CO₂ storage efficiency in saline aquifers: Insight from the numerical modeling of immiscible displacement.

This article focuses on evaluating the storage efficiency and maximum migration distance of carbon dioxide (CO₂) injected into homogeneous open saline aquifers through a vertical well, under the assumption of immiscible displacement of reservoir brine. The study identifies five key dimensionless similarity parameters—gravitational number (Gr), injection-to-gravity time ratio (Γ), capillary number (Π), mobility ratio (M), and near-wellbore anisotropy parameter (Aw)—that govern CO₂ flow behavior and storage efficiency. Two limiting flow regimes are distinguished: plume formation (PF), dominated by buoyancy in reservoirs with good vertical permeability, and anisotropic reservoir (AR), characterized by viscous-dominated flow in reservoirs with poor vertical permeability. Using reservoir simulations, the authors derive scaling laws and efficiency maps that relate these parameters to microscopic displacement efficiency, volumetric sweep efficiency, overall storage efficiency, and maximum CO₂ migration distance, providing practical tools for preliminary screening and ranking of potential CO₂ storage sites. The study concludes that a larger gravitational number Gr, which can be increased primarily by maximizing injection rate within reservoir constraints, generally leads to more efficient CO₂ storage, and that operating fewer wells at higher rates is preferable for maximizing storage efficiency.