bluuebunny/crossref_metadata_2025 huggingface dataset:
The Clipper Field, Blocks 48/19a, 48/19c, UK North Sea
Authors: Farmer R. T. , Hillier A. P.
Published: April 2008

The Clipper Gas Field is a moderate-sized faulted anticlinal trap located in Blocks 48/19a and 48/19c within the Sole Pit area of the southern North Sea gas basin. The reservoir is formed by the Lower Permian Leman Sandstone Formation, lying between truncated Westphalian Coal Measures and the Upper Permian evaporitic Zechstein Group which form source and seal respectively. Reservoir permeability is very low, mainly as a result of compaction and diagenesis which accompanied deep burial of the Sole Pit Trough, a sub-basin within the main gas basin. The Leman Sandstone Fm. is on average about 715 ft thick, laterally heterogeneous and zoned vertically with the best reservoir properties about the middle of the formation. Porosity is fair with a field average of 11.1%. Matrix permeability, however, is less than 1 millidarcy on average and is so low that some intervals in the field will not flow gas unless stimulated. Steep dipping zones of natural fractures occur in certain areas of the field; these commonly allow high flow rates to be achieved from large blocks of low-permeability matrix. Expected recoverable reserves from the most favourable part of the field are 558 BCF and Clipper Field is now being developed in conjunction with part of the adjacent Barque Gas Field. Later development of the remainder of Clipper Field will depend upon reservoir performance in the initial development area.
The Indefatigable Field, Blocks 49/18, 49/19, 49/23, 49/24, UK North Sea
Authors: Pearson J. F. S. , Youngs R. A. , Smith A.
Published: April 2008

The Indefatigable Field was discovered in June 1966 by the Amoco Operated Group well 49/18-1. The field is located 55 miles northeast of Great Yarmouth in the central part of the Southern North Sea Basin in water depths of 100 ft. The field lies in Blocks 49/18, 19 and 49/23 and 24. The reservoir section is Lower Permian Rotliegendes sandstones comprising a mixed sequence of aeolian and fluvial sediments at an average depth of 8500 ft subsea. Maximum reservoir thickness is in excess of 420 ft; however, the average pay thickness is of the order of 150 ft. The main reservoir trap is a complexly faulted NW-SE-trending anticlinal horst with a maximum vertical closure of 1300 ft. The field is approximately 17 miles long and 6 miles wide and has an areal extent of some 60 square miles. Recoverable reserves in the Field are estimated to be 4418 BCF of gas. The field is not unitized and is jointly operated by Amoco and Shell.
The Rough Gas Storage Field, Blocks 47/3d, 47/8b, UK North Sea
Authors: Stuart I. A.
Published: April 2008

The Rough Gas Field is operated by British Gas as the world's first offshore gas storage reservoir. This relatively small field (original reserves 366 BCF) is located on the western margin of the Southern North Sea Basin. The reservoir, the Rotliegendes Gp (Leman Sandstone Fm.) average thickness 95 ft, is developed in a basin-margin facies association in which aeolian and wadi-related fluvial processes have interacted. Small-scale dune and interdune sandstones, with generally excellent permeability, alternate with wadi facies sandstones with variable but mainly poorer permeability. The vertical distribution of these facies permits a three-fold zonation of the reservoir. Flow profiles obtained from Production Logging Tools show a very strong correspondence between sedimentary facies and productivity/injectivity. The Carboniferous subcrop includes several very low-permeability sandstone intervals which contact the Rotliegendes at the angular Base Rotliegendes unconformity. A small amount of gas from these sandstones seeps across the unconformity surface into the Rotliegendes. The Rough Field was discovered by Gulf in 1968, and was operated by Amoco on a conventional depletion basis with 6 development wells from 1975 until the early 1980s. In 1980 British Gas secured 100% ownership of the Field and its facilities, and converted it to storage mode. Excess summer supplies are injected into the reservoir, to be produced during the winter to meet the peak demand. Conversion to storage mode has necessitated the installation of substantial new facilities, and the drilling of 23 further wells. First injection of gas was achieved in 1985.
The Victor Field, Blocks 49/17, 49/22, UK North Sea
Authors: Lambert Robert A.
Published: April 2008

The Victor gas field lies in the Southern North Sea Gas Province on the eastern flank of the Sole Pit Basin. The field straddles Blocks 49/17 and 49/22, and is situated approximately 140 km off the Lincolnshire coast. Victor was discovered in April 1972 and is operated by Conoco (UK) Ltd on behalf of BP, Mobil and Statoil. The structure is an elongated tilted fault block, trending NW-SE. The reservoir sands are contained in the Leman Sandstone Formation (Rotliegendes Group) of Early Permian age, and consist mainly of stacked aeolian and fluvial sands with a gross thickness of 400-450 ft across the field. Porosities vary from 16-20%, with permeabilities ranging from 10 md to 1000 md in the producing zones. Initial gas in place is estimated at about 1.1 TCF with recoverable reserves of the order of 900 BCF. The field was brought on-stream in October 1984, and the five producing wells deliver, on average, 200 MMSCFD through the Viking Field 'B Complex' to the Conoco/BP terminal at Theddlethorpe in Lincolnshire
The West Sole Field, Block 48/6, UK North Sea
Authors: Winter D. A. , King B.
Published: April 2008

