Experimental investigation on wettability alteration of Glauconitic sandstone during CO2 Storage.

This study explores wettability alteration resulting from supercritical CO₂ (scCO₂) injection intoGlauconitic sandstone in the depleted Nini West oil reservoir (Danish North Sea), evaluating its potentialfor CO₂ storage. Injected scCO₂ dissolves in brine and diffuses into residual oil, displacing adsorbedhydrocarbons and shifting the rock surface toward a more water-wet state. This enhances residual oildisplacement and increases CO₂ storage efficiency. Wettability was assessed using spontaneous imbibitionexperiments on core samples from the oil and water legs. Among them, two samples from the oil leg wereflooded under reservoir conditions using brine, followed by scCO₂. Results show that scCO₂ exposuresignificantly increased water-wetness, with water saturation reaching 55% in scCO₂-flooded oil-leg cores.In contrast, cores cleaned using Soxhlet extraction or flow-through solvent methods remained less waterwet, with average water saturations below 30%. These findings indicate that scCO₂ acts as an effective agentfor altering wettability in previously oil-wet, watered-out porous media systems, altering CO₂ trappingpotential. This work supports the use of depleted oil reservoirs for geological CO₂ storage, emphasisingscCO₂’s role in improving storage performance through wettability modification.