ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1993.tb00336.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

A geochemical study of the argillaceous sequences of Turonian—early Santonian age penetrated by ten shallow boreholes in the Upper Benue Trough was carried out.The average total organic carbon contents of the sampled sections of the Bima, Yolde, Pindiga, Sukuliye and Jessu Formations were 0.30, 1.40, 0.85, 0.60, and 0.54%, respectively. Apart from the Bima Formation, all exceed the minimum value (0.5% TOC) normally required for a petroleum source rock. In spite of the moderate TOC, however, the content of soluble organic matter (SOM) and saturated hydrocarbons (SHC) was generally low.In terms of organic‐matter type, a predominantly marine fades with some terrigenous input is inferred for the Sukuliye and Pindiga Formations. This indicates that open‐marine conditions might not have been established during the Turonian marine transgression, which deposited these units.Within the updip sector of the basin, the organic matter is thermally immature. The most promising zones seem to be located south of the study area, where source rocks that have attained optimum levels of maturity for hydrocarbons

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1993.tb00337.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

The offshore West Korea Bay (WKB) Basin is one of a series of NE‐SW rift basins which formed in Korea and eastern China over thin continental crust during the Late Mesozoic and Early Cenozoic, and is characterised by a two‐layered structure — a Cenozoic basin is superposed on a pre‐Tertiary basin. In Part I of this paper (Massoud et al., 1991), paraffinic oils recovered from Mesozoic and Tertiary sandstone intervals were found to have been generated from different source beds. Also, a probable thick (400–500 m) Jurassic source bed for the Mesozoic oil was geochemically identified in the basinal offshore area of the lacustrine Sim Uuju sequence penetrated by Well 606In this Paper, the Authors complete the hydrocarbons survey on the formation by studying the type, amount and maturity of organic matter present, and the history of hydrocarbon generation. They conclude that the Jurassic bed could be considered as a major source for the Mesozoic oil in the WKB Basin, provided that it is of a sufficient extent to have produced large volum

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1993.tb00338.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Experimental and natural examples illustrate the influence of sub‐salt horizon basement faults on diapirism. In a series of experimental models, viscous diapirs were observed to form above or close to basement faults. In all the models, basement faults initiated a half‐graben, where thicker overburden units enhanced differential loading on an underlying buoyant layer. The buoyant material flowed updip to the low‐pressure zones in the uplifted block, and updip along the tilted upper boundary of the hanging‐wall. Basement faulting extended the overburden, and provided the space through which the buoyant layer could rise. Subsidence and faulting of overburden layers allowed diapirism along the faulted zones. In all cases, the deformation in the overburden was accommodated within a wider zone of faulting than the discrete basement fault which initiated the deformation. Differential compaction enhances differential loading and accumulation of thicker overburden on the downthrown sides of basement faults.Seismic profiles from the Danish Basin, Dutch Central Graben, Gulf of Mexico and North Sea show that diapirs are spatially associated with basement faults. However, model results show that diapirs triggered by basement faults are not necessarily located directly above the faults.Basement faults extend the cover sequences. If detached from the cover by a ductile layer, thick‐skinned extension is accompanied by thin‐skinned extension and decoupling of the cover. The influence of basement faults on diapirs depends on: the thickness and effective viscosity of the ductile layer (e.g. rock salt); the thickness ratio between the buoyant layer and the overburden; the mechanical properties of the brittle cover in the case of clastic sediments; the rate of sedimentation; the displacement rate throw and the dip of the base

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1993.tb00339.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

In theSamgorifield, near Tbilisi in the Republic of Georgia, changes in reservoir properties caused by alteration of middle Eocene volcanogenic rocks control the amount of oil and gas these rocks will yield. These changes, which include fracturing, development of vugs, and laumontite zeolitization, impart a vertical and lateral variability, thus giving rise to irregular petrophysical properties of the rock such as filtrational capacity, elastic deformational properties, and productivity. Indicative of such differences is the large variation in initial recovery from one well to another.According to the reservoir model proposed here, productivity atSamgoriis dominantly controlled by fracture porosity and permeability. Fractured bodies of oil‐bearing laumontized tuffs are enclosed within a thick layer of andesite‐basalt tuffs and tuffites, which act as a seal. As a result, the fractured tuffs are relatively isolated from the action of geostatic and geotectonic loads, which would otherwise result in closure of the fractures and microfractures. In addition, the fluid pressure of the reservoir tends to maintain open fractures. As fluid pressure declines over the producing life of the field, effective stress increases and the fractures close. This results in the isolation of producing zones and the consequent development of reservoir heterogeneity. An understanding of this effect is essential to proper management of the reservoir so as to ensure optimum recovery of oil.The contribution of matrix porosity to productivity is also recognized. Fluid injection analysis has established that matrix porosity and permeability vary according to lithology, with the highest values in laumontized tuffs: laumontite inter‐crystalline voids can also be observed, using scanning electron micro

