As we are risking to exceed the 1.5-degree target in the next decade, effective measures to cut back greenhouse gas emission are necessary. Methane became the focus of attention as the target to mitigate global warming, since the mean atmospheric lifetime of this strong greenhouse gas is at least an order of magnitude shorter than carbon dioxide. Here we will focus on the oil and gas sector, which represents the second largest anthropogenic methane source after agriculture. Abandoned oil and gas wells are seen as important targets, since they can (in some cases) emit up to several tons of methane per day. However, only about a dozen countries have measured data on methane emissions and even less include it in their yearly greenhouse gas inventory. Germany has about 20,000 abandoned wells, which are generally filled and buried, however, it is unclear, whether they are emitting methane or not.
Here, we present an overview of methane emission and microbial methane turnover at about 50 onshore oil and gas wells in Northern Germany covering both abandoned exploration and production wells. Using isotopic methane composition we were able to link the methane emissions at three well sites in an active peat-cutting area to methanogenesis. Furthermore, elevated potential methane oxidation rates suggest that the majority of the microbially formed methane was oxidized before reaching the atmosphere. Our data demonstrates the necessity for detailed knowledge on methane cycling and background emissions to assess abandoned wells, particularly in areas where natural methanogenesis is present.