A dynamic deterministic model of hydrocarbon generation in the Midgard Field drainage area offshore Mid-Norway

The Midgard Field offshore mid-Norway is a gas-condensate accumulation with a thin oil leg reservoired in Early and Middle Jurassic sandstones. There are two potential source rocks in the area; the Late Jurassic Spekk Formation is a marine shale with type II kerogen and a rich potential for oil, and the Åre Formation of Early Jurassic age which is a thick coal-bearing sequence with type III kerogen and potential mainly for gas. Geochemical analyses indicate that both the condensate and the oil leg are sourced mainly from the coal-bearing Åre Formation. Any contribution from the Spekk Formation appears to be of minor importance. Computer simulation of hydrocarbon generation in the drainage area for the Midgard Field indicates that huge volumes are formed, and confirms that hydrocarbon generation from the Åre Formation is volumetrically far more important than from the Spekk Formation. The simulation results also exclude any contribution to the reservoired gas from the Spekk Formation.

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Zusammenfassung Das Midgard Feld vor der Küste Mittelnorwegens ist eine Gas-Kondensat-Akkumulation mit einem nur geringen Ölanteil innerhalb unter- und mitteljurassischer Sandsteine. In diesem Gebiet gibt es zwei mögliche Muttergesteine: Einmal die oberjurassische Spekk-Formation, bei der es sich um einen marinen Schiefer mit Typ II Kerogen handelt und die ein hohes Ölpotential darstellt. Zum anderen gibt es die unterjurassische Åre-Formation, eine mächtige Kohle-führende Folge mit Typ III Kerogen und ein möglicher Gaslieferant. Geochemische Analysen deuten darauf hin, daß sowohl das Gas-Kondensat als auch das Öl des Midgard Feldes auf diese Kohle-führende Åre-Formation zurückzuführen sind. Jede Zufuhr aus der Spekk-Formation scheint von geringer Bedeutung zu sein. Eine durch Computersimulation rekonstruierte Kohlenwasserstofferzeugung im Einzugsgebiet des Midgard Feldes spricht für eine hohe Bildungsrate und bestätigt die Annahme, daß die Kohlenwasserstoff-produktion der Spekk-Formation gegenüber der Åre-Formation zu vernachlässigen ist. Die Simulation ergab ferner, daß keinerlei Gas von der Spekk-Formation dem Reservoir zugeführt wurde.

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Résumé Le champ off-shore de Midgard (Norvège moyenne) est une accumulation de gaz condensé accompagnée d'un mince corps d'huile, accumulation renfermée dans des grès d'âge jurassique inférieur et moyen. Il existe dans le secteur deux sources possibles: la formation de Spekk (shale marins du Jurassique tardif, à kérogène de type II, possédant un riche potentiel en huile) et la formation d'Åre (série épaisse jurassique inférieure, à couches de charbon, à kérogène de type III et potentiel essentiellement en gaz). Les analyses géochimiques montrent que le gaz condensé et l'huile ont tous deux comme origine la formation charbonneuse de Åre. La formation de Spekk ne semble être intervenue que de manière subordonnée. Une simulation par ordinateur de la genèse de l'hydrocarbure dans l'aire d'alimentation du champ de Midgard fait apparaître que des volumes importants ont été formés et confirme la large prépondérance de la formation de Åre parmi les roches-mères. De plus, cette simulation exclut toute expèce de contribution de la formation de Spekk dans la genèse du gaz.

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Meteorology of the terrestrial planets

The thermodynamics, dynamics, weather and general circulation (climate) of the atmospheres of Venus, Earth and Mars is reviewed, in the light of present knowledge. These three terrestrial planets each have a gaseous sunlit envelope, but the realizations of motions in them are quite different. This makes comparisons of their meteorology very interesting and challenging.     

Transverse baroclinic oscillations in Lake Überlingen

An episode of velocity measurements in the epilimnion at a midlake station in Lake Überlingen and taken from the campaign in October 1972 discloses a uni-nodal Poincaré-type baroclinic mode response with a 4 h period. We discuss the data and interpret it in terms of a two-layered linear wave model on the rotating Earth.

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Variation among fossil chironomid assemblages in surficial sediments of Bodensee-Untersee (SW-Germany): implications for paleolimnological interpretation

In paleolimnology, subfossil head capsules of chironomids play an important role as ecological indicators of lake history. It is important to determine, therefore, whether fossil assemblages are representative of former biocoenoses. There is evidence that headcapsules washed in from other places can make up a significant percentage of the total. As interpretations are usually drawn from the examination of a single core, it is of special interest to know whether a fossil assemblage of a single site properly reflects limnological conditions of the whole lake. This study examined the taxonomic distribution of subfossil chironomids in the surficial sediments of the Bodensee-Untersee, with the aim of assessing the variability in chironomid assemblages. Apparently, most of the head capsules of the profundal fossil assemblages in the Untersee had been washed in from the littoral zone or from the slope. Although the Bodensee-Untersee is a rather large lake, variability is surprisingly low among all samples. Therefore a correct interpretation from a single core may be possible.     

Hydrophobic and electrostatic parameters in bacterial adhesion

Recently it has been shown that the initial stages of bacterial adhesion to a model-surface of sulphated polystyrene can best be described using hydrophobic and electrostatic parameters. In the present study it is tested whether these parameters can generally be applied to predict bacterial adhesion by using (i) glass, as a model for hydrophilic and natural surfaces of silicates and oxides, (ii) polystyrene coated with proteins, as a model for a surface coated with an organic layer, and (iii) river Rhine sediment, as an example of a natural surface. Adhesion to glass was dominated by electrostatic interaction, whereas adhesion to polystyrene coated with various types of proteins depended on the surface characteristics of the bacteria and the type of protein. By relating Van der Waals interactions to hydrophobicity of the interacting species, the adhesion of bacteria to the various surfaces including the river Rhine sediments could be interpreted in terms of the DLVO-theory. It is therefore concluded that the conceptual principles of the DLVO-theory (interplay of Van der Waals and electrostatic interactions) are suitable to describe, at least qualitatively, the initial processes of bacterial adhesion to a wide range of surfaces.     

How does landfill leachate affect the chemical processes in a lake system downgradient from a landfill site?

A field study on the geochemical properties of a chemically-stressed limnic environment was performed in Lake Silbersee, which receives leachate water of high inorganic loading from an upgradient landfill site. The highly concentrated sulfate ion in groundwater, when entering the pore water system of the lake, gives rise to an intensive microbial sulfate reduction. A diagenetic approach was used to explain the existence of a marine-like aqueous system within a geologically slightly acidic aquifer, consisting of a well-buffered lake water and an alkalinity producing, excess sulphide containing sediment pore water system.     

Complete synthetic seismograms for high-frequency multimodeSH-waves

We present an efficient scheme to compute high-frequency seismograms (up to 10 Hz) forSH-waves in a horizontally stratified medium with the mode summation method. The formalism which permits the computation of eigenvalues, eigenfunctions and related integral quantities is discussed in detail. Anelasticity is included in the model by using the variational method. Phase velocity, group velocity, energy integral and attenuation spectra of a structure enable the computation of complete strong motion seismograms, which are the basic tool for the interpretation of near-source broad-band data.Different examples computed for continental structures are discussed, where one example is the comparison between the observed transversal displacement recorded at station IVC for the November 4, Brawley 1976 earthquake and synthetic signals. In the case of a magnitudeM _L =5.7 earthquake in the Friuli seismic area we apply the mode summation method to infer from waveform modeling of all three components of motion of observed data some characteristics of the source.On leave from Institute of Geophysics, ETH, Zürich, Switzerland.