Legacy plugged and buried wells: A limited contribution to Germany's methane emissions

Methane (CH 4 ) emissions from abandoned oil and gas wells are increasingly recognized as potential contributors to anthropogenic greenhouse gas inventories. However, empirical data regarding the long-term integrity of plugged and buried wells in Germany remains sparse. This study aims to quantify CH 4 fluxes from legacy wells in Lower Saxony (Northern Germany) to evaluate their environmental relevance. We conducted a field survey of 92 wells. The study design employed a multi-tiered approach, integrating surface flux measurements with soil gas analysis. To distinguish between deep thermogenic leakage and shallow biogenic signals, we analyzed soil gas compositions (hydrocarbons, CO 2 ) and stable carbon isotope ratios at both, well locations and reference grids. Statistical analysis reveals no significant differences in methane concentrations or flux rates between well locations and reference sites. Of the 92 wells examined, 20 showed at least one positive emission at the surface. Only 3 indicate time-varying and low leaking of natural gas (max 40 mg/h/well); two revealed an anomaly (possible shallow biogenic gas) and the remainder are considered natural background levels or are caused by other processes (e.g. peat mining). The findings suggest that plugged and buried wells in Germany do not reveal systemic integrity failures and indicates that abandonment practices are effective. Further, microbial methane oxidation in the vadose zone may also serve as an efficient natural filter. While caution is warranted when upscaling these results to the >25,000 legacy wells nationwide, this study implies that these features represent a limited contribution to Germany’s methane emissions.