CO ₂ –Water–Oil–Salt–Rock Interactions on Reservoir Properties, Enhanced Oil Recovery, and CO ₂ Storage: A Mini Review

The injection of carbon dioxide (CO 2 ) into reservoirs triggers complex physical and chemical interactions among CO 2, water, oil, salt, and rock, affecting the seepage properties of reservoirs and the effect of CO 2 -enhanced fluid (oil or saltwater) recovery (EFR) and CO 2 storage. Therefore, the mechanism and resulting impacts of CO 2 -induced precipitation of organic asphaltenes, inorganic minerals, salts, and particle migration within reservoirs are discussed in this review. Due to the higher interfacial tension (IFT) between CO 2 and saltwater compared to CO 2 and formation oil, saltwater is mainly recovered from large pores in formations with low capillary resistance after CO 2 injection. However, oil from both small and large pores is recovered, and more CO 2 is stored in the oil reservoirs after CO 2 injection. When CO 2 is used as the cushion gas for underground hydrogen storage, the IFT between CO 2 and saltwater is significantly higher than that between H 2 and saltwater, which promotes the capillary sequestration of CO 2 in the storage but enhances the recovery of H 2 . The injected CO 2 also causes the dissolution and precipitation of inorganic minerals and solute transport as well as induces the precipitation of asphaltene and salt in the oil and saltwater within reservoir pores. Therefore, the physical and chemical reactions induced by CO 2 injection simultaneously improve and damage the seepage properties of reservoirs, and the final impact effect mainly depends on factors such as the mineral composition, the cementation characteristics of reservoirs, the salt concentration in the formation water, the asphaltene content in oil, and reaction time. For a reservoir with more easily soluble minerals, such as calcite and feldspar, good cementation, low water salinity, and low asphaltene content in oil, the seepage parameters of porosity and permeability are improved after long-term CO 2 –water–rock interactions. Conversely, the seepage ability is damaged for reservoirs with more mudstone minerals, asphaltene, salt, and poor cementation after a short-term CO 2 injection because of severe asphaltene/salt precipitation and particle migration in the reservoirs.