ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1992.tb00714.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Oil exploration in Madagascar has been concentrated on the Morondava Basin in the SW of the island, which is well‐known for its large deposits of tar sand and heavy oil at Bemolanga and Tsimiroro. Petroleum shows have frequently been encountered in exploration wells, but source‐rock identification has remained inconclusive. Thus, the present study of a wildcat was originally related mostly to geochemical prospect appraisal. Due to the inform oraganic matter type and wide range of thermal evolution stages sampled, the case history has more general implications, however, as regards relationships between thermal maturation and hydrocarbon generation.Evaluation of eleven rock samples taken at depths of between 1,100 and 2,500m by Rock‐Eval, solvent extraction and vitrinite reflectance (Rr) methods revealed only poor source rocks for oil with marginal through to post‐mature Type III kerogens (Rr between 0.5% and 1.4%) Discrepancies in yield profiles of total C15+ ‐hydorcarbons peaking at higher Rrin the Morondava and Dauala Basin (Cameroon) wells than in a Deep Basin (West Canada) well are tentatively attributed to their different geothermal histories. However, yield trends of specific saturated and aromatic hydrocarbon families, as determined by capillary gas chromatography, did not testify to the suspected effect of geothermal rate variations on generation curves, which hence remain unproven.Based on systematic changes with depth in the distribution of methylated di‐ and tri‐aromatics, the interpretration of maturation levels with respect to hydrocarbon generation was refined. When converted to vitrinite reflectance equivlents (Rc), molecular parameters such as the Trimithylnaphthalene Ration (TNR 1) and the Methylphenanthrene Index (MPI I) were able to disclose gradual marurity changes.In contrast to the large Morondava Basin, the smaller Majunga Basin in NW Madagascare has been the site of little explortion activity until recently. Based on organic‐geochemical analysis of seven rock samples from two exploration wells by the above‐mentioned methods, it was found that good source rocks for oil are absent. Some of the samples may have a considerable gas generation potential, which at best has been partially reasised. Certainly, maturities inadequate for substantial gas generation are indicated by ar

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1992.tb00715.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

A selection of Brent Group reservoir sequences from the Murchison field were chosen to study the nature of permeability variation within the Brent Group, with particular emphasis on the Etive Formation, which forms one of the main reservoirs in the field.Preliminary core examination of potential permeability barriers, as identified using wireline log response, has indicated that permeability heterogeneities can be placed into a five‐fold hierarchy. Permeability heterogeneities resulting from depositional or syndepositional processes comprise the first four orders of heterogeneity and include formations, facies transitions, bedding surfaces and laminations. Permeability heterogeneities which are the product of diagenetic processes are classified as fifth‐order heteorgeneities.Two major types of permeability barrier have been identified in core and on wireline logs within the Etive Formation. They include permeability heterogeneities associated with a transition between the two major facies associations (tidal channel and beach/foreshore sandstones); and heterogeneities associated with the development of inactive channel‐fill sandstones and siltstones within the tidal‐channel facies association.A detailed sedimentological model has been developed which demonstrates the complexity of reservoir zonation in the Etive Formation within the Murchiso

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1992.tb00716.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

The unexpected phenomena that measured vitrinite reflectance (Ro) values are lower (suppression) or higher (enhancement) than expected values at a given regional rank are defined as vitrinite reflectance anomalies. Such phenomena have been found in many basins in China, both in coal seams and in oil source rocks, and representative examples are presented in this paper. The cause and mechanism of vitrinite reflectance anomalies have been investigated by comparing the hydrogen contents and chemical structure of vitrinite macerals from immature Type I, Type II and Type III kerogens, and by studying the effects of early diagenetic oxidation on the thermostability of humic organic matter (OM). The results demonstrate: (1) depending on the anoxic or oxic nature of the depositional conditions, that lignocellulosic tissues can form a series of vitrinite macerals with different initial hydrogen contents and slightly different initial reflectivities; (2) that vitrinite macerals with different initial hydrogen contents have different reaction kinetics, with hydrogen‐poor, oxygen‐rich vitrinite maturing at an enhanced rate compared to vitrinite with a higher hydrogen content and a lower oxygen content; (3) that variations in the hydrogen content and the thermostability of vitrinite macerals are the main causes of Ro suppression and enhancem

