Comparison of Quantitative Blowout Risk Assessment Approaches

Abstract

Abstract The risk of a blowout is one of the major contributors to the total risk picture on oil and gas installations. The consequences can be significant with respect to loss of lives, material assets and damages to the environment. Even though much effort is put in to describe how blowouts occur, and how to prevent it to happen, the risk of blowouts will remain a threat to this industry. Historical data show that the variation in the frequency of a blowout strongly dependents on several risk elements identified in the well, on the platform, in the procedures and in the organization. In order to prohibit blowouts it is of importance to evaluate well conditions, but also the system and the equipment on the platform and in the organization. A brief comparison has been made between the approach of BlowFAM (Blowout Frequency Assessment Model1) and a more traditional approach based on kick frequency and BOP reliability. Introduction In 1993 a joint industry project was started with several large companies in the oil and gas industry, with the purpose of establishing a model that based on drilling and well technology, frame conditions and historical trends. The model was supposed to identify interrelating parameters to support risk assessments and to understand the events that cause blowouts. This resulted in a computer based model that handled more than 300 risk elements which contribute to the blowout risk, giving the site specific blowout frequency. The model covers risk elements in the well, on the platform, in the procedures and in the organization. Risk assessments of blowouts are traditionally based on historical data for the purpose of Safety Cases. Traditionally when quantitatively evaluating the blowout risk, well parameters and BOP are the most common factors to set focus on for argumenting adjustment of the generic blowout frequency. Through the approach of BlowFAM, the 300 risk elements are to be evaluated covering all operational phases, reservoir aspects, frame conditions, management, equipment and procedures. These are elements that are found contributing more or less to the blowout risk. Blowout Statistics - the Common Starting Point One of the major tasks in a blowout model is to obtain reliable historical blowout data as a basis level, further to treat the data in a manner appropriate to the purpose of the project objectives and to present the data in a format suitable for the blowout model. During reviews of safety cases it is found that several operators apply, as a starting point, a kick frequency based on documents that can be up to 10 years old. These frequencies are based on historical incidents and do not always reflect today's practice. There are a few offshore blowout databases commercially available. Through the development of BlowFAM the SINTEF Offshore Blowout Database was found to be the most updated, and it included the most reliable and informative data. Today, more than 480 blowouts and well release incidents, i.e. "near misses" to blowouts, are found in the database. The starting point for the BlowFAM approach is blowout frequencies that are updated once a year based on the SINTEF data base. In the North Sea region (British, Dutch and Norwegian shelves) the largest oil companies have started to use these data as an "industry standard" in the region. The "industry standard" frequencies are sometimes applied in quantitative risk analyses without further adjustments. Methods of Predicting Blowout Frequency for a Specific Site The identification and evaluation of risk elements is one of the most important steps in a quantitative risk analysis. In a blowout risk analysis, the BlowFAM approach uses indicative well data, i.e. data that can be used to predict pore pressure, fracture pressure, possibilities of faults in the formation, etc. to sort out relevant blowout causes that could occur on the specific site.