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The uncontrolled eruption of a well is one of the most critical accidents that can occur both during exploration and exploitation of hydrocarbon fields. Significant HSE issues are associated to this event that introduces safety risks for the field operators, potential health injury for the population living in the area and impacts, mainly associated to the hydrocarbon contamination, on the environment. This paper describes a methodology, developed by ENI E&P in the framework of a specific R&D project, permitting the complete analysis of the phenomenology associated to the blow-out event. The procedure, implemented in a PC user friendly software supplies all the information necessary for the complete characterization of the accident from a HSE point of view. In particular, the following data can be derived from the methods:release characterization;not ignited jet characterization;not ignited toxic and flammable gas and oil dispersion characterization;ignited jet characterization;dynamic killing design. The above set of data is calculated making use of a constellation of models simulating the various physical phenomena characterizing the blow-out event. Part of these models have been developed in the framework of the R&D project being relevant to phenomena (e.g. oil atomization, two-phase jet, two-phase combustion) not sufficiently treated in the literature. In some cases literature/commercial models have been selected after a State of the Art study. All the models included in the procedure have been validated both with experimental and/or numerical (CFD) data. The methodology is presently successfully applied in most of the ENI E&P developments. In the paper the description of the methodology structure and models is reported with validation results and some application scenarios. Introduction The availability of validated predictive tools for application during an accident scenario is essential. Their use should not be restricted to design activities. They generate vital information on the evolution of an accident and can be readily applied to optimise the emergency response. One potentially major accident event that is associated with the exploration and exploitation of hydrocarbon fields is an uncontrolled release of formation fluid from the reservoir e.g. a blow-out (See Figure 1). When a blow-out event occours, it is essential to implement a contingency plan as quickly as possible to minimise the potential damage, particularly for onshore wells where the oil and gas is dispersed into the atmosphere and over the land and can have an impact also on people. To improve the evaluation of the safety and environmental consequences of a blow-out the ENI - E&P Division commissioned a multi-disciplinary R&D project. This project utilises technical and scientific support from Eni Technologie, TEA Sistemi and ENI DATA companies. Due to the wide range of knowledge and expertise required by this project (e.g. safety, reservoir, drilling, completion and well fluid dynamic, discharge phenomena, not-ignited/ignited jet characterization and atmospheric dispersion) it proved necessary to "integrate" the various disciplines to ensure a good quality of project deliverables. The key features of the developed methodology are described in the following sections.

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 un-ignited;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. "Blow-out Project" Objectives e Work Phases Eni E&P is developing the methodology, for the simulation of a blow-out event, in the framework of three subsequent specific R&D project phases, in order to allow the complete analysis of the phenomenology associated to the blow-out event:Phase 1: 1998 - 2000: "Blow-out 1";Phase 2: 2001 - 2004: "Blow-out 2";Phase 3: 2005 - 2007: "Blow-out 3". The main objectives of the project have been:Provide tools to evaluate the consequences of a blow-out during the various drilling stages and exploitation activities.Supply information on the evolution of the event that can be used as a basis to:Support authorization phases, providing important and reliable information direct to the authorities;Optimize the location of the well area taking into account the possible consequences of a blow-out just from the first step in the drilling activities;Plan and manage the emergency actions to mitigate real blow-out situations, providing decision making tools to key people;Produce the data required to prepare a Contingency Plan. The Methodology includes all the kind of impact associated with a blow-out event and with pipeline releases accidents also including underwater discharges, oil spill analysis and transient releases (typical of a pipeline leakage). "Blow-out 1" and "Blow-out 2" phases allowed to obtain two PC softwares (for the "Short-Cut" and "Standard" Approaches) for an exhaustive simulation of the consequences of a blow-out. The software has just been presented in other Conferences,5,6,7. Presently, Eni E&P and TEA Group are carrying out a 3rd phase of the project (2005–2007) "Blow-out 3". This activity will allow to improve the model and the methodology, taking into account problems, results and the know-how resulting from a great number of applications performed and scenarios analyzed. CFD investigation is one of the most important activities of the "Blow-out 3" phase.

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