Enhancement of mechanical properties of oil well cement by nano-SiO2/h-BN

In this study, high-strength oil-well cement with hybrid nanosilica (NS) and nanohexagonal boron nitride (h-BN) additives was prepared to reduce effectively the environmental pollution caused by fluid leakage from oil wells owing to weakened cementing rings and extend the lifetimes of oil wells. It was confirmed that NS/h-BN can enhanced the mechanical strength of oilwell cement at 7 and 28 days. The effects of NS and h-BN on the mechanical properties of oil-well cement at 7 days (d) and 28 d were investigated by varying the nanomaterial content to determine the weight percentages of the nanomaterials that optimized the mechanical properties. The experimental results showed that the ideal ratio content of nanomaterials was 2.5 wt% NS and 0.5 wt% h-BN, and the minimum porosity measured by a low-field nuclear magnetic resonance test was 16.48%, which was 50.24% lower than that of the blank group. After 28 d of curing, the compressive, flexural, and splitting tensile strengths were 12.15 MPa/25.99%, 3.75 MPa/ 42.86%, and 1.39 MPa/41.25% higher than those of the blank group. The mechanical strength of the oil-well cement increased with the NS content, whereas with the increase in h-BN content, sequential rising and falling tendencies were observed. The microstructure, pore structure, and hybridization modification mechanism of the NS/h-BN oil-well cement were analyzed using X-ray diffraction, thermogravimetric analysis, and scanning electron microscopy. This high-mechanical strength and low-porosity hybrid nanomaterial oil-well cement system can provide an experimental basis for the application of novel high-strength cement types in oil fields.