In the North Sea, fewer wells are leaking methane than expected

Less than two percent of abandoned wells in the Dutch part of the North Sea are leaking methane, which comes from shallow gas accumulations. This conclusion was reached by researchers from NIOZ and TNO in collaboration with the Dutch state mining regulator SodM, published in Marine and Petroleum Geology. The result of this study allays concerns from previous German research, which concluded that a third of all wells were leaking methane from near-surface gas accumulations.

The investigation was carried out in response to questions from the Dutch Parliament in 2017 and 2020 about alarming reports following previous German investigations into leaks from disused wells. These reports concluded, based on research in the Norwegian and English North Seas, that all (100%) abandoned wells drilled through near-surface gas (methane) would leak methane. Wells drilled near surface gas also leaked methane more frequently. They also found that one in three wells were drilled through near-surface gas. From this they concluded that shallow gas is emerging from a third of all wells in the entire North Sea.

Shallow gas occurs in loose sand and clay to a depth of one kilometer. Natural gas is usually produced at depths of three to four kilometers. To find these gas fields, wells are sometimes drilled through near-surface gas. Many of these wells become plugged and abandoned after drilling because deep gas was not found.

There are 1,450 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 near-surface gas (and not 1 in 3). For this study, we visited 57 of these abandoned wells with the research vessel RV Pelagia, 33 of which were drilled through near-surface gas.

Six of the 33 wells showed methane leaks from near-surface gas deposits. That is less than 20% (and not 100%, as the German study for the Norwegian and English parts of the North Sea suggests). Wells drilled near surface gas (8) did not leak. Extrapolating these numbers, less than two percent of abandoned wells in the Dutch part of the North Sea are leaking methane from near-surface gas deposits.

In principle, the consequences of a methane leak can be major. Methane is a much more potent greenhouse gas than CO₂. Still, the researchers conclude that the consequences of this limited number of leaky wells are likely small. Natural leaks of near-surface gas also occur frequently in the area.

Compared to this natural spring, the number of bubble plumes observed at the abandoned wells was much lower. The exact extent of the methane leaks is still being measured.