Recognition and Correlation of Reservoir-Scale Permeability Barriers - an Ichnofabric Approach

BLIGHT, RICHARD D

n the highly bioturbated Jurassic sandstone reservoirs of Tartan Field (Outer Moray Firth, UK North Sea), a trace fossil approach is used to facilitate correlation of mud- and sand-dominated maximum flooding surfaces. Correlation of these surfaces is important as they may act as field-scale permeability barriers compartmentalising the reservoir. In Tartan Field there are three main problems prohibiting easy correlation: (1) the lack of a high-resolution biostratigraphic scheme over much of the interval; (2) variable erosional truncation at the top of the reservoir unit, which in places has removed several maximum flooding surfaces; and (3) large numbers of normal faults which may cut out substantial thicknesses of reservoir.

Maximum flooding surfaces are correlated through recognition of the ichnofabrics of both the surfaces and their underlying transgressive units. Proximal-distal trends along the surfaces, and hence the direction of pinchout of muddy units, can be calculated using changes in their associated ichnofabrics; for instance from Phycosiphon- to Teichichnus-dominated fabrics. This would not be possible using only lithofacies or ichnofacies schemes, which have lower resolution.

The basinwide maximum flooding surfaces of other North Sea workers are compared to the fieldwide permeability barriers recognised in Tartan in order to place the field in the wider context of Outer Moray Firth paleogeography. 

AAPG Search and Discovery Article #91021©1997 AAPG Annual Convention, Dallas, Texas.