bluuebunny/crossref_metadata_2025_split huggingface dataset:
Sequence stratigraphic control on Middle and Upper Jurassic reservoir distribution within the UK Central North Sea
Authors: DONOVAN A. D. , DJAKIC A. W. , IOANNIDES N. S. , GARFIELD T. R. , JONES C. R. 
Published: April 2010

An integrated sequence stratigraphic analysis, utilizing seismic data, well-log cross-sections, biostratigraphic information, and core descriptions, provides a chronostratigraphic framework to analyse and predict the distribution of reservoir sandstones within the Middle to Upper Jurassic section of the UK Central North Sea.
The Callovian (Middle Jurassic) through Ryazanian (lowermost Cretaceous) section in the UK Central North Sea forms a depositional wedge that thins towards the western graben margin. This wedge is bounded by surfaces traditionally interpreted as the Middle Cimmerian and Late Cimmerian unconformities. Marginal marine (Fulmar) sandstones are present within this wedge, and can be subdivided into informal lower and upper Fulmar members. Each member has a unique spatial and temporal distribution within the basin that can be related to primary depositional palaeogeography, post-depositional erosion, and basin tectonics.
The lower member of the Fulmar Formation is Callovian to Early Oxfordian in age, and is restricted to the Central Graben. This member overlies Middle Jurassic strata of the Pentland Formation, and is conformably overlain by Oxfordian-age strata of the Kimmeridge Clay. The upper member of the Fulmar Formation is Early Kimmeridgian in age, and is distributed along the western graben margin. The upper member is conformably overlain by Kimmeridgian-age strata of Kimmeridge Clay, and typically overlies Triassic deposits of the Skagerrak Formation.
Post-depositional erosion, association with relative falls in sea-level and accentuated by basement and salt tectonism, is the major factor that modifies primary depositional patterns within the Fulmar Formation. Truncation associated with unconformities interpreted as the 142 Ma, 138 Ma, and 136 Ma sequence boundaries affect the distribution, fades patterns, and thickness of the upper member of the Fulmar. These unconformities, as well as the 155.5 Ma, 150.5 Ma and 144 Ma sequence boundaries, may also affect the lower member of the Fulmar.
Application of sequence stratigraphy and trace fossil analysis to reservoir description: examples from the Jurassic of the North Sea
Authors: TAYLOR A. M. , GAWTHORPE R. L. 
Published: April 2010

Recent sequence stratigraphic schemes proposed for the North Sea Jurassic have been developed primarily as exploration tools to predict reservoir distribution away from well control. As a result, most of these schemes are at the megasequence and depositional sequence scale. In field-scale studies where significant core is available, integration of trace fossil studies with other available correlation data (sedimentological, biostratigraphic, seismic, well log) can increase the precision and resolution of the sequence stratigraphic framework so that it is applicable to development and production problems.
Trace fossils effectively provide an in situ record of environment and environmental change. They can be used to identify depositional facies and facies shifts, as indicators of salinity change, as direct indicators of stratal surfaces and condensed sections, and in evaluating the significance of palaeosols. This often allows stratal surfaces to be identified where other data fail (e.g. tracing marine flooding surfaces into the coastal plain and offshore shelf) and provides a way of tackling highly bioturbated shallow marine reservoirs.
On a field scale, parasequence correlation is usually at a higher resolution than biostratigraphy and provides a deterministic approach to the evaluation of sandbody architecture and permeability barrier geometry. Such a sequence stratigraphic framework is crucial to (i) identifying field-wide permeability barriers (e.g. marine shales and cemented zones associated with marine flooding surfaces); (ii) understanding the stacking pattern, connectivity and anisotropy of reservoir sandbodies; and (iii) identifying horizons of incision (sequence boundaries) which may erode through units that would otherwise form field-wide permeability barriers. High-resolution, field-scale sequence stratigraphy thus provides a framework for prediction of reserves, reservoir simulation and field development planning.
Case studies from (i) the Halten Terrace (Lower to Middle Jurassic); and (ii) the Central Graben area (Upper Jurassic), both from the Norwegian Continental Shelf, are presented to illustrate the use of high-resolution sequence stratigraphy in the stratigraphic description of hydrocarbon fields.
Late Jurassic plays along the western margin of the Central Graben
Authors: WAKEFIELD L. L. , DROSTE H. , GILES M. R. , JANSSEN R. 
Published: April 2010

