A new study published in the Marine and Petroleum Geology journal has revealed potential risks associated with the formation of bitumen in Carbon Capture and Storage (CCS) locations in the North Sea in Denmark.
The Danish North Sea is home to chalk rocks that hold depleted oil and gas reserves in specific zones below the sea bed, making it an ideal spot for storing sequestered carbon dioxide as the infrastructure built for the fossil fuel industry can be repurposed and utilized for decarbonization operations.
However, the newly published study highlights concerns regarding the future interaction between the stored carbon dioxide and hydrocarbon (oil and gas) residues left in the rock.
The research suggests that the stored carbon dioxide could react with the hydrocarbon remains, resulting in the formation of bitumen. Bitumen is a highly viscous form of petroleum, and its presence could pose risks to the overall effectiveness and safety of the CCS initiative.
Researchers Rasmus Stenshøj from Aarhus University and associates from the Energy & Environmental Research Center, U.S., performed an experiment on a 66 to ~100 million-year-old chalk sample collected from the Halfdan Field in the North Sea.
Recreating the environment in which this sample exists on the seabed, the research team injected supercritical carbon dioxide (CO2 that exhibits characteristics of both a gas and a liquid beyond specific temperature and pressure thresholds) into the chalk specimen over a period of nine days.
They then used physical and chemical processes to analyze the presence of hydrocarbons in rock samples before and after such an injection.
The results showed that under supercritical carbon dioxide influence and specific temperature and pressure conditions, lighter hydrocarbons were able to mobilize through the rock structure, while heavy hydrocarbons such as bitumen were left behind.
These immobilized components could potentially obstruct the movement of carbon dioxide through the rock, diminishing the effectiveness of the CCS system, which highlights the importance of considering potential risks and developing appropriate mitigation strategies for future decarbonization initiatives.