Published jointly by the Netherlands Centre for Geodesy and Geo-informatics (NCG), SkyGeo and TU Delft, the map shows the movement of billions of measurement points across the entire country.
The accompanying website – in Dutch – allows people to zoom in to areas of interest and to plot subsidence data on a trendline, thereby gaining a better understanding of the rate of subsidence per area over the past four years.
Even the untrained eye would immediately spot the red area in the north-eastern part of the country. This is the area of the Groningen field, discovered in 1959 and in production since 1963.
Until 2012, relatively small earthquakes occurred in the vicinity of the Groningen field, but the 3.6 earthquake near the village of Huizinge triggered a raft of research into the effects of gas production and induced seismicity.
As the map shows, seismicity is not the only problem associated with the Groningen field; subsidence is another phenomenon that is a matter of serious concern. Subsidence in the centre of the field amounts to around 9 mm/year over the past four years, whilst the areas surrounding the field show values of around 2 mm/year. According to the NLOG website maintained by the Geological Survey of the Netherlands, the maximum total subsidence in the area of the Groningen field observed until 2016 was 33 cm.
What about smaller fields?
An interesting observation that can be made from the subsidence map is that although the Groningen field clearly shows the effects of gas production on land subsidence, smaller onshore fields would be much more difficult to discern on the basis of the map alone. This suggests that a certain reservoir size and volume are needed before the effects of production become a prominent feature at surface.
The combined effects of subsidence and seismicity has led the Dutch government to decide that after a period of reduced production, the Groningen field will cease to produce in 2022.
The Groningen gas field consists of eolian and fluvial sandstones of the Upper Rotliegend Group of Late Permian age. The reservoir is located at depths of between 2600 and 3200 m, where the thickness ranges from approximately 100m in south-southeast to approximately 300m in north-northwest. Initially, the field held an impressive 2,800 Bm3 or 99 TcF.