West Sole is located in the Sole Pit area of the Southern North Sea Permian Basin in UK Block 48/6. The field was discovered in 1965 and was the first commercial discovery in the UK Continental Shelf. Gas Production commenced in 1967. Initial reserves are 1.873 TCF of which 1.335 TCF had been produced by the end of 1989. Gas is trapped in aeolian sandstones of the Permian Lower Leman Sandstone Formation. Three depositional facies are recognized, comprising aeolian dune, fluvial and sabkha. The aeolian dune facies form the principal reservoir sandstones, in units up to 40 m (131 ft) thick. However, permeability is reduced due to pervasive illite cementation, such that it averages 3 md in the dune sandstones. Productivity is enhanced in the southern part of the field by 'open' gas-filled fractures, generated during the Alpine inversion. The trap was also amplified at this stage and comprises a faulted inversion anticline trending NW-SE. The source rock is the Westphalian Coal Measures, lying directly beneath the reservoir.
The South Morecambe Field, Blocks 110/2a, 110/3a, 110/8a, UK East Irish Sea
Authors: Stuart I. A. , Cowan G.
Published: April 2008

The South Morecambe Gas Field has been developed as a seasonal supply field to boost supplies to the National Transmission System at times of peak demand. This mode of operation has led to a requirement for exceptionally high reliability in all aspects of the development. This requirement has prompted the generation of an accurate and comprehensive geological model so that reservoir performance can be predicted as reliably as possible, and that wells can be drilled in optimum locations. The exceptional shallowness of the structure (crest at -2400 ft TVSS, GWC -3750 ft TVSS), coupled with the need to drain the reservoir cost-effectively and to minimize the risk of well interference has led to the use of slant drilling techniques for the first time in European waters. The field is located in the East Irish Sea Basin. The Triassic Sherwood Sandstone Gp forms the reservoir, and the Mercia Mudstone Gp provides the seal. The reservoir sands were laid down in a rapidly subsiding basin under continental semi-arid conditions, and comprise a complex interplay of major channel-fill sandstones, secondary channel-fill sandstones associated with non-channelized sheetflood sandstones, and localized, very high permeability (> 1000 md) aeolian and reworked aeolian sandstones. A vertical organization of these facies has been observed, with some intervals dominated by channel deposition, others by non-channelized deposits, due to periodic adjustments of the whole basin, and this has permitted the establishment of a reservoir zonation. A complex diagenetic history is recognized, with several phases of dolomite and quartz cementation. Differential compaction is also a major control on the disposition of reservoir properties. The greatest control on permeability (but not porosity) is platy illite which formed beneath a palaeo-GWC at an early stage in the growth of the structure, and which gives rise to a diagenetic layering of the reservoir into a high permeability Illite-Free Layer and a deeper, low permeability Illite-Affected Layer. The data presented herein is based upon the results of development drilling on South Morecambe.
Early Precambrian crustal development: changing styles of mafic magmatism
Authors: Hall R. P. , Hughes D. J.
Published: April 2008

The work of Sutton & Watson (1951) was one of the cornerstones in the interpretation of the evolution of early Precambrian (Archaean and early Proterozoic) gneiss complexes and in the documentation of mafic dyke swarms that intruded recently accreted Archaean cratons. Since then, the concept of geological terranes and terrane accretion has been extended back to the Archaean, and different events can be distinguished by increasingly precise isotopic dating techniques. There is growing evidence that, with certain clear provisos, the principle of uniformitarianism can be applied as equally to the early Precambrian as it can through the rest of the geological record. In terms of mafic magmatism, there are similarities between some ancient and modern suites, both intrusive and extrusive, but there are also some major differences, such as the presence of komatiites in the Archaean and the formation of large-scale layered intrusions and extensive dyke swarms at the end of the late Archaean and in the early Proterozoic. The mantle has evolved continuously with the progressive extraction of mafic magmas but, allowing for this, continental tholeiites appear to have changed little with time. Ancient mid-ocean ridge basalts are elusive because of their poor preservation record. The geochemistry of mafic volcanics occurring in many greenstone belts commonly suggests a continental contamination component and that these volcanic rocks are most closely akin to those from present-day arc systems. The relative abundance of early Precambrian intrusive mafic suites parallels the crustal growth curve, reflecting the global crustal accretion-differentiation superevent towards the close of the Archaean. Bimodal tholeiitic-noritic mafic magmatism associated with many of these intrusive suites stems from this rapid turnover in the mantle-mafic crust-continental crust system. This, in turn, gives a possible link between the respective evolutions of Archaean to Recent komatiitic, noritic and boninitic suites.
W. Q. Kennedy, the Great Glen Fault and strike-slip motion
Authors: Bluck B. J.
Published: April 2008

At the time it was written, Kennedy’s paper on the Great Glen Fault had clear evidence for a known lateral displacement, and the evidence was so well presented that it convinced a sceptical geological world that such movements were possible. The acceptance of large scaled lateral movements led to the concept of great fundamental fractures and, with the advent of plate tectonics and a climate of mobilistic thinking, many of these great fractures were later recognized as plate or terrane boundaries.

Along with this thinking, new criteria evolved for recognizing those fractures that had been involved in major displacements—in fact the concept of throw became replaced by the concept of role. Role was identified from the history of the blocks on either side of the fracture, and where that history was incompatible with them being together, then a large role was possible for the fault itself.

