Structural Styles and Related Accommodation Zones Associated With the Collapse of Salt Anticlines: Implications for Fluid Flow in Salt-Controlled Basins

Abstract

Extension- and dissolution-related subsidence at the crests of salt structures is ubiquitous within salt-controlled basins, and is associated with significant remaining hydrocarbon potential in Upper Jurassic plays of the UK Central North Sea (CNS). The small scale and relative complexity of associated crestal fault systems means that they are often poorly resolved on conventional seismic data. A better understanding of the structure and development of crestal fault systems is key to making informed assessments of trap integrity and risk. This study combines the results of field mapping from the Paradox Basin, Utah, where a series of collapsed salt anticlines are preserved in outcrop, with interpretations of equivalent structures from the UK CNS based on 3D seismic data. Field data are used to identify and characterize the range of structural styles involved in salt anticline collapse, and thus bridge the resolution gap between field- and seismic-scale structures. Field-based interpretations show substantial variations in deformational geometry along the axis of salt anticline collapse structures. Well-constrained structural models are constructed across parts of the collapse structures in order to identify key structural geometries and sub-seismic-scale characteristics. Collapse geometries incorporate both ductile and brittle components of deformation, and are typically dominated by axial half-grabens that show numerous reversals in orientation. Accommodation zones between oppositely-dipping half-grabens typically generate narrow grabens and are often characterised by oblique structural trends. Fluid flow simulations demonstrate that these accommodation zones may also be associated with structural lows that contribute to the along-axis compartmentalisation of any potential reservoirs. This work identifies spatial relationships that link different styles of salt anticline collapse, and expands on existing models of collapse by taking in to account the principal mechanisms by which they develop. Idealised models based on field data provide insight into the likely sub-seismic-scale structural characteristics of different structural styles, which can be used as a guide when evaluating potential reservoirs using seismic data.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016