Understanding how geological heterogeneity influences CO₂ plume behaviour is critical for designing secure and efficient storage projects in saline aquifers. Features such as intraformational baffles, heterolithic intervals, and subtle facies transitions can significantly impact plume migration by slowing vertical rise, enhancing lateral spread, or promoting trapping mechanisms. Yet in low dip, low relief structural settings, a key challenge remains: to what extent can these small scale heterogeneities offset buoyancy driven migration?

This study presents a pre-injection geological modelling workflow for a small saline aquifer CO₂ storage site (<6 km²) targeting a thin reservoir (~50 m). With seismic data resolution insufficient to resolve internal architecture, we relied on high resolution core descriptions, image logs, and stratigraphic interpretation to characterize key depositional elements. Particular attention was given to low permeability features such as heterolithic baffles and sharp facies transitions that may affect vertical CO₂ movement.

These heterogeneities were incorporated into a 3D static model using stochastic methods to represent the variability in facies connectivity and lateral discontinuities. Dynamic simulations assessed the associated CO₂ plume behaviours, ranging from slow, fingering migration controlled by intraformational baffles to rapid channelised flow through connected high permeability streaks. 

Results highlight that in low-relief structural settings; even subtle heterogeneity can significantly influence plume architecture and migration pathways. This was validated through the correlation with high resolution saturation logs. Incorporating realistic geological complexity enhanced our ability to anticipate plume behaviour, guiding injection strategy, monitoring design, and contingency planning for uncertain migration outcomes. This work reinforces the value of integrating detailed sedimentological analysis with geological modelling to better constrain reservoir performance, reduce geological uncertainty, and support safer and more reliable CO₂ storage outcomes.