Taking a new look at the Great Glen Fault in these terms, it becomes clear that there are insufficient data on the rocks on either side to allow any conclusions about the nature and timing of its role to be deduced. If the later, displacements, which are at present the main concern of researchers, are the sum of the movements on the fracture then it is ironically the least significant of the four NE-SW fractures in Scotland.
Triassic pebbles, derived fossils and the Ordovician to Devonian palaeogeography of Europe
Authors: Cocks L.R.M.
Published: April 2008

Papers published by Salter (1864) and Davidson (1870) on the faunas from pebbles in a Triassic conglomerate at Budleigh Salterton, Devon, are reviewed. After modern reassessment, these pebbles, although of apparently similar quartzites, have been found to be of four different ages, two Ordovician (mid-Arenig and late Llandeilo) and two Devonian (Lochkovian-Pragian and Frasnian). By comparing these four faunas with those contemporary in adjacent palaeocontinents, it can be shown that, apart from the earliest one, they have affinities closer to those of the Armorican peninsula of Brittany and Normandy than to the rest of Britain and that these Armorican faunas are in clasts which were transported northward by Triassic rivers. Consideration of all the various faunas in the whole of northwest Europe reflect the earliest Ordovician of southern Britain as part of the vast Gondwanan continent, from which it became detached by the mid-Ordovician, with a widening Rheic Ocean between the two palaeocontinents; and the subsequent merging of Avalonia with Baltica and Laurentia to form Laurussia by Mid-Devonian times. New palaeogeographical maps depicting phases from the Ordovician to the Devonian are presented.
Flood basalts versus central volcanoes and the British Tertiary volcanic Province
Authors: Walker George P. L.
Published: April 2008

A controversy in the final decades of the last century developed between Geikie and Judd over the nature of the volcanoes in the British Tertiary Province. Geikie regarded the lavas as in Antrim and Skye as plateau basalts (today called flood basalts) erupted from widely scattered fissures, while Judd regarded the intrusion complexes as in Central Mull and Skye as eroded stumps of major central volcanoes from which the lavas originated. Soon after, instigated by the controversy, British volcanology flowered for several decades in what may be called its ‘Classic Period’. Detailed mapping projects were undertaken, and new concepts were developed that are basic to volcanology. This paper views the controversy and its aftermath, and also briefly reviews recent conceptual developments in the North Atlantic Volcanic Province of which the British Tertiary rocks are a part. The paper discusses the present understanding of flood basalts and central volcanoes, and presents new criteria based on structural features of lava flows (such as the dependence of lava thicknesses, and the occurrence of pipe vesicles, on ground-slope angle) to distinguish between them. Magnetic fabric study of magma-flow directions in intrusions and lava flows, and palaeomagnetic study of post-emplacement tilting of igneous rocks, have great unrealized potential.
Magmatic differentiation
Authors: Wilson Marjorie
Published: April 2008

During the past 150 years, a wide range of processes have been invoked to explain the mechanism by which magmas differentiate.These may be divided into those which operate essentially in the liquid state, such as liquid immiscibility and thermogravitational diffusion, and those which involve some form of crystal-liquid fractionation. It is now generally accepted that the latter are the most important. Many of the models developed during the past twenty years to explainmagmatic differentiationhave their roots in ideas first proposed in the early years of this century. This review presents some of the historical background to the subject and attempts to summarize some of the more recent developments.

Alfred Harker’s perceptive study of in-situ crystallization within a high-level intrusion (Carrock Fell in the English Lake District), published in volume 50 of theQuarterly Journal of the Geological Societyin 1894, clearly laid the foundations for many modern theories. In 1900 he introduced the oxide–oxide variation diagram, which is still widely used to depict the geochemical variations within suites of cogenetic igneous rocks. Studies of phase equilibria in synthetic and natural systems by Bowen and his contemporaries, during the 1920s and 30s, provided the theoretical background needed to understand the complex processes involved in fractional crystallization of magmas. In the past decade mathematical modelling has allowed a more quantitative approach to the problem.
Carbonate magmas
Authors: Bailey D.K.
Published: April 2008

For 40 years, the case for the existence of carbonate magmas rested on field observations of carbonatite intrusions, in which the lack of thermal effects raised an apparent conflict with the high melting temperatures of pure carbonates. Since 1960, the position has changed, with the growth of experimental studies and increasing observations of effusive carbonate rocks. A nephelinite/phonolite volcano in Tanzania is currently erupting Na-Ca-K carbonate magma (around 600 °C). This is unlike all other intrusive and effusive carbonatites (350 examples worldwide) which are dominantly composed of Ca, Mg, Fe carbonates, and have negligible alkali contents. Although a number of effusive calcio-carbonatites are considered to be degraded alkali carbonatites, there are several examples (including one magnesio-carbonatite) which are close to their erupted composition, and substantiate the existence of high
T
carbonate magmas lacking essential alkalis at the time of eruption. In these associations silicate magmas are absent (or minor), and in most the effusive carbonatites have been erupted directly from the mantle (with entrained peridotite debris and minerals). They provide a link with the ultramafic association (peridotite and pyroxenite), seen in some carbonatite intrusions, with the commonly associated ultramafic lamprophyres (which may also carry mantle xenoliths), and with carbonate-rich kimberlites. Many carbonatite intrusions also have little or no associated silicate magmas, putting in question a popular view that carbonatites normally form only minor parts of alkaline igneous complexes of nephelinite/phonolite type. The corollary, that the carbonatites are normally differentiates is even less sound, because in alkaline complexes the carbonatite is always last in the eruption sequence. Here the carbonatite may represent the final residua expelled from the source region. Most large carbonatite intrusions seem to have been emplaced at lower
T
than effusives, probably as a near-solidus mush, with the interstitialfluid metasomatizing the country rocks. A wider perspective of carbonate magma genesis is called for, to encompass various kinds of differentiation from alkaline silicate magmas, and primary carbonate magmas from various depths in the mantle (with or without silicate melts). The strongly bimodal composition distribution of calcic and dolomitic carbonatites is a further factor awaiting explanation. Half of the known carbonatites are in Africa, and their timing and distribution indicate that the activity is a response to lateral forces acting across the plate. Carbonate magmatism is waiting to be unleashed. This activity demands attention because it is now clear that carbonate magmatism is a crucial surface expression of deep mantle processes.
The Sicilian gateway: anatomy of the deep-water connection between East and West Mediterranean basins
Authors: Reeder Michael S. , Rothwell Guy , Stow Dorrik A. V.
Published: April 2008

