Risk-informed decision-making with an improved risk-based approach to evaluate plug and abandonment designs

Abstract

A risk-based approach has been established to evaluate the quality of plug and abandonment oil and gas well designs that differ from the regulatory requirements on the Norwegian continental shelf. A move away from the prescriptive requirements to a more performance-based approach implies a reliance on the risk-based approach's ability to treat and reflect all the relevant uncertainties. The quality measure in this context is the leakage risk, expressed in terms of failure probability and the associated leakage rate, where uncertainties are treated by probability distributions. It is reasonable to question whether the probability distributions provide adequate representations of all the relevant uncertainties. To improve the current risk-based approach, we propose an improved approach that complements the probability distributions by highlighting the uncertainties rather than the probabilities, assesses the risk of deviation from the assumptions and reflects the knowledge-base.