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Площадь: 33930.78 км²
North Celtic Sea
Ireland is almost completely surrounded by Upper Palaeozoic to Cenozoic sedimentary basins, many of which have largely untested hydrocarbon potential (Fig. 1). Upper Palaeozoic (Carboniferous) basins occur onshore but have only local gas potential in the northwest of the country. Basins lying offshore northeast and east of Ireland are typically Upper Palaeozoic to lower Mesozoic half-grabens containing 3-5kin of pre-Middle Jurassic sediments. Source rocks occur in Upper Carboniferous coals and shales and, where encountered in the Kish Bank Basin, are mature for gas generation. Reservoir rocks chiefly comprise Permo-Triassic fluvial, alluvial and locally aeolian sandstones. Cap rocks are Permo-Triassic evaporites and marls. Traps include four-way dip-closed folds, tilted fault blocks and stratigraphic pinchouts against basement highs. Eight exploration wells have been drilled in these basins, four of which had shows reported. Water depths in the region are generally less than 100m.
Fig. 1. Location map of sedimentary basins offshore Ireland. The general location of some basins in adjacent UK waters is also shown.
Basins to the south of Ireland typically have thick (up to 9km) Triassic to Cretaceous successions. Source rock claystones occur in the Lower Jurassic (oil and gas), Middle and Upper Jurassic (oil) and locally in the lowermost Lower Cretaceous (oil). Gas is produced commercially from the Lower Cretaceous shallow marine Albian sandstones (Greensand) and shoreface to fluvial Wealden (Aptian-Albian) sandstones. Oil shows have been recorded from these and from older Wealden (BerriasianBarremian) sandstones, from Upper Jurassic (Oxfordian) fluvial sandstones and from Middle Jurassic shelf limestones. Reservoirquality intervals have also been encountered in Lower Jurassic deltaic sandstones and Triassic fluvial-aeolian sandstones. Traps comprise Triassic, Jurassic and Lower Cretaceous tilted fault blocks, Lower Cretaceous stratigraphic pinchouts and early Tertiary inversion structures. Sealing claystones occur at Upper Triassic, Lower, Middle and Upper Jurassic and Lower Cretaceous levels. Water depths are typically in the range 100-200 m. Eighty exploration and appraisal wells have been drilled to date in the Irish sector of the Celtic Sea (North Celtic Sea, South Celtic Sea and Fastnet Basins), with 13 flowing oil or gas on test and the majority of the others recording shows (Fig. 2). The Kinsale Head and Ballycotton gas fields are in production, while the Helvick and Seven Heads accumulations represent the most significant of the currently sub-commercial oil discoveries.
Fig. 2. Well test results and hydrocarbon shows for released wells in Celtic Sea basins
Basins west of Ireland contain up to 10 km of Upper Carboniferous to Tertiary sediments.
They are only very lightly explored, with no wells in the Irish sector of the Rockall Trough (the largest of the Irish offshore basins) or in the Hatton Basin, one well in the Goban Spur, 25 wells in the Porcupine Basin and four wells in the northwest basins (Slyne Trough, Erris Trough and Donegal Basin). Source rocks in the Porcupine Basin occur at Middle Jurassic (oil), Upper Jurassic (oil) and Lower Cretaceous (oil) levels. Further source potential exists locally in the Carboniferous (gas), Lower Jurassic (oil) and Lower Tertiary (oil). Produ- cing sandstone reservoirs have been encountered in the Middle and Upper Jurassic (fluvial- shallow marine), and Upper Jurassic and Lower Cretaceous (deep marine turbidites).
Other reservoir-quality sandstones occur in Upper Carboniferous (fluvio-deltaic), Triassic (non-marine), Lower Cretaceous (fluvio-deltaic) and Lower Tertiary (turbidite and fluvio-deltaic) sequences. Cap rocks are plentiful at Carboni- ferous, Permo-Triassic, Jurassic, Cretaceous and Tertiary levels. Potential traps, including tilted fault blocks at Carboniferous and Jurassic levels, and stratigraphic onlaps, pinchouts and differential compaction features in the Jurassic, Cretaceous and Tertiary, are seen to exist. Four wells flowed good quality oil (32-41 ~ API), with many others recording shows. The Connemara (Block 26/28) discovery contains an estimated 195 million barrels of oil-in-place.
Water depths in the Porcupine Basin range from approximately 300 m in the north to more than 2000 m in the south. Water depths in the other basins to the north and west vary from less than 200 m to more than 2000 m.
Data source: The petroleum geology of Ireland's offshore basins: introduction. P. F. Croker, P. M. Shannon. 2013
Следующий Бассейн: Cheshire - Worcester