The Sicilian gateway is a narrow, deep, interconnected series of basins, sill valleys and passageways that cuts across the broad, shallow Sicilian-Tunisian Platform in the Central Mediterranean. This deep connection allows dense Levantine Intermediate Water (LIW) formed in the Eastern Mediterranean to flow in a westerly direction through the gateway and exit into the Tyrrhenian and Balearic basins of the Western Mediterranean. LIW is replaced by a strong surface flow of Modified Atlantic Water (MAW). A complex and still active tectonic regime has been an important control on the development of physiography and on the style and distribution of sediments across the Platform.

Within the deep gateway basins, turbidites, debrites and megabeds are intercalated with a background of predominantly muddy and calcareous, hemipelagic and contourite sediments. Evidence for the influence of bottom currents on sedimentation is seen in the construction of small mounded drifts and irregular patch drifts, in zones of scouring and non-deposition, in local photographic evidence of a current-smoothed or rippled seafloor, and as a subtle combination of features present in the background sediments. These include: extensively reworked microfossil assemblages, rare diffuse lamination, coarse lenses of mixed composition within a pervasively bioturbated sediment, and relatively high rates of accumulation.
The Columbia Channel-levee system: a fan drift in the southern Brazil Basin
Authors: Faugères J.-C. , Lima A. Franca , Massé L. , Zaragosi S.
Published: April 2008

The Columbia Channel is a turbiditic channel elongated W-E on the rise of the south Brazilian basin (4200 to 5000 m water depth). The whole area is swept by the northward flowing Antarctic Bottom Water. As a consequence, depositional processes have built a fan drift system. This system displays a levee along the northern flank of the channel while no levee occurs on its southern flank due to the Coriolis effect. The levee (400 km in length and 100 to 200 km in width) is bounded to the north by the Vitoria-Trindade Seamounts. It shows, first, a W-E trend parallel to the channel axis and predominantly turbiditic pattern, and then a S-N trend parallel to the rise contours with a predominant contouritic pattern. Its thickness is up to 1000 m. The distribution of sedimentary processes and associated deposits were investigated on the basis of water gun seismic and 3.5 kHz echosounding profiles, and core lithology. On the lower S-N part of the levee, the deposits consist of muddy contourites. On the shallowest part, turbidites that originate from the upper continental margin in the channel and on the southern part of the levee close to the channel, and from the Vitoria-Trindade Seamounts on the northern part of the levee, are interbedded with contouritic muds, and top-truncated silty turbidites. Areas subjected to turbidity current processes show chaotic to well-stratified, high amplitude reflections, in the subsurface, and more or less prolonged echofacies with or without sub-bottom reflectors, at the seabed. Areas subjected to contour currents show, in the subsurface, transparent seismofacies with some discontinuous low amplitude wavy reflections, and, in the surficial deposits, predominant wavy echofacies with sub-bottom relectors, frequently associated with tangential hyperbolae.
Contour currents, sediment drifts and abyssal erosion on the northeastern continental margin off Brazil
Authors: Gomes P. O. , Viana A. R.
Published: April 2008

Seismic reflection data collected as part of the Brazilian Continental Shelf Survey has allowed the recognition of large sediment drifts related to bottom currents along the continental rise off northeastern Brazil. Antarctic Bottom Water (AABW), which flows northward across a physiographic constriction - the hotspot-related Bahia Seamounts - has controlled the deposition of these contourite drifts. Following this pathway since the Middle Oligocene, AABW has also led to the formation of regional unconformities and the excavation of the 800 km long and up to 470 m deep Pernambuco Seachannel. This feature, which represents the 'trunk channel' of a complex submarine drainage system, flows into the Pernambuco Abyssal Plain, building a large fan-like deposit - the Pernambuco Countourite Fan. As observed elsewhere along continen–tal margins, the geometry of the sediment drifts alternates from mounded to sheeted, channel-related or confined, depending on the physiographic setting and on the velocity of the flow. The so-called 'modified drift-turbidite systems', formed by an interplay between downslope sediment gravity flows and alongslope bottom-current-controlled deposition, are well developed near the continental slope region, particularly in the Sergipe Basin, where the São Francisco River has built its deep-sea fan.
Evidence of bottom current influence on the Neogene to Quaternary sedimentation along the northern Campos Slope, SW Atlantic Margin
Authors: Viana Adriano R. , Hercos Cízia M. , De Almeida Waldemar , Magalhães José Luís , De Andrade Sinara B.
Published: April 2008

