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Camilla Thrana, StatoilHydro ASA (Norway)
Mali Brekken, StatoilHydro ASA (Norway)
Arve Nęss, StatoilHydro ASA (Norway)
Simon Leary, StatoilHydro ASA (Norway)
Stuart Gowland, Ichron Limited (United Kingdom)
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The Jurassic reservoirs of the Heidrun Field, offshore Mid-Norway, have so far produced over 114 MSm3 of oil. The oil recovery of the fluviodeltaic (Rhaetian-Sinemurian) Åre Formation is the lowest among the reservoir formations, which makes this an important stratigraphic interval when it comes to remaining reserves and IOR potential. In order to address challenges related to stratigraphic correlation and detailed reservoir modelling, a major core and wireline log based reservoir characterisation study of the Åre Formation has been performed. Main results from this study include a new facies description and interpretation, and a revised stratigraphic reservoir zonation. The new stratigraphic framework defines seven main zones, reflecting the overall transgressive development of the Åre Formation; from non-marine coastal plain in the lowermost part (Åre 1 - 2), marginal-marine lower delta plain in the middle (Åre 3 - 5) and finally tidally-dominated estuarine and open marine in the uppermost part (Åre 6 - 7).
These zones represent packages of genetically linked facies, bounded by field-wide, correlateable key surfaces. The bounding surfaces are typically characterised by extensive mudstone intervals displaying distinct wireline log signatures, and have been interpreted to represent candidate flooding surfaces. Sub-division of this stratigraphic framework produced 17 reservoir zones, enabling better and more accurate predictions of the distributions and geometries of hydrocarbon bearing facies.
The implementation of the new reservoir zonation in the Heidrun Field was completed in 2007. All the 90 wells with Åre Formation stratigraphy have been re-interpreted, and this new stratigraphic framework has been applied in a recent update of the full-field geological model. This new reservoir zonation scheme has proven to be more robust than previous models and has provided a good platform for improved stratigraphic control during drilling operations. Long-term benefits would also include more precise production forecast, better drainage strategies and well solutions. In addition, the new concepts of the Åre Formation geology are easier to communicate and allow for improved inter-discipline collaboration in the production asset.
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