The Central North Sea (CNS) has proven an important source of oil and gas for over 50 years. As we reduce carbon dioxide emissions over the coming decades, the region will play a dual role. On one hand it will provide geological storage space in which to store carbon dioxide, and on the other it will continue to provide oil and gas. Key to these roles is the Zechstein Supergroup, a salt-rich rock sequence (in some regions kilometres thick) that is both mobile (i.e. flows like toothpaste in the subsurface over geological time, deforming surrounding rocks) and traps fluids and gases beneath it. Improved understanding of how the Zechstein salt has influenced the geology of the CNS is thus critical. Current understanding and concepts were developed around 30 years ago, based largely on seismic images of limited quality, and on now dated principles and models. A fresh look at CNS salt is thus long overdue.
The ZechTec project aims to make breakthroughs in understanding the evolution of the salt-influenced, but poorly-understood, Late Permian and Triassic intervals. This is now possible in the CNS due to the wealth and quality of modern seismic data and the opportunity to apply cutting-edge principles of salt behaviour. Our approach will blend observations from seismic and well data with those from physical and numeric models that mimic the behaviour of salt in the CNS. The project comprises four work packages to tackle core questions such as: i) What is the variability of the Zechstein ‘salts’? ii) What triggered the movement of salt in different parts of the CNS? iii) What types of salt structures developed in different parts of the CNS and why? iv) How has Zechstein salt movement influenced landscape development and the deposition of sediments?
The results of this project will significantly advance understanding of CNS salt tectonics, and provide knowledge to help locate safe carbon dioxide storage sites and optimise hydrocarbon exploitation across the CNS.
The Central North Sea (CNS) has been a world-class hydrocarbon province for several decades, with flow of the salt-rich Zechstein Supergroup (ZSG) (Lopingian) having contributed to the accumulation of significant hydrocarbon reserves. As a result, many of the founding concepts of salt tectonics were developed in the CNS, although: (i) difficulties with near- and intrasalt seismic imaging; and (ii) a focus on shallower, better imaged, and arguably simpler petroleum systems, mean fundamental questions remain regarding the salt-tectonic development and structure of the CNS during the Lopingian (Late Permian) and Triassic. By helping answer these questions, ZechTec will provide a step-change in our understanding of the link between salt deposition, deformation, and related sedimentation, helping unlock the hydrocarbon potential of the Lopingian and Triassic petroleum systems.
Now is the time to answer these questions, given that: (i) near-field reserves are urgently required to extend the life of existing fields; (ii) there has been a substantial increase in the quality and quantity of seismic and borehole data in the CNS; and (iii) 3D seismic data quantity and quality has fueled an explosion of new salt-tectonic concepts, based largely on the study of salt basins outside the CNS. The ZechTec project is thus timely, multidisciplinary, and ambitious, integrating geophysical and geological data to provide the first-ever basin-scale synthesis of ZSG salt deposition and tectonics, and the impact these jointly have on the Lopingian and Triassic evolution petroleum systems. Concepts arising from our subsurface analysis of a natural salt-tectonic system will be tested and refined with novel scaled physical and finite element numerical models. Our next-generation tectono-sedimentary models will help refresh industry practices and knowledge in the CNS, with the concepts arising from our work being applicable to other salt basins, and in the derisking of C02 storage sites.