Petroleum geochemistry of the Kimmeridge Clay of onshore Southern and Eastern England

The Kimmeridge Clay is considered a major oil source rock for the North Sea hydrocarbon province. The formation is also developed onshore in an organic-rich mudstone facies. This paper examines the possibility of onshore oil generation from the Kimmeridge Clay. Geochemically, onshore basin margin sediments contain rich, potential source horizons with mainly Type l/Type ll oil-prone kerogen, but are immature. Some deeper Cleveland Basin sediments have reached marginal maturity. Burial history reconstruction suggests significant formation palaeoburial depths in central areas of the Cleveland and Wessex Basins. Computed vitrinite isoreflectance contours show the Wealden and Isle of Wight Kimmeridge Clay to be thermally mature. Basin modelling suggests an early Palaeogene onset of oil generation in parts of the Cleveland Basin, while maximum oil generation could have been reached by the formation base in the Isle of Wight area during the late Cretaceous. Although basin subsidence ceased in the Neogene, in the Weald and Isle of Wight, where the formation is still deeply buried, oil generation probably continued for some time during uplift. Thus significant quantities of oil could have been generated. Whether or not this oil is present today however, would depend on the correct timing of suitable migration and trap structures.