bluuebunny/crossref_metadata_2025_split huggingface dataset:
ALUM SHALE BITUMEN MATURATION AND MIGRATION: IMPLICATIONS FOR GOTLAND'S OIL
Authors: Dahl J. , Chen R. T. , Kaplan I. R. 
Published: December 2007

Thermal maturation of Swedish Alum Shale kerogen and bitumen has been determined from core samples from Eastern and Central Sweden. In samples from Eastern Sweden (Öland and Gotland), the kerogen and bitumen are thermally immature with respect to petroleum generation. In some areas of Central Sweden (Närke, ÖstergÖtland, and Kinnekulle in VästergÖtland), the kerogen is immature, whereas the bitumen is marginally mature to mature. In other areas of Central Sweden (Halleberg‐Hunneberg in VästergÖtland), the kerogen is supermature and the bitumen mature. This suggests that bitumen from a mature source‐rock has migrated into the Alum Shales of Central Sweden. Migration in Central Sweden is further evidenced by the occurrence of obviously‐migrated bituments in vugs and voids in the organicpoor Ordovician limestone overlying the Alum Shale in Central Sweden, and in concretions within the Alum Shale itself.Based on biomarker distributions of extracted bitumen, Alum Shale kerogen pyrolysate and obviously‐migrated oils, and the fact that the Alum Shale in most of the areas studied is the only petroleum source‐rock extant, it is suggested that the migrated bitumen in Central Sweden is from the Alum Shale itself. Bitumen has migrated from areas where the Alum Shale is in close proxmity to Permo‐Carboniferous intrusions, such as Halleberg‐Hunneberg, into nearby areas such as Närke and ÖstergÖtland, where there is no evidence of intrusion and the indigenous organic matter is thermally immature. Other areas, where Alum Shales were associated with intrusions and consequently sourced oil, may have been eroded away.There are producing wells on the island of Gotland, where the Alum Shale is also thermally immature. It is therefore assumed that heating which was responsible for generating Gotland's oil was very localized (such as by an intrusion) or that the oil has migrated from a thermally moremature, distant area. On the basis of reservoir rock porosity, and the fact that the Alum Shale of Gotland contains no migrated component, localized heating is favored.
PLASTIC FLOW AND CONTRAFLOW IN SUPERPOSED ZECHSTEIN SALT SEQUENCES
Authors: Jenyon M. K. 
Published: December 2007

A competent band within a salt‐rock sequence can be a useful indicator of the form taken by any plastic deformation movement that occurs in the salt. The acoustic impedance contrasts provided by such a band often result in strong seismic reflection events that exhibit the effects of all stages of deformtion accompanying salt movement, from gentle undulations through complete disintegration the competent unit.Examples are shown in seismic data from the North Sea Zechstein of deformation of the Plattendolomit band that separates the underlying Z2 ‐ cycle salt from the salt of the overlying Z3 cycle. Cases are discussed in which the evidence suggests contraflow in the two salts, where the Z2 salt has flowed bi‐directionally away from the axial trough of a salt‐withdrawal basin. This has led to flow of the overlying Z3 salt bi‐directionally towards the same axis. The observations tell us something about the rheological behaviour of superposed salts, and about the deformational behaviour of competent carbonate/anhydrite bands within a salt sequence. They also highlight potential problems of well correlation in the absence of good seismic data, or due to misunderstanding of salt‐flow phenomena.
THE GULF OF ADEN RIFT: HYDROCARBON POTENTIAL OF THE ARABIAN SCETOR†
Authors: Haitham F.M.S. , Nani A.S.O. 
Published: December 2007

