrophobicity of the alkyl tails,electrostatic force and hydrogen bond, etc. The properties of these mixtures are alsounusual and complicated. There are many obstacles needing further cognition,although deep studied were performed increasingly, since aqueous two phase system(ATPS) was studied in the mixture. Therefor, cetyl trimethyl ammonium bromideand(CTAB) and sodium dodecyl sulfate (SDS), which is representative as ionic surfactant,were chose in this paper. The phase behaviors, rheological property, microstructure andits applications in enhancive oil recovery (EOR) were studied.Firstly, the phase behaviors of mixed SDS/CTAB/H₂O were strongly affected bymole ratio (γ) of SDS and CTAB. Deposit is formed when theγis nearly 1:1. However,ATPS were found inγ=1:3 or 3:1. These two ATPS regions in ternary phase diagramare symmetry and very narrow. Salt can enlarge the ATPS regions, especially somesmall molecular weight organic salts, which have big ionic radius and deformability ofelectron cloud. The positions of ATPS were also changed with salt.Secondly, the self-assembly of the surfactant mixtures were studied with freezefracture transmission electron microscope (FF-TEM). The mixtures have variousmicrostructures, such as lamellar, hexagonal and cube structure. In upper phase ofATPS, lamellar structure was formed; in the lower phase, however, spherical and shortstick micelles were found. Salt can induce the structural transformation.Thirdly, the mixtures have high viscosity in same certain composition, which wasincreased by additive electrolyte. In same special additive, like sodium salicylate(NaSal), the mixtures have large viscosity, which was benefit for EOR, when lowsurfactant concentration considering recovery cost. The interaction between NaSal and SDS/CTAB nonrandom structure was complex and special. They were adsorbed intothe micelle and participate in forming the long range ordered structure.Fourthly, synthesis and properties of comb-like hydrophobic modified associationpolymer (HM-polymer) were studied system in this paper. It is similar that thisHM-polymer solution has both high viscosity and surface activity, when comparedwith SDS/CTAB mixture, although it is macromolecule. To same extent, these twoincompatible properties were united in these systems. It gives us guidance and morescope to choose surfactant in EOR and helps us to understand surfactant mixture better.Finally, the rheology property of HM-polymer and mixed SDS/CTAB system arestudied in different simulation stratum condition. Physical simulation experiments ofEOR were performed. Mixed SDS/CTAB system shows its own advantages.SDS/CTAB mixture has both lower surface and interfacial intensive and high viscosity,which make this system an excellent flooding agent in EOR.