Study on low thermal conductivity cement reinforced by sepiolite fiber for deep geothermal well

To address the significant heat loss in the thermal insulation layer of geothermal wells and the failure of the cement sheath, expanded perlite (EP), hollow glass microspheres (HGM), and SiO₂ aerogel (SA) were integrated into oil well cement slurry to achieve optimal low thermal conductivity. Hydrothermal-acid-treated sepiolite fibers (T-SEP) were utilized to enhance the mechanical properties of oil well cement paste with low thermal conductivity, and the strengthening process was examined. The findings indicate that the inclusion of EP, HGM, and SA diminishes the thermal conductivity and compressive strength of cement paste. The integration of T-SEP markedly improved the compressive strength of cement paste with low thermal conductivity at elevated temperatures, with a 73.88 % enhancement seen in the cement paste cured at 180 °C for 7 days compared to pure cement paste. The inclusion of T-SEP decreased the reduction rate of compressive strength in cement paste subjected to thermal cycling. In contrast to the 24.14 % reduction in compressive strength of pure cement paste after the fifth thermal cycle, the compressive strength loss of cement paste with T-SEP is merely 12.5 %. The microstructure test indicates that the addition of T-SEP at elevated temperatures enhances the development of cement hydration products, including C-S-H, C₅S₆H₅, and C₆S₂H₃, hence improving the mechanical properties of cement paste with low thermal conductivity. An effective interface is established between T-SEP and cement paste, enhancing the compressive strength and thermal shock resistance of cement paste with low thermal conductivity.