ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1990.tb00835.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Uncertainties remain concerning the common assumption that economic oil pools result only from deep, catagenic oil generation. These uncertainties stem from the many geological criteria that point to early oil entrapment and, furthermore, from the failure to resolve problems of oil migration out of, and through, consolidated sediments.Early oil emplacement is indicated by the preferential charging of paleostructures, inhibition of diagenesis and compaction by reservoired oil, folded oil‐water contacts, and by evidence supporting the immaturity of huge heavy‐oil deposits.The uncemented and uncompacted nature of the Athabasca “tar sands”, the perfect preservation of fossil wood within them, and the tilted oil‐water contacts at the Athabasca, Peace River and Cold Lake accumulations, support geological deductions of very‐early oil emplacement, and geochemical criteria for its immaturity.If such huge volumes of oil are immature, this would be in harmony with geological observations which conclude that pools of mature oil most probably result from in‐reservoir maturation of early‐expelled, biogenically‐generated heavy oil and methane.Hydrocarbons that remain in source rocks are maturated during burial, but are immobilised by progressive loss of effec

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1990.tb00836.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

The Tibet (Qinghai‐Xizang) Plateau is underlain by many thousands of mters of Ordovician (and possibly Cambrian) through Middle Eocene, gently‐dipping, essentially undeformed, stable platform sequences. These are largely qf shallow‐water, marine‐shelf origin in the Ordovician‐Triassic sections, but are of mixed continental and marine facies in the Jurassic through Midle Eocene sections. Two east‐west fault troughs ‐ the Banggong Co ‐ Nu Jianand Indus River ‐Yarlung Zangbo ‐ contain thick sections of Triassic, Jurassic, and/or Cretaceous marine flysch associated with ophiolites. The only severe deformation to affect the plateau was during the Mesozoic, and it was concentrated close to the through‐going east‐west fractures.Post‐early Eocene beds are entirely continental, and are concentrated nsmall‐to‐large grabens. One of these, the Lunpola Basin, has been moderately explored. Drilling here during the 1970s recovered small amounts of heavy, biodegraded oil of non‐marine origin, from a sectionthat ranges in age from Middle Eocene through QuaternaryPlateau‐wide stratigraphic studies reveal that the Ordovician through Early Carboniferous, and Late Permian through Middle Eocene, sections were deposited on a monolithic stable block. All were deposited in essentially warm tropical seas in close proximity, as demonstrated by the, facies, faunas, and floras. These same studies, plus related tectonic investigations, reveal that the through‐going east‐west fracture zones, popularly interpreted as “sutures,” are not sutures at all. Rather, the facies belts in rocks of all ages studied in detail routinely cross the so‐called “sutures,” commonly at very sharp angles, proving that these east‐west fault zones exerted no control overthe general lithofacies deposition patterns of the Himalaya‐Tibet block. The oniy facies control exerted by the fracture zones was in the small, narrow troughs that developed along them. Thus, the Himalaya‐Tibet block behaved as a single structural unit through time, and was never segmen red in to various microcontinents.Although some potential for commercial petroleum discoveries exists in the post‐middleEocene grabens. the greatest potential of the Himalaya‐Tibet block is in the Paleozoic‐Mesozoicsection. with its promise of multiple source‐beds. reservoirs, traps, and seals. We predict that, one

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1990.tb00837.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

