Risk Assessment and SIL Allocation of Safety Instrumented Functions for Open Water Workover System - Considerations and suggested approach

Abstract

Well intervention/workover system (WOS) allows major maintenance or remedial treatments of an oil or gas well. This thesis focuses on open water WOS. Offshore environment is a high risk environment with numerous hazards. WOS operation themselves are also high risk with numerous hazards. Therefore, there are common practices to implement risk reduction technique to WOS. Implementation of risk reduction is guided by several international standards and national guidelines. One of such guidelines is NOG 070, developed by PSA Norway. At the moment, NOG 070 is being expanded to include guidelines specific to WOS operation. Risk reduction depends on risk analysis. Risk to WOS must be analyzed before any reduction of risk can be performed. Risk analysis depends on data, especially occurrence of accident and reliability of protection layers. Current NOG 070 provides some of these data and provides guidelines on how to reduce risk. If NOG 070 is to be expanded to include WOS, it needs all relevant accident occurrence data and reliability data of all protection layers that prevent accident from occurring. Current guideline allows data that are unavailable to be assumed by engineer when they are performing risk analysis. This thesis performs risk analysis of open water WOS located in Angola. WOS located away from Norway is necessary because if the risk assessment is done in Norwegian continental shelf (NCS), then experts may find their assumptions robust due to the extensive data for North Sea oil exploration. Meanwhile, there is limited data available with respect to Angolan offshore. The aim of researching WOS that is going to be deployed in Angolan offshore is to expose all the assumptions taken by experts and their validity while designing safety functions by implementing current guidelines and standards. Results of this thesis may uncover items that are not yet covered in current standards and guidelines. This would help in creating a better guidelines and standards in the future. This thesis also gives recommendation to companies performing risk assessment with respect to such system.