Inventory of wells through shallow gas layers in the Dutch North Sea
During a dertigledendebat on the 14th of November 2017 regarding a new gas discovery to the North of Schiermonnikoog, the House of Representatives called attention, amongst others, to methane emissions related to gas production. This debate referred to recent publications by Vielstädte et al. (2015, 2017). These publications state that wells penetrating sediments containing biogenic shallow gas leak behind the casing of the borehole, thereby releasing 3,000 to 17,000 tons (= 1,000 kg) of methane per year into the North Sea. Apart from this, SodM visited a symposium (on 21 and 22 March 2018) of the EUOAG (EU Offshore Authorities Group) with a technical workshop and amongst others a presentation of the Vielstädte publications.
Subsequently, SodM decided on the 18th of June 2018 to assign TNO-AGE for a study specifically for the Dutch part of the North Sea. The details of the assignment can be found in the Minister's response (11 October 2018) to the earlier parliamentary question of the dertigledendebat. SodM requested TNO-AGE to determine whether the above-mentioned geological conditions can also occur on the Dutch Continental Shelf and which wells are drilled through 'shallow gas'.
Using seismic interpretation and well data, TNO-AGE compiled a list of wells in the Dutch North Sea that pierce through shallow gas. The presence of gas in shallow sediments causes anomalies (bright spots) in seismic data. In addition, gas can be observed during drilling. The analysis of bright spots and drilling data shows that about 10% of the wells pierce through shallow gas (216 of the 2027 offshore wells).