Geophysical and sedimentological data indicate that bottom currents have played a fundamental role in deposition along the Campos continental slope, especially during the Neogene and Quaternary. Sediment drifts are clearly observed in 2D and 3D seismic data. The external geometry and internal reflection pattern of these drifts suggest the predominant action of northward-flowing currents (Southern Ocean Current) along the middle and lower slope (650-1200 m). Upper Quaternary sediments within that zone are composed of highly bioturbated, silty to sandy mud, with rare lamination and no other primary structures. On the upper slope, below the southward flowing Brazil Current, sub-bottom profiles and side-scan sonar records indicate the development of several bedform styles. On the uppermost slope, between 200-300 m, longitudinal lineations and transverse bedforms (2D and 3D dunes) are observed. Sediments are siliciclastic to mixed silty to muddy sand, with rare primary traction structures preserved. Downslope, from 300 to 650 m, linear crested bedforms, a few metres high (2-7 m) are developed. In this zone, an alongslope similarity in the depositional style over more than 50 km suggests bottom current control on sedimentation. The deposits are composed of 1 m of silty muds overlying a decimetric layer of silty sand that grades downslope to a highly oxidized, bioturbated, fine-grained interval. The variability of sediment accumulation rate (2 to 30 cm ka
_1
) is related to high frequency temporal and local modifications
Contourite sedimentation in the Falkland Trough, western South Atlantic
Authors: Cunningham Alex P. , Howe John A. , Barker Peter F
Published: April 2008

The Falkland Trough is a west-east bathymetric deep that separates the Falkland Plateau from the North Scotia Ridge in the western South Atlantic. It lies in the path of Circumpolar Deep Water flowing within the Antarctic Circumpolar Current (ACC), and Weddell Sea Deep Water flowing beneath the ACC east of Shag Rocks passage. Marine geophysical and sediment core data demonstrate the influence of ambient bottom currents on deposition in this area, and reveal two styles of contourite sedimentation: (1) deposition of glauconite-rich sandy contourites in exposed areas of the Falkland Plateau and Falkland Trough, where vigorous ACC bottom currents control sedimentation, and (2) deposition of biogenic sandy contourites, muddy contourites and hemipelagites (western Falkland Trough), and muddy diatom ooze (eastern Falkland Trough), in the form of two elongate sediment drifts, which have developed in the presence of more sluggish bottom currents. The drift sediments contain a depositional record of bottom current flow through the glacial cycle (southern-origin bottom water flow in the east, and probably ACC flow in the west); analyses of core data from the western Falkland Trough suggest a reduction in bottom current strength during the Last Glacial Maximum at present depths of > 2500 m below sea level.
Ordovician carbonate contourite drifts in Hunan and Gansu Provinces, China
Authors: Luo Shunshe , Gao Zhenzhong , He Youbin , Stow Dorrik A. V.
Published: April 2008

abstract

The Early Ordovician continental margin at the southern edge of the Yangtze Platform, China, is represented by a succession of deep-water carbonate sediments near Jiuxi. A distinctive elongate mound-like form, some 120 km long, 25 km wide and 350-450 m thick, has been identified between shallow-water platform carbonates and deeper-water mudstones, and interpreted as the
Jiuxi
drift. The principal facies include calcilutites, calcisiltites, calcarenites, calcirudites, and bioclas-tic contourites, interpreted as contourites on the basis of their slope location, alongslope palaeocurrent indicators, features of traction flow processes coupled with intense bioturbation, and distinctive contourite sequences. During the Middle Ordovician, along the western slope of the Ordos Platform, Gansu Province, a narrow deep gateway (here called the
Pingliang gateway
) opened up between two deep-water basins. An elongate, mounded, carbonate body (70 km X 15 km X 150 m thick), developed along the eastern slope of this gateway, has been interpreted as the
Pingliang
contourite drift. A similar suite of contourite facies and sequences is found as at Jiuxi, although there is a greater abundance of calcarenitic contourites in the Pingliang drift, as well as other evidence that suggests a more active bottom current regime in this Ordovician gateway region
Fossil contourites: type example from an Oligocene palaeoslope system, Cyprus
Authors: Stow Dorrik A. V. , Kahler Gisela , Reeder Mike
Published: April 2008

As part of a wider programme on the recognition and decoding of contourite sediments, we propose the adoption of part of the Lefkara Formation on Cyprus as the first in a series of type examples of fossil contourites in ancient series exposed on land. A clear case can be made for interpreting these mainly Oligocene age sediments as carbonate-rich contourites. They combine faint structures due to current action with pervasive bioturbation, typically show cyclic grain size alternation, and have compositional differences from the more easily identifiable calciturbidites. One particularly diagnostic contourite facies is a lenticular, thin-bedded calcarenite-cacisiltite from which the finer bioclastic material and terrigenous clays have been winnowed away. This facies is a well developed condensed unit, which occurs at the same stratigraphic interval throughout Cyprus. Variations in thickness and rates of sedimentation of the contourite units, as well as the presence of widespread hiatuses and alongslope palaeocurrent trends are consistent with drift development on a lower slope apron in the closing Tethys ocean.
Lessons from oil and gas exploration in and around Britain
Authors: Hardman R. F. P.
Published: April 2008

After 35 years, exploration in and around Britain has reached a mature stage. Pure oil and gas exploration has with certain exceptions given way to the search for small fields close to infrastructure and maximizing recovery from existing fields. To examine the lessons of 35 years of exploration before many of the major players leave the stage is opportune. Lessons learned can be applied elsewhere.

