CO2-EOR Process and CO2 storage during EOR
Maja Arnaut, mag.ing.petrol.
Enhanced Oil Recovery (EOR) methods are used to produce additional oil after the primary production phase (where production is based on natural reservoir energy) or, most often, after waterflooding (secondary phase). Some EOR methods are related to CO2 injection (CO2-EOR), which is attractive since part of injected CO2 retained in the reservoir, enabling a positive effect on storage capacity and cost-effectiveness of CO2 storage. Therefore, these methods are of particular importance due to the emission reduction obligations under European Union international agreements within the climate change domain (Kyoto protocol from the year 1997 and Paris agreement from the year 2015). Carbon Capture Utilization and Storage (CCUS) comes to focus when possibilities of CO2 storage and reduction of storage cost are assessed. Although there are other utilization types such as utilization through beverage production or in agriculture, only the CO2 enhanced oil recovery (CO2-EOR) is implemented at a commercial level on an industrial scale –.
By injecting CO2 above the miscibility pressure (or minimum miscibility pressure, MMP), microscopic displacement efficiency is improved due to viscosity reduction, oil swelling, lower interfacial tension and change of density of oil and brine . Regardless of the injection conditions, part of the CO2 is always re-produced so injected CO2 includes recycled CO2 and CO2 that should be brought to complete the total required injected volume (Figure 1)