Synthesis And Performance On Surfactant-Acrylamide Copolymer For Oil Displacement

Nowadays it has been the period of tertiary oil recovery in many oil-field of China. The application of ASP flooding could greatly improve oil recovery, however, the addition of alkali agent also caused the increment of technical difficulties and processing cost in oil recovery. Research on enhancing oil recovery is developing towards weak-alkali or non-alkali surfactant-polymer combination flooding in recent years. But phase separation and chromatography separation would occur for these binary systems, which decreases oil displacement efficiency. Thus, it is necessary to explore oil-displacing agent with high viscosity and high interface activity for enhancing oil recovery.In this paper, four kinds of maleic acid diester surfactant monomers with different chain lengths were synthesized via esterification and sulfonation reactions by using maleic anhydride, aliphatic alcohols, and allyl chloride as raw materials. The synthetic conditions were optimized and FTIR was applied for the structures characterization of products. A series of different chain lengths copolymers of maleic acid diester sulfonate with acrylamide were obtained in aqueous solution under the reaction of redox initiator system. The optimal conditions of the copolymerization were as follows: the dosage of maleic acid diester sodium sulfonate was 1%; the content of initiator was 0.4%; reaction temperature was 55℃; the total amount of monomers was 25%; the hydrolyzing degree of acrylamide was 25%. And the structures of products were confirmed by FTIR.Surface properties of these four maleic acid diester surfactant monomers with different alkyl chain lengths were studied, and the results showed that they all had low critical micelle concentration and low surface tension. The critical micelle concentration decreased gradually as the increase of chain length, while the minimum surface tension firstly increased and then decreased. C18H31O4 Na had the lowest surface tension of 24.21 mN/m. Thermodynamic parameters calculation showed that the Amin value of surfactants and pC20 value increased firstly and then decreased with the increase of carbon number, but chain length has little influence on ΠCMC.Viscosity tests of copolymer aqueous solution showed that the apparent viscosity of aqueous solution increased with the increasing copolymer concentration; the solution exhibited a certain shear thickening properties at low shear rates, and the viscosity of solution dropped rapidly with the increase of shear rate; the change of apparent viscosity was little with the increase of temperature, which showed good thermal endurance. As the salinity concentration increasing, the apparent viscosity of copolymer solution showed a trend of decline, and the resistance of the copolymer to univalent sodium ion(Na+) was better than that of divalent calcium ion(Ca2+).Viscoelasticity tests of the copolymer aqueous solution indicated that the copolymer mainly possessed viscosity at low concentrations; with the increase of copolymer concentration, the copolymer gradually showed some elastic modulus; and with the increase of frequency, the viscoelasticity of copolymer gradually transformed from viscosity mode into elastic mode.The copolymer concentration, slug size and slug composition were optimized as follow: the recovery efficiency increased most when adopting the technique of "pre-slug(2500 mg/L 0.05 PV) + main slug(1200 mg/L, 0.38 PV) + water flooding(to 98%)" under experimental conditions, which could increase the recovery efficiency by 21.0%.