Integrated petroleum systems (PeST) studies and seep evaluations of the East Shetland Platform and SW Approaches area of the UKCS.  The studies were carried out as an industry collaboration as part of the 21CXRM initiative.  The studies were completed in Q3 2018 and remained confidential to the participant group until the 31st Licence Round offers of award were made.  APT led the technical evaluation team under contract to the NSTA on behalf of the participant group.

The SW Approaches and East Shetland Platform are two areas of the UKCS perceived within the industry as being relatively under explored.  The reasons for this are many and complex but, as part of the 21CXRM initiative that seeks to support the industry in exploring under-explored areas, this work addresses questions around the existence and effectiveness of petroleum systems within the areas.  The evaluation builds on earlier work providing a fully integrated, very high-quality geochemistry and thermo-chronology dataset and basin modelling studies of the two basins of interest. Additionally, appropriate biomarker studies allow age-diagnostic assessment of any oils sampled allowing oil-source correlations to be attempted.

East Shetland Platform:

Analysis of Devonian source rocks suggests that oil-prone Middle and potentially Lower Devonian source rocks, albeit with relatively modest TOC, exist across the study area. Geochemically at least two Palaeozoic oil families have been identified, both of which can seemingly be differentiated from Kimmeridge Clay Formation sourced oils. The highest risk associated with play models in this area which utilise an intra-platform Devonian source rock is related to its maturity timing, with the most pessimistic scenarios being of pre-Jurassic hydrocarbon expulsion. The eastern portion of the Crawford-Skipper Basin is prospective, if material source rocks exist in the Devonian sequence. The geochemistry of the oil stains characterised in this study in Quad 9 are suggestive of the presence of oils not related to the KCF system and lends credence to the potential for Palaeozoic source plays in this area.

SW Approaches:

Material source rocks in the Early Jurassic are proven to exist; the oil shows reported have largely been proven    and typed to Early Jurassic source rocks. Some of these shows occur in Triassic stratigraphy, suggesting some complex migration paths are operating, at least locally. Basin modelling suggests the principal sensitivity to the volumes generated is the location of the source rock with the Lower Jurassic stratigraphy (reflecting its thickness); with an order of magnitude difference in volumes for modelling at the uppermost versus lowermost Lower Jurassic. Many of the wells drilled in the vicinity of the kitchens mapped in this study were either targeted at base Cretaceous closures (e.g. 73/12-1) or apparently failed to target any genuine trapping feature (e.g. most wells in the South Celtic Sea) potentially reflecting the vintage of these wells, which were drilled on 2D data. There seem to be few valid tests of the potential petroleum system(s). Basins in the area are likely be challenged by an absence of reservoir. Where penetrated the Triassic is comprised of thick intervals of mudstone, non-reservoir limestones and claystones (e.g. 93/2-2). No locations have been mapped that would set up a geometry comparable to that at Wytch Farm, where the Purbeck monocline places Triassic reservoir sands above mature Liassic source rocks. The Paleozoic potential to the North of the Cornubia Massive is very poorly constrained and warrants further analysis.