Abstract The Buzzard Field remains the largest UK Continental Shelf oil discovery in the last 25 years. The field is located in the Outer Moray Firth of the North Sea and comprises stacked Upper Jurassic turbidite reservoirs of Late Kimmeridgian–Mid Volgian age, encased within Kimmeridge Clay Formation mudstones. The stratigraphic trap is produced by pinchout of the reservoir layers to the north, west and south. Production commenced in January 2007 and the field has subsequently produced 52% over the estimated reserves at commencement of development, surpassing initial performance expectations. Phase I drilling was completed in 2014 with 38 wells drilled from 36 platform slots. Platform drilling recommenced in 2018, followed in 2019 by Phase II drilling from a new northern manifold location. The evolution of the depositional model has been a key aspect of field development. Integration of production surveillance and dynamic data identified shortcomings in the appraisal depositional model. A sedimentological study based on core reinterpretation created an updated depositional model, which was then integrated with seismic and production data. The new depositional model is better able to explain non-uniform water sweep in the field resulting from a more complex sandbody architecture of stacked channels prograding over underlying lobes.

Abstract The Solan Field is a Jurassic reservoired oil accumulation located in Block 205/26a in the East Solan Basin, West of Shetland. The field was discovered in 1991 by the 205/26a-4 well which encountered oil in the Kimmeridgian to Early Volgian age Solan Sandstone and appraised between 1992 and 2009 by four wells and four sidetracks. Premier Oil farmed into Licence P.164 in 2011 and became operator. The reservoir, which is up to 100 ft thick, is a basin-floor turbidite sequence and is informally subdivided into a thick and good quality Upper Solan sandstone unit and a thinner, poorer quality, Lower Solan sandstone unit, separated by the laterally extensive Middle Solan unit. Whilst the reservoir sandstones are relatively clean (texturally and compositionally mature) and laterally extensive, sub-seismic structural and stratigraphic complexity resulted in a challenging field development. The field development to date comprises four subsea wells (two oil producers and two water injectors) tied back to a small jacket and topsides with an innovative subsea oil storage tank. Oil export is via shuttle tanker. First oil was achieved in April 2016. The field oil in place volume is in the range of 55–85 MMbbl.

Abstract The Middle Jurassic–Lower Cretaceous in the eastern Dutch offshore provides excellent examples of sand-rich sediments that locally accumulated in the vicinity of rift basin margins affected by salt tectonics. These types of deposits are often geographically restricted and difficult to identify, but can be valuable targets for hydrocarbon exploration. The distribution, thickness and preservation potential of fluvio-lacustrine, shallow- and deep-marine sediments is discussed to provide new insights into the regional and local tectonostratigraphy of the Dutch Central Graben, the Terschelling Basin and their neighbouring platforms. New sedimentological, geochemical, biostratigraphic, stratigraphic and structural information have been analysed and integrated into a new tectonostratigraphic model for the Callovian Lower Graben Formation, Oxfordian Middle and Upper Graben formations, Early–Middle Volgian Terschelling Sandstone and Noordvaarder members, and the Late Volgian–Early Ryazanian Scruff Greensand Formation. It is demonstrated that salt withdrawal at the basin axis was the primary control on the generation of high accommodation during the Callovian–Early Kimmeridgian. Incised valleys developed on the platforms providing lateral sediment input. During the Late Kimmeridgian–Ryazanian salt migration shifted laterally towards the basin margins, providing accommodation adjacent to active salt bodies and deposition of overthickened sandy strata.

ABSTRACT The growth- and throw-rate variability on normal faults can reflect fault interaction, plate tectonic forces, and, in gravity-driven systems, variations in sediment loading. Because earthquakes may occur as faults slip, it is important to understand what processes influence throw rate variability on normal faults to be able to predict seismic hazards in extensional terranes. Furthermore, the rate of normal fault growth directly controls rift physiography, sediment erosion, dispersal and deposition, and the distribution and stratigraphic architecture of synrift reservoirs. Instrumental (e.g., geodetic) data may constrain the coseismic movement on, or relatively short-term (i.e., <10 3 yr) throw rate history of, normal faults, whereas paleoearthquake data may provide important information on medium-term (i.e., 10 3 –10 5 yr) rates. Constraining longer term (i.e., >10 6 yr) variations typically requires the use of seismic reflection data, although their application may be problematic because of poor seismic resolution and the absence of, or poor age constraints on, coeval growth strata. In this study, I use 3-D seismic reflection and borehole data to constrain the growth and (minimum) long-term throw rate variability on a gravity-driven, salt-detached normal fault (Middle–Late Jurassic) in the South Viking Graben, offshore Norway. Using these data, I recognise five main kinematic phases: (1) Phase 1 (early Callovian)—fault initiation and a phase of moderate fault throw rates (0.06 mm yr −1 ); (2) Phase 2 (early–end Callovian)—fault inactivity, during which time the fault was buried by sediment; (3) Phase 3 (early–late Oxfordian)—fault reactivation and a phase of moderate throw rates (up to 0.03 mm yr −1 ); (4) Phase 4 (latest Oxfordian)—a marked increase in throw rate (up to 0.27 mm yr −1 ); and (5) Phase 5 (early Kimmeridgian–middle Volgian)—a decline in throw rate (0.03 mm yr −1 ) and eventual death of the fault. These rates are comparable to those observed on other gravity-driven normal faults, with the variability in this example apparently kinematically coupled with the growth history of the thick-skinned, basin-bounding normal fault system. Fluctuations in sediment accumulation rate and loading may have also influenced throw rate variability. Shallow-marine reservoirs deposited when throw rate was relatively low (Phase 1) increase in thickness but do not change in facies across the fault, principally because sediment accumulation rate outpaced fault throw rate. In contrast, deep-marine turbidite reservoirs, despite being characterized by relatively high sediment accumulation rates, were deposited when the throw rate was relatively high (Phase 4), thus are only preserved in the fault hanging wall. Variations in throw and sediment accumulation rate may therefore act as dual controls on the thickness and distribution of synrift reservoirs in salt-influenced rift basins.

