摘要:

Thermodynamic calculations for the C‐O‐S‐Hsystem indicate that at a fixed oxygen fugacity methane is in a stable phase relative to carbon dioxide at high pressures and low temperatures. At a constant temperature and pressure, methane is favored at low oxygen fugacities. Volcanic gases and near‐surface igneous rocks exhibit high values of oxygen fugacity. However, direct measurement of the oxygen fugacity of spinels from peridotites of deep origin indicate that the oxygen fugacity of these rocks is low, corresponding to an iron‐wüstite buffer. The relative abundance of the carbon isotopes C12and C13varies widely in natural gases. Methane formed by bacterial fermentation is highly enriched in the lighter isotope, while methane from deep deposits is much less so as is the methane flowing from hydrothermal vents on the East Pacific Rise. Except in extreme cases, the carbon isotope ratio cannot be used alone to assess whether methane is biogenic or abiogenic. The carbon isotope ratio in coexisting methane and carbon dioxide can be used to estimate the temperature at which the two gases came into isotopic equilibrium. This ratio indicates a high temperature of equilibration for a number of gas deposits. The carbon and helium isotope ratios together with their geologic settings are strongly suggestive that the large quantities of methane in Lake Kivu and the gases venting along the East Pacific Rise are abiogenic. Methane associated with the Red Sea brines and various geothermal areas may also be in part abiogenic. The high abundance of carbon in the Sun, the atmosphere of the outer planets, carbonaceous chondrites and comets, suggests that carbon may be more abundant in the Earth than it is in near‐surface igneous rocks. Such a high abundance could lead to a progressive outgassing of methane at depth, which then is oxidized near the surface or in the atmosphere. Methane hydrates are stable at low temperatures and high pressures. Today, methane hydrates are found in areas of permafrost and in ocean sediments. Methane hydrates in ocean sediments were first formed about 20 mya (million years ago) when the Antarctic ice sheet reached sea level. Terrestrial methane hydrates formed more recently during the glaciations beginning 1.6 mya. Methane hydrates and trapped gas are probably abundant under the Antarctic ice sheet. The formation of methane hydrates may be related to the low values of carbon dioxide in the atmosphere some 20,0

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1983.tb00588.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

The injection of steam into oil reservoirs is a technique commonly used for improving the production of heavy crude oils. Very often, a change in the composition of the oil and gas produced may be observed during steam flooding. In general, corrosive gases, such as H2S and CO2, are produced in increased quantities.In laboratory experiments on sulphur‐bearing reservoir minerals and crude oils the origin of the change in oil and gas composition was investigated. Temperatures up to 370°C were applied to study temperature‐ and rate‐dependent phenomena. By means of X‐ray fluorescence, gas chromatography and chemical precipitation methods, the change in the sulphur material balance was studied.It was shown that gas evolution depends strongly on the temperature of the steam injected. Furthermore, it was possible to prove that the gases evolved during steam flooding (such as CO2, H2S etc.) originate from the decomposition of crude oil components. Besides these investigations, a drastic viscosity increase of the residual crude oil was observed after steam injection was applied.It is concluded that the production of H2S and CO2may be controlled by temperature adjustment of the steam being

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1983.tb00589.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Carbonate deposition through the Earth's history shows two distinct changes in terms of volume and chemistry. Whereas carbonates comprise a very small percentage of the total sedimentary rocks in the Proterozoic, they constitute 20–25% at the present time. From the Archaean to Early Palaeozoic, carbonates are dominantly dolomites, whereas afterwards they are dominantly limestone.87Sr/86Sr, δ180 and δ13C trends show an increase with decreasing age.All these features of carbonate rocks are explicable as being related to the increased episodic outgassing of CO2and CH4from the upper mantle throughout the Earth's history.The Mesozoic carbonates of Himalaya are correlatable with the CO2outgassing associated with rifting and magmatism during the birth of the Tethys oc

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1983.tb00590.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

A coefficient of elimination derived from Information Theory is proposed. The coefficient expresses the mixing of the elements C, H and O in kerogen, based on chemical analyses. It is shown to have meaning in terms of the products of kerogen evolution, as well as the changes in the chemistry of the kerogen itself. It is suggested that this parameter, plotted against percentage hydrogen, is a useful addition to the conventional van Krevelen diagram. Points representing the accepted stages of kerogen evolution are indicated with reference to the chemistry of the processes in vol ved and are shown to be similar to those determined from physical studies, in particular reflectivity.

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1983.tb00591.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

The contributions of uranium, thorium and potassium to the natural radioactivity of shaly sediments have been estimated. Average shales have high contributions from potassium (50%) and Th (40%) and minor contributions from U (10%).

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1983.tb00592.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

On the basis of the triaxial stress concept, the tectonic stress required for faulting and sliding in a sedimentary basin can be estimated. The horizontal tectonicstress necessary for thrust faulting, for example, increases with depth from the surface to about 9,000 ft (2.7 km), and decreases below 9,000 ft (2.7 km), primarily because of a changing Poisson's ratio. Changing the vertical effective stress caused by generation of abnormal fluid pressure would also change the tectonic stress requirements for faulting.The internal friction of sedimentary rocks in the subsurface must be exceeded by the tectonic stress applied to the basin for faulting or sliding to take place. Estimates of the internal friction suggest that there is a high probability of faulting at depth if there are thick undercompacted and geopressured sections. Diapirs may also occur in such a physical environment. If the sedimentary rocks are normally compacted and the fluid pressure is hydrostatic from the surface to depth, on the other hand, the rocks are generally too rigid to cause any significant sliding. There would be very little chance of faulting and diapirism in such a case.The concepts developed in this paper may have a practical application in the under‐standing of the physical conditions and constraints of faulting and diapirism in a relatively‐young sedimentary basin with significant geopressuring at de

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1983.tb00593.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Cavities of freshly fractured surface and the exterior surface texture of detrital quartz grains were examined and photographed with the help of the scanning‐electron microscope at different magnifications. Three formations of Egyptian clastic sediments are used for this purpose namely: (a) Carboniferous sandstone of west‐central Sinai, (b) the so‐called Nubian sandstone of Early Cretaceous(?) age from southern Egypt, and (c) Oligocene sand accumulations from the vicinity of Cairo.It is concluded from the present study that in most cases the intracrystalline cavities have an average diameter of less than 10 microns. Different shapes can be acquired by these cavities‐ranging between irregular and negative crystal forms. The distribution of ca vities seems to be mainly along the fractures and the planes of growth but random distribution is sometimes observed.Examination of the surface features also shows that the depositional environment for Sinai and Aswan sandstones is aeolian with more effective diagenetic alteration in the first type of deposit. In the case of Cairo sandstone, the surface impressions of the quartz confirm the alluvial environment of dep

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1983.tb00594.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1983.tb00595.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1983.tb00596.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1983.tb00597.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY