The assessment of risks for human health and environment is a crucial step of the design of subsea pipeline systems. Well-recognized standards, such as DNV-RP-F107, recommend carrying out periodic risk assessment throughout the whole life cycle of a subsea pipeline system. The purpose of this paper is to present the upgrade of a lean and proprietary tool to assess the consequences of CO2 and H2 releases from subsea pipelines whenever a Quantitative Risk Assessment (QRA) is required. To quantify the risk for people and the environment involved in an accidental loss of containment of CO2 or H2 sealines, the physical effects of subsea releases need to be evaluated. The mathematical model described in this paper is based on state-of-the-art integral models developed for subsea releases. It models subsea plumes or subsea gas blowout considering the effects of sea current, sea salinity, sea temperature as well as the effects of impurities in the released stream. The model was validated through a comparison with a detailed Computational Fluid Dynamic (CFD) simulation and case studies available in literature. At present, the assessment of subsea CO2 and H2 releases, for QRA purposes, is performed either by very simplified and not validated approaches, which can lead to an overestimation of the consequences, or by complex CFD tools which require specific skills, high computational costs, and long duration of analysis often not in compliance with tight project schedules. The results of this paper show a sufficient level of accuracy of the in-house integral model with respect to other well-recognized integral models in the estimation of underwater plume behaviour, bubble zone extension at the sea surface, void fraction, and mean plume speed. Therefore, it can provide a suitable set of input data for simulation of atmospheric dispersion of CO2 and H2. The comparison of the results, carried out by means of a CFD tool on a set of case studies, shows a good agreement of the main predictive parameters. The model described is a suitable tool for consequences assessment in QRA studies for CO2 and H2 offshore pipeline projects concurring at the Net Zero objective, contributing to understand release impacts on safety and environment.

The objective of decarbonizing the Oil and Gas (O&G) industry has led to investigations regarding offshore power generation, one of the major sources of emissions in offshore activities. Some investigations have been carried out on the integration of wind turbines into local power generation grids, supported by the developments in floating wind technologies and the increasing size of turbines, unlocking far offshore applications. The specificity of offshore O&G applications is that power should be continuously supplied to maintain production. The intermittent nature of wind energy requires back-up power solutions. Industry has been working on such local wind-based power systems with solutions, integrating the back-up power systems onto the turbine floater. Energy storage is an interesting option to further increase the decarbonization potential associated with wind-based local microgrids, but it comes with several challenges in terms of technology, and sizing and rationalization of the overall scheme. Statistical approaches allow quick analysis of the wind resource potential for a specific location, relevancy of wind-based solutions, and the need for back-up solutions. When looking at energy storage feasibility and associated sizing to cope with wind downtime, the dynamic charge and discharge phases are very important. A dedicated methodology and associated tool based on wind time series has been built to analyze the wind energy resource and the local power generation with a dynamic approach to the energy storage system. This tool allows computation of the wind power available, the need for back-up at each timestep of the time series and integrates the charge/discharge cycles of energy storage. This is specifically useful to properly size the energy storage system and to assess the overall green share of the energy mix, as well as the actual CO2 emissions savings. Storage sizing is not only based on raw average downtime duration but also on the ability of the storage solution to be recharged by excess wind power, considering also the storage process efficiencies. It has been demonstrated that the power system cannot be sized by only considering the worst or average low wind durations. The dynamic behavior of the local microgrid has to be taken into consideration for proper design. The presented paper is based on a representative case study to illustrate the major challenges, specificities and balance of such local-microgrids, as well as explain the need for optimization and rationalization of the solution design. There is a need for rational wind-based power system sizing, as CO2 emission reduction targets can be reached through various configurations. Some opportunities to further valorize the green energy from the local power microgrids are also discussed.