Fault traps in the Northern North Sea

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Abstract The 250 hydrocarbon finds in the northern North Sea have total resources of 8000 × 10 6 Sm 3 oil-equivalent and 70% are in fault block traps, all with Jurassic or older reservoirs. They can be classified into plays by reservoir age: pre-rift is pre-Jurassic and Lower-Middle Jurassic; syn-rift is Upper Jurassic. 40 finds have sufficient published information to allow analysis of the geological relationships, structural and stratigraphic, which have given rise to their faulted hydrocarbon traps. All of the pre-rift and some of the syn-rift finds are traps in footwall blocks. They form a series with respect to the amount of conformable versus unconformable cap rock. In many the up-dip seal is due to stratigraphic truncation of the reservoir below an unconformable cap rock: the hydrocarbon pool does not extend to the bounding fault. The amount of erosion on the fault blocks and the footwall uplift which occurred seem to be related to the magnitude of fault throw. Most of the other syn-rift finds are hanging wall traps with entirely conformable cap rocks. The Brae-trend finds are classic syn-rift traps, located in the hanging wall of a major fault, movement on which was responsible for the supply of the reservoir clastics. The traps in the Central Graben are the most varied: all are different, probably due to complications produced by the underlying Permian salt.