Microstructure of a type G oil well cement-nanosilica blend

Motivated by the need to improve oil well integrity for potential carbon capture and storage through CO₂ sequestration, nanosilica was hypothesized capable of improving the quality of oil well cement (OWC) in medium and deep oil wells. In this study, OWC was mixed with 1 and 3% nanosilica by weight to produce OWC pastes with water to binder ratio (w/b) of 0.45. The specimens were cured under high temperature and pressure, simulating what occurs in oil wells. A method of analysis combining ²⁹Si nuclear magnetic resonance (NMR) and nanoindentation is proposed. The results are compared with observations extracted from nanoindentation in which classification of hydration products is based on the elastic modulus of the different categories of calcium silicate hydrate (C-S-H). The results show that the degree of hydration, the degree of reactivity, and silicate polymerization increase under the elevated curing condition compared with the ambient condition. It seems that C-S-H generated by the pozzolanic reaction of nanosilica in OWC paste has not only different composition but also different packing density sensitive to curing conditions.