AAPG Bulletin, V. 82, No. 9 (September 1998), P. 1627-1651.

High-Resolution Stratigraphy and Seismic Attribute Mapping of a Fluvial Reservoir: Middle Jurassic Ness Formation, Oseberg Field¹

Alf Ryseth,² Hege Fjellbirkeland,³ Inger Kloster Osmundsen,³ Åshild Skålnes,³ and Eli Zachariassen³

©Copyright 1998.  The American Association of Petroleum Geologists.  All Rights Reserved

¹Manuscript received November 21, 1996; revised manuscript received October 28, 1997; final acceptance March 19, 1998.
²Norsk Hydro Research Centre, Sandsliveien 90, N-5020 Bergen, Norway.
³Norsk Hydro Production, Sandsliveien 90, N-5020 Bergen, Norway.

We wish to thank Norsk Hydro Production and partners of the Oseberg Unit, Statoil, Saga, Mobil, Total and Elf, for permission to publish this manuscript. AAPG reviewers William Helland-Hansen and M. A. Uliana provided many useful suggestions to the original manuscript. 

ABSTRACT

Continental successions of alternating fluvial reservoir sandstones and fine-grained interfluvial deposits make hydrocarbon production planning and reservoir management difficult. The vertical and lateral distribution of fluvial sandstones within the surrounding nonreservoir rocks, in particular, is a critical factor that needs to be investigated before production or injection wells can be successfully drilled.

In the Oseberg field of the Norwegian North Sea, about 21.7 million Sm³ (standard cubic meters) of recoverable oil is stored within fluvial channel sandstones of the Middle Jurassic Ness Formation. The Ness Formation reservoir is characterized by a relatively low proportion of good-quality reservoir rocks (approximately 30% of the total rock volume). Sedimentological studies indicate that reservoir sandstone bodies are developed mainly as elongate, laterally restricted sandstone bodies concentrated within certain stratigraphic levels and geographic areas. Identifying and accurately mapping these sandstone-rich intervals are important in defining possible drilling targets.

The distribution of reservoir rock within the upper Ness Formation has been the focus of detailed geological and three-dimensional (3-D) seismic mapping. Inverted seismic data, integrated with geological well data, give an empirical correlation between acoustic impedance and sandstone proportion. In turn, these relationships provide the basis for defining areas with a higher probability of encountering reservoir sandstone. Subsequent production drilling into the Ness Formation has confirmed the existence of reservoir sandstones within areas defined by the integration of high-resolution stratigraphic mapping and the geophysical analysis. The integration of sedimentological and 3-D seismic techniques presently offers the best potential for defining drilling targets within the Ness Formation in the Oseberg field.