ABSTRACT: The Geology and Geophysics of the Everest Complex, Central North Sea

P. J. Thompson, P. D. Butcher

The gas condensate Everest Complex lies on the eastern margin of the North Sea Central graben in UKCS blocks 22/5a, 22/9, 22/10a, and 22/14a. The complex was discovered in 1982 by well 22/10a-2 and has been delineated by seven other successful appraisal wells. The hydrocarbons are trapped within two reservoirs formed of submarine fan sandstones of the Paleocene Montrose Group. The primary reservoir comprises turbiditic sandstones of the Forties Formation laid down in an inner to middle fan setting. Paleotopographic control of sand deposition is well illustrated by seismic stratigraphy that shows the development of a bifurcated sandstone fairway on the flanks of the Jaeren High with a major channel-lobe feature in the southwest, apparently separated from a more lobate body in the northeast by a northwest-southeast-trending paleotopographic high. The trapping mechanism in both fairways is a combination of sandstone shale-out and downdip structural closure. Mapping suggests the presence of two separate Forties traps, known as North and South Everest, although pressure data imply connectivity.

The sandstones of the underlying Andrew Formation, deposited in a more distal middlt to outer fan setting, provide the reservoir in the accumulation known as East Everest. A combination of stratigraphic pinch-out over the Jaeren High to the northeast and downdip closure to the west provides the trapping mechanism for this field. The internal stratigraphy of the Andrew Formation is complex and, although pressure data indicate vertical reservoir connectivity, log analyses and drill-stem test results suggest the presence of three gas layers and an oil rim.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990