Parliamentary Questions Prompted This Investigation
The research was conducted in response to questions asked by the House in 2017 and 2020 about alarming reports in earlier German research on leakage from abandoned wells. This concluded on the basis of research in the Norwegian and English North Sea that all (100%) abandoned wells drilled through shallow gas would leak methane. Wells drilled near shallow gas also leaked methane more often. They also found that 1 in 3 wells was drilled through shallow gas. From this, they concluded that in the entire North Sea, one-third of all wells leak.
Shallow Gas
Shallow gas is found in loose sand and clay up to a depth of one kilometer. Natural gas is usually extracted at depths of three to four kilometers. In order to find these gas fields, sometimes drilling through the shallow gas is also done. Many of these wells are closed off and abandoned after drilling because no deep gas was found.
This Research 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, 33 of which were drilled through shallow gas. In 6 of the 33 wells, methane from shallow gas deposits appeared to be escaping. That is less than 20% (and not 100%, as the German study suggested for the Norwegian and English parts of the North Sea). Wells drilled near shallow gas did not leak. When these figures are extrapolated, less than two percent of the abandoned wells in the Dutch part of the North Sea leak methane from shallow gas deposits.
Potent Greenhouse Gas
The consequences of leaking methane could potentially be significant. Methane is a much stronger greenhouse gas than CO2. However, the researchers conclude that the consequences of this limited number of leaking wells are probably minor. In the area, shallow gas also bubbles up naturally from the seabed. Compared to this natural source, the number of bubble plumes observed at the abandoned wells was much smaller. The precise size of the methane leaks will still be measured.
