The global race toward net-zero emissions places underground CO₂ storage at the heart of large-scale decarbonization. However, accurately predicting storage performance in heterogeneous aquifers remains challenging due to the computational burden of numerical simulations and the complex interplay of reservoir-scale processes. This study develops a novel analytical framework for CO₂ injection in layer-cake aquifers, explicitly accounting for three critical yet often overlooked phenomena: (i) permeability reduction from fines migration, (ii) the role of water-bearing (“wet”) CO₂, and (iii) partial miscibility between CO₂ and brine.

The model builds on vertical equilibrium principles to reduce dimensionality, enabling robust and efficient predictions of CO₂ plume migration, injectivity, and sweep efficiency. Fines migration is described through capillary-driven detachment and transport of particles, which dynamically alter permeability. The inclusion of water content in injected CO₂ captures non-ideal fluid behaviour relevant to field-scale operations, while partial miscibility extends displacement theory beyond the classical immiscible framework.

Results demonstrate that fines migration, while impairing injectivity, can enhance sweep efficiency and storage capacity by delaying CO₂ breakthrough. This phenomenon highlights the dual role of fines migration as both a risk and a benefit in subsurface CO₂ storage.  Likewise, water-bearing CO₂ and partial miscibility strongly influence fractional flow and trapping dynamics, underscoring their importance in risk assessment and design of storage projects. Key sensitivities include heterogeneity, viscosity ratio, concentration of detachable fines, and formation damage coefficient.

By coupling fines migration, wet CO₂ effects, and partial miscibility into a rapid analytical tool, this work closes a critical gap in CO₂ storage modelling in geological aquifers. The framework complements full-physics simulators, enabling efficient sensitivity analyses and providing actionable insights for site screening, injection optimization, and the large-scale deployment of CO₂ storage technologies.