Integrated geochemical and attribute modelling of the Kimmeridge Clay Formation (KCF) in the UK North Sea: Implications for unconventional hydrocarbon exploration

Unconventional resource plays (i.e., shale oil and gas) may play an important role in increasing the UK’s secure access to energy during the transition to net-zero carbon energy sources. For several decades, the UK North Sea has been a prolific oil and gas province, with numerous conventional discoveries sourced predominantly by the Kimmeridge Clay Formation (KCF). However, only a few studies have analysed the potential of the KCF for unconventional resources, which could also contribute significantly to maximising the production of known plays.
This study combines i) geochemical data analysis and 1D basin modelling to evaluate KCF hydrocarbon generation potential and oil saturation, with ii) 3D geostatistical modelling to predict the distribution of KCF reservoir properties, and iii) 3D basin modelling and mineralogical data interpretation to further investigate KCF thermal maturity, residual hydrocarbon saturation and frackability. Together, these give an indication of the potential for shale oil and gas exploitation in the Outer Moray Firth region, UK North Sea.
The compiled geochemical data from KCF samples in 18 wells within the study area were analysed using geochemical interpretation plots generated in p: IGI+ software. This was followed by 1D basin modelling of 20 selected well locations. Machine learning techniques and established rock property equations were used to generate total organic carbon, hydrocarbon yield, hydrogen index, total porosity and brittleness index logs for 16 of the wells. The generated well logs and KCF depth maps are utilised for 3D geostatistical property modelling across the study area. A 3D basin model was constructed using 10 depth maps, and KCF mineralogical composition was analysed in four wells using XRD.
Most of the well sites indicate excellent hydrocarbon generation potential and oil saturation for the KCF. An overall sweet spot map, created by integrating the modelled KCF reservoir properties and thermal maturity, shows key prospective areas for shale oil and gas exploitation within the central Witch Ground Graben, and to a lesser extent regions of the Piper Shelf and Claymore-Tartan Ridge. These areas indicate good potential in all investigated reservoir properties and thermal maturity, with respect to industry thresholds.
The results of basin modelling further show that free residual hydrocarbon saturation within KCF sweet spots reaches up to 95.6 mmbls/km2 of oil and 73.6 bcf/km2 of gas. The modelled P90 - P50 - P10 free in-place volumes are also significant, with 2.7 - 5.7 - 12.1 billion barrels of oil and 0.5 - 1.2 - 2.7 trillion cubic feet of gas in place. The calculated mineralogical brittleness indices for the KCF further indicate favourable conditions for hydraulic fracturing in the sweet spot area.
Whilst alternative forms of energy production are increasing, the onshore production of shale oil and gas has not significantly materialised in the UK for a number of socio-economic reasons. This study has therefore improved and simplified the identification of producible areas for shale oil and gas from the KCF in the offshore UK North Sea, a resource that may prove essential to UK energy security during the net-zero carbon transition.