Molecular insights into supercritical CO2 adsorption on calcium silicate hydrate

Abstract

In carbon capture, utilization, and storage (CCUS) systems, cement is injected into the annular space between the well casing and the surrounding rock formation to create a zonal isolation barrier. This barrier prevents vertical migration of CO₂ along the wellbore, thereby ensuring long-term containment within the target reservoir and safeguarding well integrity. In subsurface CCUS environments, supercritical carbon dioxide (scCO₂) permeates calcium silicate hydrate (C-S-H), C-S-H the primary binding phase of cement. Molecular dynamics simulations investigate scCO₂-C-S-H interactions at the molecular scale, by systematically varying calcium-to-silicon (C/S) ratios, hydration degrees, and temperatures. These variations elucidate the effects of interfacial chemistry on CO₂ adsorption and material responses. Lower demonstrates that elevated C/S ratios (≥1.5) increase CO₂ uptake through enhanced Ca–CO₂ coordination, while in aqueous scCO₂ containing 5 mol% water, hydroxyl-rich surfaces are stabilized and pore collapse is inhibited. Lower temperatures strengthen ionic bonding at the interface, enhancing CO₂ sequestration stability. These mechanistic insights reveal cement degradation pathways during scCO₂-induced carbonation and provide foundational knowledge for designing durable wellbore cements, thereby ensuring long-term containment security in CCUS infrastructure.