Carbonation of calcium-magnesium pyroxenes: Physical-chemical controls and effects of reaction-driven fracturing

July 05, 2021

Konstantinos Giannoukos (1,2), Sean P. Rigby (2), Christopher A. Rochelle (3), Antoni E. Milodowski (3), Matthew R. Hall (1,2)
Applied Geochemistry, 131, August 2021. DOI: 10.1016/j.apgeochem.2021.105007


Geological storage; Cement carbonation; Rate of carbonation; Carbonation front; Reactive transport; Calcium silicate hydrates; Portlandite


Cementitious grouts are a vital component for the economically-viable implementation of the geological storage of CO2 in providing an engineered long-term seal. In this study a class G cement was carbonated at 80 bar, at either 60 °C or 120 °C, whilst immersed in a synthetic brine for durations of up to 5 months. X-ray computed tomography was used to evaluate the advancement of carbonation depth, whilst SEM/EDXA and XRD were used to characterise microstructural alteration of the cement phases. The microstructure of the ‘main carbonation front’ was found to be representative of the governing reactive transport mechanism. An ill-defined ‘main carbonation front’ during carbonation at 80 bar/60 °C showed a carbonation mechanism controlled by the rate or precipitation/dissolution reactions; diffusion in that case was not the controlling factor. The faster local supersaturation conditions in the pores at 60 °C (with respect to Ca2+ and HC) created a dynamic system of aragonite precipitation from the carbonated to the inner regions of the cement. At 80 bar/120 °C a clearly defined ‘main carbonation front’ with higher compositional density than at 60 °C, was correlated with the fast reactions and diffusion limited evolution of the ‘main carbonation front’. Calcite, as the main result of those fast reactions at 120 °C, filled ubiquitously previously unmineralized voids, creating a system less prone to compositional alterations by chemical changes due to the CO2 plume. This study showed, that the formation of calcium carbonate polymorphs depends on the kinetics of carbonation reactions for a class G cement that is determined by temperature and time. The findings of the current paper can be further used for the understanding of reaction processes within the cements of the CO2 injection wells and assess their long-term chemical stability.

How Our Software Was Used

Dragonfly was used to perform the post-processing and visualisation of CT data.

Author Affiliation

(1) Nottingham Centre for Geomechanics, Faculty of Engineering, University of Nottingham, University Park, Nottingham, NG7 2RD, UK.
(2) Geo-Energy Research Centre1, Department of Chemical and Environmental Engineering, University of Nottingham, University Park, Nottingham, NG7 2RD, UK.
(3) British Geological Survey, Environmental Science Centre, Nicker Hill, Keyworth, Nottingham, NG12 5GG, UK.