Analysis of the physicochemical detectability and impacts of offshore CO₂ leakage through multi-scale modelling of in-situ experimental data using the PLUME model

Carbon storage is required to keep rising global temperatures below 2°C, meanwhile, storage reservoirs monitoring is required for assurance of early detection of potential leakages. Projects such as QICS and STEMM-CCS have used small in-situ experiments to develop detection techniques, tools, and strategies. Given the expense of experiments it is crucial to develop accurate simulation models that replicate observed behaviours and can be extrapolated to many different scenarios. However, anomalies occur between modelled and experimental data, and a key question has been how can the models be improved? This has been approached through the development of a complex modelling system to include the effects of coastal hydrodynamics on very localised experiments, with a new multi-phase leakage model – PLUME, integrated into a high-resolution hydrodynamic model, and linked to a carbonate system for CO₂ analysis. The resolution of the nested domains range from 2.5 km at the boundaries to approximately 0.5 - 1.0 m at the release sites. The efficacy of the PLUME model is demonstrated with application to the STEMM-CCS and QICS experimental sites in 120 and 9-12 m water depths respectively. Results show that the newly developed model can predict observed pCO₂ and pH changes within acceptable errors. Local effects are shown to be affected greatly by both the resolution and the water currents, with momentary spikes in pCO₂ and reductions in pH caused by tidal oscillation. The spatial impacts of the releases are shown to move with the tide, covering a far greater area over a tidal cycle.