Set-Regulation Performance of High-Temperature Hydration in Silicate/Aluminate Cements by Phosphorus-Doped Carbon Dot Polymers

To address the challenges of uncontrolled high-temperature hydration and strength retrogression of cement slurries in the development of ultradeep oil/gas and geothermal resources, this study proposes a phosphorus-doped carbon dot polymer. Phosphorus-doped carbon dots (CDP) were synthesized using citric acid, urea, and phosphoric acid as precursors. Subsequently, a retarder (CDP@P) featuring a multilevel interfacial architecture of "network-like encapsulation plus carbon dot anchoring" was constructed via silane coupling agent grafting and copolymerization with multicarboxyl monomers. Results demonstrate that the phosphorus components in CDP@P exert a synergistic effect of chelation and steric hindrance, preventing the formation of a dense passivation film while enhancing the thermal stability of the polymer. In terms of engineering performance, CDP@P extends the thickening time of Portland cement to 549 min at 240 °C without compromising the early-age strength of the set cement. For aluminate cement, the retarder mitigates the uneven mechanical development induced by nonuniform hydration under high-temperature conditions, thereby improving overall mechanical strength. By coupling "suction-cup-like" multipoint anchoring with a physical barrier, CDP@P achieves precise regulation of cement hydration kinetics, avoids the irreversible blocking issues associated with conventional phosphorus-rich compounds, and provides a new design strategy for high-performance additives in unconventional well cementing.