The UK Atlantic Margin: are big prizes still out there?

R.W. Gatliff, H. Johnson, J.D. Ritchie and K. Hitchen of the British Geological Survey in Edinburgh follow the previous article's assessment of recent drilling by offering some geological evidence . The first well drilled on the UK Atlantic margin was spudded in 1972. Since then, drilling activity has fluctuated (Figure 1) with peaks of activity in 1977 (when the Clair oilfield was discovered), 1984-86 (deep water step-out into the Faroe-Shetland Basin), 1991 (mainly licence round related) and 1994-1996 (related to the Foinaven and Schiehallion discoveries). Initially, exploration tested the major structural highs of the West Shetland and North Rona basins and the Rona Ridge beneath the shallow water shelf areas. Subsequently, exploration stepped out into the deeper water associated with the Faroe-Shetland and Rockall basins. Exploration interest in the area seemed to be waning until the Foinaven and Schiehallion discoveries gave the area renewed impetus. Within the last few years the agreement of the international boundary between the UK and the Faroe Islands has resulted in some renewal of drilling activity in both countries close to the newly agreed median line. This latest phase of exploration seemed to be stalling after a series of disappointing tests across a range of ‘play types’ in the Faroe-Shetland Basin and the Rockall Basin. However, it remains to be seen whether the Amerada Hess Marjun discovery in Faroese waters (well 6004/16-1Z) and particularly the recent Dooish discovery by Enterprise in Irish waters (well 12/2-1) within the Rockall Basin will lead to another surge in drilling activity. The Marjun discovery, with a 170 m hydrocarbon column, is in a Paleocene structural trap (Smallwood 2002). Details of the Dooish discovery have yet to be released but the Petroleum Affairs Division of Ireland (2002) describes it as a ‘significant’ hydrocarbon accumulation. It is speculated that the trap may comprise a pre-rift succession within a tilted fault block on the eastern margin of the Rockall Basin. This discovery establishes that a working petroleum system is present within the Rockall Basin and consequently that the potential for further hydrocarbons discoveries is significant. Tilted block structures have already been identified on both east and west flanks of the Rockall Basin (Walsh et al. 1999).