La banque de données platform de l'Institut français du pétrole : un outil de base pour des études de risque
Ifp's Platform Databank: a Basic Implement for Risk Analysis
Institut Français du Pétrole
La banque de données PLATFORM de l'Institut Français du Pétrole (IFP) concerne les accidents survenus depuis 1955 aux engins pétroliers de forage, de production et d'habitation en mer, de type fixe (plates-formes en acier, en béton . . . ) ou mobile (submersibles, auto-élévatrices, semi-submersibles, navires, barges . . . ) et ayant donné lieu à un arrêt de travail ni programmé, ni prévisible, d'au moins 24 heures. Ce critère, éliminant les nombreux incidents mineurs, peu ou mal connus, lui confère une certaine homogénéité indispensable à la validité de toute banque de données d'accidents. Comportant : - une banque de connaissanceconstituée de fiches détaillées sur le déroulement et des conséquences de chaque accident, et - une banque informatiséebasée sur les seuls paramètres principaux mis en mémoire d'ordinateur, la banque PLATFORM présente le double avantage de : - regrouper, sous une forme ramassée et facilement interrogeable, l'ensemble des accidents connus d'une branche industrielle, - fournir des résultats chiffrés (comptages, statistiques, . . . ) qui, même approximatifs, sont irremplaçables pour les études de risque, de sécurité et de fiabilité. Différents exemples d'application illustrent les possibilités de PLATFORM en s'appuyant sur des paramètres aussi variés que les types d'engin, d'accident, d'activité au moment de l'accident, de facteurs préliminaires, de zones géographiques.
IFP's PLATFORM databank concerns accidents since 1955 to all kinds of off-shore drilling, production or accomodation platforms, both fixed (steel, cement, etc. ) and mobile (jackups, submersibles, semi-submersibles, drillships, barges, etc. ) having caused an unplanned and unforeseen work stoppage of at least 24 hours. The databank is designed to underline the homogeneity of the data gathered, which is an indispensible condition for obtaining valid statistics. PLATFORM consists of (1) a knowledge base made up of an ongoing information file, including a synthesis data sheet for each accident giving a selection of important facts (date, location, type of accident, etc. ) and summarizing the most probable sequence of events of the accident and their consequences, and (2) a computerized databank giving the most important facts for each accident in a strictly controlled language of codes and abbreviations for use in statistical analysis. The computerized databank contains 25 different parameters. Some are made up of multiple components (there are three preliminary factors, four sequences of events, etc. ), and others are codes with sub-elements. Data has been entered in three different ways : as uncoded facts, as simple codes, or as complex codes. The latter have enabled a detailed analysis to be made of certain important factors, such as : (a) 72 possible preliminary factors preceding the accident (b) 74 different kinds of events making up a sequence of events (including 5 different types of blowout and 13 types of collision)(c) 196 countries, provinces or states (d) 30 major geographic zones(e) 139 different constructors of platforms, drillships or barges. An analysis of the number of accidents per year from 1972 to 1988 shows a good correlation with the evolution of the price of crude oil during the same period and that of world rig utilization. A comparison with the number of new rigs put onto the market from 1977 to 1988 shows a peak in accidents for the same years, reflecting the fact that new rigs are often subject to accidents at the start of operations. These comparisons serve to demonstrate the good correlation of the PLATFORM databank with results from other studies. PLATFORM can be used to draw up simple data sheets, such as the two lists given of the accidents having caused the most human casualties as well as those having caused the greatest oil spills. It can be used to furnish the probabilities of occurrence of unusual types of accidents, or to give a figure for well-known high-risk activities having actually led to accidents. Such figures are very much appreciated in safety risk analysis. Several statistical results are given to illustrate PLATFORM's capacities. An analysis of activity at the time of the accident shows that most accidents occurred (in order) during exploration drilling, during production, while rigs were under tow, while rigs were shut down during a storm, during development drilling, and during jacking-up or jacking-down for this type of mobile platform. In fact, 76. 6% of the accidents to jackups occurred either during towing (30. 9%), exploration drilling (27. 1%) or jacking operations (18. 6%). Accidents to fixed platforms occurred predominantly during production (53%). The most frequent types of accident were found to be (in order) blowouts, explosions or fires, damage to legs or mats often due to the sea floor, capsizing of the rig, gas kicks and structural cracks. But the major risk varied according to the type of platform : gas blowouts for submersibles, fire/explosions for fixed production platforms, capsizing for barges, sea floor accidents for jackups, gas kicks for drillships and semi-submersibles. A geographic analysis gives the Louisiana sector of the Gulf of Mexico a higher percentage of accidents (37%) than the Texas sector (7. 5%) or the Scottish North Sea (8%). This can easily be explained both by the relative importance of petroleum activity in the sector (especially barges and submersibles operating in swamps, lakes and deltas) and by the comparable wealth of information made public in this region. A further analysis of the region shows more gas blowouts (28%) than the world average (21%) and, on the other hand, a chronological decrease in accidents linked to structural resistance, reflecting better rig design and reliability over the years. In general, statistics of accidents, correlated to offshore oil activity, show that accidents are decreasing in the Gulf of Mexico and in Persian Gulf, whereas there are more in the North Sea sector and in general in new areas outside the four major areas of petroleum activity. A monthly analysis of accidents in the northern hemisphere shows that many accidents to production platforms take place in October, which is an unfavorable period for the Gulf of Mexico as well. May to September is a favorable period for the North Sea, and April to July are favorable months for mobile platform activity. A study of different kinds of blowouts during exploration drilling (54. 8% of all accidents), development drilling (30. 4%) and production (14. 8%) show a predominant number of gas blowouts occurring during production operations. A comparison of jackups and semi-submersible platforms shows a greater blowout risk (40%) for semi-submersibles that can be explained by the subsea position of the BOP for these platforms. Preliminary factors leading to blowouts are mainly due to the absence or failure of the BOP or diverter, and casing or drillstring problems. The weather factor virtually disappears after 1974. A study of personnel evacuation reveals little use of life rafts (5. 1%) or survival capsules (6. 2%). In the final phase of emergency rescue, crew members are picked up by service vessels three times as often as by helicopter. In general the PLATFORM databank shows an increase in platform safety and reliability excluding acts of war, as evidenced by the progressive disappearance of such factors as metal fragility and the lessening impact of bad weather. As demonstrated by these examples, the PLATFORM databank fulfills two important functions : (1) providing a body of essential data for each of these important industrial accidents that is homogeneous, concise and easy to consult, and (2) due to this homogeneity, being able to furnish figures that, even if they are approximate, can make up the indispensable basis of risk, safety and reliability analyses.
© IFP, 1991