bluuebunny/crossref_metadata_2025 huggingface dataset:
The Auk Field, Block 30/16, UK North Sea
Authors: Trewin Nigel H. , Bramwell Mark G.
Published: April 2008

The Auk field is located in Block 30/16 at the western margin of the Central Graben. Oil is contained in a combination stratigraphic and structural trap which is sealed by Cretaceous chalk and Tertiary claystones. An oil column of up to 400 ft is contained within Rotliegend sandstones, Zechstein dolomites, Lower Cretaceous breccia and Upper Cretaceous chalk. Production has taken place since 1975 with 80% coming from the Zechstein, in which the best reservoir lithology is a vuggy fractured dolomite where porosity is entirely secondary due to the dolomitization process and leaching of evaporites. Both Rotliegend dune slipface sandstones, and the Lower Cretaceous breccia comprising porous Zechstein clasts in a sandy matrix, also contribute to production. Poor seismic definition of the reservoir results in reliance on well control for detailed reservoir definition. The field has an estimated ultimate recovery of 93 MMBBL with 13 MMBBL remaining at the end of 1988.

The Auk field is situated in Block 30/16 of the Central North Sea about 270 km ESE from Aberdeen in 240-270 ft of water (Fig. 1). The field covers an area of about 65 km2 and is a combination of tilted horst blocks and stratigraphic traps, located at the western margin of the South West Central Graben. The Auk horst is about 20 km long and 6-8 km wide, with a NNW-SSE trend. It is bounded on the west by a series of faults with throws of up to 1000 ft, and the eastern boundary fault has a throw of 5000 ft in the north reducing to zero in the south (Fig. 2). The horst is a westward tilted fault block in the north which grades into a faulted anticline in the south. The Auk accumulation is largely contained within Zechstein dolomites and is ultimately sealed by Cretaceous chalk which overlies the base Cretaceous erosion surface. An E-W cross-section of the field is illustrated by Fig. 3. Auk was the first of the alphabetical sequence of North Sea sea-bird names used for Shell/ Esso fields.
The Buchan Field, Blocks 20/5a and 21/1a, UK North Sea
Authors: Edwards C. W.
Published: April 2008

The Buchan Oilfield is located in Blocks 21/la and 20/5a of the UK North Sea, on the southern side of the Witch Ground Graben. The Buchan structure is a complex tilted and dissected fault block formed during Jurassic extension and rifting. The Upper Devonian-Carboniferous reservoir is composed of fluvial Old Red Sandstone facies sandstones sealed by Lower Cretaceous mudstones and contains a 585m (1919 ft) thick oil column. Poor matrix porosities and permeabilities are enhanced by a pervasive fracture system, although faulting in the reservoir restricts communication between several of the nine producing wells. Hydrocarbon migration has occurred from a mature Upper Jurassic source rock north of the field into the structure across the flank faults. Production of the highly under-saturated oil is by depletion drive with some aquifer sweep to a floating production facility and onward transmission to the Forties Field by pipeline. Production commenced in 1981 and original recoverable reserves are estimated at 90 MMBBL of which 71.5 MMBBL have already been produced.
The Chanter Field, Block 15/17, UK North Sea
Authors: Schmitt H. R. H.
Published: April 2008

The Chanter Field is located 11 krn southeast of the Piper Alpha platform location in Block 15/17. The field was discovered by the 15/17–13 well, which tested 37.8° API crude from Galley sandstone turbidites and 52.1& API gas-condensate from the shallow marine sands of the Piper Formation. The Galley sandstone reservoir is overpressured, whereas the Piper sandstone reservoir is normally pressured. The bulk of the field occupies the culmination of a structural terrace on the downthrown side of the main E-W fault forming the northern margin of the Witch Ground Graben in this area. It has dip closure to the east, south and west and fault closure to the north. The 'main block' gas-water contact of 13 080 ft TVSS in the Piper sandstone and the oil-water contact of 12 240 ft TVSS in the Galley sandstone were deduced from wireline pressure measurements and have not been encountered in wells. Estimated proved reserves of 4.6 MMBBL of crude oil and condensate liquids and 20.8 BCF of gas will be produced through a cluster of wells tied back to the Piper Field by a subsea pipeline.
The Highlander Field, Block 14/20b, UK North Sea
Authors: WHITEHEAD M. , PINNOCK S. J.
Published: April 2008

Highlander Field, discovered in 1976, is a small oil accumulation located 7½ miles northwest of the Tartan Platform and 114 miles northeast of Aberdeen in UK Block 14/20b. The Field lies on the NW-SE-trending Claymore-Highlander Ridge which forms the southern margin of the Witch Ground Graben. Upper Jurassic sandstones of the shallow marine Piper Formation and deeper marine turbidites (the 'Hot Lens Equivalent') within the Kimmeridge Clay Formation form the principal reservoirs. An additional important reservoir occurs within Lower Cretaceous turbidite sandstone and a small crestal accumulation occurs in Carboniferous deltaic sandstone. The structure is a tilted NW-SE-trending fault block downthrown to the northeast. The sandstone reservoirs all dip to the south and southwest and become thin due to onlap or truncation to the north. The Field has a combined structural-stratigraphic trap configuration. Seal is provided by Upper Jurassic siltstone and Lower Cretaceous calcareous clay stone. The accumulations have been sourced from the Kimmeridge Clay Formation in adjacent basins. Eight wells delineate the structure and production is currently 30 000 BOPD. Ultimate recoverable reserves are 70 million barrels of crude oil. Development has been achieved utilizing an innovative remote subsea system, connected to the Tartan Platform 7½ miles to the southeast.
The Ivanhoe and Rob Roy Fields, Blocks 15/21a-b, UK North Sea
Authors: Parker R. H.
Published: April 2008

