Zwitterionic copolymer for controlling fluid loss in Oilwell cementing: Preparation, characterization, and working mechanism

The present investigation deals with the problems of unsatisfactory high-temperature resistance, inferior salt tolerance and poor comprehensive performance for the domestic fluid loss additives. In this study, a zwitterionic polymer, 2-acrylamido-2-methylpropanesulfonic acid/diallyldimethylammonium chloride/N,N-dimethylacryl amide/acrylic acid used as fluid loss agent for oil well cementing, was synthesized by free radical polymerization in aqueous solution with ammonium persulfate and N,N,N,N-tetramethylethylenediamine as initiator. The optimal synthesis conditions were obtained via single-factor variable analysis. The compositions, micro-structural morphologies, and thermal-stability of polymer were characterized by FT-IR, H-1 NMR, SEM, DTG, and DSC techniques. The results manifested that the synthetic polymer cement slurry exhibited prominent advantages such as excellent fluid loss control capacity, thermal stability (up to 200 degrees C), salt-tolerance (saturated brine) and rheological behavior. Even more strikingly, the zwitterionic polymer showed less impact on hardening cement and accelerated the post compressive strength of set cement, verified through the ultrasonic method. Additionally, the mechanism of fluid loss control was found to rely mainly on improving the filter cake quality and the polymer chemisorptions on the surface of hydrated cement through SEM, permeability and TOC analysis. In consequence, the zwitterionic polymer enhanced the comprehensive properties of cement slurry and had great potential to apply in high temperature and high salinity oil-well cementing. POLYM. ENG. SCI., 57:78-88, 2017. (c) 2016 Society of Plastics Engineers