--> Abstract: The Use of Quantified, High Resolution Biostratigraphical Data to Resolve Detailed Reservoir Sequence Stratigraphy: The Troll Field -- A Case Study, by L. Bolle and M. Foley; #90987 (1993).

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BOLLE, LUCIEN, and MARY FOLEY, A/S Norske Shell, Tananger, Norway

ABSTRACT: The Use of Quantified, High Resolution Biostratigraphical Data to Resolve Detailed Reservoir Sequence Stratigraphy: The Troll Field -- A Case Study

The super-giant Troll Field is located approximately 80 km offshore

the Norwegian mainland on the north-western edge of the Horda platform adjacent to the eastern margin of the Viking Graben. A revised sedimentological model has been developed by integrating probabilistically quantified biostratigraphical data with sequence stratigraphical techniques.

The Callovian to Volgian age Viking Group reservoirs, the Fensfjord, Heather, and Sognefjord formations, were deposited on a shallow marine shelf during the overall sea-level rise in the upper LZA supercycle. The multi-cycle sequence comprises an alternating and interfingering stack pattern of siltstones and fine micaceous to coarse clean sandstones, but is void of any shale or claystone interbeds.

Due to the large areal extent of the field (710 km sq.), and the absence of clear shale breaks between the stacked sequences, biostratigraphical techniques are essential for the construction of a valid correlation framework.

A detailed reservoir stratigraphy over the up to 250 meter thick hydrocarbon bearing reservoir was constructed by reconciling the observations of almost 5000 palynological samples from 28 wells in the field into a single PC-based database.

A quantitative biostratigraphic computer program was used to derive a probabilistic, Most-Likely-Sequence, of Bio-Events scaled in relative band a graphical correlation program was used to extend the biozonation to a Composite Standard Sequence between all wells. The technique used all recorded bio-events to create a field-wide high resolution biostratigraphical framework.

Guided by the field-wide probabilistic biostratigraphical framework representing relative time-lines, the reservoir interval was broken down into "Inter-Maximum-Flooding Surface" intervals. These were then further subdivided into sequence tracts.

Although the overall correlation pattern has not changed dramatically compared to prior zonations, some intervals, previously thought to be diachronous, are now shown to be contemporaneous. This results in a refined depositional history model and allows the construction of a more realistic reservoir architecture model.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.