The Southern North Sea is dominated by gas fields in Permian (Rotli...

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The Southern North Sea is dominated by gas fields in Permian (Rotliegend Formation) reservoirs sealed by evaporites, also of Permain age (Zechstein Formation), charged by coals in the underlying Carboniferous. There is also potential in Carboniferous sandstone reservoirs, and in Triassic (Bunter Formation) sandstone reservoirs, provided that a migration pathway through the Zechstein salt can be established.

The Permian and earliest Triassic sediments were deposited in a broad sag basin that extended from the UK through northern Germany to Poland. It is not entirely clear when extensional tectonics where initiated, but this phase of deformation culminated in the Upper Jurassic, and is some instances continued into the lowermost Cretaceous. It is also not clear whether there was a single phase of extension, or a number of separate extensional events with different stress orientations.

The early part of the Cretaceous represents a period of post-rift sag, but this was punctuated by inversion events, most notably in the late Cretaceous, during Chalk deposition and in the late Palaeogene.

The aim of this exercise is to try and unravel some of these events by focussing on the deformation in the post-salt sequence. It is very difficult to tell the timing of movement on faults below the salt as deformation is accommodated by ductile deformation of the salt – hence faults terminate at this level and are separated from syn-extensional packages in the overlying units. Because the salt is ductile, the fact that faults terminate at this horizon does not mean that they are Permian in age! They may have formed much later, but can’t propagate up through the ductile salt, which also causes them to be detached from faults of the same age in the overburden. However, by working out the timing of deformation in the overburden, it may be possible to say something about the timing of trap formation in the underlying Rotliegend reservoirs.

a) Establish a structural and stratigraphic framework.
b) Interpret the main faults.
c) Make a detailed interpretation of the Top Corallian horizon.
d) Structural Evolution

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