Irish sea the Irish Sea

Cardigan Bay Basin[edit]

Cardigan Bay
The Cardigan Bay Basin forms a continuation into British waters of Ireland's North Celtic Sea Basin, which has two producing gas fields. The basin comprises a south-easterly deepening half-graben near the Welsh coastline, although its internal structure becomes increasingly complex towards the southwest. Permian to Triassic, syn-rift sediments within the basin are less than 3 km (1.9 mi) thick and are overlain by up to 4 km (2.5 mi) of Jurassic strata, and locally also by up to 2 km (1.2 mi) of Paleogene fluvio-deltaic sediments. The basin has a proven petroleum system, with potentially producible gas reserves at the Dragon discovery near the UK/ROI median line, and oil shows in a further three wells. The Cardigan Bay Basin contains multiple reservoir targets, which include the Lower Triassic (Sherwood Sandstone), Middle Jurassic shallow marine sandstones and limestone (Great Oolite), and Upper Jurassic fluvial sandstone, the reservoir for the Dragon discovery.
The most likely hydrocarbon source rocks are Early Jurassic marine mudstones. These are fully mature for oil generation in the west of the British sector and are mature for gas generation nearby in the Irish sector. Gas-prone, Westphalian pre-rift coal measures may also be present at depth locally. The Cardigan Bay Basin was subjected to two Tertiary phases of compressive uplift, whereas maximum burial that terminated primary hydrocarbon generation was probably around the end of the Cretaceous, or earlier if Cretaceous strata, now missing, were never deposited in the basin. Despite the Tertiary structuration, the Dragon discovery has proved that potentially commercial volumes of hydrocarbons were retained at least locally in Cardigan Bay. In addition to undrilled structural traps, the basin contains the untested potential for stratigraphic entrapment of hydrocarbons near synsedimentary faults, especially in the Middle Jurassic section.^[17][18]
Liverpool Bay[edit]
The Liverpool Bay Development is BHP Billiton Petroleum's largest operated asset. It comprises the integrated development of five offshore oil and gas fields in the Irish Sea:
Douglas oil field
Hamilton gas field
Hamilton North gas field
Hamilton East gas field
Lennox oil and gas field
Oil is produced from the Lennox and Douglas fields. It is then treated at the Douglas Complex and piped 17 km (11 mi) to an oil storage barge ready for export by tankers. Gas is produced from the Hamilton, Hamilton North and Hamilton East reservoirs. After initial processing at the Douglas Complex the gas is piped by subsea pipeline to the Point of Ayr gas terminal for further processing. The gas is then sent by onshore pipeline to PowerGen's combined cycle gas turbine power station at Connah's Quay. PowerGen is the sole purchaser of gas from the Liverpool Bay development.
The Liverpool Bay development comprises four offshore platforms. Offshore storage and loading facilities. The onshore gas processing terminal at Point of Ayr. Production first started at each field as follows: Hamilton North in 1995, Hamilton in 1996, Douglas in 1996, Lennox (oil only) in 1996 and Hamilton East 2001. The first contract gas sales were in 1996.
The quality of the water in Liverpool Bay was historically contaminated by dumping of sewage sludge at sea^[19] but this practice became illegal in December 1988 and no further sludge was deposited after that date.^[20]