A novel hybrid micro-nano cement system for high-temperature oil-well cementing was developed. This system incorporates silica flour (SF) to achieve thermal stability, along with nano-silica (NS) and nano-titania (NT) to provide multi-scale reinforcement in order to address the significant challenges of strength retrogression, poor cement-formation bonding, excessive fluid loss, and the high carbon footprint of ordinary Portland cement (OPC) production. Cement slurries, ranging from single, binary, and hybrid blends, were prepared in accordance with API specifications and cured for 28 days at 80 °C. Thorough rheological, fluid loss, mechanical, and microstructural evaluations (SEM, XRD, and TGA) were conducted. With near-Newtonian flow behavior (n = 0.89), a 46.7% decrease in API fluid loss (80 mL/30 min), a 33.4% increase in compressive strength (48.03 ± 2.40 MPa), and a remarkable 129.1% improvement in shear bond strength over neat OPC, the ideal hybrid formulation, NE2 (82% OPC + 15% SF + 2% NS + 1% NT), showed superior results. A multi-scale synergistic mechanism is responsible for these improvements. By consuming portlandite to form additional C-S-H and preventing the transition to high-temperature strength-retrogression phases, the SF component offers thermal stability. By serving as nucleation sites, filling nano-pores, and causing pore water to reorganize inside the C-S-H gel, the NS and NT nanoparticles simultaneously contribute through the nano-core effect, resulting in a densified, low-permeability microstructure. The improved mechanical integrity and fluid loss control are simply explained by this optimized pore structure. Additionally, the 15% bwoc replacement by silica flour from clinker offers a sustainable route, lowering CO 2 emissions associated with cement by up to 135 kg per ton of blend. This study shows that balanced, multi-scale engineering that takes into account both thermal stability and microstructural densification can result in high-performance, low-carbon oil-well cement systems. • A novel hybrid micro-nano oil-well cement (82% OPC + 15% SF + 2% NS + 1% NT) is engineered for high-temperature (80°C) applications. • The optimal blend exhibits improved rheology (n=0.89) and a 46.7% reduction in API fluid loss. • Compressive and shear bond strength increase by 33.4% and 129.1%, respectively, versus plain OPC. • A multiscale densification mechanism via portlandite consumption and C–S–H gel enhancement is revealed. • The formulation reduces the cement carbon footprint by ~135 kg CO₂ per ton via clinker substitution.
Mohamedy et al. (Sun,) studied this question.