Feasibility of monitoring CO₂ injection in depleted UKCS and NCS gas fields using 4D seismic Open Access

This study investigates the CO₂ storage potential and 4D seismic monitoring capabilities of 64 depleted gas fields across the UKCS and NCS, providing critical insights for optimizing carbon storage strategies. By analysing 4D seismic signal strength, time-shift measurements, and theoretical storage capacities, the research identifies significant regional and field-specific variations. Overall, UKCS fields exhibit stronger amplitude responses which can be attributed to distinct CO₂ phase behaviour during injection where injected CO₂ transitions from gaseous to supercritical phase. Time-shift analysis (0.2-3.1 ms in UKCS, 0.1-2.6 ms in NCS) consistently exceeds the minimum detectability threshold for towed streamer surveys (0.5 ms) and proves more reliable than amplitude changes, which rarely reach the required 17% NRMS threshold. The non-linear relationship between seismic response and geological characteristics points the need for tailored monitoring approaches. These findings highlight the critical role of reservoir properties, stratigraphic age, and site-specific monitoring plans in guiding the design and deployment of effective carbon storage strategies in the North Sea.