The of the basins. Additionally, a marine

The North Sea structural framework is mainly the result of a rift in the Upper Jurassic – Lower Cretaceous, partly controlled by older structural elements. In Carboniferous to Permian periods, rifting occurred due to volcanism followed by a deposition of reddish eolian and fluvial sandstones (Rotliegendes). This caused two basins to develop with sedimentation of thick evaporate sequences (Zechstein). After deposition of younger sediments, the buoyancy force displaced the salt to the top- essential in closing structures and trapping hydrocarbon as in the south of North Sea. This influenced the topography and further sedimentation. In the Triassic period, major N-S to NE-SW rifting occurred along with deposition of thick coarse fluvial sediments at the rift margins which grade into finer-grained sediments, and lake sediments in the centre of the basins. Additionally, a marine transgression from north to south marked the transition from Triassic to Jurassic. Following the transgression, a volcanic dome grew beneath the triple point between the Viking Graben, Central Graben, and Moray Firth Basin which caused uplift and erosion, and was followed by another phase of rifting. This produced several fields. In the northern North Sea and Horda Platform (Brent Group), large deltaic systems consisting of coal, sand, and shale were deposited (Balson, Butcher, Holmes, Johnson, Lewis, and Musson, 2001). The most notable rifting phase occurred in the Late Jurassic to Early Cretaceous. During this rift-phase, major fault blocks were uplifted and tilted which created sediment supply by erosion. Anoxic basins in the North Sea, with accumulated shales created a crucial source rock, and also the Draupne Formation- an important seal for hydrocarbon traps. Once the rifting has ceased during the Upper Cretaceous, thermal subsidence occurred and gave way to two distinct lithologies- chalk deposition in the south, and siliciclastic, clay-dominated sediments in the north. A major phase of basin inversion took place at the end of the Upper Cretaceous which affected many basins in the NW of Europe and may have reactivated some basement faults during the Oligocene to Miocene times (Glennie and Boegner, 1981). In the Cenozoic period, subsidence in the North Sea formed a syncline towards a depositional axis- extending from the Viking Graben, through the Central Graben, to the Netherlands (Balson et al., 2001).?Petroleum Geology of the Northern North SeaThe Dire Straits acreage is located in the northern North Sea. Research of the petroleum system of the northern North Sea at present have been detailed. It consists of an Upper Jurassic source rock, migration pathways, and reservoirs ranging from Devonian to Eocene strata, traps, and mudstone seals (Balson et al., 2001).The source rock is known as the Kimmeridge Clay Formation of the Humber Group. It is from the Upper Jurassic syn-rift, consisting of organic-rich marine mudstones. The post-rift thermal subsidence and burial of the Cretaceous and Cenozoic times have created an optimal environment for the source rocks to mature for hydrocarbon generation, beginning from the Palaeogene times (Johnson and Fisher, 1998).The hydrocarbon migration has travelled vertically, and is restricted laterally to the Upper Jurassic and Palaeogene successions. According to Balson et al. (2001), hydrocarbon extractions can be made in successions of clastics or carbonates ranging from the Devonian and Eocene strata. Brooks et al. (in press) suggest that the reservoirs with producing fields are of Upper Jurassic to Lower Cretaceous syn-rift reservoirs with various trapping mechanisms such as tilted fault block, domes and stratigraphic closures. Additionally, the post rift Lower Cretaceous mudstones also provide a regional seal for many traps. The reservoir of both periods comprises of both shallow and deep marine sandstones.