The Ivanhoe and Rob Roy Fields are located in the Outer Moray Firth Basin, seventy nautical miles off the northeast coast of Scotland. The Ivanhoe Field was discovered in 1975, and the Rob Roy Field in 1984. The reserves in both fields occur in tilted fault block traps of Upper Jurassic, Piper Sandstone Formation. Estimated total recoverable reserves amount to 100 MMBBL and 62 BCF. The fields are separated by a water corridor approximately 1 km wide. Both fields contain two reservoir sandstone units, an upper and lower, locally termed the Supra Piper Sandstone and Main Piper Sandstone respectively. The reservoirs in both fields exhibit excellent rock' properties with porosities up to 28% and permeabilities of several Darcies.

Each field is developed via a subsea manifold surrounded by a cluster of production and injection wells, of which two were pre-drilled on Ivanhoe and six pre-drilled on Rob Roy. This allowed rapid achievement of the 60 000 BOPD plateau oil production rate soon after commissioning of facilities in July 1989. The two subsea manifolds are tied into a single subsea production manifold which connects with a Floating Production Facility. Crude oil is exported to the Claymore A Platform and gas to the Tartan A Platform.
The Hewett Field, Blocks 48/28-29-30, 52/4a-5a, UK North Sea
Authors: Cooke-Yarborough P.
Published: April 2008

The Hewett Field complex, discovered in 1966, is located in the southwestern part of the Southern North Sea Basin. Gas is currently being produced from four reservoirs: Upper and Lower Bunter sandstones in the Triassic and Rotliegendes sandstones and Zechstein dolomites in the Permian.
The Thames, Yare and Bure Fields, Block 49/28, UK North Sea
Authors: Werngren Oonagh C.
Published: April 2008

The Thames, Yare and Bure Fields, discovered in 1973, 1969 and 1983 respectively, are located in the UK sector of the Southern Gas Basin. The reservoir is made up predominantly of aeolian dune sandstones of the Rotliegendes Leman Sandstone Formation. The fields lie on the upthrown side of NW-SE-trending fault blocks in the central part of Block 49/28. The Thames complex came on production in October 1986 and is estimated to have a field life of 10 years. Current estimates put gas in place for the three fields at approximately 350 BCF, with recoverable reserves of 240 BCF.
The Viking Complex Field, Blocks 49/12a, 49/16, 49/17, UK North Sea
Authors: Morgan C. P.
Published: April 2008

The Viking complex consists of several separate gas accumulations within Blocks 49/12a, 49/16 and 49/17 of the southern North Sea. The entire field is located on the northeast flank of the Sole Pit Basin, approximately 140 km off the Lincolnshire coast. North Viking was discovered in March 1969; South Viking was discovered in December 1968. Conoco (UK) Ltd operates the Viking complex on behalf of BP. North and South Viking consist of two parallel elongated faulted anticlines trending NW-SE. The gas-producing structures are largely fault controlled. The reservoir comprises Rotliegendes Group sands of Early Permian age. The gas-bearing Rotliegendes consists of stacked aeolian and fluvial sands with a gross thickness range of 430-720 ft (131-222 m, thickest on South Viking). Porosities range from 7-25% and the average permeability range is 0.1 md to over 1000 md in the producing zones. The total Viking gas-in-place is almost 3.2 TCF, with recoverable reserves estimated at 2.83 TCF. North Viking came onstream in October 1972 and is developed by a five-platform complex. South Viking came onstream in August 1973 and is developed by a three-platform complex into which are linked five unmanned satellite platforms. The average daily production in March 1989 was 196 MMSCFD, peaking to 311 MMSCFD with seasonal demand. Gas is piped to the Conoco/BP terminal at Theddlethorpe in Lincolnshire.
Introduction
Authors: Le Bas M. J.
Published: April 2008

Science advances by taking new and unexpected turnings, pioneers opening up pathways which later workers follow and explore. This book takes the reader along several such geological paths that have followed from observations and theories first printed in
The Quarterly Journal of the Geological Society of London
(since 1971, the
Journal of the Geological Society
). Following the paths, one sees the history of geological thought during the nineteenth and twentieth centuries.

To achieve this desired structure for the book, leading geologists were invited to present their personal views on significant topics that had been brought to the fore in earlier contributions to the
Journal
, to evaluate the evidence presented and to give their view of how these seminal papers affected our present understanding of geological processes, and further to hazard where future paths of investigation may lie.

