Density-driven convection in layered and stochastically heterogeneous formations: Implications for CO₂ geological sequestratione

Geological carbon sequestration relies on the efficient conversion of injected supercritical CO₂ into dissolved CO₂, a process accelerated by density-driven convection. Yet, most assessments still consider the subsurface as homogeneous, offering limited guidance for the layered and heterogeneous architectures typical of sedimentary basins. Building on this shortcoming, this work examines how stratigraphic structure -- such as homogeneous, randomly layered, stochastic, positive rhythmic, reverse rhythmic, coarse-first, and fine-first formations -- governs the onset and efficiency of convective dissolution. Using a two-dimensional model, this work tracks the dissolved-to-total CO₂ mass fraction and relate system-scale kinetics to plume morphology. The findings reveal that stratigraphy exerts first-order control on both the timing and mode of CO₂ transformation. Architectures with high-permeability pathways near the top, or those with strong small-scale heterogeneity, trigger early convection, promote vertically continuous fingering, and accelerate dissolution relative to a homogeneous benchmark. Randomly layered formations that divert flow produce moderate slowdowns. In contrast, low-permeability caps suppress vertical exchange, favor lateral spreading, and substantially delay conversion; coarse-first formations exhibit early lateral channeling that retards late-time mixing. Overall, the distribution of permeability in the upper reservoir and the scale of heterogeneity jointly control convective onset and dissolution efficiency, providing actionable guidance for formation screening, well placement, and monitoring horizons in geological carbon sequestration projects.