New research by STRATEGY CCUS partners at the University of Zagreb in Croatia suggests that the use of carbon dioxide (CO₂) in enhanced gas recovery (EGR) could result in carbon negative scenarios, whereby CO₂ is permanently removed from the atmosphere.

The peer-reviewed study, published in Energies, presents findings from tests carried out at EGR operations at a gas condensate reservoir in Northern Croatia.

The researchers analysed all three elements of the CO₂ life cycle within the EGR process: namely, the CO₂ emitted by the combustion of gas from the start of production; the CO₂ separated from the original reservoir gas at the processing plant; and the volumes of CO₂ injected into the reservoir as part of EGR.

The test reservoir chosen represents a typical gas-condensate reservoir in Northern Croatia and, more specifically, in the Drava basin. The produced gas from this area usually contains around 50% of CO₂.

The tests carried out by the University of Zagreb scientists converted a production well to a CO₂ injection well in order to focus on CO₂ storage rather than maximising hydrocarbon gas production.

Lucija Jukić, lead author, Faculty of Mining, Geology and Petroleum Engineering at the University of Zagreb, said: “Our studies have concluded that, even when the hydrocarbon gas in question has such high CO₂ content, enhanced gas recovery using CO₂ injection can be carbon negative. In almost all of our simulated CO₂ injection scenarios, the process was carbon-negative from the time injection started. In the scenarios where CO₂ injection begins earlier, it is carbon-negative from the start of gas production. This opens up the possibility of cost-effective storage of CO₂ while producing natural gas with net negative CO₂ emissions.”

Graphic: Contour map of formation top depths with gas/water contact. Credit: University of Zagreb