Experimental and numerical study of gas to liquid ratio in stratified gas-saturated liquid blowouts’ plumes

Abstract

During underwater live-oil blowouts, some fraction of dissolved gas separates from oil upon pressure drop. The excessive buoyancy flux caused by free gas, as well as dominated gas bubbles slip velocity, heightens the plume peeling level when compared with pure-liquid blowouts. A series of laboratory experiments with CO2 saturated water and pure water blowout in an open-top stratified basin was carried out. The structure of the single-phase plume has coherent eddies around it due to instabilities. These coherent eddies are mainly responsible for entrainment, and hence widening of the plume as expected. Visual observation of gas-saturated liquid plumes compared with pure-liquid plumes suggests that the instabilities are hampered, hence generating weaker more elongated coherent structures and less entrainment. This lets the plume widen less and contributes to heightening the plume peeling level to a greater extent. This seems to be due to off-source buoyancy enhancement as a result of off-source bubble formation in the plume. Experimental results were also compared with a series of equivalent numerical simulations conducted with OSCAR and Gas Track modules of SINTEF MEMW. In different steps of the experiments, the amount of dissolved CO2 in water, as well as volumetric gas to liquid ratio in numerical simulations, was changed. Non-dimensional form of plume peeling heights shows that peeling heights in numerical results would be more compatible with the experimental results when the volumetric gas to liquid ratio was set equal to the amount of gas separates due to pressure drop across the opening.