New insights into the stratigraphic evolution of SW Britain: implications for Triassic salt and hydrocarbon prospectivity

The discovery of Wytch Farm field in the Wessex Basin, and Kinsale Head field in the North Celtic Sea Basin in the early 1970s, led to exploration interest offshore in the Western Approaches Trough. Despite this activity, little evidence for prospective hydrocarbon resources has been found. To better understand the failures and analyse remaining hydrocarbon potential in this region, we make use of a large collection of new seismic reflection and well data to map Carboniferous to Neogene stratigraphy. The improved seismic imaging has allowed a better interpretation of the hitherto poorly understood, salt related structures in the South Melville and the Plymouth Bay basins. The implications of the new interpretations for Carnian (Late Triassic), and Carboniferous stratigraphic and geodynamic evolution are assessed and contextualised with regional salt deposition in the Wessex, Bristol, and South Celtic Sea basins. From a petroleum system perspective, the Lias and Carboniferous source rocks are evaluated and modelled to analyse the maturity and evolution of the petroleum systems. We conclude that the Lias is an ineffective petroleum system due to timing and source maturation risk. However, the Triassic salt and associated subcropping faults have produced several possible pre-salt hydrocarbon traps. The traps may be charged from sporadic Mid-Late Carboniferous coal-bearing post-orogenic basins, a petroleum system previously overlooked.

Automated summary

The use of new seismic reflection and well data has allowed us to map the stratigraphy of the Carboniferous to Neogene and analyze the potential hydrocarbon resources in the region more effectively. The improved seismic imaging has provided better understanding of salt-related structures, leading to new interpretations and implications for the geodynamic evolution of the Carnian and Carboniferous formations. The evaluation and modeling of the Lias and Carboniferous source rocks have revealed the presence of possible pre-salt hydrocarbon traps.