Carbon dioxide plumes, pressure space and legacy well risk for Southern North Sea CO2 storage projects

Unsecured legacy wells pose significant risks to carbon capture and storage (CCS) as they present potential leakage pathways for stored CO 2 to return to the atmosphere. In the UK, legacy wells must be assessed for a carbon storage permit to be granted and high-risk wells require costly remediation. We use a well risk assessment scheme to evaluate the risk of wells in the Southern North Sea. We then combine our well risk assessment with investigation using the analytical tool CO2BLOCK, which relies on a gravity current model to estimate pressure and plume migration distances. We evaluate the Viking, Camelot and Poseidon projects, which plan to inject CO 2 into the depleted reservoirs of Southern North Sea gas fields. Carbon dioxide plumes are typically several kilometers wide, and it should be possible to avoid plume migration to high-risk legacy wells. In contrast, pressure fields produced by CO 2 injection are tens of kilometers wide and low magnitude pressure increases frequently extend beyond the bounds of storage licence areas. The pressure fields encounter hundreds of wells and in the cases of the Camelot and Poseidon projects, interact with each other. • A risk assessment of Southern North Sea wells with analysis of the Viking, Camelot and Poseidon CO 2 storage projects conducted. • Simplified physics models suggest high-risk legacy wells could be avoided with careful site selection. • Pressure fields produced by CO 2 storage projects extend beyond the bounds of storage licence areas.