From Sediments to Storage: Geological Controls on CO2 Flow and Trapping in Shallow-Marine Reservoirs

Abstract

Stratigraphic and diagenetic heterogeneities exert a strong control on CO₂ plume dynamics and long-term storage performance in shallow-marine reservoirs. Using multiphase flow simulations conditioned to a geologically realistic reservoir model, this study demonstrates that repeated cemented barriers and stratigraphic baffles significantly slow vertical plume ascent and promote lateral plume spreading. This behavior increases overall CO₂ storage through a combined action of stratigraphic trapping, capillary pinning, residual trapping, and dissolution. Plume dispersion and local spreading were found to strongly enhance dissolution trapping. By subdividing a single buoyant plume into smaller, vertically confined accumulations, stratigraphic barriers increase CO₂–brine interfacial area and prolong residence times, resulting in substantially greater solubility trapping than would occur in homogeneous reservoir models. Structural configuration further modulates this behavior, with reduced buoyant drive leading to higher dissolved fractions. The strong sensitivity of plume migration and trapping behavior to geological heterogeneity highlights the importance of fitness-for-purpose modeling in CCS site assessment. While simplified models may be appropriate for early-stage screening, they may fail to capture critical plume dispersion and trapping processes if applied beyond their intended scope. These findings emphasize the need for detailed geological characterization and advanced modeling approaches tailored specifically to CCS applications.