DeepBlow - a Lagrangian plume model for deep water blowouts

This paper presents a sub-sea blowout model designed with special emphasis on deep-mater conditions. The model is an integral plume model based on a L agrangian concept, This concept is applied to multiphase discharges in the formation of water, oil and gas in a stratified water column with variable currents. The gas may be converted to hydrate in combination with seawater, dissolved into the plume water, or leaking out of the plume due to the sli p between rising gas bubbles and the plume trajectory, Non-ideal behaviour of the gas is accounted for by the introduction of pressure- and temperatur e-dependent compressibility z-factor in the equation of state. A number of case studies are presented in the paper. One of the cases (blowout from 100 m depth) is compared with observations from a field experiment conducted i n Norwegian waters in June 1996, The model results are found to compare fav ourably with the field observations when dissolution of gas into seawater i s accounted in the model. For discharges at intermediate to shallow depths (100-250 m), the two major processes limiting plume rise will he: (a) disso lution of gas into ambient water, or (b) bubbles rising out of the inclined plume. These processes tend to be self-enforcing, i.e., when a gas is lost by either of these processes, plume rise tends to slow down and more time will be available for dissolution, For discharges in deep waters (700-1500 m depth), hydrate formation is found to be a dominating process in limiting plume rise. (C) 2000 Elsevier Science Ltd. All rights reserved.