Study on the mechanism of nano-metakaolin in enhancing the mechanical properties of cement slurry under large temperature difference

Abstract In order to address the contradiction between safe pumping of cement slurry at high temperatures (100 ∼ 140 °C) and insufficient early strength at low temperatures (20 ∼ 40 °C) in large temperature difference cementing, this study prepared nano-me takaolin material (NMK-1). The structure and morphology of NMK-1 were characterized via XRD and SEM. The fluidity, water loss, and compressive strength of the cement slurry under different temperature cycling conditions were tested, while the hydration products and microstructure were analyzed to investigate the mechanism by which NMK-1 enhances the mechanical properties of the cement slurry. The results show that NMK-1 exhibits good compatibility with admixtures. Under the conditions of pre-set temperatures of 100 ∼ 140 °C and return temperatures of 20 ∼ 40 °C, the 3-day com pressive strength of cement stone mixed with 6% NMK-1 increased by 12.8% ∼ 18.7% compared with the non-added group, and the strength increases with increasing return temperature difference. XRD and SEM analyses indicate that NMK-1 reduces porosity and enhances microstructure compactness by means of physical pore filling and pozzolanic reaction that consumes Ca(OH)₂ to generate C-(A)-S-H gel. In conclusion, through a novel physicochemical synergy mechanism combining physical pore filling and pozzolanic reaction, NMK-1 effectively resolves the technical contradiction of excessive retardation at high temperatures and insufficient early strength at low temperatures for large temperature difference cement slurry, providing key technical support for improving the cementing quality of long cementing sections in deep and ultra-deep wells.