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1992.tb00717.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Integration of lithofacies, inferred depositional environments and organic petrology of a lacustrine delta sequence in the Permo‐Triassic Gunnedah Basin of eastern Australia has provided a logical explanation for the patterns of distribution of the dispersed organic matter. The data show that: (i) sedimentary processes, such as size sorting and transportation, control the association of maceral assemblages in the dispersed organic matter with depositional environments; (ii) the extent of oxidation of organic matter increases downstream, from floodplain lake to interdistributary bay, delta front, prodelta and off‐shore lake deposits; (iii) coarse, woody material, mostly oxidised to semifusinite, is concentrated in the deta‐front environment; (iv) leaf material is transported preferentially to the prodelta, via the delta front. On the basis of organic matter type, the prodelta was probably the most favourable environment in this depositional system for the accumulation of oil‐prone sour

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1992.tb00718.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

A number of oil‐ and gasfields have recently been discovered on the continental shelf of Southern Vietnam, the largest of which is White Tiger. The main pay‐zone in this field is in the basement, which is composed of granites and granodiorites, lithologies which are found in the basement elsewhere on the shelf. The granites have undergone severe alteration as a result of tectonic, hydrothermal and surface weathering processes.Reservoirs are related to cavernous fracture porosity in deep basement zones, and to “porous cavernous” fracturing at more shallow levels. Total reservoir thickness exceeds 1 km, and the oil‐water contact has not yet been located. Flow‐rates reach 2,000 cu. m/d. Drilling data indicates that the granitoids are overlain by argillaceous‐terrigenous rocks of Oligocene and younger ages which have a thickness of 2.5‐4.4 km (up to 8 km in places, according to seismic data).Source rocks are mostly early Oligocene argillites, from which oil probably migrated into upthrown

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1992.tb00719.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

The Permian Dalan and Khuff Formations contain extensive gas reservoirs in the Greater Persian Gulf area. The Permian transgressive sea covered a vast area in the Middle East, and deposited a fairly thick sequence of shallow, epicontinental carbonates. These carbonates were deposited a fairly thick sequence of shallow, epicontinental carbonates. These carbonates were deposited unconformably on Lower Paleozoic rocks in western Iran and on the basement in Central Arabia. The term “Khuff Formation” has been widely used by oil companies in the region, but its equivalent, the Dalan Formation, is a new name currently being used in Iran.The Permian Basin was an elongate trough, trending NW‐SE, parallel to the Cretaceous‐Tertiary Zagros geosyncline. The deepest part of the Permian Basin was in the extreme SE portion of the trough, in the vicinity of the present Oman Mountains, in which nearly 6,000 ft (1,830 m) of Permian sediments were deposited.Porosity and permeability are generally low in these carbonates. However, secondary fracture porosity and dolomitization are commonly developed throughout these rocks. Permian reservoirs are capped by impervious strata, and the gas seems to be sourced from within the Permian

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1992.tb00720.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

A study of oilfield brines in the Afam, Imo River, Bodo‐West and Umuechem oilfields in the Eastern Niger Delta petroleum sub‐province of Nigeria was undertaken in an attempt to determine their genetic affinities.On the basis of their contents of bicarbonate, chloride and sulphate ions, and total dissolved solids, most of the formation waters from the Imo River oilfield are shown to be meteoric in origin, whereas those from Afam, Bodo‐West and Umuechem are connate waters. The relationship betwen salinity and total dissolved solids can be expressed by a simple linear equation.Formation‐water resistivity and total dissolved solids from these oilfields are parabolically related. The amount of total dissolved solids is also depth‐controlled, and increases with depth. This relationship is thought to be a function of post‐depositiona

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1992.tb00721.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1992.tb00722.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1992.tb00724.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY