Upscaling and Analytical Modeling of Injectivity Impairment During CO2 Injection in Aquifers

Summary This study aims to develop an analytical model for axisymmetric gas-water flows in heterogeneous geological formations applicable to CO2 storage in deep saline aquifers and depleted gas and oil fields. The novel method integrates numerical upscaling with an analytical reservoir model for predicting injectivity impairment during CO2 injection. Pseudo-phase permeabilities are obtained from two dimensional numerical simulations, based on an averaging across layers and explicitly capturing velocity-dependent permeability reduction caused by fines-migration-induced formation damage. Using these upscaled properties, an exact analytical solution for radial gas-water flow is derived, providing explicit expressions for pressure drop, saturation distribution, sweep efficiency, and impedance. It is discovered that injectivity is highly sensitive to the vertical permeability profile and the extent of fines-induced damage. When permeability decreases with depth, gravitational segregation amplifies rate-dependent injectivity loss. In contrast, formations with permeability increasing with depth sustain a two-phase mixture zone that propagates outward, producing a different injectivity response. The analysis shows that incorporating velocity-dependent pseudo-permeabilities altered by formation damage is essential for accurate injectivity prediction. The developed framework offers a fast, physics-based tool for quantifying injectivity losses in heterogeneous aquifers.