Fewer leaking wells in the North Sea than expected

Less than two percent of the abandoned wells in the Dutch part of the North Sea are leaking methane originating from shallow gas accumulations. That conclusion is reached by researchers from NIOZ and TNO, in collaboration with the Dutch State Supervision of Mines, SodM, published in Marine and Petroleum Geology on 12 November 2024. The outcome of this study alleviates concerns from earlier German research that concluded that one-third of all wells would leak methane from shallow gas accumulations.

Parliamentary questions prompted this investigation

The investigation was conducted in response to questions raised by the Parliament of the Netherlands in 2017 and 2020 about alarming reports following earlier German research on leakage from abandoned wells. Those reports concluded, based on research in the Norwegian and English North Sea, that all (100%) abandoned wells drilled through shallow gas (methane) would leak methane. Wells drilled near shallow gas also leaked methane more often. They also found that 1 in 3 wells were drilled through shallow gas. From this, they concluded that across the North Sea, one-third of all wells leaks shallow gas.

Shallow gas

Shallow gas is found in loose sand and clay up to one kilometer deep. Natural gas is usually extracted at depths of three to four kilometers. To find these gas fields, wells are sometimes drilled through shallow gas. Many of these wells are plugged and abandoned after drilling because no deep gas was found.

This study shows that the number of leaking wells is lower

There are 1450 abandoned Dutch wells in the North Sea. Based on subsurface mapping, we know that in the Dutch North Sea, only 1 in 10 wells were drilled through shallow gas (and not 1 in 3). For this study, we visited 57 of these abandoned wells with the research vessel RV Pelagia, of which 33 were drilled through shallow gas. Six of the 33 wells showed methane escaping from shallow gas deposits. That is less than 20% (and not 100% as the German survey suggested for the Norwegian and English parts of the North Sea). Wells drilled near shallow gas (8) did not leak. When these figures are extrapolated, less than two per cent of abandoned wells in the Dutch part of the North Sea leak methane from shallow gas occurrences.

Strong greenhouse gas

In principle, the consequences of leaking methane can be large. Methane is a much stronger greenhouse gas than CO₂. Yet the researchers conclude that the consequences of this limited amount of leaking wells are likely to be minor. In the area natural seepage of shallow gas is also common. Compared to this natural source, the number of bubble plumes observed at the abandoned wells was much smaller. The exact extent of the methane leaks will still be measured.