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1993.tb00340.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

The Tabei Uplift in the northern Tarim Basin, the Tadong Depression in the eastern Tarim Basin, and the Tarim Central Uplift were formed as a result of mantle diapirism. Four stages in the geological development of this area can be recognized: an initial “embryonic” stage in the late Proterozoic; a “formational” stage in the Sinian; a “developmental” stage in the Early to mid‐Palaeozoic; and a “completion” stage in the late Palaeozoic.With long‐term Palaeozoic subsidence and well‐developed marine source rocks, the Tadong area is thought to be a promising source region for hydrocarbons. The Tabei and Central Uplifts, located respectively north and south of the Tadong Depression, are ancient, well‐preserved structures in which hydrocarbons may have accumulated, and could therefore constitute prospective areas for the location of “giant” oil‐ and gasfields in Palaeozoic sequences. Palaeozoic oil prospects have been confirmed in the Tabei area by the highly‐productiveSachan 2well. It is expected that intensified exploration will result in the location of both oil‐ an

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1993.tb00341.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

This paper discusses models of bitumen formation. Most liquid bitumens are formed during the middle stages of catagenesis (between approx. Ro equivalents of 0.4 and 1.15, respectively).“Progressive”naphthide formation is a process whereby organic matter and its derivatives gradually pass through a number of stages of alteration — three stages are generally recognized. By contrast, “regressive”naphthide formation is a “superimposed” process, involving microbial alteration and biochemical oxidation.In addition to the above two general processes, three other, less important schemes of naphthide formation are recognised:“Pyrodestructive bitumogenesis”results in the formation of “naphthoids”; these are bitumens generated close to an intruded heat source, which causes thermal destruction of organic matter.“Dynamic‐hydrothermal bitumogenesis”results in the generation of a complex group of bitumens, known as “naphthido‐naphthoids”, which are formed under conditions of dynamic metamorphism and hydrothermal activity accompanied by metasomatism.Thirdly, the processof “phase‐migrational” bitumogenesisresults in the formation of two groups of bitumens: “asphaltenites” and “beta‐asphaltenites”.This paper summarizes the Author's views on bitumen format

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1993.tb00342.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

The Hamada Basin of NW Libya is an intracratonic basin in which a thick sequence of clastic rocks was deposited during the Palaeozoic. These sediments were derived from a PreCambrian basement of felsic igneous and metamorphic rocks, and include both sands and clays; almost all the clays in formations of Palaeozoic age were produced from the alteration of feldspar. Structures were developed as these sediments were draped over the surface of the basement.Reservoirs in the Lower Palaeozoic (Lower Devonian, Lower Silurian and Cambro‐Ordovician Sandstones) appear to have developed as a result of synsedimentary processes, such as winnowing and washing‐out of clayey material from the sand by percolating waters, and sliding and slumping on the steep depositional surface during or soon after deposition. Oil traps are independent of structural elevation, but appear to have developed on those surfaces which were sufficiently steep to have initiated the above synsedimentary processes.This theory has been successfully tested in many places in the basin, and may provide a lead for exploration in other basins in Libya that have similar geological setti

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1993.tb00343.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

A number of depositional cycles have been defined from the Zubair Formation in central Iraq (East Baghdadfield). Each cycle represents the growth of a deltaic lobe (construction phase), followed by a hiatus during which the delta margin was subjected to wave and tidal activity (destruction phase), succeeded by a marine transgressive shale by which the cycle was concluded. When the growth of the deltaic lobe is renewed over a shale base, a new cycle begins.For each depositional cycle, four facies were identified from sections of core samples. These are: low‐sinuosity (distributary) channels (facies A); marsh (facies B); chenier (facies C); and shelf (facies D). Facies A. B and C comprise the lobe, i.e. indicate a marine regression, whereas facies D concludes the cycle and indicates a transgression.The sandstones of the Zubair Formation are classified as quartz arenites: they are mineralogically and texturally mature, fine‐ to very‐fine grained, well‐ to moderately‐well sorted, fine‐ to nearly‐symmetrical, skewed and mesokurtic.The rocks of the source area are acidic‐igneous. The source area, located within the Arabian Shield, underwent successive periods of tectonic renewal giving rise to high values of sediment supply, and lower values during intervening periods. The detrital materials supplied were to a large

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1993.tb00344.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1993.tb00345.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY