Petroleum geology of the Slyne Trough and adjacent basins

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Abstract
The Slyne Trough lies to the west of Ireland, northeast of the Porcupine Basin and southeast of the margin of the Rockall Trough. The Slyne Trough can be demonstrated to have adequate source, reservoir and seal rocks, but the timing of hydrocarbon migration is more problematical. Structures exist on both large and small scales within the Central and Northern Slyne Troughs, with the possibility of hydrocarbon entrapment at a number of horizons. An excellent source rock has been identified in the Toarcian (Portree Shale Formation) with up to 7% TOC. A secondary source exists within the Sinemurian/Pleinsbachian (Pabba Shale Formation) with up to 4% TOC. Reservoir quality sands have been encountered in the Bathonian (Elgol Sandstone Formation) and Hettangian/Sinemurian (Broadford Beds Formation). A possibility for further reservoir development can be demonstrated in the Bajocian and Pleinsbachian. Sealing intervals have been found in the Bathonian (various levels in the Great Estuarine Group), the Toarcian/Aalenian (Portree Shale Formation/Dun Caan Shale Member) and the Sinemurian/Pleinsbachian (Pabba Shale Formation). The Liassic source rocks are marginally mature in the 27/13-1 well. In the deeper parts of the basin they are probably mature for generation and migration. The Lower and Middle Jurassic evolution of the basin can be estimated with fair accuracy from the 27/13-1 well. The Post-Middle Jurassic history can be interpreted from analogous basins in the region. The North Porcupine sub-basin section shows the complete erosion of the Liassic source horizons. The oil found within the Porcupine basin is believed to be sourced from the Upper Jurassic, which are mature here due to a post-Jurassic history different to that of the Slyne Trough. The Erris Trough is believed to have had a similar Jurassic evolution to the Slyne Trough, but with locally much greater erosion during the Lower Cretaceous. The Jurassic petroleum potential within this basin relies on preservation of the full Liassic sequence in downthrown fault blocks.