R. Hesketh and J. R. Underhill

Dept. of Geology and Geophysics, The University of Edinburgh, Grant Institute, Kings Buildings, West Mains Road, Edinburgh, U.K.

ABSTRACT: Biostratigraphic Calibration and Sequence Stratigraphic Interpretation of the Upper Jurassic Succession of the North Sea: Implications for the Spatial and Temporal Correlation of Clastic Reservoirs

The Outer Moray Firth forms part of the western arm of the North Sea trilete rift system. Upper Jurassic clastic reservoirs from this part of the basin are highly productive, with hydrocarbon accumulations in excess of 2 billion bbls in the Witch Ground Graben area alone. In the 1980’s, exploration drilling of blocks 15/21 and 15/22 by Amerada Hess Ltd yielded a number of cored sections through both the Kimmeridge Clay Formation (the principle source rock throughout the North Sea Basin) and the stratigraphically older, highly prospective, clastic reservoir units of the Humber Group. Inhouse examination of these cored sections revealed that a number of intercalated shale units from within the reservoir intervals contained ammonites of varying states of preservation and completeness. Further analyses suggested that a conflict existed between the age of these reservoirs based on datings derived from these ammonites and consultancy-based palynological studies. Brealey (1990) cited extended ranges of key dinoflagellate cyst (‘dinocyst’) taxa within block 15/21 as the cause of the two apparently incompatible biostratigraphic schemes. This led to a revision of the Upper Jurassic biostratigraphy for these blocks. Boldy & Brealey (1990) used this revised, ammonite -based stratigraphy to reinterpret the tectonic and depositional histories of this part of the North Sea Basin.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado