ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1990.tb00854.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

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 struct

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1990.tb00855.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

A systematic lithostratigraphical description is presented of those Jurassic rocks encountered in Egypt north of 29d̀N, at surface and in the subsurface. Based upon the scheme first proposed by Al‐Far (1966), five formations (Masajid, Khatatba, Bir Maghara, Shusha and Rajabiah) are shown to make up a continuous succession from late Pliensbachian probably up to early Tithonian: the Gebel el Maghara Group. The compositions of stratigraphically‐useful and diverse biotas are outlined, and used to erect a chronostratigraphical framework. From this, reliable comparisons are made with the Jurassic sequences of Palestine and Saudi Arabia. Furthermore, this more refined means of correlation enables a fuller understanding of the distribution of potential Jurassic source and reservoir rocks in northern

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1990.tb00856.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

During Upper Albian times, the Haplophragmoides gigas and Inoceramus comancheanus sea occupied the interior of the North American continent. Deltas draining the Cordilleran mountains around Jasper and Long. 49d̀ funnelled clastics into the Albertan sector of this sea, particularly during Viking time (early Late Albian). These Viking reservoir sands were distributed along the strandline and offshore environments during a relatively still‐stand phase of the sea.Along the western shoreline, wave, longshore and tidal currents shaped these sands into NW—SE trending barrier islands, comprising 11 sub‐facies (ebb‐tidal delta, marginal spillover channel, middle shoreface, marine shale, upper shore‐beach, dune, back‐barrier mudflat, lagoon‐washover, mixed tidal flat, tidal‐creek channel and overbank), about 32‐m thick and over 116‐kms long. These sandstone islands migrated imbricatedly in a NE direction.In the offshore setting, about 20–250 kms from shore, tidal currents fashioned the sands into NW ‐ SE trending, parallel, linear, large‐scale sandridges, two to 30‐m thick, and about 25‐to 75‐kms long on average. The tidal sandridge sub‐facies, from base to top, include: lower bioturbated, heterolithic, cross‐stratified, upper bioturbated and chert pebble conglomerate units. Deposition of some of the ridges occurred below effective wave‐base. Storm‐and gravity‐induced curr

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1990.tb00857.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

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 sedimenta

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1990.tb00858.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Major, trace and rare‐earth elements show significant variations in concentration with depth. Akam Shales are characterised by relatively high contents of alumina, volaties and iron, and low contents of magnesia, lime, soda and potash. The major‐element chemistry is significantly different from that of the Akiri‐1 onshore oilwell, Niger Delta.Based on selected major‐and trace‐element concentrations, the Akam Shales have been discriminated into marine and non‐marine groups, and are found to be associated with calcareous sediments. This observation correlates with the Type II source rock, which is oil‐and gas‐proven in the Niger Delta.Elemental abundances could be explained on the basis of the terrigenous and authigenic constituents of the samples. Changes in elemental abundances and ratios were observed at a depth of about, 1,733 m; this could be correlated with a change in the source area, a facies change, or a change in depos

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1990.tb00859.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1990.tb00860.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Book reviewed in this article:“Introduction to the petroleum geology of the North Sea”: 3rd edition, edited by K. W Glennie.“Petroleum and tectonics in mobile belts”: edited by J. Letouzqv“Thermal history of sedimentary basins”: edited by N. D. Naeser and T H. McCulloh“New Perspectives in Basin Analysis”: edited by K. L. Kleinspehti arid C. Paola“Physical principles of Jedirnerito

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1990.tb00861.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY