Adsorption behavior and mechanism of a copolymer used as fluid loss additive in oil well cement

The polymer-based additives, which are widely used in the field of well cementing operation, are copolymers synthesized using monomers by free radical copolymerization. Undoubtedly, the hydration process of oil well cement with variety of additives is complicated and can be affected by multi-factors. The experimental methods combined with computational simulations were performed to explain the interaction between the fluid loss additive (FLA) and oil well cement. From both macroscopic properties and microscopic structures, the adsorption mechanism of fluid loss additive on the surface of cement particles was explained. Adsorption kinetics and isotherms in dilute solutions were performed and proved that the adsorption process is monolayer adsorption on the surface of cement with finite sites, which is the characteristic of chemisorption. The negatively charged carboxylic acid and sulfonic acid groups in FLA promote Ca2+ ions diffusion from the oil well cement to the cement pore solution. Meanwhile, ion exchange occurs between Ca2+ ions and Na+ ions, and the copolymer chelates with the Ca2+ ions from oil well cement to form a chelate structure, making the harden cement paste more compact. Therefore, the fluid loss of oil well cement slurries is controlled due to the strong chelation, while the formation of cement hydration products and the induction period of cement hydration are delayed. (C) 2018 Elsevier Ltd. All rights reserved.