Boreholes present in the North Sea could possibility constitute a significantly more important source of methane, a strong greenhouse gas, than earlier thought. This has been established by a new study of the GEOMAR Helmholtz Centre for Ocean Research Kiel recently featured in the international peer-reviewed journal Environmental Science & Technology.
The authors explain that huge amounts of methane are discharged from the sediments surrounding boreholes, probably over long time periods.
Oil production platform in the North Sea. Photo: L. Vielstädte, GEOMAR.
The pictures were circulated all over the world. In April 2010, large amounts of methane gas escaped from a well beneath the Deepwater Horizon platform in the Gulf of Mexico. This "blow-out" resulted in an explosion, causing the death of 11 people. Oil spilled from the damaged well into the ocean for several weeks. Such catastrophic "blow-outs" are fortunately rather rare. Nonstop discharges of smaller amounts of gas from old or active and abandoned wells occur very often.
New data has been published by Scientists from GEOMAR Helmholtz Centre for Ocean Research Kiel and the University of Basel in the international journal Environmental Science & Technology. The data indicates that gas migration along the outside of wells could be a much greater problem than earlier assumed. This type of leakage is currently neither considered by regulators or operators, but could be as vital as fugitive emissions via damaged wells, which are generally recognized and rapidly repaired.
We estimate that gas leakage around boreholes could constitute one of the main sources of methane in the North Sea.
Dr. Lisa Vielstädte from GEOMAR, the first author of the study.
The scientists discovered a number of methane seeps around abandoned wells during expeditions to gas and oil fields in the central North Sea in 2012 and 2013. It is interesting to note that the gas originates from shallow gas pockets buried less than 1,000 meters below the seabed. They are just penetrated when drilling into the underlying, economically remarkable hydrocarbon reservoirs.
These gas pockets usually do not pose a risk to the drilling operation itself. But apparently disturbing the sediment around the well enables the gas to rise to the seafloor.
Dr. Matthias Haeckel from GEOMAR, who initiated the study.
Seismic data obtained from the subsurface of the North Sea further illustrate that about one third of the boreholes perforated shallow gas pockets and are thus possible of leaking methane.
Considering the more than 11,000 wells that have been drilled in the North Sea, this results in a fairly large amount of potential methane sources.
Dr. Vielstädte who is currently based at the Stanford University in California, USA.
The team’s calculations reveal that shallow gas migration along wells could release almost 3,000 to 17,000 tons of methane from the North Sea seafloor every year.
This would reflect a significant contribution to the North Sea methane budget.
Methane is generally degraded by microbes in the ocean, thus locally acidifying the seawater.
About half of the wells in the North Sea are located in such shallow water depths causing the methane leaking from the seabed to reach the atmosphere, where it behaves as a potent greenhouse gas, which is considered to be much more efficient than carbon dioxide.
Natural gas, thus methane, is often praised as the fossil fuel that is most suitable for the transition from coal burning towards regenerative energies. However, if drilling for gas leads to such high atmospheric methane emissions, we have to rethink the greenhouse gas budget of natural gas.
Kiel’s research vessel POSEIDON will explore further gas seeps in the vicinity of gas and oil wells in October in order to better quantify the human impact on the methane budget of the North Sea.