Performance comparison and adsorption mechanism analysis of polyanionic and zwitterionic copolymer fluid loss additives for oil-well cement paste: An experimental and computational study

Zwitterionic copolymers, which are synthesized by introducing cationic groups into traditional polyanionic copolymer, are widely used in cementing engineering for complex geological environments for their superior adsorption capacity and antipolyelectrolyte behavior. However, conformational transitions with the temperature and salt of copolymer admixtures remain unclear, thus making it difficult to clarify the adsorption mechanism. In this study, performance comparison and adsorption mechanism analysis of zwitterionic and polyanionic copolymer fluid loss additives (CFLAs) for oil-well cement (OWC) paste were conducted. Results demonstrated that zwitterionic CFLA reduced fluid loss volume and improved compressive strength, despite retarding cement hydration, compared with polyanionic CFLA. Adsorption measurements and molecular simulation revealed that zwitterionic CFLA enhanced its adsorption ability by improving the extension of segment and enhancing electrostatic interaction. The water solubility and adsorption ability of the CFLA decreased due to the shielding effect of multiple counterions gathered near the functional groups and weakening of hydrogen bond.