.
Journal of Petroleum
Geology, vol. 21(2), April 1998, pp. 125-152
AN ASSESSMENT OF IRISH OFFSHORE BASINS AND PETROLEUM PLAYS
P. M. Shannon* and D. Naylor*
The
Irish offshore contains a large number of Late Palaeozoic to Cenozoic sedimentary basins,
most of which are only lightly explored. These are grouped into the Irish Sea, Celtic Sea
and Atlantic Margin basins. The basins developed in response to multi-phase rifting which
preceded the development of the North Atlantic Ocean. The major rift phases occurred
during the Permo-Triassic, Late Jurassic and Early Cretaceous. The Irish Sea basins
contain a preserved succession of predominantly Permo-Triassic and Early Jurassic age,
with younger strata largely absent due to Cretaceous and Tertiary inversion. The Celtic
Sea basins have a thick series of Triassic to Cretaceous strata, overlain by a generally
thin Tertiary succession. The Atlantic Margin basins have a variable sedimentary
thickness, with the larger basins characterized by a thick Tertiary succession. Two
gasfields are currently in production in the North Celtic Sea Basin, while a number of
undeveloped oil and gas accumulations have been discovered in both the North Celtic Sea
Basin, and the Porcupine Basin on the Atlantic margin. A wide range of reservoir and
source-rock horizons have been encountered in the various basins. Most of the exploration
to date has concentrated upon structural traps, but the recent resurgence of exploration
interest is centred mostly upon a variety of stratigraphic traps, especially at Cretaceous
and Tertiary levels, similar to successful plays further along strike in the UK and
Norwegian sectors of the Atlantic Margin.