An examination of the history suggests that lessons can be grouped under four headings: organization, technical skills, personal qualities and tactics. Successful companies optimize all of these. Unsuccessful companies, on the other hand, often fail because of a particular flaw in one of them.

It is concluded that successful exploration companies would field a team captained by a technically competent open-minded manager closely linked to skilled geoscientists, all of whom would have a deep understanding (through relatively long service) of the area being explored. Both managers and geoscientists would be able to take sensible risks and would not confuse the primary concern of the technical merits of a prospect with the secondary concern of the economics of success. Finally, luck appears to play an important part but there is no doubt that successful companies work hard for their luck.

Other lessons centre on the quirkiness of individual behaviour. This is something that no amount of study can eliminate.
The Douglas Oil Fields, Block 110/13b, East Irish Sea
Authors: Yaliz A. , McKim N.
Published: April 2008

The Douglas Field, on stream in February 1996, is the first oil field to be developed in the East Irish Sea Basin, with an estimated STOIIP of 202 MMBBL. The field structure consists of three tilted fault blocks formed during extensional faulting in Triassic-early Jurassic times, and later readjusted by contractional movements during Tertiary inversion. The oil is trapped in the Triassic Ormskirk Sandstone Formation, which comprises moderate to high porosity aeolian and fluvial sandstones. The reservoir depth is shallow (2140 ft) with a maximum oil column of 375 ft. The reservoir can be divided into several laterally extensive units based on vertical facies variations. The reservoir quality is principally controlled by primary depositional processes, and authigenic clay minerals are not important. However, bitumen is formed extensively in specific areas of the field causing significant permeability reduction. The hydrocarbon filling history of the field was complex, with the occurrence of at least two phases of oil generation and migration. The field contains a relatively 'dead' oil with a low GOR (170scf/bbl). Pressure maintenance is achieved through sea water injection, and to date ten production and six injection wells have been drilled. The crude is light (44° API) and contains high levels of H2S (0.5mol%) and mercaptans, which are removed during processing offshore.
The Hamilton and Hamilton North Gas Fields, Block 110/13a, East Irish Sea
Authors: Yaliz A. , Taylor P.
Published: April 2008

The Hamilton and Hamilton North Fields are located in Block 110/13a in the East Irish Sea, and contain 627 BCF and 230 BCF GIIP, respectively. First gas was produced from the Hamilton North Field in December 1995. The fields are being developed with four producers in the Hamilton Field and three in the Hamilton North Field. The Hamilton Field structure consists of a N-S trending horst block with dip closure to the north and south, while the Hamilton North structure is defined by major faults to the north and west with dip closure to the east and south. The gas is trapped in the highly productive Triassic Ormskirk Sandstone Formation. The reservoir comprises high porosity aeolian and fluvial sandstones. Depth to reservoir is shallow (2300-2600 ft) with the gas-water contact being at 2910 ft in the Hamilton Field and 3166 ft in the Hamilton North Field. Reservoir quality is principally controlled by primary depositional processes and no significant diagenetic effects are observed. The hydrocarbon filling history was complex, with at least two phases of hydrocarbon generation. Hamilton North gas is sweet whereas the Hamilton gas contains up to 11OOppm H
2
S, which is removed during processing at the Douglas complex and at the Point of Ayr gas terminal. Cumulative gas production to May 1999 was 180 BCF and no water-cut has been observed to date.
The Lennox Oil and Gas Field, Block 110/15, East Irish Sea
Authors: Yaliz A. , Chapman T.
Published: April 2008

The Lennox Field, located in blocks 110/15 and 110/14, was the second oil field to be developed in the East Irish Sea Basin. It contains 184 MMBBL of oil in-place within a 143 ft thick oil rim overlain by a large gas cap up to 750 ft thick. The GIIP is estimated to be 497 BCF. The field came on stream in February 1996, and it is now being developed with seven horizontal oil producers, including two multi-lateral wells and two crestal gas injectors. Production from the field can be divided into two distinct phases; the oil rim development phase, and the gas cap blow-down phase. The latter phase is currently anticipated to commence in 2004. The field structure consists of a roll-over anticline formed in the hanging wall of the Formby Point Fault during extensional faulting in Triassic-early Jurassic times, and later readjusted by contractional movements during Tertiary inversion. The oil and gas are trapped in the highly productive Triassic Ormskirk Sandstone Formation. The reservoir comprise high porosity aeolian and fluvial sandstones occurring at a shallow depth (
c.
2500 ft) with a maximum gas column of 750 ft above an oil rim of 143 ft. The reservoir quality is principally controlled by primary depositional processes as no significant adverse diagenetic effects are observed. The hydrocarbon filling history was complex, with at least three phases of oil and gas generation. The field contains a light, saturated oil (45° API) with a GOR of 650 SCF/BBL. The crude contains high levels of H
2
S (0.1 mol%) and mercaptans (450 ppm), which are removed during processing at the Douglas complex. Water cut from the field is currently around 2-5%, and no free gas production has been observed to date. Gas production from Lennox is anticipated to start in 2004.
The Armada development, UK Central North Sea: The Fleming, Drake and Hawkins Gas-Condensate Fields
Authors: Stuart I. A.
Published: April 2008

abstract

In 1994 the Armada partnership sanctioned the simultaneous development of the Fleming, Drake and Hawkins Gas-condensate Fields by means of shared facilities; the overall project was called the Armada Development. The operator is BG International (formerly British Gas). The development was interesting because the component fields are not only separate accumulations, but are of completely different geological type.