Bringing these together under one cover serves two purposes: first to celebrate 150 years of continuous publication of papers by the Geological Society of London: second, it makes a British review of the current 'battle lines' across many fields of geological research. Not only will the serious research investigator discover the several turning points which have governed the paths of his study, but the general reader also will discover the delights, the fortunes and machinations taken by many leading British geologists. Others will use the chapters to answer the question: 'Does historical contingency govern the paths of geological exploration, as it has been said to govern the evolution of living creatures?'

most of
Historical origins of the Geological Society's
Journal
Authors: Rudwick Martin J. S.
Published: April 2008

The Geological Society's
Transactions
, its earliest periodical (from 1811), published the full texts of a few selected papers, with fine illustrations, but generally long after they had been read at one of the meetings. Conversely, the
Proceedings
(from 1826) recorded all the papers soon after they had been delivered, but only in abstract and without illustrations. The launching of the
Quarterly Journal
(1845) was an attempt to combine the advantages and eliminate the disadvantages of the earlier periodicals. After a shaky start, it proved highly successful through the rest of the nineteenth century and much of the twentieth, and was the direct forerunner of today's
Journal
.
Uniformitarianism today: plate tectonics is the key to the past
Authors: Windley Brian F.
Published: April 2008

James Hutton published the first two volumes of
The Theory of the Earth
in 1795 and the third volume was published posthumously by the Geological Society in 1899. Charles Lyell in his four addresses (1836, 1837, 1850, 1851) to the Society put the uniformitarian paradigm of Hutton (the present is the key to the past) into the perspective of his era. Uniformitarianism today can be expressed in the view that plate tectonics is the key to the past. This paper summarizes key data and ideas which confirm that the plate tectonic paradigm can be applied convincingly back to the beginning of the geological record. In spite of the fact that heat production was greater in the early Precambrian than now, tectonophysical and geochemical processes that produced oceanic and continental rocks since the early Archaean have not been fundamentally different from those that operate today.
The development of Early Palaeozoic global stratigraphy
Authors: McKerrow W. S.
Published: April 2008

The major steps in the development of Early Palaeozoic stratigraphy are examined, with special emphasis on early
Journal
papers by Murchison and Sedgwick, and on their conception of systems and series, which permitted long-distance correlation. Unlike other periods, the Ordovician and Silurian were originally split into series; most stages have only been defined in the past 60 years. From 1880, Lapworth’s graptolite zones have allowed much greater chronological precision. More recently, other methods have been developed for recognizing small time divisions, including studies in gradational evolution. A significant new advance is the correlation (by biostratigraphy) of short-lived physical events such as magnetic reversals and sea-level and climatic changes.
Charles Lapworth and the biostratigraphic paradigm
Authors: Fortey Richard A.
Published: April 2008

Lapworth’s paper on ‘The Moffat Series’ (1878) provided a model for deciphering the ‘interminable greywackes’ of the Southern Uplands, and one which lasted for a century. The same paper established graptolites in a dominant position in Lower Palaeozoic biostratigraphy. The changes in the biostratigraphic paradigm are discussed with reference to Lapworth’s contribution; issues implicit in his 1878 paper are still contentious. Graptolites have exemplified the conflict that can arise between the use of fossils as stratigraphic ciphers, on the one hand, or as complex organisms to be interpreted biologically on the other. They have been subjected to the vicissitudes of stratigraphic fashion. It is shown that Lapworth’s biostratigraphy has been enduring in contrast to his structural or palaeogeographic interpretations. However, the subsequent separation of litho- and chrono- from biostratigraphy, while conceptually necessary, has encouraged an idealistic pursuit of the perfect stratigraphic section for the purpose of defining stratigraphic boundaries. This has not always been constructive, not least because such boundaries often coincide with events which militate against the preservation of ideal sections. But Lapworth’s close integration of biostratigraphic range with observations on lithology, ‘barren beds’ and fossil preservation may have a new lease of life in the context of event stratigraphy.
Dinantian (Lower Carboniferous) biostratigraphy and chronostratigraphy in the British Isles
Authors: Riley N. J.
Published: April 2008

Vaughan’s (1905) zonation of the Carboniferous Limestone in the Bristol district was a pioneer biostratigraphical study, which because of its meticulous execution can be reinterpreted in a modern context. The replacement of his scheme with a chronostratigraphical one by George
et al.
(1976) had a similar revolutionary affect on British Dinantian stratigraphy. However, it is now time to revise the British Dinantian stages so that they more closely correspond to biostratigraphical events. Dinantian biostratigraphy still requires considerable refinement, but it has now achieved a diversity of techniques and resolution far beyond that which was available at the time of these earlier proposals. It is the most pragmatic and closest approximation to widespread chronostratigraphical correlation available. This paper discusses these and related issues and presents a review and correlation of current biozonations.
Time from fossils: S. S. Buckman and Jurassic high-resolution geochronology
Authors: Callomon J. H.
Published: April 2008

