摘要:

The extensive, thick Paleogene carbonate platform (Amapá Formation) of the Foz do Amazonas Basin, probably the largest coralgal‐foraminiferal platform of the geological record, developed through four depositional cycles expressing global eustatic changes of sea level. It shows five environmental belts: slope, apron, coralgal platform, large foraminifer shoal, finger coral bank and restricted lagoon, all of which associate bioaccumulated and bioclastic microfacies. At all times, a terrigenous environment consisting of fan deltas and lagoonal fine‐grained clastics existed immediately behind the carbonate platform and was connected with the open ocean by transverse troughs filled with shales and carbonate olistoliths. This combination of clastic and carbonate environments is unique in the geological record, and today only the Belize Shelf displays comparable conditions.The patterns of distribution of porous carbonates are different for each depositional cycle and the percentage of porous carbonates increases from cycle II to cycle IV. This indicates distinct and successive reservoir conditions generated during episodes of subaerial exposure of an expanding platform by large‐scale circulation systems at the end of each depositional cycle when high‐stand sea level changed to low‐stand. Porosity is mainly enlarged interparticle and moldic with a minor contribution of intercrystalline type related to dolomitization by mixing freshwater‐marine waters. It is not known to what extent the terrigenous environment contributed to the meteorically supplied groundwater system and related dolomitization, but the scale of the circulation is comparable to that presently displayed by Florida and Yucatan.The possibility of hydrocarbon flushing from such carbonate reservoirs is an important factor in the evaluation of the petroleum potential of the Amap

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1981.tb00521.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Upper Eocene immature subarkoses derived from Cretaceous sedimentary rocks, older granites and metamorphic rocks, form the reservoir sandstones of the Ossu‐Izombe oilfield, Imo State, Nigeria. These sandstones accumulated as part of a deltaic deposit. The vertical section of deltaic facies consists, from base to top, of a progradational sequence (prodelta and delta front), an aggradational unit (delta plain, marsh and interdistributary bay), and an overlying transgressive shallow marine interval. This sequence was penetrated by nearly all of the 15 wells drilled in the area. Reservoir sandstones are present within the distributary mouth bars, point bars, braided stream deposits, and the shallow marine interval.Thin section studies, electric‐log analyses, and data from modern deltas have aided in establishing the environments of deposition of these sandstone bodies. The principal results of this study are: (1) the basal C sandstone represents distributary mouth bar sands deposited at water depths of about 10 m; (2) the intermediate B group consist of point bar and distributary channel sandstone deposits of the lower delta plain; (3) the A‐2 sandstone tops the deltaic cycle as a product of braided streams; and (4) a shallow marine deposit, the A‐1.1 and A‐1 sandstones, occurs at the top of the delt

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1981.tb00522.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Oil migrates from a source into a reservoir rock and then, inside the reservoir rock, into a trap, and from the trap into a series of traps and reservoir rocks. The movement of oil is continuous and the interchange of oil between several reservoir rocks is totally independent of the source rock after a certain stage of migration. Each migration stage may cause quality changes in the properties of oil. A model is devised to account for oil migration and re‐entrapment, and to explain the distribution of different quality oils in time and space. Variations in the API‐gravity of oil, formation‐water salinity, reservoir temperature and pressure, sulphur‐content of oil, initial water content and recoverable oil reserves of oilfields can be important clues for the determination of migration directions and new prospects. These concepts were applied in a petroleum migration study of the Mardin Group (Aptian‐Turonian) which is the most important reservoir rock of SE Anatolia.Quantitative modelling shows that oil migration is directed towards two main uplifts which control the distribution of oilfields in SE Anatolia. Active water movement inside the reservoir rock has resulted in the accumulation of oil inside very young structural traps. Because almost all the fields have tilted oil‐water contacts, wildcat locations must be selected with special emphasis on hy

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1981.tb00523.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Surface mapping in the Asl area of Sinai, which was carried out in the year 1937, established the presence of 18 gypsum beds alternating with shales, marls and sandy beds, folded into gentle flexured structures with very little faulting. In contrast, the structures at depth, as revealed by the information from 28 wells, consist of numerous tilted blocks bounded by faults; most of these faults die out before reaching the surface.The task of finding locations for producing wells proved difficult; only 12 of the wells drilled have yielded commercial supplies of oil. The value of seismic records is limited in such a geological environment, where deep‐seated, block‐faulted structures are overlain by a thick evaporite succession.Three producing horizons, two of Miocene age and one at the top of the Eocene, have yielded an aggregate of more than six million tons of

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1981.tb00524.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Previous criticisms of primary petroleum migration by molecular solution have been: (1) the large compositional and molecular weight differences between hydrocarbons most readily dissolved in water and those found in crude oils, and (2) previously‐measured aqueous petroleum solubilities were not high enough to account for petroleum deposits using reasonable geologic assumptions. New crude oil aqueous solubility data remove both of these criticisms. Above 275° C, with both increasing gas content and temperature, the solute hydrocarbons become compositionally more and more similar to, and eventually exactly match, the starting material. Mass balance calculations, using experimentally‐measured crude oil solubilities, show that between 275° and 375° C, under realistic geologic assumptions, crude oil aqueous solubility is high enough to account for petroleum deposits. These new data also show that molecular solution is not a viable agent of primary petroleum migration below 275° C.Although the new data remove these two criticisms, three others are immediately raised: (1) there is inadequate water in sediments at temperatures between 275° to 375° C for migration by molecular solution, (2) sediment hydrocarbons will be thermally destroyed by these temperatures, and (3) these high temperatures are not present in most petroleum basins. Consideration of existing data suggests these criticisms can be satisfactorily answered. It is therefore concluded that a deep‐hot origin of petroleum and its migration by solution could fall within the restraints of the natural system.It is possible much or most of the world's oil has undergone primary migration by molecular solution; however two other mechanisms may also be viable: gaseous solution, and in the case of extremely rich source rocks, some form of a bulk phas

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1981.tb00525.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1981.tb00526.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1981.tb00527.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Book reviewed in this article:The “Brown Book”: “Development of the oil and gas resources of the United Kingdom, 1981”. A Report to Parliament by the Secretary of State for Energy.“Introduction to Petroleum Geology” by G. D. Hobson and E. N. Tiratsoo.Petroleum Geology of the Continental Shelf of NW Europe. ISBN 0 85501656 6. Eds. L. V. Illing and G. D. Hobson.“Who's Who in Technology”. ISBN 3–921220–246. $155. Publi

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1981.tb00528.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY