Late Cretaceous basin development of the southern Danish Central Graben

Abstract

The Danish oil and gas production mainly comes from fields with chalk reservoirs of Late Cretaceous (Maastrichtian) and early Paleocene (Danian) ages located in the southern part of the Danish Central Graben in the North Sea. The area is mature with respect to exploration with most chalk fields located in structural traps known since the 1970s. However, the discovery by Mærsk Oil and Gas A/S of the large nonstructurally and dynamically trapped oil accumulation of the Halfdan Field in 1999 north-west of the Dan Field (e.g. Albrechtsen et al. 2001) triggered renewed exploration interest. This led to acquisition of new high quality 3-D seismic data that considerably enhanced imaging of different depositional features within the Chalk Group. Parallel to the endeavours by the operator to locate additional non-structural traps in porous chalk, the Geological Survey of Denmark and Greenland took advantage of the new data to unravel basin development by combining 3-D seismic interpretation of a large number of seismic markers, well log correlations and 2-D seismic inversion for prediction of the distribution of porous intervals in the Chalk Group. Part of this study is presented by Abramovitz et al. (in press). In the present paper we focus on aspects of the general structural development during the Late Cretaceous as illustrated by semi-regional time-isochore maps. The Chalk Group has been divided into two seismically mappable units (a Cenomanian–Campanian lower Chalk Unit and a Maastrichtian–Danian upper Chalk Unit) separated by a distinct basin-wide unconformity.