The distribution of the Lower Kimmeridgian Fulmar sands along the edge of the Western Platform of the Central Graben is intimately related to Triassic halokinetic activity. Withdrawal of Zechstein evaporites resulted in the development of thick packages of Triassic Smith Bank claystones, the so-called ‘Smith Bank Pods’. The crests of the Zechstein evaporite highs were later subjected to groundwater dissolution, resulting in topographic lows, which controlled the pattern of drainage during the deposition of the Triassic Skagerrak sands.
The Triassic salt movements associated with this phenomenon also exercised the underlying control on later drainage patterns in the Jurassic. The relative sea-level rise in the Early Kimmeridgian flooded the margin of the Western Platform which reworked the original valley fill and, together with erosion products from the hinterland, resulted in the deposition of the shallow marine sands of the Fulmar Formation.
3D seismic can reveal the extent of these palaeovalley systems draining into the Central Graben. The Fulmar sand packages are effectively encased in shales; a lateral seal is formed by the Smith Bank Formation and the top seal consists of Kimmeridgian shales. They represent an attractive possibility for stratigraphically trapped hydrocarbons.
Appraisal geology of the Saltire Field, Witch Ground Graben, North Sea
Authors: CASEY B. J. , ROMANI R. S. , SCHMITT R. H. 
Published: April 2010

Saltire is a structurally and stratigraphically complex field that lies within the Witch Ground Graben. It is located 200 km northeast of Aberdeen, Scotland in UK North Sea Block 15/17. Three sandstone reservoirs contain an estimated 224 × 10
6
BBL of oil-in-place within a 2500 acre closure.

The field was discovered in 1988. Subsequent appraisal drilling incorporated 3D seismic and detailed stratigraphic studies to produce the coherent geological reservoir models needed for development planning. Field production will begin in 1993.
The Upper Jurassic section contains the Piper and Galley sandstone reservoirs which occur within a broad, E-W-orientated fault terrace. Northerly closure results from a down-to-the-south normal fault. Southern and westerly closures result from Piper sandstone erosional truncation and Galley sandstone pinch-out. Both reservoirs have easterly dip closure.
The Piper Formation is a fluvial to wave-influenced deltaic marine sequence of latest Oxfordian to mid-Kimmeridgian age. It is up to 280 ft thick. The reservoir is fault separated into Main and Western areas with API oil gravities of 42.5° and 38°, respectively.
The Galley sandstone reservoir contains 42.5° API gravity oil and occurs within the northeast area. It is a deep marine turbidite sequence of late Kimmeridgian age and has a maximum reservoir thickness of 205 ft.
An Early Cretaceous sandstone reservoir occurs within the upper Valhall Formation. It comprises two marine turbidite sandstones of late Barremian to early Aptian age, with up to 95 ft of composite thickness. The reservoir has three-way dip closure, pinches out by onlap to the north and contains 33° API gravity oil.
Salt control on Triassic reservoir distribution, UKCS Central North Sea
Authors: SMITH R. I. , HODGSON N. , FULTON M. 
Published: April 2010

During Triassic deposition in the Central North Sea, synforms developed on the surface of the extending Zechstein salt. In the ensuing continental environment, coarse-grained clastic sediments were deposited in such depressions. These were later preserved as sediment ‘pods’. A progressive increase in coarse clastic input to the Central North Sea Basin during the Triassic was concurrent with continued salt movement and pod subsidence. During Late Triassic times the best initial reservoir quality sands were developed in the axes of TR30 sediment pods (e.g. Marnock facies). Early Fe-rich chloritization of these high-quality reservoir facies, combined with overpressure development, has resulted in the subsequent, relatively local, preservation of high-quality Triassic reservoirs, often at substantial depths.
Understanding the basin-scale halokinetic controls on Triassic sequence and facies development, as well as the subsequent diagenetic effects, is crucial to establishing a framework for Triassic reservoir prediction.
We have combined the re-interpretation of newly acquired and reprocessed seismic data with sedimentological and diagenetic studies of available core material. This has enabled the generation of a model for evaluating the distribution of Triassic reservoir and hence exploration potential in the Central North Sea.
Low-angle faulting in the Triassic of the South Viking Graben: implications for future correlations
Authors: MORGAN R. K. , CUTTS P. L. 
Published: April 2010

