Coupled effects of hydrophilic nano silica oxide and anatase nano titanium oxide on strengths of oilwell cement

Abstract

The life of oilwells depends on the stability of cement sheath and bond strength with the formation and casing. Extreme subsurface conditions cause substantial stresses on the cement sheath resulting in a serious impact on well integrity. The recommended API cement for oilwell fails to provide the required durability of the cemented well due to such conditions. Supplementary cementitious materials such as nanoparticles are added to improve the cement for long-lasting zonal isolation. In this study, the compressive and shear bond strengths of oilwell cement containing nano-SiO₂ and nano-TiO₂ were studied at 80 °C for 3, 7, 14, and 28 days of hydration. The XRD, TG, and DSC were used for the analysis of cement hydration products. The results revealed that both nano-SiO₂ and nano-TiO₂ increased strength evolution. A ternary system made with 2% nano-SiO₂ and 2% nano-TiO₂ improved compressive strength by 22.6 and 48.4%, while the shear bond strength increased by 110.6 and 55% at age of 3 days and 28 days, respectively, compared to their corresponding binary systems. Therefore, these results remark the potential of replacing an appropriate proportion of oilwell cement with coupled nano-SiO₂ and nano-TiO₂ to ensure cement sheath structure durability in the annular and long-lasting zonal isolation.

Keywords: Nano-silica, nano-titanium, compressive strength, shear bond strength, oilwell cement