The effect of geological structure and heterogeneity on CO2 storage in simple 4-way dip structures: a modelling study from the UK Southern North Sea

The Bunter Sandstone Formation in the Southern North Sea is folded into a number of simple 4-way dip-closed structures (domes). Most of these structures are saline water-bearing, although some of them do contain significant gas accumulations, suggesting that the brine-saturated domes may have potential for the long-term storage of CO2. This study investigates the effect of geological structure and heterogeneity on CO2 storage through the use of geological models and reservoir simulation. Dynamic modeling focussed on the determination of the storage efficiency of a particular dome and from this, its CO2 storage capacity. Under initial modeling conditions, a storage efficiency of around 19% was derived, though this is shown to be highly sensitive to a range of uncertain parameters. An interesting interplay exists between the reservoir heterogeneity and dome structure, whereby the evolving CO2 plume is prevented from rising buoyantly to the top of the formation by the presence of impermeable horizons, which facilitates rapid migration towards the structural spill-points. Sensitivity analysis further emphasizes the importance of characterizing reservoir heterogeneity in studies for long-term carbon capture and storage.