A detailed study of bedding geometry in the Triassic strata of the Crawford Field, South Viking Graben, has revealed steep-bedding dips, in excess of 40° towards the west, sandwiched between Permian and Middle Jurassic to Cretaceous strata dipping gently eastwards. Reconstructions show an area of Triassic strata to be cut out at a high angle against the underlying Permian. This bedding geometry has been interpreted to indicate the presence of a detachment horizon towards the top of the Permian section onto which faulting within the Triassic has flattened. This faulting is pre-Middle Jurassic in age and affects the entire Triassic section in the region of the Crawford Field. The extent of bedding rotation is such that a considerable thickness of Triassic section has been cut out against the fault and detachment surface.
The formation of planar shear fractures is associated with faulting in the Triassic strata. Most of these fractures parallel the fault trend and are interpreted to have formed during the early stages of fault movement, as they presently dip at a low angle towards the east. Cataclastic processes have dramatically reduced porosity along the fractures which may now represent permeability baffles.
Recognition of this intra-Triassic structure means fault and roll-over geometries must be carefully modelled before any attempt at stratigraphic correlation within the Triassic can be made. Equally, if this style of faulting is more widespread, then areas of Triassic strata previously considered internally ‘uncorrectable’ may well benefit from a closer examination of bedding attitude and structure.
Late Paleozoic plays in East Greenland
Authors: CHRISTIANSEN F. G. , LARSEN H. C. , MARCUSSEN C. , PIASECKI S. , STEMMERIK L. 
Published: April 2010

A series of Late Paleozoic–Mesozoic basins, which formed as the result of rifting between Greenland and Norway following the Caledonian orogeny, are exposed in East Greenland between 70° and 76°N. The Paleozoic part of the sedimentary basin fill has a cumulative thickness of up to 13 km.
The region seems prospective but exploration is still at an early stage without exploration wells. Basic petroleum-related studies of outcrops have been carried out throughout the region, and 1800 km of high-quality multi-fold seismic data have been acquired in Jameson Land between 70° and 72°N.
A number of pre-, syn- and post-rift play types are suggested on the basis of inferred source and reservoir rock distribution as well as structural and thermal history. Some of the play concepts have been identified in outcrop, others have been recognized during the seismic interpretation.
The principal Upper Paleozoic source rocks include Upper Devonian shales (freshwater), Upper Carboniferous lacustrine shales (freshwater to slightly saline), and Upper Permian marine shales (some carbonate influence). The main reservoir facies are fluvial sandstones in the Upper Devonian to Lower Permian succession and Upper Permian platform and build-up carbonates.
Syn-rift Carboniferous plays (mainly structural) and post-rift Upper Permian carbonate plays (essentially stratigraphic) seem most promising. The syn-rift plays have lacustrine shales as source rocks, fluvial Carboniferous to Lower Permian sandstones as reservoirs, and overlying fluvial/lacustrine shales as seal. The post-rift Upper Permian plays have carbonate build-ups and platforms as reservoir targets and the juxtaposed marine shales as source rock and seal.
Carboniferous depositional systems of the Southern North Sea
Authors: COLLINSON J. D. , JONES C. M. , BLACKBOURN G. A. , BESLY B. M. , ARCHARD G. M. , McMAHON A. H. 
Published: April 2010

A study of the Carboniferous sequences in some 93 wells from onshore England to onshore Netherlands has provided data on variations of depositional styles, sandbody dimensions and petrographic composition, both through time and, in the Upper Carboniferous, across the basin. Three separate sources of sediment input are recognized: a dominant, and petrographically fairly uniform, north to south-flowing sediment distribution system which shows a general southerly decrease in channel sandbody size and abundance; a less important source on the Anglo-Brabant Massif; and a probable third source in SE Holland.
Through time, there was a progressive increase in petrographic maturity, while channel sandbody percentages decrease to a minimum in the Westphalian B and then begin to increase again through the Westphalian C and D. Compared to the UK onshore, there is a close similarity between the Dinantian successions on the Mid North Sea High and in the Northumberland Basin and marked contrasts in sedimentation styles between the offshore Red Beds sequences in the centre of the basin and those seen onshore in the English Midlands. Regional mapping of channel sandbody statistics for different stratigraphic intervals could guide future exploration efforts towards areas with greater reservoir potential.
Structural and sedimentological controls on diagenesis in the Ravenspurn North gas reservoir, UK Southern North Sea
Authors: TURNER P. , JONES M. , PROSSER D. J. , WILLIAMS G. D. , SEARL A. 
Published: April 2010