Stratigraphic results from eight offshore exploration wells drilled between 1979 and 1983 are described, and the successions penetrated are compared with the adjacent land outcrops and facies; these are also depicted in lithostratigraphic correlation charts/sections for the area. The Oligo‐Miocene Shihr Group is divided into formations which are described and correlated between the wells, and a new post‐Shihr formation is likewise described and correlated.Mesozoic succession thickness variations or erosion cut‐outs and syn‐ and post‐rift sediment thickness increases in some of the wells reflect the extension of structural episodes of uplift and erosion (or of basin subsidence and thick sedimentation) seen on land, into the offshore domain; they highlight the major role these have had on source, reservoir/seal and trap development, within the context of regional and local basin evolution.A number of source rocks, including Upper Jurassic, Upper Cretaceous and Paleocene‐Eocene argillaceous sediments, are identified, and the results of oil/oil and oil/source‐rock correlations on fluids recovered from Paleogene carbonate reserviors in the Sharmah and Ras Ghashwah wells, and an Upper Cretaceous sandstone reservoir in the Sarar well, are, respectively, correlated with sources in the Paleocene‐Eocene formations, and the Upper Cretaceous Mukalla Formation. The geothermal gradient, calculated from differing results in each well, is high, and averages 3.5°C/100m, which indicates an oil “window” ranging between depths of 1,750 m and 3,500 m; this is broadly supported by vitrinite reflectance and Thermal Alteration Index (TAI) measurements carried out on the samples. It is concluded that favourable conditions exist for commercial hydrocarbon accumulations in the offshore area
PETROLEUM AT THE ROOF OF THE WORLD: The geological evolution of the Tibet (Qinghai‐Xizang) Plateau Part II
Authors: Taner I. , Meyerhoff A. A. 
Published: December 2007

Abundant field data collected within the past twelve years or so show that all published explanations for the origin of this 2.4MM sq. km region violates some of these data. Among them, one fact is of paramount importance. This is the discovery that none of the great east‐west fracture zones is a boundary between different, but coeval, lithofacies. Instead, several major facies boundaries (in rocks of various ages) form a zigzag pattern across the various blocks of the region. This fact, in turn, means that most published tectonic interpretations, including those of plate tectonics, are incorrect.In Part 2 of this paper, the Authors now point out that the recently‐proposed surge‐tectonics hypothesis explains all field data. If the surge‐tectonics hypothesis is correct, most of the Tibetan Plateau, including its Cambrian‐through‐Tertiary section, is prospective. They conclude, therefore, that Tibet could eventually become a major petroleum‐producing province of the world.
THE SEDIMENTOLOGY OF THE BRENT GROUP IN THE CORMORANT BLOCK IV OILFIELD
Authors: Livera S. E. , Caline B. 
Published: December 2007

Cormorant Block IV is one of four, large‐scale fault‐bounded accumulations which together comprise the Cormorant oilfield. The field lies some 150 kms NE of the Shetland Islands, in the East Shetland Basin. Oil is trapped in the Middle Jurassic (Aalenian‐Bathonian) Brent Group. Block IV is a separate accumulation in a downthrown area formed by a large synsedimentary listric fault, which produced a dome‐shaped structure with further internal fault‐block compartmentalisation. A concerted data‐gathering effort on the accumulation included the coring of 43% of the reservoir section penetrated by wells.The Brent Group in Block IV fits into the “classical” overall regressive/transgressive, wavedominated delta model widely accepted for these sediments. However, the synsedimentary boundary fault has had some influence on the shallow‐marine Broom and Tarbert Formations and the coastal‐plain Upper Ness sediments, in each case preserving a unique and thicker sequence on the downthrown eastern side. The lowermost Broom Formation includes a shallow‐marine, Gilbert‐delta type deposit that infilled a topographic feature formed by the fault, and is genetically distinct from the rest of the Group. The Rannoch and Etive delta‐shoreface sediments, the main resrvoir interval, appear to have prograded through the area towards the NNE so rapidly that no fault influence was felt. Lateral variability at this level can be explained by the location of distributaries in the upper shoreface, controlling the grade of sediment supply and progradation rates of the entire system. The barrier‐attached coastal‐plain sequence of the lower Ness is chronostratigraphically equivalent to the Etive. and thins rapidly towards the north. The upper Ness is strongly layered by repeated periods of emergent coastal‐plain development separated by at least block‐wide lagoonal drowning events. Erosion at the base of the shallow‐marine Tarbert Formation, and the marked variability of sediment type and thickness in this horizon, suggests that it formed over a considerable time‐period at the end of Brent Group deposition, as the structure of the block was still developing.
THE TECTONIC MOSAIC OF THE SOUTHERN LEVANT: IMPLICATIONS FOR HYDROCARBON PROSPECTS
Authors: Cohen Z. , Kaptsan V. , Flexer A. 
Published: December 2007

