Organic Facies Mapping and Modeling of the Viking Group (Middle Jurassic-Earliest Cretaceous), Northern North Sea

KANGAS, REIJO J., University of Bergen, Bergen, Norway

The organic facies are mapped and modeled here using an exploration-oriented, geological approach where geological and geophysical data are integrated with organic petrological and petroleum geochemical data. The aim is to come up with a comprehensive model/models to explain the observed organic facies distribution patterns and variations both vertically and laterally in relation to the palaeoenvironmental changes.

The Viking Group is traditionally divided into the Heather Formation and overlying Draupne Formation, the Kimmeridge Clay Formation Equivalent, comprising the major oil and gas source rocks in the area and beyond. In this study, the formations are further subdivided into basin-wide correlatable units, the distribution patterns of which, as well as the sedimentation rates for decompacted units calculated, are then mapped in space and time. The factors governing the sediment distribution patterns and the vertical transgressive-regressive trends observed are discussed.

The vertical and lateral changes in the quantity and quality/type of the organic matter present is studied in selected wells. The organic petrographical techniques, especially the quantitative maceral analysis on whole-rock polished blocks, have turned out to be of irreplaceable significance in identifying and characterizing different organic facies and in integrating geological concepts and observations with geochemical data.

Organic facies models are proposed and discussed. The models are basically of two types, where either a physically induced organic matter preservation alone is critical or where the better organic matter preservation is brought about by high primary productivity in the photic zone. In this study, it is realized that more complex combined-type models are often more valid.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)