The Rotliegend Lower Leman Sandstone Formation has been studied near the northern limit of its development in Ravenspurn North to determine the influence of structure, sedimentology and diagenesis on reservoir quality. The Lower Leman Sandstone in this area is about 300 ft thick and comprises six depositional cycles which reflect alternating periods of relatively dry and wet climate. Aeolian sands form the best reservoir and formed as small westward-migrating transverse dune fields and draa, at most 60 ft thick. These dunes were frequently reworked by southerly derived, strong fluvial sheetfloods which drained into the Silverpit playa lake.
The Ravenspurn area is divided into main northwest-southeast-trending fault blocks which are markedly different in terms of their diagenetic evolution and reservoir performance. The northeasterly B structure contained gas earlier and was unaffected by mid- to late Jurassic illitization. The southwesterly A structure was uplifted later and received accumulated gas after reservoir quality was reduced by pervasive illitization.
A hierarchy of factors influenced the diagenesis. These were the primary lithological variation, burial history and the structural development of the Ravenspurn North area. Depositional processes also influenced diagenesis; the deposition of allogenic clay and the formation of early quartz, non-ferroan dolomite and anhydrite reduced the reservoir quality of fluvial sheetfloods. Burial diagenesis resulted initially in ferroan dolomite, kaolinite and later quartz precipitation in available primary and secondary porosity. Stable isotope and fluid inclusion studies indicate that ferroan dolomite and later quartz precipitated at about 100°C in Triassic-early Jurassic times from reduced fluids derived partly from the Carboniferous basement. Mixing of these fluids with more alkaline connate water was the main triggering mechanism for authigenic mineral formation.
Gas accumulation took place first in the northeasterly B structure which had early closure; the last authigenic phase to precipitate here was poikilotopic siderite at temperatures of about 120°C. Elsewhere diagenetic fluids evolved to a more alkaline state and widespread illitization took place which particularly affected more permeable aeolian facies. The illitization reduced the reservoir quality of the Lower Leman Sandstone and contributed to diagenetic sealing (to the northwest) of the field. K–Ar dating indicates that peak illitization took place between 150–170 Ma (mid–late Jurassic). Subsequent periods of uplift in the late Cimmerian and particularly during the early Tertiary–Miocene produced the final structure of Ravenspurn North and the spillage of gas into this structure. The combination of structural and diagenetic events explains the differences in reservoir quality and well performance of the two structural blocks in the field.
The Fleetwood Dyke and the Tynwald fault zone, Block 113/27, East Irish Sea Basin
Authors: ARTER G. , FAGIN S. W. 
Published: April 2010

A series of Tertiary dolerite intrusions, the Fleetwood Dyke Group, is intruded into Triassic sediments of the northern East Irish Sea Basin (EISB). Well 113/27-1 penetrated a total of 375 m of dolerite within the Mercia Mudstone Group (MMG). Samples of dolerite have been dated (K–Ar) at between 61 and 65 Ma. Apatite fission track analysis on samples from the same well indicates that approximately 2000 m of uplift occurred in the early Tertiary, at about the same time as dyke intrusion.
Using seismic and marine magnetic data, the Fleetwood Dyke Group has been mapped in the vicinity of Block 113/27 to reveal a complex set of dykes and sills. The presence of these intrusions within the MMG results in velocity pull-ups on the underlying Ormskirk Sandstone Formation (OSF), a potential exploration pitfall.
The geometry of the igneous intrusion has been influenced by the structure of the Tynwald fault zone. This feature is interpreted to have formed in the Triassic as a result of listric faulting detached on Permian evaporites. This interpretation is supported by balanced section reconstruction.
The effect of Late Caledonian and Variscan continental escape tectonics on basement structure, Paleozoic basin kinematics and subsequent Mesozoic basin development in NW Europe
Authors: COWARD M. P. 
Published: April 2010

