EXPLORING FOR FAN AND DELTA SANDSTONES IN THE OFFSHORE FALKLANDS BASINS

P. Richards*1, I. Duncan2, C. Phipps2, G. Pickering3,4, J. Grzywacz3, R. Hoult1,5 and J. Merritt1

1 British Geological Survey, West Mains Rd, Edinburgh, EH9 3LA.

2 Desire Petroleum plc, Mathon Court, Mathon, Malvern, Worcestershire.

3 RPS Energy, Goldsworth House, Denton Way, Goldsworth Park, Woking.

4 Now at: Granby Oil and Gas plc, Antholin House, 71 Queen Street, London.

5 Now at: GETECH, University of Leeds, Leeds, West Yorkshire.

†*Author for correspondence, email: pcr@bgs.ac.uk

Four basins surround the Falkland Islands, but only the North Falkland Basin has been drilled; six wells were drilled there in 1998. Although all six wells encountered good quality sandstones, none of them targeted the basin margins, on what are now thought to be the optimum migration pathways associated with the basinís thick lacustrine source rocks. Subsequently, a 3D seismic survey acquired in 2004 was designed to identify potential basin margin-derived sandstones entering the basin along transfer zones. From this survey, a number of basin margin-attached fans have been identified; these prograded into lacustrine waters of varying depths. These Early Cretaceous alluvial/fan delta/deep-lacustrine fan systems are interpreted to provide excellent potential reservoir facies as they are intimately associated with thick, mature source rocks. They will provide the focus for the next planned phase of exploration in the North Falkland Basin.

A phase of drilling is also planned for the basins to the south of the Islands, where large deltaic and fan systems, slightly younger than those imaged in the North Falkland Basin, are seen on seismic to prograde from the same Palaeozoic hinterland that produced the older, North Falkland Basin fans.

This paper attempts to show how sedimentary models derived from targeted seismic programmes following initial exploration can be utilised to plan and improve new drilling campaigns in a frontier basin. It presents an analysis of sediment dispersal patterns in basins of marine and lacustrine origin linked to a single hinterland area, and highlights the nature of the relationship between relay ramp/transfer zone development and sediment dispersal patterns in the sub-surface.

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