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1  Department of Thermodynamics and Energy Engineering, Faculty of Engineering, University of Rijeka, Croatia
Academic Editor: Juan Francisco García Martín


The application of carbon dioxide (CO2) in enhanced oil recovery (EOR) projects for partially depleted oil reservoirs is becoming increasingly more of interest in the petroleum industry because it can boost oil production rates while potentially reducing greenhouse gas emissions. This EOR technique uses a water-alternating-gas (WAG) process to displace and mobilize crude oil more efficiently than primary or secondary techniques. The injected CO2 reduces the viscosity and density of crude oil, making it easier to flow from the reservoir rock fractures to the production wells. This article studies the performance of the first EOR-CO2 project in Croatia, which started inoperation in 2014. The CO2 is supplied via a DN500 88 km pipeline from a natural gas sweetening unit using an amine solution. The CO2 that was previously discharged into the atmosphere is now compressed, liquefied, and pumped into the EOR fields of Ivanić and Žutica. These two oil reservoirs were discovered in 1963, and the primary recovery stage lasted until the mid-1970s, after which secondary recovery operations continued via water injection. The oil recovery factors after the primary and secondary stages were 9% and 38% in the Ivanić field, and 9% and 32% in the Žutica field. The tertiary (EOR) stage is expected to continue until 2040 and will increase the oil recovery factors to around 55%. Over the course of the project's lifetime of 25 years, the Ivanić and Žutica oil fields will produce an additional 3.4 million tonnes of oil and 600 million standard cubic meters of natural gas. Simultaneously, a total of 5000 million standard cubic meters of CO2 in supercritical condition will be injected and stored into the reservoirs.

Keywords: enhanced oil recovery (EOR); carbon capture and storage (CCS); tertiary oil recovery; natural gas processing; supercritical CO2