Caledonian structures in NW Europe formed by northwestward accretion of continental fragments and magma tic arcs onto the Proterozoic North Atlantic Craton. The main crustal fabrics were formed by Caledonian basin development, subsequent inversion, collision tectonics with thick-skinned and thin-skinned thrusts and large NW–SE strike-slip faults. These fabrics were modified and offset by late Caledonian displacement on NE–SW-trending strike-slip faults.
Late Caledonian (Devonian and Early Carboniferous) tectonics in NW Europe resulted from the lateral expulsion of the English–North Sea–Baltic Block away from an Acadian indentor. The block was approximately triangular in shape bounded by (i) the Ural Ocean to the east, (ii) the left-lateral Great Glen–Midland Valley–North Atlantic shear systems to the NW and (iii) the right-lateral English Channel–South Polish Trough shear systems (in Devonian times) and the South Wales–Southern North Sea–Polish Trough shear zone (in Early Carboniferous times) to the south. During the Early Carboniferous the block expanded NW–SE, as it was released from the indentor, into space created by back-arc extension related to Variscan subduction.
Pull-apart basins which developed along the shear systems include the following, (i) In the Northern North Sea, the West Orkney Basin–East Shetland Platform–Viking Graben formed as a large pull–apart basin in the left-lateral shear systems during Devonian/Early Carboniferous times, (ii) In the Southern North Sea and East Midlands, NW-trending Carboniferous basins developed in a right-lateral shear system, associated with clockwise rotation of Caledonian basement blocks.

The Devonian and Carboniferous basin-fill depended on the position of the block boundary shear systems in the Caledonian and Variscan orogens and their thickened crust. The northern shear boundary affected crust
c.
50 km thick following Caledonian collision and hence the syn-rift and post-rift sediment fill was dominantly intracontinental. In the south the basin developed in crust of average thickness and hence marine conditions were dominant during the extension. However, Devonian and Carboniferous basins in the Northern North Sea provided channels for sediment fill from the Caledonian mountains into the southern basins.

During the Late Carboniferous, closure of the Ural Ocean and Ural plate collision reversed the sense of shear along the block margins and the wedge-shaped block was pushed back between the Acadian collision zones. This shear reversal caused inversion of the pull-apart and expansion basins in northern Britain. Subsequent reactivation of these basins during the Mesozoic was responsible for the tectonic framework of the North Sea.
Regional structural evolution of the North Sea: oblique slip and the reactivation of basement lineaments
Authors: BARTHOLOMEW I. D. , PETERS J. M. , POWELL C. M. 
Published: April 2010

Basement lineaments pre-dating the dominant Mesozoic basin formation of the North Sea are fundamental controlling features within the polyphase tectonic evolution of NW Europe. These inherent zones of weakness were repeatedly reactivated during the evolution of the North Sea rift system. The regional and geometrical constraints imposed by the presence of these pre-existing tectonic grains during the Mesozoic extensional deformation suggest that oblique-slip movement must have occurred along many of the basin-bounding faults in a non-preferential orientation for dip-slip reactivation.
While the North Sea can be considered in broad terms as a series of linked, elongated grabens developed in response to dominantly E–W extensional intra-plate stresses, the orientation, distribution and character of pre-existing shear zones ultimately controlled the geometry of many Mesozoic basins and their faulted margins.
Four types of inherent basement features are recognized as having influenced subsequent basin development: (a) wide, diffuse zones of NW–SE and NE–SW basement shear, e.g. in the Central Graben; (b) narrow shear zones oblique to primary Mesozoic extensional faults, e.g. in the East Shetland Basin; (c) E–W-trending discrete fault systems, e.g. on the Western Platform; and (d) massive palaeohighs, e.g. the Halibut Horst.
The distribution of these distinct structural features throughout the North Sea was controlled by Early Paleozoic plate tectonic evolution. Repeated Mesozoic and Cenozoic reactivation along fundamental zones of weakness, including oblique-slip displacements and basinal inversion, has led to areas of highly complex structuration. Hence, there is the potential for numerous structural and stratigraphic hydrocarbon trapping mechanisms associated with these underlying basement lineaments.
Although the total amount of horizontal crustal movement may be limited, understanding of the role of oblique-slip along pre-existing zones of weakness and the effect of long-lived palaeohighs within the basin is crucial to place Mesozoic and Tertiary hydrocarbon accumulations within a realistic North Sea tectono-stratigraphic framework.