ABSTRACT Synrift to early postrift Upper Jurassic submarine fan sequences form the reservoirs of numerous large oil and gas condensate fields in the South Viking Graben. The largest of these fields are in the Brae area, on the western side of the graben. Here, proximal conglomerate and sandstone facies of the Brae Formation host the South Brae, Central Brae, and North Brae fields, each within its own discrete submarine fan unit. More distal, basin-floor sandstone facies derived from the later episodes of South Brae and North Brae fan activity host the Miller, Kingfisher, and East Brae fields. Interfan areas comprise thick sequences of fine-grained sediments, which provide very significant lateral stratigraphic trapping elements for all the fields. An extensive well and seismic data set now allows a more detailed tectonostratigraphic evaluation of the Jurassic reservoir sequences in the context of the development of the graben and footwall than was previously possible. The submarine fans resulted from the uplift of the Fladen Ground Spur footwall to the west, with the consequent erosion and redeposition into the graben of very large volumes of gravel, sand, and mud. A prerift sequence of the Bathonian alluvial to paralic Sleipner Formation, which culminated with deposition of an extensive coal unit, extends across the graben and was probably also deposited on the footwall. Late Jurassic rifting began in the early Callovian, with deposition of the Hugin Formation in a shallow marine setting, with sand and mud supplied from the low-relief platform area to the west. Episodes of abrupt but slight deepening of the basin, caused by initial fault movements at the graben boundary, are suggested by numerous sharp-based coarsening-upward sequences within this formation. Following a period of apparent quiescence, when the Fladen Ground Spur may have been flooded, the main rift phase began in the late Oxfordian when subsidence of the graben margin and uplift of the footwall resulted in a deep marine trough and subaerial relief on the footwall probably totaling several thousand feet (hundreds of meters). Early submarine fan systems are likely to have been relatively unorganized cones of conglomerate and sandstone deposited from noncohesive debris flows and high-density turbidity currents. Fan systems became more organized upward as accommodation space close to the graben margin was filled following the climax of rifting in the late Kimmeridgian, and two large proximal to basin-floor fan systems developed at South Brae and North Brae, with conglomeratic channels in the proximal areas and sheetlike sandstone units on the basin floor. In the later stages of Brae Formation deposition, the top of the footwall is likely to have been close to sea level, which allowed periodic flooding of the source area and deposition of regionally extensive, relatively thin mudstone units across the fans, which act as internal reservoir baffles within fields. At the peak of fan deposition, during the early Volgian, the three main fan systems in the area (the South, Central, and North Brae fans) plus several smaller fans were all active. However, fans became inactive sequentially, with deposition first on the Central Brae, then on the South Brae, and finally on the North Brae fans ceasing relatively abruptly as the Fladen Ground Spur was progressively transgressed. Deposition of mudstones of the Kimmeridge Clay Formation, which are the hydrocarbon source rocks and the top seals for the fields and with which the Brae Formation interdigitates, continued after fan deposition ceased, into the earliest Cretaceous. The current sub-Upper Jurassic basement rock types of the footwall in the immediate area of the Brae fields comprise well-lithified Devonian sandstones and a significant but minor area of Silurian granite. However, the origin of the coarse clastic detritus, particularly the sands, within the Upper Jurassic fan systems was not simply a result of erosion of these rock types. Regional mapping and provenance studies suggest that a considerable thickness of Middle Jurassic, Triassic, and Permian sedimentary rocks previously overlay the present-day basement rocks of the footwall. These strata were probably almost completely eroded from the area immediately west of the fields where footwall uplift is likely to have been the greatest and redeposited into the graben during the Late Jurassic.