Distribution and origin of carbon dioxide in the East Irish Sea Basin: implications for carbon storage: implications for carbon storage

The natural occurrence of carbon dioxide in subsurface reservoirs is proof of concept that it can be securely stored over geological timescales. Gas accumulations naturally enriched in CO₂ were identified in the East Irish Sea Basin, and their origin was evaluated using a large well and geophysical database. Legacy petroleum fluid samples indicate that CO₂ is regionally negligible, except within the proximal North Morecambe and Rhyl gas fields in the northern basin. Despite relatively elevated ionic concentrations within the northern basin, interpretations of CO₂ dissolution from formation water samples are not conclusive due to widespread contamination. Geochemical measurements of Carboniferous coal and shale samples indicate that units are typically mature and are lacking any further generative potential. While the accumulated CO₂ may have been generated from Carboniferous limestones or formerly organic-rich units, this is likely to have been limited based on their burial history and widespread extent compared to the local present-day distribution of CO₂. Instead, thick and densely spaced Paleogene igneous dykes were mapped near the Rhyl Field. Despite being the most likely origin, igneous intrusions are interpreted across the northern basin and near several accumulations that lack CO₂, suggesting that other geological elements have influenced its contemporary distribution, such as the cap rock or migration.