The Fleming Field is a Palaeocene, Maureen Formation high-density turbidite reservoir, sourced from the north but pinching out eastwards against the N S Utsira/Jaeren High and Hawking-Varg Ridge, and therefore forming a 20 km long, continuous, but very narrow reservoir. The drake Field is an Upper Jurassic. Fulmar Formation, shallow marine, shore-face reservoir, with excellent reservoir quality in a compact fault block. The Hawkins Field reservoir is poorer quality Fulmar Formation, typical of a more distal setting; the trap is formed by closure over a salt dome, and the structure is consequently quite heavily faulted.

The challenge was to develop these disparate reservoirs from a single surface site. to capture the askward shape of Fleming and the distance between Drake and Hawkins. This was achieved by means of extended each drilling; although the high cost of such wells meant that every one had to be designed for maximum yield. Overall eifht wells were drilled, five to Fleming, two to Drake and one to Kawkins (these numbers being approximately proportional to gas-in-place). These wells are capable of delivering the project design peak rate of 450 mmscfd off-platform (equivalent to about 480 mmscfd reservoir gas), and up to 24000 BOPD condensate. Armada began production on schedule in October 1997.
The Birch Field, Block 16/12a, UK North Sea
Authors: Hook J. , Abhvani A. , Gluyas J. G. , Lawlor M.
Published: April 2008

The Birch Field is an oil field located in Block 16/12a on the UK Continental Shelf (UKCS) and is part of the well-established 'Brae Trend'. Birch produces an undersaturated volatile oil from the Brae Conglomerate, a locally thick conglomeratic unit within the Late Jurassic Brae Formation. The reservoir was deposited as a small submarine fan in the hanging wall of the main fault bounding the western side of the South Viking Graben. The current estimate for oil in place is about 70MMSTB with expected ultimate oil reserves of 30MMSTB. The field was brought on stream in September 1995 as a phased waterflood subsea development, tied back to Marathon's Brae 'A' platform in neighbouring Block 16/7a. During Phase I the discovery and both appraisal wells were re-completed as two oil producers and one water injection well. Phase II comprised a third oil production well and a second water injection well drilled and completed in 1996-1997. Oil production peaked at
c.
28 000 BOPD in the second half of 1996. The field is currently in decline and production in June 1999 was
c.
7000 BOPD with a water-cut of
c.
40%. Cumulative oil production to end June 1999 was 21 MM STB and remaining oil reserves are estimated as 9MMSTB.
The Central Brae Field, Blocks 16/07a, 16/07b, UK North Sea
Authors: Fletcher Keith J.
Published: April 2008

abstract

The Central Brae Oilfield is the smallest of three Upper Jurassic fields being developed in UK, Block 16/07a. The field was discovered in 1976 and commended production in September 1989 through a sub-sea template tied back to the Brae 'A' platform in the South Brae Oilfield. The field Stooip is 244 MMBBLs, and by May 1999 cumulative exports of oil and NGL reached 44 MMBBLs.

The Central Brae reservoir is a proximal submarine fan sequence, comprising dominantly sand-matrix conglomerate and sanstone with a minor mudstone units. The sediments were shed eastwards off the Fladen Ground Spur and were deposited as a relatively small and steep fan at the margin of the South Viking Graben. Mudstone facies border the submarine fan deposits to the north and south, forming stratigraphic seals. The structure is a faulted anticline developed during the latest Jurassic and early Cretaceous, initially formed as a hangingwall anticline during extension but subsequently tightened during compressional phases. The western boundary of the field is formed by a sealing fault, whilst to the east, there is an oil-water contact at 13426 ft TVDss. The overlying seal is the Kimmeridge Clay Formation, which also interdigitates with the coarser facies basinwards and provides the source of the hydrocarbons.
The South Brae Field, Blocks 16/07a, 16/07b, UK North Sea
Authors: Fletcher Keith J.
Published: April 2008

The South Brae Oilfield lies at the western margin of the South Viking Graben, 161 miles NE of Aberdeen. Oil production began in July 1983 from a single platform located in 368 ft of water. The field STOOIP is 795 MMBBLs, and in May 1999, cumulative exports of oil and NGL reached 265 MMBBLs. The reservoir lies at depths in excess of 11 800 ft TVDss, has a maximum gross hydrocarbon column of 1670 ft, and covers an area of approximately 6000 acres.

