Oil and Natural Gas in Northeastern Netherlands1
The Northeast Netherlands basin forms the western extension of the Northwest German basin; it is separated from the North Sea basin to the west by the Netherlands ridge," a northnorthwest-to south-southeast-trending barrier which lies in the north-northwest prolongation of the Geldern-Krefeld horst. This ridge is formed by an area in which a positive tendency prevailed during Upper Permian, Triassic, Jurassic, and Cretaceous time.
In the post-Carboniferous stratigraphy, five sedimentation cycles separated by folding phases can be distinguished. From old to young, these are—
1. Upper Permian-Triassic, followed by the Upper Triassic old Kimmeric folding phase.
2. Upper Rhaetic-Jurassic, followed by the Upper Jurassic (Malm) young Kimmeric folding phase.
3. Upper Jurassic-Neocomian (Portlandian-Aptian inclusive), followed by the Lower Albian folding phase.
4. Albian-Upper Cretaceous, followed by the Laramic folding phase.
Flowage of the Upper Permian rock salt played an important, though not exclusive, role in the folding of the anticlines in Northeastern Netherlands, several of which are Variscic in origin, the others being Saxonic.
Natural gas is produced from dolomitic members in the Upper Permian evaporites. The gas, here, was both generated and accumulated in the dolomites and their associated argillaceous deposits. Rock salt formed the sealing cap rock.
Where the rock salt seal is lacking, the Upper Permian gas has been dissipated through leakage, leaving only traces of dead oil shows. In the Wanneperveen-De Wijk and Staphorst gas fields, the dissipated gas re-accumulated in the basal beds—sands and sandy clays—of the Barremian, which here transgress over Lower Bunter. These gas fields occupy an area which, during the Cretaceous, formed a single gentle dome. Staphorst became a separate anticline during the Tertiary; the structures in the area acquired their present shape during the Pliocene. The youth of these structures, and the poor permeability of the reservoirs, together with the probable presence of zones of nonpermeability, may account for the gas-water table not lying in a horizontal plane.
In the Schoonebeek oil field middle Valanginian sands produce an oil with a gravity of 250 A.P.I. at a rate of 2,900 cubic meters per day.
Oil source rocks are to be found in the upper Liassic, perhaps also in the Portlandian and Wealden formations; furthermore, migration from a remote source is likely—that is, from the deeper parts of the Northwest German basin.
Migration of oil occurred in two phases—during the Neocomian, and then again from Albian to Upper Cretaceous. Accumulations in Northeastern Netherlands due to the earlier migration were destroyed during the pre-Albian erosion, leaving only traces of dead oil and, at Zweelo, a negligible amount of heavy oil; the accumulation at the Schoonebeek field is due to the later Albian-to-Upper Cretaceous migration.
The Schoonebeek structure is an eastward-plunging anticline; closure to the west is effected by the Albian unconformity.