Effect of different temperatures on the strength and hydration products of phosphoaluminate cement

Phosphoaluminate cement (PAC) exhibits superior potential for oil/gas well cementing in environments that are rich in carbon dioxide due to its high-temperature resistance, strength, and corrosion durability. The effects of wellbore temperature (particularly high temperatures) on the strength of PAC and its hydration products were investigated in this study. The evolution of PAC’s properties under curing at 90–150°C curing was studied using compressive strength tests, permeability analysis, X-ray diffraction, scanning electron microscopy, thermogravimetric analysis and Fourier transform infrared spectroscopy. It was found that the compressive strength of the PAC cured at 150°C was significantly increased (>100%) as compared with curing at 90°C. The permeability of the PAC remained extremely low (<7.23 × 10−3 mD (∼7.14 × 10−14 cm2)). Key hydration products include hydrated phosphoaluminate, hydroxyapatite, hydrated aluminate and aluminium hydroxide. Elevated temperatures (>110°C) promoted the conversion of C2AH8 in hydrated aluminate to denser C3AH6, contributing to a permeability increase. Aluminium hydroxide morphology transitioned from nordstrandite at 90°C to aluminium hydroxide gel and boehmite (γ-AlOOH) at 150°C. Hydroxyapatite and C3AH6 demonstrate exceptional thermal stability, serving as critical drivers for PAC’s high-temperature strength enhancement. The microstructure of hydrated PAC remained stable across the tested temperature range. These findings clarify the high-temperature performance mechanisms of PAC, supporting its application in challenging well cementing environments.