A comprehensive study of the Levant region, using geophysical, well and surface data, has elucidated the tectonic regime which preceded the Late Cretaceous tectonic inversion in the Levant region. A tectonic mosaic existed in the study area during the Paleozoic and Mesozoic, and was made up of NE‐trending grabens (e.g. the Pleshet, Judea and Galilee grabens) and their neighbouring horsts, and a number of NW‐trending blocks. These tectonic elements were bounded by regional faults.The grabens were formed in three known phases: pre‐Upper Permian: Early to Middle Triassic; and Early to Middle Jurassic. Formation of each graben resulted in a depositional sag basin centered above the graben and extending beyond its boundaries.Two types of inversion were active—inversion of regional tilts, and inversion of vertical tectonic movements. Examples of regional tilts are the SE landward Middle Triassic Anisian sedimentary wedge. and the NW basinward wedge of the Early Cretaceous (Berriasian to middle Aptian) sequence. A vertical inversion occurred in the Late Cretaceous. The Paleozoic‐Mesozoic grabens became raised blocks, whereas the horsts turned into depressed areas, in which synclinal sediments, rich in organic matter, accumulated in asymmetrical fault‐fold sag basins. These events occurred as a result of intraplate stresses, and are related to major global orogenies.The grabens, the sag basins, and also the argillaceous parts of the basinward sedimentary wedges, are considered to be sites of hydrocarbon generation. Commercial and sub‐commercial production, as well as abundant oil and gas shows, confirm the presence of source rocks. Traps of various forms are widely available; in the horsts, in the grabens, in the sedimentary wedges, and in the sedimentary sag basins.
COMPUTER SIMULATION OF PRIMARY OIL MIGRATION IN KUWAIT
Authors: Özkaya I. 
Published: December 2007

Primary oil migration from a source rock has been simulated using a computer. The simulation model is based on a finite difference solution of one‐dimensional fluid‐flow differential equations. Oil generation is simulated by the time‐temperature index. Shale porosity is reduced by compaction. Oil saturation rises as organic matter is conversed to oil, and the source‐rock porosity decreases during burial. When oil saturation reaches an irreducible level, surplus oil is expelled by capillary and excess pore fluid pressure.The model is applied to an actual case. Oil generation and migration from a possible source rock in Kuwait is simulated. A reasonable estimate of the time of oil expulsion is obtained. even though values of several parameters had to be assumed. The results confirm the validity of the model and point to the possible use of such computer simulation models in oil exploration.
OIL AND GAS EXPLORATION IN CUBA
Authors: Echevarria‐Rodriguez G. , Hernandez‐Perez G. , Lopez‐Quintero J. O. , Lopez‐Rivera J. G. , Rodriguez‐Hernandez R. , Sanchez‐Arango J. R. , Socorro‐Trujillo R. , Tenreyro‐Perez R. , Yparraguirre‐Pena J. L. 
Published: December 2007

Oil and gas exploration in Cuba began with the discovery of the Motembo oilfield in 1881. and some 25 oilfields have subsequently been discovered. the largest of which are Boca de Jaruco and Varadero.Two oil‐bearing provinces are known: the Northern Cuban Province, which includes the overthrust belt; and the Southem Cuban Province, to the south of the overthrust belt, which includes a number of Cretaceous‐Tertiary basins.Rocks in the overthrust belt are intensely faulted and folded. with folds trending NE in western Cuba and NW elsewhere on the island. The Northern Cuban Province is about 1,000–kms long and 80– to 100–kms wide: sediments here are generally 10– to 12–kms thick. Seven overthrust surfaces have been identified by drilling, and correspond to different oil zones: thus, oilfields are characteristically located within different tectonic‐stratigraphic units.The Southern Cuban Province covers an area of about 60.000 sq. kms, and is composed of several basins. whose development was different from those to the north. Oil has been located in the Central Basin, where oilfields are present in positive structures, but not so far in any other basins here, although surface and subsurface oil seeps are common in this area.
GEOLOGIC AND HYDROCARBON EVOLUTION OF BARBADOS
Authors: Speed R. C. , Barker L. H. , Payne P. L. B. 
Published: December 2007

