Human reliability analysis (HRA) has become an increasingly important element in many industries for the purpose of risk management and major accident prevention; for example, recently to perform and maintain probabilistic risk assessments of offshore drilling activities, where human reliability plays a vital role. HRA experience studies, however, continue to warn about potential serious quality assurance issues associated with HRA methods, such as too much variability in comparable analysis results between analysts. A literature review highlights that this lack of HRA consistency can be traced in part to the HRA procedure and a lack of explicit application of task analysis relevant to a wide set of activity task requirements. As such, the need for early identification of and consistent focus on important human performance factors among analysts may suffer, and consequently, so does the ability to achieve continuous enhancements of the safety level related to offshore drilling activities. In this article, we propose a method that clarifies a drilling HRA procedure. More precisely, this article presents a novel method for the explicit integration of a generic task analysis framework into the probabilistic basis of a drilling HRA method. The method is developed and demonstrated under specific considerations of multidisciplinary task and well safety analysis, using well accident data, an HRA causal model, and principles of barrier management in offshore regulations to secure an acceptable risk level in the activities from its application.
A study (JIP) on reliability of well completion equipment ("Wellmaster Phase III") was completed by SINTEF in November 1999. This has resulted in a comprehensive database on well completion equipment, with a total of 8000 well-years of completion experience represented and more than 1000 downhole failures included, given as input from the 16 funding oil companies of this JIP. The database represents all categories of downhole equipment, from tubing hanger level down. The paper points towards the major contributors to well interventions and downtime, indicating industry average and benchmark failure rates of the most vital completion components. A historical evolution in reliability of subsurface safety valves (SCSSV) is demonstrated, and the industry wide effect of reliability improvements is shown through specific examples. In the North Sea, reliability data has gained widespread acceptance for use in decision making. The paper lists several cases where reliability data of downhole equipment has been used with a major impact on field development and subsequent operational expenditures. 1. Introduction Reliability data has gained widespread use in the offshore business due to industry studies like OREDA, Wellmaster and others. The introduction of statutory codes and regulations in a number of oil producing countries has also strongly accelerated this development. During the last decade, offshore industry managers have become increasingly aware of the potential benefits which can be drawn from such databases. Some industry cases are now established which have demonstrated the cost saving potential of such databases. Examples of applications of reliability data are:Risk and reliability studiesLCC/LCP analysisTender evaluations and purchasing decisionsRig contracting strategiesIncentive based contract definitionsDownhole barrier acceptance criteria definitions Cautiously defined and consistent reliability data collection requirements is a prerequisite for successful reliability databases. The new ISO 142241 standard constitutes a valuable reference in this context. The Wellmaster Phase III project objective has been to contribute to improvement in completion equipment reliability through systematic collection, analysis and feedback of reliability data to participating oil companies and equipment manufacturers. The main deliverable from the project has been the new Wellmaster data collection software for completions with an integrated analysis tool, an updated database on completion equipment and reliability statistics and a summary report2 on main findings. Data analysis has focused on in-service equipment failures, defined as failures occurring from 6 days after landing the tubing hanger on the wellhead. Failures occurring prior to that are defined as installation failures, and a fair amount of these failures have also been reported. All failure reported are also listed in a web-application where the Wellmaster JIP member companies have access.
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