Petroleum geology and future hydrocarbon potential of the Irish Sea

The East Irish Sea Basin is hydrocarbon prolific with ten gasfields, two oi lfields and another eight gas or oil discoveries. Production is from a wide spread Triassic fluvio-aeolian reservoir (the Ormskirk Sandstone) which is sealed by salt-prone mudstones. Three episodes of hydrocarbon generation oc curred from a rich, Namurian-age source rock during deep burial in the Late Carboniferous-Early Permian, in the Early Jurassic and in the Late Cretace ous. All of the discoveries are in structural traps which are controlled to some degree by N-S trending normal faults probably active in the Late Jura ssic. Consequently, the third (Cretaceous) phase of hydrocarbon generation is the most important. Another phase of uplift and erosion occurred in the Early Tertiary leading to the almost complete removal of Cretaceous and Jur assic strata. This event led to significant primary and tertiary migration as a result of overpressuring in the source rock and gas expansion within t he reservoir Although similar good quality Triassic reservoir occurs in oth er basins in the Irish Sea, rift-related uplift and erasion in the Middle P ermian caused the widespread removal of potential Carboniferous source rock s in these areas, severely limiting the chance of hydrocarbon charge.