Establishment of a Quantitative Risk-Based Approach for Evaluation of Containment Performance in the Context of Permanently Plugged and Abandoned Petroleum Wells

Abstract

Abstract A large number of offshore oil and gas wells need to be plugged and abandoned on the Norwegian Continental Shelf in the coming decades, implying significant costs to the industry. To develop a methodology for evaluation of the quality of the barrier system of permanently plugged and abandoned wells from a risk perspective, the research project "Leakage risk assessment for plugged and abandoned oil and gas wells" has been initiated. The chosen quality measure to quantify containment risk in this context is the "leakage risk" expressed in terms of probability of barrier failure and potential future leakage rates. Reviewed papers consist of fragmented contributions to a complete framework for leakage risk assessment of plugged and abandoned wells. However, they do not provide a complete risk assessment framework with a corresponding detailed analysis. Without such a framework, regulations will be limited to prescriptive approaches. As an alternative to the currently prescriptive approach to plug and abandonment operation, this article presents how a risk-based approach can be used in practice by incorporating assessments of probability of leakage and the consequence (leakage rate), as well as uncertainty quantification. A comprehensive methodology and workflow, encompassing required steps for risk-based evaluation of containment performance, is established and presented in the paper. It is shown that this approach can provide a quality measure for a given plug and abandonment design and subsurface conditions.