Footprint and detectability of a well leaking CO2 in the Central North Sea: Implications from a field experiment and numerical modelling.

• CO 2 gas bubbles are completely dissolved within 2 m above the seabed. • CO 2 is not emitted into the atmosphere but retained in the North Sea. • Dissolved CO 2 is rapidly dispersed by tidal currents in the North Sea. • Harmful effects on benthic biota occur in the direct vicinity of the leak. • Monitoring has to be performed at the seabed and close to the leak. Existing wells pose a risk for the loss of carbon dioxide (CO 2) from storage sites, which might compromise the suitability of carbon dioxide removal (CDR) and carbon capture and storage (CCS) technologies as climate change mitigation options. Here, we show results of a controlled CO 2 release experiment at the Sleipner CO 2 storage site and numerical simulations that evaluate the detectability and environmental consequences of a well leaking CO 2 into the Central North Sea (CNS). Our field measurements and numerical results demonstrate that the detectability and impact of a leakage of <55 t yr⁻¹ of CO 2 would be limited to bottom waters and a small area around the leak, due to rapid CO 2 bubble dissolution in seawater within the lower 2 m of the water column and quick dispersion of the dissolved CO 2 plume by strong tidal currents. As such, the consequences of a single well leaking CO 2 are found to be insignificant in terms of storage performance. Only prolonged leakage along numerous wells might compromise long-term CO 2 storage and may adversely affect the local marine ecosystem. Since many abandoned wells leak natural gas into the marine environment, hydrocarbon provinces with a high density of wells may not always be the most suitable areas for CO 2 storage. [ABSTRACT FROM AUTHOR]