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Recognition of
Preserved Beach-Ridges in the Etive Formation and Their Impact on the Dynamic
Reservoir Behavior of the Lower Brent Group in the Oseberg East Field,
Norwegian
Grünhagen, Henrike, Frede Bøen, Rolf Aasheim, Norsk Hydro ASA, Bergen, Norway
The well-known and frequently described Rannoch and Etive
Formations represent the prograding shore-line deposits of the economically
important Jurassic Brent Delta in
On geophysical attribute maps a set of 20-30 E-W trending
stripes cover an area of more than 10x10km. Around thirty wells on Oseberg East
and several further wells in the surrounding area confirm that the amplitude
anomalies are caused by rhythmic thickness variations within the Etive
Formation. While shoreface sediments are generally deposited as homogenously
thick sheet-sands, these bands of thick Etive formation are interpreted as
preserved beach-ridges that have formed along an E-W trending paleo-shoreline
during progradation of an extended strand plain. Seismic modeling indicates
that infill of the resulting paleo-topography with coals of the overlying Ness
Formation contributes significantly to the seismic response.
The presence of
the beach-ridges combined with significant vertical heterogeneities within the
Rannoch and Etive formations are complicating oil production from that zone on
Oseberg East. Attic oil is trapped in the beach-ridges while the underlying
coarse-grained and high-permeable foreshore facies acts as ‘thief-zone’ that
causes early water/gas breakthrough. This new understanding of the geometry
and sedimentology of the Etive Formation on Oseberg East is beeing implemented
into 3D facies, property and reservoir simulation models to investigate the
formation’s dynamic behavior and to plan wells that can increase oil-recovery.