Basalt-CO₂-brine wettability at storage conditions in basaltic formations

CO₂ geo-storage in basaltic formations has recently been demonstrated as a viable solution to rapidly sequester and mineralize CO₂. In case CO₂ is injected into such basalt reservoirs in supercritical form, a two-phase system (reservoir brine and supercritical CO₂) is created, and it is of key importance to specify the associated CO₂-basalt wettability so that fluid distributions and CO₂ flow through the reservoir can be predicted. However, there is a serious lack of data for basalt CO₂-wettability. We therefore measured water contact angles on basalt substrates in CO₂ atmosphere. The results indicate that at shallow depth (below 500 m) basalt is strongly water-wet. With increasing depth the basalt becomes less hydrophilic, and turns intermediate-wet at a depth of 900 m. We conclude that basalt is more CO₂-wet than chemically clean minerals (quartz, calcite), especially at depths below 900 m. However, the basalt had a CO₂-wettability similar to some caprock samples and a gas-reservoir sandstone. The data presented in this paper will thus aid in the prediction and optimization of CO₂ geo-storage in basalt formations.