Dynamic Evolution of Cement Composition and Transport Properties under Conditions Relevant to Geological Carbon Sequestration

Abstract

Assessing the possibility of CO2 leakage is one of the major challenges for geological carbon sequestration. Injected CO2 can react with wellbore cement, which can potentially change cement composition and transport properties. In this work, we develop a reactive transport model based on experimental observations to understand and predict the property evolution of cement in direct contact with CO2-saturated brine under diffusion-controlled conditions. The model reproduced the observed zones of portlandite depletion and calcite formation. Cement alteration is initially fast and slows down at later times. This work also quantified the role of initial cement properties, in particular the ratio of the initial portlandite content to porosity (defined here as φ), in determining the evolution of cement properties. Portlandite-rich cement with large φ values results in a localized “sharp” reactive diffusive front characterized by calcite precipitation, leading to significant porosity reduction, which eventually c...