Chronostratigraphical classification of rocks can be approached from two directions. The first is a ‘top-down’ process of subdivision of the geological column in a hierarchy of successively finer units. These units are therefore
defined
by their boundaries, which are time-planes, and form complete continuous series or scales. They are chosen to be widely
recognizable
, and hence correlatable, by means, in the Phanerozoic, of their contained guide-fossils,
i.e.
by their characteristic biozones. This was the approach of d’Orbigny and Oppel in the Jurassic, leading to a
standard chronostratigraphy
down to Subzonal level notably espoused by Arkell and widely adopted today. The second approach is one of ‘bottom-upwards’ integration: the assembly into time-ordered sequences of the most minutely distinguishable local faunal horizons—distinguishable in the sense of evolutionary change—which may or may not subsequently be found to have more widespread value for time-correlations and biochronology. This was the method introduced by Buckman a hundred years ago to describe the ammonite biostratigraphy of the Inferior Oolite of Dorset, in response to the need for the finest attainable time-resolution in phylogenetic palaeontology. The time-equivalents of such faunal horizons were termed
hemerae
.

Polyhemeral chronostratigraphy went into abeyance with Buckman’s death in 1929, but its equivalent, in terms of the faunal horizons themselves, has been revived. A faunal horizon is defined as a stratigraphical entity within which no further biochronological subdivision can be made, so that the bed or beds embodying that horizon must, on the evidence of the fossils alone, be regarded as internally isochronous. A succession of faunal horizons becomes the record of well-spaced instants: the record is presumed
a priori
to be full of gaps of unknown duration waiting to be filled by new discoveries. The measure of chronostratigraphical finesse is the average time-interval between the moments represented by the faunal horizons, δ̅
t̅
, the
secular resolution
. The relative ability of groups of guide-fossils to resolve time-intervals
δt
in rocks of age
t
is their
secular resolving-power, R = t/δt
.

The current state of Jurassic chronostratigraphy is reviewed. The guide-fossils of choice are the ammonites, whose secular resolving-power exceeds that of any other group and which can give time-resolutions of 150000 years in rocks of age 150 million years (it > 1000). These figures are compared with those attainable elsewhere in the Mesozoic and Palaeozoic. Resolution-analysis of the Jurassic shows that, at the level of resolution of ammonite faunal horizons, the geological record is highly incomplete, nowhere more so than in the Inferior Oolite. As Buckman concluded, the more complete the fossil record of a system becomes, the more incomplete turns out to be its lithochronology. This has important consequences in sedimentology, and in sequence stratigraphy.
Vertebrate fissure faunas with special reference to Bristol Channel Mesozoic faunas
Authors: Savage Robert J. G.
Published: April 2008

Throughout the Mesozoic and Cenozoic, tectonically activated joint fissures and karstic cave systems have acted as reservoirs for terrestrial vertebrate remains. They yield concentrations of microfaunal elements rarely if ever preserved in other situations. In the 1850s, Charles Moore realized their potential and exploited them to discover the earliest known mammals in late Triassic fissure infillings in the Carboniferous Limestone of Somerset. The history of that discovery and its associated problems of interpretation are recorded. His work greatly influenced succeeding generations of palaeontologists and, as techniques developed, fossil fissure discoveries have made a major impact on our understanding of vertebrate evolution.
Hydrothermal orefields and ore fluids
Authors: Rankin A. H.
Published: April 2008

The development of Hydrothermal Theories of Ore Genesis during the past 150 years owes much to the pioneering work of two eminent British geologists, H. C. Sorby and K. C. Dunham, who published benchmark papers in the
Quarterly Journal of the Geological Society
on the classic mining districts of Cornwall and the English Pennines. Sorby’s paper of 1858 laid the foundation for fluid inclusion studies. Despite considerable scepticism or indifference that has lasted well into the twentieth century, fluid inclusions are now widely regarded as the best way of establishing the nature and composition of ancient mineral-forming fluids. Dunham’s paper of 1934 provides a classic account of mineral zonation away from a focus of mineralization in the North Pennine orefield. By analogy with the Cornish deposits this focus was considered to be the result of ascending mineralizing fluids from a hidden granite at depth. Although subsequent drilling confirmed the existence of granite (the Weardale granite) directly beneath the North Pennine Orefield it was older than the Carboniferous Limestone which hosts the mineralization and therefore cannot be its direct source.

With the ‘coming of age’ of fluid inclusion techniques in the 1960s, widespread and systematic studies were carried out on samples from the Cornubian and Pennine orefields and other classic mining districts of the world over the succeeding three decades. These, together with stable isotope studies, established that hydrothermal, ore-forming fluids cover a wide temperature range (50° to >500°C) and compositional range (0 to >60 wt % dissolved salts), and are of diverse origin. The composite and protracted nature of hydrothermal events in Cornwall, and indeed in areas of the world where mineralization is spatially associated with granites, is now evident. Most authors agree that, whilst components of the early mineralization may be due to metalliferous fluids directly evolved from cooling granite bodies, much of the later base-metal mineralization is due to thermal convection and pulsation of meteoric fluids and basinal brines within the intrusion and surrounding country rocks.

