Abstract Onshore exploration success during the first half of the 20th century led to petroleum production from many, relatively small oil and gas accumulations in areas like the East Midlands, North Yorkshire and Midland Valley of Scotland. Despite this, the notion that exploration of the United Kingdom’s continental shelf (UKCS) might lead to the country having self-sufficiency in oil and gas production would have been viewed as extremely fanciful as recently as the late 1950s. Yet as we pass into the new century, only thirty-five years on from the drilling of the first offshore well, that is exactly the position Britain finds itself in. By 2001, around three million barrels of oil equivalent were being produced each day from 239 fields. The producing fields have a wide geographical distribution, occur in a number of discrete sedimentary basins and contain a wide spectrum of reservoirs that were originally deposited in diverse sedimentary and stratigraphic units ranging from Devonian to Eocene in age. Although carbonates are represented, the main producing horizons have primarily proved to be siliciclastic in nature and were deposited in environments ranging from aeolian and fluviatile continental red beds, coastal plain, nearshore beach and shelfal settings all the way through to deep-marine, submarine fan sediments. This chapter attempts to place each of the main producing fields into their proper stratigraphic, tectonic and sedimentological context in order to demonstrate how a wide variety of factors have successfully combined to produce each of the prospective petroleum play fairways and hence, make the UKCS such a prolific and important petroleum province.

Abstract From Permian to Jurassic times the northern Viking Graben and adjacent platform areas experienced multiple rifting, the Permian-early Triassic and middle-late Jurassic rift episodes, separated by an intervening middle Triassic-middle Jurassic inter-rift period dominated by relative tectonic quiescence. The associated syn and inter-rift strata show large variations in sedimentary architecture as a result of temporal and spatial variations in tectonic deformation and subsidence, sediment supply, climate and accommodation creation. The Permian-early Triassic syn-rift succession is believed to consist predominantly of nonmarine, arid to semiarid, aeolian, sabkha, alluvial and lacustrine strata, probably interbedded with marine strata on the Horda Platform and in the Viking Graben. The middle Triassic-middle Jurassic experienced several subsidence stages which, together with climatic variations, exerted a major control on the periodic outbuilding and retreat of rift marginal, alluvial and shallow marine clastic wedges. Evidence for fault block rotation suggests that the subsidence was caused partly by minor extensional stages. As such, the middle Triassic-middle Jurassic does not fit the type of development assumed to be typical for either post or pre-rift basins. Hence, the notation inter-rift is assigned to this period and the associated succession. The middle-late Jurassic rift episode was characterized by multiple rift phases separated by intervening stages of relative tectonic quiescence. The syn-rift infill is mixed non-marine and marine and consists of fluvial through shallow marine and shelfal deposits to deeper marine sediment gravity flow and (hemi-)pelagic strata. At the larger scale, related to the entire middle-late Jurassic rift episode, the syn-rift infill in general shows a two-fold sandstonemudstone lithology motif, typical of underfilled rift basins. At the intermediate scale, related to single rift phases, threefold sandstone-mudstone-sandstone, twofold sandstone-mudstone and single mudstone lithology motifs are present, typical of sediment overfilled/ sediment balanced, sediment underfilled and sediment starved rift basins, respectively. The spatial and temporal variations in the syn-rift infill reflect relative distance to the rift basin hinterland areas (which had a large sediment yield potential) and overall increased tectonic subsidence and enhanced rift topography as the rift basin evolved. This suggest that the tectonostratigraphic evolution of the northern North Sea rift basin can be viewed at several scales: at the largest scale the rift basin evolved through multiple rift episodes, which commonly had a duration of several tens of Ma. The rift episodes are separated by inter-rift periods. Rift episodes are subdivided into intervals representing distinct rift phases. These rift phases were separeted by tectonic relatively quieter intervals, here referred to as tectonic quiescence stages. Inter-rift periods are subdivided into prolonged tectonic quiescence intervals separated by short-lived rift stages or minor rift phases. Distinct rift phases and inter-rift tectonic quiescence intervals commonly represent periods of a few to 10+ Ma, and correspond to second-order sequences or ‘megasequences’. At the smaller scale, syn-rift successions can be subdivided into packages related to distinct rotational tilt event or faulting events (deformation spans), representing hundreds of ka to few Ma and corresponding to third-order sequences. Solitary, large-magnitude faulting events (deformation clines) are likely to exert a major control on high frequency base or sea level fluctuations and thus on the development of higher-order sequences. However, such a control is difficult to prove and can probably only be recognized in sub-basins with abundant wells and a dense well spacing.

Abstract Slides and mass-transport-related materials constitute large volumes of sediments in deepwater settings. During the past decade, extensive interpretations of 3D seismic data, done by many companies, have indicated that such deposits are quite common along most deepwater margins. In some basins, individual depositional sequences in the upper Pleistocene may consist of more than 50% slides and/or deformed sediments. For example, in deepwater Brunei, such elements comprise 50% of the depositional sequences ( McGilvery and Cook, 2003 ), offshore Nile they average 50% of the depositional sequences and in some areas they constitute as much as 90% of the sequences ( Newton et al., 2004 ), and offshore Trinidad they comprise 50% of the depositional sequences (C. Shipp, personal communication, 2004). Slides and mass-transport-related sediments are rarely primary reservoirs and are certainly not primary exploration targets in siliciclastic settings. However, we review these deposits here because (1) they constitute important aspects of deepwater sediment fill, (2) they can be important regional seals and, most critically, (3) their distribution in the shallow subsurface is an important factor that should be identified in any assessment of drilling hazards and in geotechnical studies for exploration and development planning. Specifically, the transportation and deformation of mass-transport complexes and slides causes water expulsion. As a consequence, these features commonly are overcom-pacted in the shallow subsurface, so that drilling through them can decrease drilling rates significantly. With rig costs in deep water averaging $0.25 to $0.4 million/day, shorter drilling times are imperative. The accomplishment of shorter drilling

Abstract Slides and mass-transport-related materials constitute large volumes of sediments in deepwater settings. During the past decade, extensive interpretations of 3D seismic data, conducted by many companies, have indicated that such deposits are quite common along most deepwater margins. In some basins, individual depositional sequences in the upper Quaternary may consist of more than 50% slides and/or deformed sediments. For example, in Basin 4 of the Brazos Trinity system in the northwestern Gulf of Mexico, 50–60% of the ponded sequence is composed of mass–transport deposits ( Beaubouef et al., 2003 ); in deepwater Brunei, such elements comprise 50% of the depositional sequences ( McGilvery and Cook, 2003 ); offshore the Nile they average 50% of the depositional sequences, and in some areas, they constitute as much as 90% of the sequences ( Newton et al., 2004 ); and offshore eastern Trinidad they comprise 50% of the Quaternary depositional sequences (C. Shipp, personal communication, 2004). Slides and mass-transport-related sediments are rarely primary reservoirs and are certainly not primary exploration targets in siliciclastic settings. However, we review these deposits here because (1) they constitute important aspects of deepwater sediment fill, (2) they can be important regional seals, and, most critically, (3) their distribution in the shallow subsurface is an important factor that should be identified in any assessment of drilling hazards and in geotechnical studies for exploration and development planning. Specifically, the transportation and deformation of mass-transport deposits and slides appear to cause water expulsion. As a consequence, these features commonly are overcom-pacted