Qualification of Bismuth-Based Plugs for Plugging and Abandonment: Where Do We Stand?

The surge in plugging and abandonment (P&A) activities has led to an “arms race” of new sealing technologies being developed and deployed in the field. In this context, alternative materials have been proposed to replace - partially or fully - cement as a barrier material considering uncertainties over its long-term sealability. One of them is bismuth, a unique metal that expands when solidified, providing mechanical bonding with tubulars to ensure that permanently abandoned wells will not leak in the future. In this context, the qualification of this technology is mandatory for approval by regulators for widespread field use. In this work, we assess the current qualification status of bismuth-based plugs, discussing where they stand regarding the industry’s existing standards and best practices. This is achieved by addressing three different qualification criteria: a TRL scale view, proposed by DNV and Norsk Olje og Gass; a well barrier element view, proposed by the NORSOK D-010; and a risk-based view, proposed by Offshore Energies UK (OEUK). The three methodologies and their status are discussed. We conclude that the technology is mature despite being novel and has been field-proven for a particular combination of bismuth alloy, application, and deployment method, thus requiring more efforts to extend the technology’s suitability and applicability in other well scenarios, using other alloys and deployment methods, and documenting potential failure modes.