Numerical investigation of class H cement deterioration under CO2-O2 co-exposure in down-well conditions

Abstract:

The environmental benefits of CO₂ sequestration in geological formations are well established; however, the process has significant operational and maintenance challenges. Primarily, cement well plugs are vulnerable to deterioration in high temperature and high pressure underground storage settings, and the ability to accurately predict their service performance in these unfavorable conditions is necessary for successful implementations. In this work, a coupled reactive transport model is developed using the finite element method to investigate Portland Class H cement deterioration under both CO₂ and CO₂-O₂ co-sequestration in high pressure and temperature downhole conditions. The numerical model involves the solution of Nernst-Planck equations for transport of relevant ionic and gaseous species in hydrated cement in the presence multiple reactive processes (e.g. carbonation and secondary mineral formation) which also affect microstructural properties. The predictions of the developed model are compared with available experimental data and benchmarked with existing models. Parametric investigations are conducted to study the effects of operational pressure and temperatures, cement composition, brine composition, and CO₂ gas exposure.