Experimental Investigation on the Effect of Rice Husk Ash on the Hydration and Microstructure of Lightweight Cement Slurry

Summary The global energy transition toward decarbonization and expanding deepwater hydrocarbon development are driving increased demand for sustainable, ecofriendly well cementing materials. Rice husk ash (RHA) has garnered attention in well cementing for its low-carbon footprint and high silica content. For this study, we incorporated RHA into conventional lightweight cement slurry (LCS) to develop a novel low-carbon system engineered for deepwater environments and low fracture-pressure formations. First, thermogravimetric-derivative thermogravimetric (TG-DTG), Fourier transform infrared (FTIR), scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDS), thermal conductivity, and hydration heat analyses revealed microstructural evolution and hydration mechanisms. In addition, cement slurry was evaluated for its economic and environmental friendliness. The results show that the optimal RHA dosage is 20% in LCS, enhancing microstructure and mechanics below this threshold but reducing strength above it due to dilution. The synergistic effects of pozzolanic reaction, dilution, and filling maintained stable thermal conductivity (around 0.6 W/(m·K)) and density (around 1.38 g/cm3) across all RHA concentrations. Furthermore, incorporating RHA progressively reduces the cement’s hydration heat, energy intensity, carbon dioxide (CO2) emissions, and costs. At 20% RHA replacement, these reductions reach 27.9%, 11.1%, 13.89%, and 12%, respectively. Although 50% RHA incorporation achieves greater reductions in hydration exotherm, environmental impact, and production costs, this high-dosage formulation exhibits compromised rheological performance and diminished mechanical properties. As a biomass-derived ash, RHA’s inherent alkalinity activates and enhances cement hydration and pozzolanic reactions. Its porous structure further provides nucleation sites for hydration products. Consequently, appropriate RHA incorporation (≤20%) improves cement slurry performance, offering a cost-effective and environmentally sound solution for deepwater oil and gas development.