Natural fractures and sedimentology of a heterogeneous reservoir: The Valdemar Field, Danish North Sea

The Valdemar Field (Central Danish North Sea) is a heterogeneous reservoir, with a high abundance of natural fractures, producing from chalk units within the Lower Cretaceous Upper Hauterivian–Lower Albian Tuxen and Sola Formations. The Lower Cretaceous stratigraphic interval in the Danish North Sea is characterized by chalk, argillaceous chalk, marlstones and claystones with hydrocarbons trapped in the chalk reservoir units. The reservoir (chalk) sediments are characterized by high porosity and low matrix permeability, but the presence of natural fractures strongly influences the flow properties by enhancing the effective permeability, and ultimately increases recovery. Several types of natural fractures are recognized on core scale, and some of these form a potential hydrocarbon pathway as they can significantly enhance the natural permeability in the reservoir. This is a first study that conducts a detailed analysis of natural fractures in the Valdemar Field, and relate them to stratigraphy and facies. Furthermore it is considered whether certain fracture types occur more frequent in specific stratigraphic intervals. It is investigated whether the fracture-facies relationship can enhance hydrcarbon recovery.