Underwater gas releases were investigated by experimental tests to analyze the potential hazards deriving from accidental ruptures of offshore pipelines in the oil & gas industry. The evolution of the gas released by the ruptures located in relatively shallow waters has been accurately analyzed in order to evaluate the hazards associated with the toxic and flammable gases reaching the sea surface. The experimental activity has been carried out to better characterize the gas dispersion source term.

An underwater gas release from a pressurized pipeline generates a subsea gas plume that breaks down in bubbles and could reach the neutral buoyancy level below the sea surface. The size and rising velocity of the bubbles affect the momentum of the gas reaching the sea surface, while the lateral spreading of the bubbles and the gas dissolution in water influence the bubbling area and the actual flow rate dispersed in the atmosphere. Another important phenomenon is the neutralization of the gas due to the diffusion in the air just above the sea surface. These parameters represent the basic information required to determine the behavior of the gas above the sea surface and the source term for atmospheric dispersion.

The experimental activity consisted in discharging a gas in an open tank filled with water. A set of lab tests was performed to evaluate the plume evolution for underwater releases of a neutral gas in shallow waters. The liquid velocity and gas hold-up were monitored along the plume length for different gas flow rates.

A benchmarking activity on underwater gas release models was performed comparing model equations with the experimental measurements. As a result of this work, a more accurate approach for determining the source term of atmospheric dispersion of a subsea gas plume is proposed.

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