Investigating the Gas Dispersion from Subsea Gas Releases in Shallow Waters

Although the repetitive subsea gas releases incidents occurring in the offshore oil and gas industry, the attention is limited to a case-by-case study; leading to quantitative risk assessment approaches that are limited to similar cases. A subsea gas release can result from a range of different causes including drilling operations; failures in flow lines, gas export lines, and subsea equipment. Such releases can have catastrophic impacts on the environment, offshore platforms, and human lives. Natural gas, in general, and in the Middle East, covers a large portion of the world supply and, consequently, this type of incidents could pose a significant risk for the related and nearby facilities, like Hydrogen Sulfide (Hv2S). For example, 40% of the natural gas reserves in the world are sour gas fields in which the Middle East holds the highest reserves of sour gas. While many approaches have been proposed for the description of underwater/subsea releases, these are not universal and still include deficiencies concerning plume turbulence, hydrates formation, and high flowrates water bodies. According to Olsen, 2015, experimental data for underwater releases exist but are also limited to small and medium scale (compared to the actual depth and flow rate). In this study, we investigated the available computational methods to model subsea gas releases cases applicable to the ones of the offshore facilities at the State of Qatar. An Eulerian based computational fluid dynamics (CFD) model was configured in order to study representative gas release scenarios. Earlier, the CFD model was validated successfully against experimental data from SINTEF and Statoil. It also demonstrated the required sensitivity for critical parameters such as the centerline distribution of velocities and void-fraction. Finally, the model was applied for conditions specific to Qatar’s offshore industry as a representation of shallow water and a sensitivity analysis was conducted against parameters of local interest such as high-flowrates and Hv2S presence. Finally, a discussion on the potential risk level is given concerning fire & explosion and toxicity hazards like Hv2S