'Getting to Know Brenda': Core from a Stratigraphic Trap in a Paleocene Debris-Flow Deposit, Outer Moray Firth, United Kingdom North Sea

Rod Christensen, Dan Barson, and Dean Bilous
Oilexco Incorporated, Calgary, AB

During Late Paleocene (Thanetian) time, the East Shetland and Orkney Platforms on the UKCS were sites of deltaic out-building. Uplift of these platforms due to thermal bulging caused oversteepening and periodic failure of the delta front triggering debris flows of sand-rich sediment into the basin. These debris flows travelled up to 25 km laterally and were deposited as gross fining upwards sequences. Such deposits form the Upper Balmoral sandstone reservoir for the Brenda oilfield.

Within the channel complex in the Brenda area, three distinct phases of deposition are recognizable:

• Substrate scour followed by aggradational sand infilling characterized the initial phase of unconfined debris flows. Early channel bases are often lined with hemipelagic clays deposited during quiet conditions, followed by subsequent aggradation and backfilling with sand.

• During the subsequent phase of confined debris flow deposition, characteristic sedimentation comprised massive sandstones with scattered planar and laminated bedding and occasional load and dish (water escape) structures.

• In the final stage of deposition as sand supply waned, many flow bodies were capped by thinly laminated sand and claystone beds. Finally deep water clay deposits were draped over the underlying sand.

In this presentation we showcase core from two of Oilexco's wells drilled in 2004: the 15/25b-8 and the 15/25b-10. Various parts of the depositional flow cycles discussed above are evident at a mini scale, from core examination. Recognition of different oil-water contacts in these wells confirmed definition of the two main pools in the Brenda oil field.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005