--> Abstract: Large-Scale Clastic Intrusion in the Tertiary of Block 24/9, Norwegian North Sea: Origin, Timing and Implications for Reservoir Continuity, by D. A. Lawrence, B. Sancar, and S. Molyneux; #90923 (1999)

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LAWRENCE, DAVID A., BERAT SANCAR, Fina Exploration Norway S.C.A., Stavanger, Norway, and STEPHEN MOLYNEUX, Imperial College, London, United Kingdom

Abstract: Large-Scale Clastic Intrusion in the Tertiary of Block 24/9, Norwegian North Sea: Origin, Timing and Implications for Reservoir Continuity

Recognition of a kilometre-scale clastic intrusion complex has questioned conventional ideas on stratigraphic correlation, lead to new hydrocarbon plays, and challenged reservoir modelling and oil drainage strategies.This radial injection feature is interpreted as an isolated turbidite sand which overpressured soon after deposition, resulting in 'explosive' injection as a giant-scale clastic dyke/sill complex.

Clastic dykes and sills are documented from 3D seismic, dipmeters and cores in Tertiary clastics in the axis of the South Viking Graben. Sandstones supplied from the west were confined in a fault-bounded low, and are up to 40m thick, deposited from sand-rich debris flows or high density turbidity currents. Oil encountered in massive sandstones corresponds to high amplitude seismic response.

Modification of depositional geometry is evident at all scales. Seismic data shows flat lying, continuous reflectors passing upwards at the margins of the sand body into steeply dipping high amplitude reflectors along fault planes, cross-cutting up to 200m of stratigraphy, and subsequently passing into bedding-parallel Eocene strata. The top of the reservoir is complexly faulted, and detailed mapping using Coherence Cube horizon slices, and dipmeter data, reveals isolated shale rafts and complex polygonal faulting. Discordant sandstone dykes, shear fractures and compactional features in core also suggest early sand remobilisation.

Proven oil reserves are marginal, but untested upside in the form of injected sandstones could form a connected reservoir, cross-cutting stratigraphy. If successfully appraised, field development would be optimised by locating producing wells in the higher injected portions, draining connected reservoirs lower in the intrusive complex.

AAPG Search and Discovery Article #90923@1999 International Conference and Exhibition, Birmingham, England