The basinal brine expulsion theory is generally favoured for carbonate-hosted, epigenetic, base metal deposits of the Mississippi valley type. The nature, geological setting and fluid inclusion characteristics place the Pennine ores clearly in this broad class. However, most recent work suggests that the mineral zonation patterns in the northern part and temperature differences between the northern and southern part are still best explained by the hydrogeological and geochemical influence of granite at depth.
Charles Davis Hollister, 1936-1999 A personal scientific appreciation of the father of 'contourites'
Authors: McCave I. N.
Published: April 2008

The untimely death of Charley Hollister in a climbing accident robbed the contourite community of the principal originator and proponent of the concept of deep-ocean current-controlled sedimentation. He possessed boundless enthusiasm, a strong belief that science should be and was fun, a wonderful ability to get disparate groups of people to work together and a fine capacity to see connections between varied strands of data. The latter ability in particular allowed him as a graduate student at Lamont Geological Observatory in the 1960s to put together physical oceanography from Georg Wust, early seismic profiler results from the Ewings, deep-sea photographs, stratigraphic and sedimentological data from cores with his supervisor Bruce Heezen, and develop the notion of sedimentation controlled by deep geostrophic flows.

Charley was born into a landed Californian family whose fortunes were founded on cattle ranching. Eschewing the role of sedate conformity and leadership normally reserved for elder sons, his boyhood was, by his own account (thoroughly confirmed by his family), happily irresponsible. His schooling was chequered and his undergraduate academic performance at Oregon State University undistinguished. However, although his best developed abilities were as a marksman and mountaineer, late in the day the spark of what he really wanted to do struck. Doc Ewing, director of Lamont was persuaded that Charley's enthusiasm once channelled, could lead to a successful career as a marine geologist and admitted him to the graduate programme in 1960.

In the late 1950s ideas about the deep circulation developed rapidly with Wust's (1955) recalculation
Bottom currents, contourites and deep-sea sediment drifts: current state-of-the-art
Authors: Stow Dorrik A. V. , Faugères Jean-Claude , Howe John A. , Pudsey Carol J. , Viana Adriano R.
Published: April 2008

This paper provides both an introduction to and summary for the Atlas of Contourite Systems that has been compiled as part of the International Geological Correlation Project - IGCP 432. Following the seminal works of George Wust on the physical oceanography of bottom currents, and Charley Hollister on contourite sediments, a series of significant advances have been made over the past few decades. While accepting that ideas and terms must remain flexible as our knowledge base continues to increase, we present a consensus view on terminology and definitions of bottom currents, contourites and drifts. Both thermohaline and wind-driven circulation, influenced by Coriolis Force and molded by topography, contribute to the oceanic system of bottom currents. These semi-permanent currents show significant variability in time and space, marked by periodic benthic storm events in areas of high surface kinetic energy.

Six different drift types are recognized in the ocean basins and margins at depths greater than about 300 m: (i) contourite sheet drifts; (ii) elongate mounded drifts; (iii) channel related drifts; (iv) confined drifts; (v) infill drifts; and (vi) modified drift-turbidite systems. In addition to this overall geometry, their chief seismic characteristics include: a uniform reflector pattern that reflects long-term stability, drift-wide erosional discontinuities caused by periodic changes in bottom current regime, and stacked broadly lenticular seismic depositional units showing oblique to downcurrent migration. At a smaller scale, a variety of seismic facies can be recognized that are here related to bottom current intensity. A model for seismic facies cyclicity (alternating transparent/reflector zones) is further elaborated, and linked to bottom current/climate change. Both erosional features and depositional bedforms are diagnostic of bottom current systems and velocities.

Many different contourite facies are now known to exist, encompassing all compositional types. We propose here a Cl-5 notation for the standard contourite facies sequence, which can be interpreted in terms of fluctuation in bottom current velocity and/or sediment supply. Several proxies can be utilized to decode contourite successions in terms of current fluctuation. Gravel lag and shale chip contourites, as well as erosional discontinuities are indicative of still greater velocities. There are a small but growing number of land-based examples of fossil contourites, based on careful analysis using the recommended three-stage approach to interpretation. Debate still surrounds the recognition and interpretation of bottom current reworked turbidites.
Contourites of the Nova Scotian continental rise and the HEBBLE area
Authors: McCave I. N. , Chandler R. C. , Swift S. A. , Tucholke B. E.
Published: April 2008

The Nova Scotian continental rise is swept by a Deep Western Boundary Current system comprising layers of Labrador Sea Water overlying a core of Norwegian Sea Overflow Water at depths of 3100-3900 m, and below about 4600 m a cold stream of southern-source water. Seismic-reflection data show that the rise contains sediments transported downslope in channels and debris lobes, but there is also evidence of current-controlled deposition and erosion in the post-Eocene sequence. The rise is now mantled by Holocene contourites that have accumulated at a rate of

c

. 6 cm ka
-1
and are <1 m thick. Bottom photographs show a zonation in current effects and bedform types, with longitudinal ripples and strong currents prevalent at 4800-5000 m, smaller bedforms and progressively weaker currents up to

