“Plug it and leave it! An investigation of the efficacy of plugs in abandoned hydrocarbon wells in the UK”

Abstract

Abandoned hydrocarbon wells represent a growing environmental and regulatory challenge for the United Kingdom. With decommissioning activity on the UK Continental Shelf expected to peak during this decade, ensuring that plugs provide durable zonal isolation is critical for meeting climate and safety commitments. Evidence of methane leakage from wells such as the Hardstoft 1 well demonstrates that certification at abandonment does not guarantee long-term integrity. Current UK practice, centred on AB3 classification, assumes plug permanence without statutory requirements for monitoring or lifecycle verification, raising significant questions of efficacy. This dissertation investigates plug efficacy in the UK through a desk-based comparative analysis. A three-pillar framework of prevention, detection, and accountability is applied to evaluate UK regulations, technical standards, and case evidence against international benchmarks. The study focuses on Saudi Arabia, Norway, and the United States, chosen for their contrasting strengths in material innovation, life cycle monitoring, and financial accountability. Secondary sources, including regulatory documents, peer-reviewed studies, and case data from 2011–2025, were systematically reviewed and coded against ISO 16530-1, NORSOK D-010, and U.S. Subpart Q requirements to identify structural gaps in the UK model. The findings show that the UK remains heavily reliant on Class G cement plugs, procedural certification, and cost-recovery limits that discourage innovation. By contrast, Saudi Arabia advances resin and cement-free systems, Norway mandates dual-barrier design with lifetime liability, and the United States enforces regulator-witnessed verification supported by bonding requirements. These models illustrate pathways to stronger plug efficacy that the UK could adapt. The study concludes that UK well abandonment practices are procedurally compliant but not performance-assured. Strengthening post-abandonment monitoring, enabling material innovation, and embedding accountability mechanisms are necessary to align UK practice with global standards and Net Zero targets.