Meanwhile, some of the questions as to whether Upper Jurassic Kimmerigian Clays could be a source were answered by geochemical analysis of oil from a test of the Kimmeridgian Limestones in the Balcombe-1 well, originally drilled by Conoco, in the centre of the basin, which suggested the presence of a second, less mature, source. As Chris says, “The unconventional industry in the US had breathed new life into the UK onshore. We realised that the Kimmeridgian Clays might not just be sourcing the overlying Portland Sandstone, but also a new, unexplored play: the interbedded and stacked Kimmeridgian Limestones. We needed to map out the extent of the mature Kimmeridgian Clays as well as the interbedded limestones, known as the Micrites.”