Barbados island has risen above sea‐level in the last one million years as a pinnacle on the structural high of the extensive Barbados accretionary prism. The island provides by outcrop and many wells a glimpse of the structural history of the oldest and thickest realm of the prism, and a model for evolution of oil and gas in an accretionary terrane rich in quartz sanaktones and muddy temgenous and hemipelagic rocks that are moderately rich in organic substances. The island contains four major tectonostratigraphic units: basal complex of Eocene accretionary origin: prism cover: the Oceanic allochthon, of marly forearc basin strata, that was thrust over the basal complex and prism cover: and mud‐matrix mélange diapirs. Oil and gas are sourced chiefly from the basal complex at depths below 7 km, the minimum maturation depth. Oil reservoirs are in sandstones of the basal complex in fault‐fold structures. Seals are provided by mudstones of the basal complex and, more regionally, by thick, impermeable successions of prism cover and the Oceanic allochthon. Current oil reservoirs probably evolved mainly in Late Neogene time during a late stage of deformations. Oil reservoirs are best known in southern Barbados, in the Woodboume Trough, where sealing conditions were optimized.Barbados' marine territory also includes an extensive fold‐thrust belt for some 50 km west of the island. This belt includes rocks of both the Barbados accretionary prism and strata of the Tobago Trough forearc basin. The thrusting is due to the westward wedging of the prism into the forearc basin between roof and floor detachments.
ALPINE GEOWARPINGS IN THE ZAGROS‐TAURUS RANGE: INFLUENCE ON HYDROCARBON GENERATION, MIGRATION AND ACCUMULATION
Authors: Ameen M. S. 
Published: December 2007

Megascale monoclinal flexures (‘geowarpings“) with maximum angles of dip ranging from 5° to 13° occur in the Zagros‐Taurus range of Iraq and Iran. They face south and SW. with amplitudes of 1.4 to 14.44 kms and axial lengths of 43 to 230 kms. meir axes are parallel to the host mountain range and lie in an en Pchelon configuration, and many are located in the high mountain zone, at or close to the mountain front (i.e. the border with the foothills zone). Neotectonic and stratigraphic evidence suggests the contemporaneous development of these flexures with their host fold‐belt during the collision of the Eurasian and Afro‐Arabian Plates, which culminated during Upper Miocene‐Pliocene time. Differential vertical movements caused greater shortening and thickening in the upwarded regions (10–33%). which lie closer to the plate suture zones, compared to the downwarped regions (3–17%). Development of the geowarpings resulted in circumstances favourable for hydrocarbon generation in downwarped regions. where source rocks were buried sufficiently deeply to produce oil and gas: this then migrated upwards to be trapped in the growing folds, and was sealed by Miocene evaporites. On the other hand, upwarped regions were elevated, and suffered extensive erosion, leading to a reduction in the depth of burial of potential source rocks, and consequently limited possibilities of hydrocarbon generation. Furthermore. the non‐deposition and/or erosion of Miocene evaporites in upwarped regions led to the dissipation of considerable volumes of the hydrocarbons which might have been generated. The effect of geowarpings on oil and gas reserves is evident from the distribution of oil‐ and gasfields. which are almost exclusively located in the downwarped. foothills zone. Geowarpings may be located in the Taurus Range of E Turkey and NE Syria. but a lack of accurate data makes this difficult to investigate. Further studies are needed to develop an efficient exploration plan for oil and gas in that area.
LITHOSTRATIGRAPHY OF OIL‐BEARING TERTIARY BIOHERMS IN THE SIRTE BASIN, LIBYA
Authors: Gumati Y.D. 
Published: December 2007