The reservoir consists of Upper Jurassic Brae Formation sandstones and conglomerates deposited as submarine fan complexes that are downfaulted against tight sealing rocks of probable Devonian age at the western margin of the field. The other field margins are constrained by a combination of structural dip and stratigraphic pinchout.
The Brent Field, Block 211/29, UK North Sea
Authors: Taylor S. R. , Almond J. , Arnott S. , Kemshell D. , Taylor D.
Published: April 2008

The Brent Field was the first discovery in the northern part of the North Sea, and is one of the largest hydrocarbon accumulations in the United Kingdom licence area. There are two separate major accumulations: one in the Middle Jurassic (Brent Group reservoir) and one in the Lower Jurassic/Triassic (Statfjord Formation reservoir). The Brent Field lies entirely within UK licence Block 211/29 at latitude 61°N and longitude 2°E; the adjacent Brent South accumulation extends into Block 3/4A. The water depth is 460 ft. The Brent Field discovery well was drilled in 1971, and was followed by six further exploration and appraisal wells. Seismic data over the Brent Field has been acquired in four separate vintages. The latest acquisition in 1995 allowed detailed mapping of the complex eastern margin of the field for the first time

The Brent Field is developed from four fixed platforms (Alpha, Bravo, Charlie, Delta) installed between 1975 and 1978. Production commenced in 1976 and, for the first 22 years of field life, the platforms provided production, water injection and gas injection facilities for both the Brent and Statfjord Formation reservoirs. The Brent South accumulation is produced via the Brent Alpha platform, through sub-sea tie-backs and extended reach wells. In 1992, the decision was taken to depressurize the Brent Field to recover an additional 1.5 TSCF of gas and 34 MMSTB of oil, extending the field's life by 5-10 years. In January 1998, water injection into the main field was stopped and depressurization of the field initiated. As of January 2000, a total of 220 platform wells and three sub-sea wells (173 producers, 50 water injectors) have been drilled in the Brent Field.

The original oil/condensate-in-place is currently estimated at 3.8 MMMSTB, and the estimated original wet gas-in-place is 7.5 TSCF. Total ultimate recovery for all reservoirs is expected to be 1988 MMSTB oil and condensate and 6000 BSCF gas. Cumulative oil and net gas production, as of 1st January 2000, was 1875 MMSTB oil and 4196 BSCF gas

This paper summarizes the current understanding of the field based on acquisition of new 3D seismic data, 130 new wells, detailed structural and sedimentological modelling, development of the complex crestal part of the field and finally, the initiation of an extensive brown field re-development project to depressurize the reservoir
The Deveron Field, Block 211/18a, UK North Sea
Authors: Brown A. M. , Milne A. D.
Published: April 2008

Cumulative oil production at the end of 2000 was 15.4 MMBO, which for a STOIIP of 61.3 MMBO, represents a recovery to date of 25%. Deveron shares facilities on the Thistle Alpha platform and has been on production since 1984, from two (originally three) deviated platform wells. The performance of these wells has been steady, subject to well and plant uptimes. Field management activity continues to focus on monitoring and maintaining the two production wells, and denning field and production enhancement opportunities.
The Dunbar, Ellon and Grant Fields (Alwyn South Area), Blocks 3/8a, 3/9b, 3/13a, 3/14, 3/15, UK North Sea
Authors: Ritchie J. S.
Published: April 2008

The Dunbar, Ellon and Grant oil and gas fields (also known as the Alwyn South area) are located in the southeastern part of the East Shetland Basin, approximately 140 km E of the Shetland Islands. Most of the accumulations lie in Blocks 3/9, 3/14 and 3/15, which are parts of Licence P090 operated by Total Oil Marine pic (33.33%) with Elf Exploration UK PLC as sole partner (66.67%). Ellon was discovered in 1972, Dunbar in 1973 and Grant in 1977. Dunbar consists of a number of generally N-S trending, westerly dipping Mesozoic fault blocks with variable amounts of crestal erosion. Reservoir is provided by fluvial, deltaic and shallow marine sandstones of the Middle Jurassic Brent Group, Lower Jurassic Statfjord Formation and Upper Triassic Upper Lunde Formation. The Brent oil composition of Dunbar varies with depth and evolves from volatile oil at the base of the column to gas condensate at the top without a discontinuity of composition. In addition there is a small gas accumulation within a Paleocene submarine fan reservoir in a compactional structure.

Ellon consists of two westerly dipping fault blocks with gas condensate contained within the Brent Group. Grant is one westerly dipping fault block with gas condensate in the Brent Group. In both the Ellon panels and also in Grant, thin waxy oil 'rims' are found below the gas. The depth of the shallowest structural crest within the Alwyn South complex is 3100 m TVDSS, with the deepest proven hydrocarbon at around 3800 m TVDSS. Sealing for the Alwyn South accumulations is provided by various combinations of Cretaceous, Upper Jurassic (Heather and Kimmeridge Clay Formations) and Lower Jurassic (Dunlin Group) mudstones. The source rock for the hydrocarbons is the Upper Jurassic Kimmeridge Clay Formation, which is mature and adjacent to the fields.

These accumulations are being developed from a tender-assisted minimally manned fixed platform with a total of 28 well slots located over the Dunbar Field, in a water depth of 145 m. The Ellon and Grant Fields are produced as sub-sea satellites to Dunbar from a well-head cluster located between Ellon and Grant, in a water depth of 135 m. First oil and gas production from Dunbar and Ellon was in December 1994 and gas production commenced from Grant in July 1998. The time lag between discovery and development reflects the complex geology (structure, compartmentalization, reservoir thickness variations, dia-genesis and differing hydrocarbon compositions) with a total of 28 exploration and appraisal wells being drilled in the Alwyn South area between 1971 and 1998. Total oil and gas initially in place is in the order of 850 MMBBL and 2.62 TCF respectively, with the current estimate for ultimate recoverable reserves being 200 MMBBL liquids and 1.28 TCF gas.