c

. 4000 m, and mostly tranquil seafloor above 4000 m. Bedform scales and orientations also suggest significant short-term (hours to weeks) variability in current velocity but a mean contour-following flow to the southwest at longer time scales (months to years). These structures are not preserved in the sediment because of pervasive bioturbation and the uppermost layers have negligible preservation potential. The sediments display clear current controlled effects in their grain-size structure involving both percentage of (foraminiferal) sand, and size and percentage in the 10-63 µm range, the 'sortable silt'. There is a sand-rich zone at 4800-4900 m and below 5000 m, and a decreasing silt/clay ratio from 5100 m up to 4000 m. Although much of the sedimentary sequence probably has been emplaced by downslope processes, it has been significantly modified by the Deep Western Boundary Current. Particularly strong and variable currents which rework sediments below

c

. 4800 m probably are engendered by interaction of Gulf Stream eddies with the DWBC. Although strong currents and upstream input from tur-bidites and debris flows might be thought to favour a coarse-grained deposit, the facies at the HEBBLE (High Energy Benthic Boundary Layer Experiment) site is muddy contourite with ≤ 12% sand.
The Greater Antilles Outer Ridge: development of a distal sedimentary drift by deposition of fine-grained contourites
Authors: Tucholke Brian E.
Published: April 2008

The Greater Antilles Outer Ridge, located north and northwest of the Puerto Rico Trench, is a deep (>5100 m), distal sediment drift more than 900 km long and up to 1 km thick. It has been isolated from sources of downslope sedimentation throughout its history and is formed of clay- to fine silt-size terrigenous sediments that have been deposited from suspended load carried in the Western Boundary Undercurrent, together with 0-30% pelagic foraminiferal carbonate. Because of the fine, relatively uniform grain size of the sediments, the outer ridge consists of sediments that are seismically transparent in low-frequency reflection profiles. Sediment tracers (chlorite in sediments and suspended particulate matter, reddish clays in cores) indicate that at least a portion of the ridge sediments has been transported more than 2000 km from the eastern margin of North America north of 40<sup °N. The outer ridge began to develop as early as the beginning of Oligocene time when strong, deep thermohaline circulation developed in the North Atlantic and the trough initiating the present Puerto Rico Trench had cut off downslope sedimentation from the Greater Antilles. The fastest growth of the outer ridge probably occurred beginning in the early Miocene, about the same time that large drifts such as the Blake Outer Ridge were initiated along the North American margin. Since that time, the most rapid sedimentation has been along the crest of the northwestern outer ridge where suspended load is deposited in a shear zone between opposing currents on the two ridge flanks
Late Quaternary glacigenic contourite, debris flow and turbidite process interaction in the Faroe-Shetland Channel, NW European continental margin
Authors: Akhurst Maxine C. , Stow Dorrik A. V. , Stoker Martyn S.
Published: April 2008

The Faroe-Shetland Channel is an important conduit or gateway for the southward flow of cold bottom waters formed in the Norwegian Sea. This Norwegian Sea Overflow Water (NSOW) finds several spillover channels across the Wyville-Thomson Ridge, eventually descending into the northern Rockall Trough and Iceland Basin. The Neogene channel floor succession predominantly displays a broad sheeted drift geometry. Bottom current scours and channels were apparently inherited from an episode of enhanced bottom current activity in late Oligocene/early Miocene. The late Quaternary channel-floor succession is dominated by distal glaciomarine sediments, derived from the shelf and slope during glacial stages and mostly transported by ice-rafting. Glacigenic debris flows and minor turbidity currents were also active across the slope region. Consequently, the principal channel-floor facies are glacigenic contourites that show extensive bioturbation, rare primary structures, mixed composition and marked grain size variation. These features indicate the important influence of cyclical fluctuations in bottom current velocity throughout both stadial and interstadial or interglacial periods. However, the concentration of sandy contourites, erosive surfaces and top-only contourites during interstadials/interglacials and during phases of marked cooling or warming testify to the significance of climate-control on contourite deposition.
Holocene contourite sand sheet on the Barra Fan slope, NW Hebridean margin
Authors: Stow Dorrik A. V. , Armishaw Julie E. , Holmes Richard
Published: April 2008

Surficial sediment analyses, bottom photographs and current–meter data, coupled with studies of sidescan and 3.5 kHz echodata clearly show the imprint of a strong, seasonally-affected, slope current on the Hebrides shelf and slope. The present day shelf sediments are in fact relict, coarse-grained material (gravel with boulders) of Pleistocene glacial deri–vation, which have been modified during the Holocene by winnowing, sea-floor polishing and transport of the finer fraction across the shelf to the northwest. On the outer shelf and upper slope the sharp change from gravel to sand is marked by a physiographic-textural boundary, herein termed the
sandline
, which occurs at a depth of between 170 m and 300 m. Further down the continental margin on the lower slope, the lower limit of the sand-rich facies is marked by the
mudline
. This typically occurs at a depth of around 1200 m, and marks the depth of substantially increased clay-sized material. Above the mudline the long-term (Holocene to present), time-integrated signature of bottom current flow has resulted in the relatively slow accumulation of a mid-slope sandy contourite deposit, the Barra contourite sand sheet. This covers an area of 1000-1500 km
2
with an estimated sand volume of 30 000 m
3
. Below the mudline the clay-rich deposits represent a hemipelagic drape with only minor bottom current influence and intense reworking by benthic organisms.
The Ceuta Drift, Alboran Sea, southwestern Mediterranean
Authors: Ercilla G. , Baraza J. , Alonso B. , Estrada F. , Casas D. , Farrán M.
Published: April 2008

