CO2 Injection into Oil Reservoirs: Hidden Risks and Reduced Efficiency

Russian scientists have identified potential risks associated with injecting CO₂ into oil reservoirs. The study, conducted by researchers from the Ufa Institute of Chemistry and RN-BashNIPIneft, analyzed laboratory and field data on carbon dioxide's effects on oil production and underground storage.

The injection process dissolves CO₂ in the oil, reducing its viscosity and increasing its volume, which can displace residual oil from tight rock pores. However, this interaction with rock minerals and water can trigger processes that degrade the reservoir's properties over time.

The researchers found that contact between CO₂ and formation water forms a weak carbonic acid, dissolving rock minerals and increasing porosity by up to 20%. This process also accumulates ions in the solution, which later precipitate out of the fluid flow, clogging pores. The study notes that this can reduce reservoir permeability by nearly 50% after just one injection cycle.

Another issue arises from changes in oil properties, where dissolved CO₂ causes heavy organic compounds to precipitate out, settling in rock pores and gradually blocking channels through which oil flows. This problem is particularly pronounced in low-permeability shale reservoirs with very small pores.