During expeditions to oil and gas reservoirs in the central North Sea in 2012 and 2013, scientists of the GEOMAR Helmholtz Centre for Ocean Research Kiel (Germany) discovered that methane bubbles emerged from the seabed around abandoned wells. The gas originates from shallow gas pockets, which lie less than 1000 meters deep below the seafloor and that were not the target of the original drilling operations. An initial assessment showed that these emissions could be the dominant source of methane in the North Sea.
A new study published by GEOMAR scientists in the International Journal of Greenhouse Gas Control, confirms this initial estimate on a larger data basis. ‘We have combined investigations at additional wells with extensive seismic data. The results clearly show that thousands of tons of methane are leaking from old drill holes on the North Sea floor every year,’ says the main author Christoph Böttner.
During expeditions the researchers were able to detect gas leakage at 28 of 43 directly investigated wells. ‘The propensity for such leaks increases the closer the boreholes are located with respect to shallow gas pockets, which are normally uninteresting for commercial use. Apparently, however, the disturbance of the overburden sediment by drilling process causes the gas to rise along the borehole,’ explains Matthias Haeckel who led the study.
The authors of the study encourage the industry to publish their data and recommend more independent emission measurements from abandoned wells in order to develop stricter guidelines and legally binding regulations for abandonment procedures.