The Impact of High-Resolution Biostratigraphy on Reservoir Prediction and Basin History--A Barents Sea Case Study

HUSMO, TORE, Esso Norge, Forus, Norway, and PETER HOCHULI, Esso Rep, Bordeaux, France

The Hammerfest Basin is bounded by the Troms-Finnmark Platform to the south and the Loppa High to the north. Twenty-seven exploration wells have been drilled in the basin since 1980. The objective for most of these wells was Middle Jurassic fault blocks. Until recently little attention has been paid to the Upper Jurassic to Lower Cretaceous synrift sequence.

The first well drilled on Block 7120/10 tested a rotated Jurassic fault block. This well, together with two wells in an adjacent block, penetrated thin Lower Cretaceous sands near the distal pinch-outs of fault wedges. Seismic data indicated that a basinal wedge of equivalent age was present on Block 7120/10.

High risk was put on the presence of sand in this basinal wedge, and a detailed biostratigraphic analysis was performed on wells along the basin margin in order to determine the timing of erosion on the margin and whether the Jurassic-Triassic coarse clastics were present in the provenance area.

The analysis separated reworked from in-situ palynomorph assemblages in the synrift succession in the analyzed wells. A clear inverted stratigraphy was displayed by the reworked palynomorphs. Furthermore, a dramatic increase in reworked palynomorphs was observed in all wells at the onset of Valanginian. In particular the presence of Nannoceratopsis gracilis suggested that shallow marine Jurassic clastics were eroded at this time.

Sand presence was predicted for the basinal wedge. The understanding of the basin history was also improved. Well 71Z0/10-2 drilled summer 1990 proved the success of the reservoir prediction

and hence the usefulness of incorporating biostratigraphy in the assessment.

AAPG Search and Discovery Article #91007© 1991 AAPG International Conference, London, England, September 29-October 2, 1991 (2009)