Characterising the internal structural complexity of the Southern North Sea Zechstein Supergroup Evaporites

Abstract

The internal complexity present within layered evaporite sequences is often an overlooked feature in sedimentary basins, with attention frequently concentrating on the external geometries that salt bodies form. Through the availability of large areas of 3D seismic data and new seismic imaging techniques the opportunity to view the internal structures that form within layered evaporites allows for a comprehensive characterisation of the different structural facies that may be present.The key focus of this paper concentrates on the Zechstein evaporite deposits within the Southern North Sea of the United Kingdom’s Continental Shelf. This analysis of the internal structural complexity and stratigraphical heterogeneity utilises 25,000 km2 of existing 3D seismic data together with over 96 wells from the Southern North Sea. Characterisation of the different structural facies present was undertaken alongside mapping the spatial distribution to understand the relationship they have with one another and the deformation pathways that may have been taken. Layered evaporite sequences are an important component of geo-storage systems, either for cavern emplacement or sealing carbon storage reservoirs. This work has shown; 1) there are contrasting internal geometries between different structural salt facies; 2) the internal heterogeneity is indicative of variations in the vertical strength profile of layered evaporite sequences; 3) the ability to possibly predict the internal heterogeneity of areas of poorly imaged salt, such as within salt structures, from surrounding structural facies of the salt; These findings suggest that there is significant internal complexity even within areas of the basin with minor salt mobilization and as such are important to consider in the assessment of geo-storage sites.