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Structure and geometry of accommodation zones in host and
supra-jacent sediments associated with the collapse of salt


The collapse of host sediments at the crests of salt anticlines is associated with the devel- opment of hydrocarbon traps in salt overburden rocks, and stratigraphic traps in palaeo- valleys incising salt wall crests. The capacity and integrity of these traps are controlled by complex spatial variations in the geometry of collapse structures, and are difficult to char- acterise using traditional sub-surface datasets. An in-depth understanding of the structural styles that control salt wall collapse, particularly at the ‘sub-seismic’ scale, is essential so that meaningful interpretations of potential prospects can be made based on sub-surface data.
The exceptional exposure and preservation of a number of collapsed salt anticlines and re- lated structures within the Paradox Basin, Utah and Colorado, U.S.A., provide an ideal op- portunity to study the geometry and development of salt-related collapse structures. This study combines three-dimensional seismic data from the U.K. Central North Sea with de- tailed structural mapping of exposed structural analogues from the Paradox Basin. The results are used to identify and characterise the range of structural geometries that result from salt anticline collapse, and to elucidate controls on their development.
Collapse geometries range from ductile down-warping of the overburden, creating axial synforms, to brittle deformation, creating graben and half-graben structures. Where col- lapse is brittle, half-grabens form the principle structural element of salt anticline collapse structures. Graben-like structures are generated through subsidence of the hanging-wall an- ticlines associated with half grabens, or within areas of interaction between kinematically- linked, oppositely-dipping half-grabens. Accommodation structures between oppositely- dipping half-grabens are associated with structural lows, and contribute to compartmental-isation of potential reservoirs within the overburden.

The summary models presented here can be used to guide seismic interpretation within complex, salt-controlled basins, and to identify the potential risks associated with structural traps formed by salt anticline collapse.



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