The Dunlin Field, Blocks 211/23a and 211/24a, UK North Sea

Abstract

The Dunlin Oilfield is located in the East Shetland Basin, 160 km northeast of the Shetland Islands. It lies in UK Blocks 211/23a and 211/24a in about 500 ft of water. The field was discovered in June 1973 by well 211/23-1. The oil accumulation is trapped, in a north-south oriented, tilted fault block at the western margin of the Viking Graben, at a depth of about 8500 ft TVSS. The reservoir is contained in the formations of the Middle Jurassic Brent Group. In the Dunlin area they form a 450 ft thick sequence of sands and intercalated minor shales, which has been deposited by a shore face and delta system prograding northwards across the Viking Graben. The seal is formed by the shales of the Middle/Upper Jurassic Heather Formation. Reservoir properties of the Brent sands are fair to good with porosities of up to 30% and average permeabilities in the range from 10 to 4000 md. Development of the field is carried out from a single platform, from which production started in 1978. To date 40 development wells have been drilled and the total cumulative production amounts to 282 MMBBL of an ultimate recovery of 363 MMBBL.

Influence of reservoir oil charging on diagenesis and reservoir quality: An example from Dunlin Reservoir Sandstones, East Shetland Basin, North Sea, UK

“…This paper focuses on the Dunlin Field (Figure 1), a prolific mature oil field on the UK Continental Shelf (UKCS). The field was discovered in 1973 with an estimated stock tank oil initially in place (STOIIP) of 827 million barrels (MMBBL) (Baumann & O'Cathain, 1991) of which an excess of 522 MMBBL has been produced over 37 years before entering the decommissioning phase in 2015 (Beckman, 2018).…”

“…From discovery to decommissioning, the Dunlin Field has generated a considerable amount of data, with most publications focussing on stratigraphy, petroleum system, reservoir architecture, reservoir properties, fluid properties, and reservoir performance (Baumann & O'Cathain, 1991). However, not much is known about the diagenesis and reservoir quality of the sandstone reservoir despite contributing commensurably to the world's energy demand.…”

“…In the Late Jurassic, a major extension led to the subsidence and deepening of the North Sea basin. This halted the progradation of the Brent delta, leading to the deposition of the marine Humber Group (Heather and Kimmeridge Clay formations; Baumann & O'Cathain, 1991;Richard, 1992). Baumann and O'Cathain (1991) described the Dunlin field as a complex structural trap formed by extensional horst/graben type faulting and fault-block rotation.…”

“…This halted the progradation of the Brent delta, leading to the deposition of the marine Humber Group (Heather and Kimmeridge Clay formations; Baumann & O'Cathain, 1991;Richard, 1992). Baumann and O'Cathain (1991) described the Dunlin field as a complex structural trap formed by extensional horst/graben type faulting and fault-block rotation. The field consists of several tilted fault blocks separated by major faults, with most blocks delineated by minor faults.…”

“…The structural crest of the field lies at 8500 ft (2591 m) true vertical depth subsea (TVDSS). Towards the north, the spill point is at a depth of about 9450 ft (2880 m) TVDSS, while the oil-water contact occurs at 9205 ft (2806 m) TVDSS (Baumann & O'Cathain, 1991).…”