The uncontrolled blow-out of a well is one of the most critical accidents that can occur during both exploration and exploitation of hydrocarbon fields. Significant HSE issues are associated to this event that introduces safety risks for field operators, potential health injury for the population and impacts on the environment.

Blowouts need to be evaluated through specific models: commercial packages may lead to a non-exhaustive analysis and underestimate the effects. Some phenomena that occur during a blow-out event are not sufficiently treated in literature, so that experimental or CFD investigations are sometime necessary to allow an exhaustive analysis and the expansion of a specific database, useful to develop and validate simplified models. ENI E&P has been carrying out a specific R&D project since 1998.

This paper describes some blow-out jet simulations, and the associated methodology, carried out applying the CFD approach. The jet development into atmosphere affects strongly the cloud evolution, in terms of shape and concentration, and then the flammable/toxic gas dispersion as well as heat radiation.

Different release conditions have been analyzed:

  • horizontal and vertical jet, both ignited and unignited;

  • free and restrained jet;

  • heavy and neutral gas dispersion.

Jet direction has a strong effect on cloud formation and dispersion: for example if a horizontal jet take place near the ground, it can remain glued on it (KOANDA effect), resulting in high concentration. This phenomena take place also in case of ignited jet: the flame remains glued to the ground, resulting in high temperature and radiation level. Moreover, totally restrained jet could generate a heavy-gas cloud, resulting in high concentration in the near-field. In this case, the cloud formation happens in different consequent stages, and a transition analysis is necessary to reproduce the event correctly, in terms of risk area evaluation.

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