In the early Palaeocene, a carbonate platform existed in the southern part of the Sirte Trough (a NW‐trending depression in the eastern Sirte Basin), and a shale basin in the north. A major transgression occurred during the early Palaeocene, and part of the platform subsided, resulting in the formation of a basinal re‐entrant within the carbonate province. A positively northerly‐trending ridge, which was active in the early Palaeocene, persisted within the re‐entrant during the late Palaeocene. This positive element provided a platform on which isolated bioherms grew, surrounded by shale deposits in the subsiding basin. The bioherms began as foraminiferal banks that built‐out on local mounds in shallow water. Sparse coral growth bound coralline detritus, until richer coral development resulted in a large coral reef.A barrier reef surrounding the re‐entrant developed during the late Palaeocene and grew basinwards, advancing over its own talus. A second major transgression closed the Palaeocene epoch, and clastic deposition over the Sirte Trough terminated reef growth and carbonate deposition.The reef, back‐reef and basinal environments are each characterized by distinctive lithologies and fauna. The bioherms form excellent hydrocarbon reservoirs in the Intisar A and D fields, which are probably sourced by the Sirte and Hagfa Shales. Six bioherms, some in excess of 300 m in thickness, have been discovered, and some contain commercial oil accumulations.
THE RED SEA — GULF OF ADEN: BIOSTRATIGRAPHY, LITHOSTRATIGRAPHY AND PALAEOENVIRONMENTS
Authors: Hughes G. W. , Beydoun Z. R. 
Published: December 2007

Sediments of Palaeozoic, Mesozoic and early Palaeogene ages experienced a similar geological history in Ethiopia, Yemen and Somalia. During the late Eocene, however, uplift and differential erosion took place, prior to rift development in the middle Oligocene, when the proto‐Gulf of Aden became established. To a certain extent, a similar sequence of events had also taken place in those regions of Egypt, Sudan, Ethiopia, Yemen and Saudi Arabia which border the Red Sea, but post‐Eocene subsidence is now believed to have commenced during the late Oligocene in the southern Red Sea and progressed later, during the early Miocene, in the northern Red Sea and Gulf of Suez. Timing of this progressive development of the Gulf of Aden rift complex through the Red Sea and Gulf of Suez is well constrained by biostratigraphy, and provides a new approach to the understanding of lithological variations within the region.These lithological variations have, until now, only been considered on a country‐specific basis, thus hindering establishment of a regional history of sedimentation. The well‐understood and well‐documented lithostratigraphic nomenclature of the Miocene succession of the Gulf of Suez has been used as a reference, or type, with which the lateral facies variations within the Red Sea have been compared. By this method only has it been possible to produce palaeoenvironmental maps for the entire study region, and for each formation and member. Lateral equivalents of the Gulf of Suez Nukhul, Rudeis, Kareem, Belayim, South Gharib. Zeit, Wardan and Shagara Formations have been identified within the Red Sea syn‐rift and post‐rift episodes.
THE SEDIMENTARY EVOLUTION OF THE RED SEA AND GULF OF ADEN
Authors: Crossley R. , Watkins C. , Raven M. , Cripps D. , Carnell A. , Williams D. 
Published: December 2007

Onset of rifting, and flooding by marine waters, occurred in the late Oligocene in the Gulf of Aden and southern Red Sea. The northern part of the Red Sea may have been a largely continental rift at this initial stage, but continued rifting established marine conditions throughout the system by the early Miocene. Episodic isolation of the Red Sea system, leading to evaporite deposition in some basins, commenced in the mid‐Miocene and over two kilometres of salt had accumulated in most Red Sea basins by the end of the Miocene.Re‐establishment of persistently‐marine conditions occurred in the Pliocene, and marine recharge is now sufficiently high to permit vigorous carbonate build‐ups in shallow‐water areas.Clastic sediment textures suggest that marginal escarpments, which first developed during the onset of rifting, were strongly uplifted in the Pliocene‐to‐Recent period. Subsidence of basin floors seems to have been particularly rapid during the period dominated by salt deposition.If eruption of sea‐floor basalts in the axial rift areas is excluded, volumetrically important volcanism is centred on the present Afar triangle area, and is confined to the Oligocene and early Miocene. The amount of contemporary volcanic débris in the sandstones is consequently not particularly high. Some sandstones in northern Ethiopia, Sudan and Egypt do contain abundant acidic volcanic clasts, but these are derived from the Proterozoic basement and cause less diagenetic reservoir damage than contemporary glassy volcanic ash.Sandstones deposited in freely‐drained alluvial fan settings are characterised by early diagenetic kaolinite, whereas those of sabkha and marginal‐marine settings tend to show relatively early diagenetic chlorite. Those alluvial fan sandstones which were subsequently invaded by reduced pore waters expelled from the basin axis, and those in the basin axis, often developed later diagenetic chlorite.