The Ceuta Drift is an elongated-terrace feature (up to 100 km long, 28 km wide, 400 m relief, and 700 ms thick) located in the southwestern Alboran Sea, close to the Gibraltar Strait. It extends between 200 and 700 m water depth, parallel to the Moroccan slope. The drift stratigraphy is defined by the vertical stacking of at least five seismic units bounded by discontinuities: onlap and downlap surfaces at the bottom, and erosive surfaces at the top. Sedimentologically, the most recent deposits are defined by the vertical succesion, from bottom to top, of contouritic sandy muds, muds, and silty clays. The Ceuta Drift began to develop during the early Quaternary, when the pre-existing sea-floor morphology favoured the formation of an offshoot current system from the Mediterranean water masses. The action of this current together with sea-level changes have controlled the growth pattern of this drift.
Upper slope sands: Late Quaternary shallow-water sandy contourities of Campos Basin, SW Atlantic Margin
Authors: Viana Adriano R. , De Almeida Waldemar , De Almeida Cleide Wilhelm
Published: April 2008

Upper slope sand deposits comprise a widespread but thin elongate accumulation of coarse to very fine-grained sand resulting from the action of slope boundary currents upon shelf-derived sediments. Sediment distribution on the Campos Basin upper slope responds to the action of the southward-flowing western boundary Brazil Current (BC). Linear, multi-source sediment supply to the slope is provided by shelf overspill due to the action of different forcing mechanisms: tides, storm fronts, and BC current onshelf penetration as gyres and meanders. On the slope, the sediment is pirated and redistributed by the BC Coarse-grained sediments (pebbles to very coarse sand) are found below the zone of maximum acceleration of the BC. Down–stream, fining is observed as a consequence of the morphologically controlled BC deceleration. The resultant accumulation is an elongate (c. 70 km long) and thin (> 50 m) wedge-shaped deposit. This depositional model is based on hydrographic, physiographic and sedimentologic characteristics of the modern Campos Basin margin, SE Brazil and characterizes a shallow water contouritic deposit
Contourites on the Agulhas Plateau, SW Indian Ocean: indications for the evolution of currents since Palaeogene times
Authors: Uenzelmann-Neben Gabriele
Published: April 2008

The area south of South Africa is one of the most important gateway regions for the interchange of watermasses from the Atlantic, Indian and Southern oceans. This results in a very complex flow pattern which up to now has been known only in general terms. For this study, a set of seismic reflection lines from the southern Agulhas Plateau has been analysed. These show strong indications for the effect of bottom currents on sedimentation in the form of sediment drifts, channels, erosional unconformities and sediment waves. These observations have been used to infer the development of palaeocircu-lation over the southern Agulhas Plateau since Paleogene times. Three different currents have been identified. The oldest observed flows across the Agulhas Plateau from the southwestern tip to the northeast, and probably dates from the early Eocene times. It is believed to comprise an Antarctic Bottomwater component derived from its source in the south. The eastern Agulhas Plateau is characterized by a south-flowing current, which has been active since the Lower Oligocene and appears to have remained stationary to within a distance of 10 km. The Agulhas Retroflection is considered as its most likely source. The third current observed flows along the western flank of the plateau, dates from the Middle Miocene and probably results from an Antarctic Bottomwater component re-circulated via the Cape Basin.
The Weddell Sea: contourites and hemipelagites at the northern margin of the Weddell Gyre
Authors: Pudsey Carol J.
Published: April 2008

Fine-grained contourites and hemipelagites occur in the northern Weddell Sea, deposited from the Weddell Gyre. Where bottom currents are intensified over the slope, sandy and silty contourites have been deposited above 2000 m water depth. Mudwaves are generally uncommon, but are present in Powell Basin. The area has potential for high-resolution palaeoclimate studies (particularly the history of Antarctic Bottom Water production) if difficulties in dating can be overcome.
The tectonic and stratigraphic framework of the United Kingdom's oil and gas fields
Authors: Underhill John R.
Published: April 2008

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.
The North Morecambe Field, Block 110/2a, East Irish Sea
Authors: Cowan G. , Boycott-Brown T.
Published: April 2008

abstract

The North Morecambe Gas Field in the East Irish Sea Basin was discovered by well 110/2-3 in 1976 and contains ultimately recoverable reserves of over one TCF. THe structure is fault closed on three sides and dip closed to the north. Development was by ten conventionally drilled high angle deviated wells, from a not normally manned platform. Gas is exported through a dedicated pipeline to a new terminal at Barrow. The Triassic Sherwood Sandstone Group reservoir is composed of sandstones deposited in a semi-arid, fluvial and aeolian setting. Thin aeolian sandstones dominate flow into the well bore. Platy illite reduces the permeability by two to three orders of magnitude in the lower, illite affected zone of the reservoir, RFT measurements from the first development well proved that the free water level was 25 feet higher than expected, giving a maximum gas column of 975 feet. Re-mapping after drilling has shown that 56% of the GIIP is contained in the high permeability illite-free zone.
The South Morecambe Gas Field, Blocks 110/2a, 110/3a, 110/7a and 110/8a, East Irish Sea
Authors: Bastin J. C. , Boycott-Brown T. , Sims A. , Woodhouse R.
Published: April 2008

