Combination of lignosulfonate and AMPS®-co-NNDMA water retention agent—An example for dual synergistic interaction between admixtures in cement

In this study, compatibility between Na+ lignosulfonate retarder and CaAMPS®-co-NNDMA water-retention agent, two admixtures commonly used in oil well cement, was investigated. A dual synergistic effect was found which demonstrates good compatibility of both admixtures. Na+ lignosulfonate improves the fluid loss performance of CaAMPS®-co-NNDMA while the latter greatly enhances the retarding effect of lignosulfonate. The mechanism behind is that in cement pore solution, Na+ lignosulfonate forms complexes with calcium ions and then associates into negatively charged, large agglomerates (Rh ~ 2.4 μm). These agglomerates precipitate onto the surface of cement and result in a polymer layer of low permeability. Through this mechanism, Na+ lignosulfonate retards cement hydration by hindering the migration of water to the surface of non-hydrated cement. Similarly, retarding effectiveness of Na+ lignosulfonate is enhanced by CaAMPS®-co-NNDMA, as is evidenced by prolonged cement thickening times. The effect is caused by concomitant adsorption of CaAMPS®-co-NNDMA and lignosulfonate Ca complexes.