Application of Layers of Protection Analysis (LOPA) for subsea production systems - A risk based model for determination of integrity levels in a global perspective

Abstract: Depletion of onshore and shallow water reserves, in combination with new subsea technology, has made the petroleum industry advance into deeper water. However, new technology also brings new risks. Since most widely accepted standards and regulations are not directly aimed for subsea systems, new methods have to be developed. By developing a LOPA-model, which can be used specifically for subsea context, this thesis intends to be a part of filling that gap. The models main objective is to evaluate subsea production system risk and to determine the appropriate safety Integrity level (SIL) for all present independent protection layers. The method is semi-quantitative in nature, which means that the model output is based on a combination of generic statistical data, expert judgement and logical reasoning. According to the model validation, the result seems to be credible due to what is economically and technically feasible. For example, when a single satellite well subsea system was evaluated it ended up with SIL3 requirements for the “isolation of well function” and lower SIL requirements for other less critical safety functions.