Hydrocarbon prospectivity in the Irish Sea area: insights from recent exploration of the Central Irish Sea, Peel and Solway basins

Abstract

Compared with the prolific success of the Triassic play in the East Irish Sea Basin (EISB) the lack of hydrocarbon discovery in neighbouring Permo-Triassic basins of the Irish Sea has been an enigma. However, recent exploration of the Peel, Solway and Central Irish Sea basins has provided new insights into the geology of these basins and the controls upon hydrocarbon prospectivity in the Irish Sea area. Regional seismic interpretation suggests that 12 of the 15 exploration wells drilled in the basins adjacent to the EISB tested valid structural closures at top Triassic reservoir level. Re-evaluation of the Irish Sea petrolemn system reveals that, although effective reservoirs occur in the Lower-Middle Triassic Ormskirk Sandstone Formation, and evaporites in the Middle-Upper Triassic Mercia Mudstone Group provide a regional top seal, the major factor controlling hydrocarbon prospectivity is the limited presence of effective source rocks in the underlying Carboniferous section. A further control upon prospectivity is the timing of hydrocarbon migration, from those areas where Carboniferous source rocks were deposited and preserved. The Namurian basinal marine oil-and gas-prone shales, which form the principal source of hydrocarbons for the Triassic play in the EISB, are restricted to an east-west fairway extending from the EISB into the Kish Bank Basin. Rocks of this age are absent from the Peel and Solway basins as a result of Variscan uplift and erosion. However, palaeogeographical reconstructions based on well and outcrop data suggest that, even if preserved, the depositional environment was not conducive to the formation of marine oiland gas-prone source rocks. Well and seismic data suggest that rocks of Namurian age were not deposited in the Central

The control of basin evolution on patterns of sedimentation and diagenesis: an example from the Mississippian Great Orme, North Wales

“…However, the northern margin of the North Wales Platform remained a relative topographic high throughout the Carboniferous (Williams & Eaton 1993) and burial depths for the uppermost Dinantian succession did not reach more than 1-1.5 km (Al-Fadel 1983). Surrounding basins (East Irish Sea and Cheshire) experienced burial depths of c. 1-1.5 km in the Carboniferous and maximum burial depths of c. 4 km (top Namurian) during the Cretaceous (Hardman et al 1993;Floodpage et al 2001). …”

“…The East Irish Sea Basin, north of the North Wales Platform, is invoked as a possible source of metals and mineralizing fluids. The East Irish Sea Basin experienced two burial episodes: during the Late Carboniferous (burial depth of c. 1 km, latest Namurian) and reaching a maximum burial of c. 4 km in the Late Cretaceous-Early Cenozoic (Hardman et al 1993;Floodpage et al 2001;Fig. 15).…”

“…This process of disequilibrium compaction and subsequent rupture and mass fluid flux has recently been modelled for the Edale and Widmerpool Basins adjacent to the Derbyshire Platform . Localized dolomite cementation on the northern margin of the North Wales Platform (Great Orme, Little Orme and Prestatyn) may indicate preferential activation of some faults and/or access to a (Hardman et al 1993;Newman 1999;Floodpage et al 2001) and (b) North Wales Platform (burial curve modified from Al-Fadel 1983). Major tectonic events are indicated by pale grey from the Late Carboniferous, Jurassic and Late Cretaceous onwards.…”

Three-dimensional gravity and magnetic modelling of the Irish sector of the NE Atlantic margin

“…Published seismic cross-sections (in twtt) and other data from the Peel, Kish Bank, Central Irish Sea, St Georges Channel, North Celtic Sea, Rockall, Slyne and Erris basins (e.g. Croker, 1995;Dancer et al, 1999;Dunford et al, 2001;Chapman et al, 1999;Floodpage et al, 2001;Izatt et al, 2001;Murdoch et al, 1995;Mackenzie et al, 2002) 11. Seismic interpretation from the western approaches to the English Channel from Evans et al (1990).…”

Fault distribution and timing in the Central Irish Sea Basin

“…The structural and stratigraphic evolution of the CISB has been documented in a number of publications (Maddox et al 1995;Duncan et al 1998;Corcoran & Clayton 1999;Maingarm et al 1999;Floodpage et al 2001 marine carbonates, encountered in well IR42/17-1, which are unconformably overlain by interbedded coals, shales and sandstones of Westphalian C to Stephanian age (Maddox et al 1995). No Namurian sediments have been drilled in the basin to date but the presence of a Namurian A-B section cropping out on the southern coast of the Isle of Anglesey (Racey, pers.…”