About This Item
Share This Item
The Cormorant oil field containing 1.5 billion bbl of oil in place, is situated in the United Kingdom sector of the northern North Sea. The reservoir comprises Middle Jurassic Brent Group sandstone in a westward tilted fault block. The top seal is provided by Upper Jurassic shales. The Brent Group consists of several units, which represent a single large-scale regressive and transgressive sequence of a northerly prograding delta complex.
The structure style is a product of two tectonic phases, one dominated by wrench tectonics and a subsequent one which created the westward-dipping faults blocks. This has resulted in a complex field consisting of four separate fault-bounded blocks. Each has distinctive characteristics and problems associated with varying internal geometry and sedimentology.
Block IV, resulting from crestal collapse, is internally faulted and displays a number of elongate subblocks, which are bounded by a complex interactive suite of faults. Three-dimensional seismic coverage has not allowed adequate resolution of this complex faulting. Delineation of sub-blocks is critical as development has shown that many faults are sealing.
Block II, southwest of the main culmination, presents problems of a sedimentological and structural nature. Production history shows the existence of barriers within the reservoir, probably associated with small-scale faulting, the sealing caused by juxtaposition, and/or clay smearing.
There is also evidence of permeability reduction with increasing depth. Kaolinite is the predominant clay mineral within the reservoir, whereas illite may be present in small quantities in the water-bearing zone; this differential impairment has an effect on development strategy.
End_of_Article - Last_Page 315------------