Upper Jurassic basin axial turbidites within the Gertrud Graben, Danish Central Graben

For more than twenty years, the Jurassic succession in the Danish Central Graben has been subject to intense exploration for hydrocarbons. Approximately 43 wild-cats have been drilled and most of these tested structural traps located on footwall crests. The reservoirs encountered were Middle and Upper Jurassic sandstones deposited mainly in nearshore depositional environments. Some of these wells penetrated thin turbidites of Late Jurassic to Early Cretaceous age. Within the Gertrud Graben distinct seismic anomalies indicate the presence of basin floor turbidites, which can be correlated to fan fringe turbidites encountered in the Jeppe-1, Gwen-2 and Mona-1 wells. Seismic inversion provides additional evidence of sandstone deposits in the zone characterized by high acoustic impedance. The turbidites are located within the axial zone of the NW–SE trending Gertrud Graben. Southward the turbidites pinch out gradually; the northern limit of the deposits (in Norwegian territory) is unknown. The deposition of the turbidites is interpreted to be associated with a lowstand of sea-level when conditions were favourable for deposition of coarse-grained deposits in basinal areas. The sediments were probably sourced from an area to the north. Basin axial turbidites are well-known phenomena in various basins. They are not always associated with structural closures and consequently constitute a high risk exploration target. However, in mature basins such as the Danish Central Graben this type of play should be considered in future exploration.