South Morecambe Gas Field is situated in the East Irish Sea and produces gas from the Triassic Sherwood Sandstone Group. Exploration of the basin commenced in 1966 and the discovery well, 110/2-1, was drilled in 1974. Appraisal was complete by 1983 and development was carried out in two phases with the object of providing deliverability to help to satisfy the winter peak in demand. First gas was produced in January 1985 and production during the winter can be sustained at 50MMCMD (1750mmscfd). The stratigraphic succession of the East Irish Sea Basin (EISB) consists of Carboniferous (Dinantian to Westphalian) strata unconformably overlain by 15000 to 20000 feet of continental Permo-Triassic strata. The Triassic Sherwood Sandstone Group contains reservoir rocks and the overlying Mercia Mudstone Group evaporites provide a seal. Seismic cover of the area includes 2D and 3D data, the latter providing good images that form the basis of the current structural interpretation. The structural development of the basin commenced with extension in the Permo-Triassic followed by inversions in the late Jurassic and early Tertiary. The reservoir has been zoned using a scheme that recognizes primary depositional facies as the main criterion for correlation. The petrophysical evaluation has introduced new methods of calculating porosity, S
w
and net pay. The latest reservoir pressure data has been used in a material balance study and a two tank simulation model, both give GIIP estimates which are in line with earlier estimates. The new petrophysically derived reservoir parameters were also used to make a volumetric estimate of GIIP. Remaining recoverable reserves are at least 3 Tcf.
The Heather Field, Block 2/5, UK North Sea
Authors: Kay Simon
Published: April 2008

abstract

The Heather oil field is located in Block 2/5 in the Northern North Sea. Oil is produced from sandstones of the Middle Jurassic Brent Group. at depths between 9500ft and 11600 ft below sea level. The field has been in production for over 20 years, and to date 120 MMSTB of oil have been produced out of an oil-in-place volume of 464 MMSTB. Although approaching non-commercial flow rates, an ambitious programme of field re-evaluation has been conducted since 1997 to identify remaining infill potential, and to investigate the development potential of satellite accumulations. New 3D seismic surveys shot in 1995 and 1997 have been combined to produce a continuous top reservoir map of the main field and adjacent satellite structures. The new mapping and an updated reservoir description were integrated with reservoir simulation models to identify zones of unswept oil. Main field infill projects have been identified which target the unswept oil, allowing extension of field life to be planned in conjunction with satellite field development. An additional 57 MMSTB of recoverable oil are expected to be produced from Middle Jurassic reservoirs in the main field and in satellite areas.
The Statfjord Field, Blocks 33/9, 33/12 Norwegian sector, Blocks 211/24, 211/25 UK sector, Northern North Sea
Authors: Gibbons K. A. , Jourdan C. A. , Hesthammer J.
Published: April 2008

The Statfjord Field, the largest oil field in the Northern North Sea, straddles the Norway/UK boundary and is located on the southwestern part of the Tampen Spur within the East Shetland Basin. The accumulation is trapped in a 6-8° W-NW dipping rotated fault block comprised of Jurassic-Triassic strata sealed by Middle to Upper Jurassic and Cretaceous shales

Reserves are located in three separate reservoirs: Middle Jurassic deltaic sediments of the Brent Group, Lower Jurassic marine-shelf sandstones and siltstones of the Dunlin Group; and Upper Triassic-lowermost Jurassic fluviatile sediments of the Statfjord Formation. The majority of reserves are contained within the Brent Group; and Statfjord Formation sediments which exhibit good to excellent reservoir properties with porosities ranging from 20-30% permeabilities ranging up to several darcies, and an average net-to-gross of 60-75%. The sandstones and siltstones of the Dunlin Group have poorer reservoir properties where the best reservoir unit exhibits an average porosity of 22%, an average permeability 300 raD and net-to-gross of 45%

Structurally, the field is subdivided into a main field area characterized by relatively undeformed W-NW dipping strata, and a heavily deformed east flank area characterized by several phases of 'eastward' gravitational collapse

Production from the field commenced in 1979 and as of January 2000, 176 wells have been drilled. The oil is undersaturated and no natural gas-cap is present. The drainage strategy has been to develop the Brent and Dunlin Group reservoir with pressure maintenance using water injection and the Statfjord Formation reservoir by miscible gas flood. However, a strategy to improve recovery by implementing water alternating gas (WAG) methods is gradually being implemented for both the Brent and Statfjord reservoirs. Current estimates indicate that by 2015 a total of 666 x 10
6
Sm
3
(4192 MMBBL) of oil will be recovered and 75 GSm
3
(2.66 TCF) gas will be exported from the field