An experimental program of stylolitic porosity development in stylolitic Atokan (Middle Pennsylvanian) limestones under simulated conditions of deep burial has shown that experimental dissolution preferentially occured and developed along existing styloties. The dissolution sequence was as follows: incipient pores following the traces of stylolites, grading into stylolitic lamellar pores, which enlarged eventually into non‐fabric‐selective channels. These stylolite‐controlled conduits were surrounded by adjacent incipient‐to‐complete oomolds, enlarged oomolds, incipient‐to‐complete algal bioclast molds, enlarged biomolds, and halos of intercrystalline porosity to microporosity.Trace element analysis (Mg, Sr, and Ca) of pore‐fluid samples during early phases of experimental deep burial dissolution indicated that slightly less stable protions of carbonates enriched in Mg and Sr dissolved preferentially, as observed also in natural cases. Pyrolysis data indicate that stylolites concerntrated organic matter derived from inter‐stylolite areas. This situation demonstrates the pressure‐solution origin of stylolites.Experimental stylolitic pore networks are similar in type, size, and geometry to natural stylolitic porosity. This preferential dissolution suggests that natural stylolites result from late (post pressure‐solution dissolution, are not necessarily mechanically induced during stylolite formation as sometimes postulated, and act as effective conduits for secondary porosity generation in deeply

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1990.tb00838.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

The Talisman‐1 well was drilled in 1984 at the NE end of the Dampier Sub‐basin, Western Australia, in permit WA‐191‐P. Testing of the Lower Cretaceous reservoir sequence produced an aggregated flow of 11,239 barrels of oil per day (b/d) from three drill‐stem tests. The reservior sequence consists of Berriasian to Tithonian mass‐flow sandstones (‘B’ and ‘C’ and Sands), and Hauterivian to Valanginian glauconitic shelf snadstones (‘A’ Sand), separated by claystone.An understanding of the diagenetic history of the Talisman‐1 reservoir sequence has been developed from thue integrated evaluation of petrography and petrophysics with hydrocarbon show, sulphur isotope, fromation water and oil composition data. This has, in turn, provided answers concerning controls on reservoir quality and the histroy of oil entrapment in the Talisman structure.Two pyrite/ferroan dolomite‐cemented sandstone intervals, below the present oil‐water contact in the Berriasian to Tithonian reservoir snadstones, are interpreted to have developed at palaeo‐oil‐water contacts in stacked oil accumulations formed during the Late Cretaceous to Early Tertiary. The pyrite and ferroan dolomite are considered to have developed as a result of anaerobic bacterial reduction of formation water sulphate. H2S and CO2were generated, and reacted with iron derived from dissolution of glauconite to form pyrite and ferron dolomite. Glauconite dissolution has enhanced the porosity and permeability of the reservoir sandstone.Miocene tectonism produced minor faulting in the reservoir sequence, allowing cross‐feed of oil between the stacked “pays”, redistributing the oil accumulation to its present configuration. Lighter hydrocarbons preferentially leaked up the fault during this phase of tectonism, with some accumuluting in thc Hauter

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1990.tb00839.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

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

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1990.tb00840.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

The Jurassic mudrock formations of Southern England, especially the Lower Lias, Oxford Clay and Kimmeridge Clay, show great variations in lithology, organic content and rates of sedimentation. It is here suggested that the varying sedimentation rates of these formations have been a major contributory factor, resulting in the differences in the organic richness observed between these fine‐grained Jurassic rock units. Variations in lithology have only a minor effect on the organic richness of these sediments, compared with the marked influence of sedimentation ra

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1990.tb00841.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

The motion of geological bodies is always relative. Regardless of the dimensions of a sample, our interpretation and understanding of the geological processes involved will, therefore, always depend on an external reference frame, and on the degree of subjectivity involved in our interpretation. Rarely, therefore, will geological interpretations be “correct”, and at least tow alternative answers will in most cases be available. Such alternative answers are, however, often avoided.In practical petroleum geology, these limitations to geological science appear to occur only in large‐scale interpretations, such as basin formaiton, tectonic driving forces and orogenesis. In regional and global geology, the reference framework is of primary importance, and will influence the underlying and resultant geological phil

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1990.tb00842.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.tb00843.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Book reviewed in this article:“One further aspect common to all definitions is that they consist of two parts: one i.s 'overt“Diagenesis I and II. edited by G.V. chilingarian and K.H Wolf.“Macmillaii field guide to geological structures ‘; by J. L. Roberts.“intermontane Basins:geolgy and resoures”, edited by T.Thanasuthipitak and P.ounchanum I

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1990.tb00844.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY