Reservoir Architecture Modeling of the Cook Formation, Oseberg Field, Offshore Norway: Integrated Analysis of Core, Well Log and Seismic Data

Marinus E. Donselaar¹, Rory Dalman¹, Tom Dreyer², Steen Agerlin Petersen², R.A.J. Thomassen¹, and Gerrit Toxopeus^1
1 Delft University of Technology, Delft, Netherlands
² Norsk Hydro Research Centre, Bergen, Norway

The Early Jurassic Cook Formation (Oseberg field, offshore Norway) is the focus of a new integrated technique of reservoir architecture modeling and simulating prestack depth-migrated and constrained sparse-spike inverted data. The goal is to visualize the geometry and spatial distribution of the reservoir units. Located beneath the Brent reservoir, the Cook Formation has potential as a secondary reservoir in the Oseberg field. Tidal bar sandstones deposited in a funnel-shaped estuarine environment comprise the reservoir units. The lithofacies types, facies model, sequence stratigraphy, and large-scale sedimentary architecture framework were interpreted from core and wire-line log analysis and correlation. Spectral analysis of the wire-line logs was used to determine progradational and retrogradational trends in the Cook succession.

The prestack time-migrated seismic data show very specific inclined discontinuous reflectors in the Cook Formation which are the expression of the large tidal bar accretion surfaces. Log-derived values were assigned to the tidal bar facies model, and a newly developed simulation technique based on a spatial resolution function, allowing very compute efficient simulation of prestack depth-migrated and constrained sparse-spike inverted data, was used to convert the facies model to 2D simulated prestack depth-migrated and inverted data. Comparison with the real data show promising results that warrant further evaluation of the geological data. The facies model resulting in the best fit of synthetic and real seismic and inverted data then yields a high-resolution visualization of the reservoir unit geometry and the intrinsic properties of the layers.