The Slochteren No. 1 well discovered in 1959 what now is known as the Groningen gas field in the northern Netherlands. The field is on a culmination of the large, regional northern Netherlands high which was formed during the late Kimmerian tectonic phase (Late Jurassic-Early Cretaceous). However, there is some evidence that the structure was a positive element during earlier periods, i.e., during Triassic and possibly even late Carboniferous times.

The reservoir overlies unconformably the truncated and strongly faulted coal-bearing Pennsylvanian strata which are considered to be the main source of the Groningen gas. The reservoir, 300-700 ft thick, consists of fluviatile and eolian sandstone and conglomerate of the Rotliegendes Formation (Lower Permian). These coarse clastic beds are overlain by a few thousand feet of Permian Zechstein evaporites, notably rock salt and to a lesser extent anhydrite and dolomite, which constitute the very effective reservoir seal. Because of intensive salt movements, the thickness of the overlying Mesozoic and Cenozoic strata ranges from 3,000 ft to more than 6,500 ft.

The field covers 180,000 acres, and the reserves now are estimated at 58 trillion ft³. Present production potential is 2 billion ft³ of gas per day from nine "clusters" of about six closely spaced wells each. The favorable reservoir properties of the sandstone allow, at least for the present, drainage of the field from the structurally highest southern part.