De-emulsification performance and mechanism of polyether-polyquaternium copolymers and compounding products on tight gas produced water.

As the development of tight gas fields enters the stable production stage, condensate oil forms a complex oil--water emulsifying system under the action of bubble drainage agent, corrosion inhibitor, hydrate inhibitor, and other additives to increase and stabilize production, as well as the formation of particulate matter. A new demulsification and flocculation agent suitable for condensate emulsifying system is developed to make the system unstable and the oil beads coalesce. In this paper, a polyether--quaternary ammonium salt reverse demulsifier (PPA) was synthesized by grafting a cationic group onto a five-membered block polyether X-75. A new type of demulsification--flocculation agent (CQ) was obtained through the complex modification of PPA and inorganic coagulant polyaluminum ferric chloride. Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, and gel chromatograph were used to characterize the group and molecular structure. The reaction parameters were optimized by single-factor experiment and the response surface method, and the demulsification--flocculation mechanism was determined by zeta potential, interfacial tension, and fractal dimension. Results showed the PPA demulsifier has active groups (block polyether) and cationic groups (polyquaternary ammonium salt) at the oil--water interface at the same time and can play a synergistic role between them. Single-factor experiment and response surface optimization showed CQ concentration and temperature were key factors affecting the demulsification-- flocculation effect. When CQ concentration was 547 mg/L, settling temperature was 27.9°C and PPA accounted for 71%. After settling for 30 min, the oil content and the concentration of total suspended solids (TSS) in the water decreased to 21.26 and 7.0 mg/L, respectively, which met the water quality requirements of reinjection (oil content ≤ 30 mg/L, TSS concentration ≤ 15 mg/L). By neutralizing and displacing active substances at the oil--water interface and sweeping by net trapping, CQ can coagulate oil beads and suspended particles to form large flocs and realize the efficient separation of oil beads, suspended particles, and water. [ABSTRACT FROM AUTHOR]