Abstract The most important North Sea Jurassic–lowermost Cretaceous lithostratigraphic units, as developed in the UK, Norway and Danish sectors, are summarized in this chapter (55 units from the UK, 25 from Norway and 10 from Denmark). Some significant issues remain with the use and application of lithostratigraphic terminology in the Jurassic of the North Sea Basin. In particular, there are inconsistencies in unit definition and nomenclature changes across country sector boundaries that obscure the recognition of regional stratigraphic patterns that exist across the region. To aid clarity and to overcome some issues of definition, some revisions are made to the existing lithostratigraphic schemes. Several informal lithostratigraphic units are described, a number of unit definitions are revised and various formerly informal units are formalized (Buzzard Sandstone Member, Ettrick Sandstone Member and Galley Sandstone Member). It is recommended that use of the Heno Formation in offshore Denmark is discontinued. In addition, four new lithostratigraphic member terms are introduced (Home Sandstone Member, North Ettrick Sandstone Member, Gyda Sandstone Member and Tambar Sandstone Member). All described units are placed into a sequence stratigraphic context. All significant lithostratigraphic boundaries conform with key sequence stratigraphic surfaces.

Abstract The Penguins Cluster of fields are owned jointly (50:50) by Shell UK Ltd (Shell) and Esso Exploration and Production UK Ltd (Esso), with Shell as the operator. The cluster was discovered in 1974 and is composed of a combination of oil and gas condensate accumulations located 50–65 km north of the Brent Field, at the northern end of the North Viking Graben. Two main producing reservoirs are present: the Penguins West Field (Penguin A) consists of an Upper Jurassic Magnus Sandstone Member reservoir, while the Penguins East Field (Penguin C, D and E) consists of a Middle Jurassic Brent Group reservoir, underlain by currently undeveloped Statfjord and Triassic (Cormorant) reservoirs. The Magnus reservoir is composed of turbidite sands with an average porosity of 15% and permeabilities of 0.10–300 mD. The Brent reservoirs are composed of deltaic shoreface deposits with an average porosity of 14% and permeabilities of 0.01–1000 mD. The fields were brought on stream in 2003 as a subsea development via what at the time was the world's longest comingled tieback to the Brent Charlie facility. A total of nine producing wells have been drilled from four subsea manifolds, producing c. 78 MMboe to date through depletion drive.