Experimental validation of the PolPlumePlus™ integral model for the analysis of the consequences of accidental releases from offshore CO₂ pipelines

Carbon Capture and Storage (CCS) technologies are essential for achieving the 2015 Paris Agreement target of net-zero emissions by 2050, particularly for mitigating emissions in hard-to-abate industrial sectors. Despite this, the current deployment of CCS infrastructure is lagging behind expectations, hindered in part by a lack of robust regulatory frameworks and uncertainties in risk assessment analysis. A critical element of the CCS value chain is the offshore transport of CO2 via pipelines, where accidental loss of containment (LOC) poses a significant safety hazard due to the formation and dispersion of a toxic subsea CO_2 plume. To ensure the safe deployment of CCS infrastructure, reliable consequence modelling is crucial for Quantitative Risk Assessment (QRA). This thesis focuses on the experimental validation of PolPlumePlus™, an integral subsea dispersion model developed by Saipem in collaboration with Politecnico di Milano. The model's capacity to simulate the physical phenomena governing CO2 jet and plume behavior is evaluated by benchmarking its outputs against Computational Fluid Dynamics (CFD) tools and experimental data derived from two Joint Industry Project (JIP) campaigns. The validation process demonstrates that PolPlumePlus™ successfully simulates the temporal and geometric evolution of the subsea CO2 plume. Analysis indicates that an initial input bubble diameter of 4 mm, in line with observations and theory indications, yields the highest degree of concordance with empirical observations. For QRA applications, the study recommends adopting a sensitivity analysis approach that deliberately overestimates the initial bubble diameter to ensure conservative safety margins. Furthermore, while dissolution dynamics require further quantitative investigation, discrepancies can be effectively mitigated by adopting conservative physical criteria, such as a 10 nm threshold for the gas bubble radius. Ultimately, PolPlumePlus™ offers a significantly higher degree of accuracy compared to standard industry geometrical methods, providing a robust tool to enhance risk assessment methodologies and support the large-scale deployment of CCS technologies.