Geochemical processes associated with ‘marine band’ formation in the Lower Carboniferous Bowland Shale Formation, Northern England

Abstract

Natural gas is needed and used by the global population to minimise our reliance on coal powered electricity generation. Gas is also used to manufacture hydrocarbon-based products such as fertilizers, fabrics and pharmaceuticals. Gas can be extracted from low permeability “unconventional” systems, where laterally extensive beds enriched in hydrocarbons (“sweet spots”) are targeted for hydraulic fracturing. Mudstone dominated formations require complex techniques such as geochemistry to identify sweet spots. This study investigates the recent unconventional target, the Bowland Shale Formation in the Bowland Basin, Lancashire (UK), as a case study and as a promising target for gas production. As a case study, we use the Bowland Shale Formation to investigate the applicability of outcrop organic geochemistry to exploration (Chapter 4). The Bowland Shale Formation is also used as a case study to investigate key stratigraphic boundaries (e.g. highstands) that are globally recognised hydrocarbon targets and are used for targeting directional drilling (Chapter 5). As a target for natural gas, the palaeoceanography of the Bowland Shale Formation in the Bowland Basin is investigated to interpret organic matter burial, spatially across the basin (Chapter 6), and to select a suitable analogue (Chapter 7). This requires a multi-disciplinary approach using geochemistry (X-ray diffraction, X-ray fluorescence, RockEval pyrolysis, molecular analysis and organic carbon isotopic analysis); sedimentology (logging and scanning electron microscopy); biostratigraphy and computational statistical modelling. We find that outcrop-derived total organic carbon and extractable organic matter contents are not representative of subsurface exploration cores from the same formation; X-ray fluorescence (redox sensitive Mo and U) and RockEval pyrolysis (oil saturation index) can be used to identify highstands; the Upper Mississippian Bowland Basin was anoxic in the centre as well as at the basin margin and that the Barnett Shale is a suitable palaeoceanographic analogue to the Upper Mississippian Bowland Shale Formation.