Seepage Mechanisms Near Offshore Wells: Understanding Contributing Factors

Abstract Greenhouse gases, particularly methane, pose significant environmental risks due to their contribution to climate change, ocean acidification, and broader ecological degradation. These emissions can originate from natural marine seeps or leakage from hydrocarbon wells, making it crucial to assess the effectiveness of PP&A in preventing anthropogenic leaks. This review first examines PP&A regulations, noting their alignment with recent governmental guidelines, including the EU rules from November 2023. Subsequently, we analyze diverse PP&A case studies to highlight operational variations between wells. The critical impact of shallow gas zones on cementing integrity is addressed, along with a clarification of the inconsistent definition of "shallow." Finally, we identify and discuss conflicting studies on methane leakage from abandoned wells, examining debates surrounding drilling-induced fractures versus well integrity failures and the potential overestimation of anthropogenic contributions. Our findings underscore significant uncertainties and conflicting evidence in the current understanding of methane leakage. Therefore, we recommend implementing pre-drilling baseline surveys and systematic before-and-after comparisons of emissions at well sites to accurately differentiate anthropogenic leakage from natural background, thereby informing more effective well decommissioning strategies.