Effect of rice husk ash on the compressive strength and microstructural characteristics of low-density cement slurry under different temperature conditions

This study investigated the potential of highly doped (50 %) rice husk ash (RHA) as a sustainable alternative to conventional oil well cement and hollow glass microsphere (HGM) in formulating a novel, environmentally friendly, low-density cementing slurry (LDCS) for wellbore applications in deepwater oil and gas wells. Two groups of LDCSs were evaluated in this study, G100H20 and G100H20R50, which were doped with 0 % and 50 % RHA. The mechanical properties, mineral composition and microstructural characteristics of LDCS cured at 20 °C, 50 °C and 80 °C for 1, 7, 28, 56 days were characterized by X-ray Diffraction (XRD), thermogravimetric analysis (TGA), X-ray micro-computed tomography (Micro-CT) and scanning electron microscope-energy dispersive spectrometer (SEM-EDS), etc. Besides, a comparative analysis of Material Sustainability Indicators (MSIs) and associated costs was conducted. The results showed that the compressive strength of G100H20R50 is lower than G100H20 when cured at 20 °C and 50 °C. However, the compressive strength of G100H20R50 exceeds G100H20 when cured at 80 °C for 56 d. The introduction of RHA inhibits the transformation of the hydrated C-S-H gel to the porous α-type hydrated dicalcium silicate crystals (α-C₂-S-H) and optimizes the pore size distribution of the cement slurries. The internal curing effect of RHA extends the hydration time and improves the durability of the cement system. MSIs and cost analyses show that G100H20R50, prepared with zero net CO₂ emissions and low-cost RHA, is both environmentally friendly and economical, reducing the environmental impact of RHA.