Experimental formation of massive hydrate deposits from accumulation of CH₄ gas bubbles within synthetic and natural sediments     

Megan Elwood Madden  Shannon Ulrich  Phillip Szymcek  Scott McCallum  Tommy Phelps 《Marine and Petroleum Geology》2009

In order for methane to be economically produced from the seafloor, prediction and detection of massive hydrate deposits will be necessary. In many cases, hydrate samples recovered from seafloor sediments appear as veins or nodules, suggesting that there are strong geologic controls on where hydrate is likely to accumulate. Experiments have been conducted examining massive hydrate accumulation from methane gas bubbles within natural and synthetic sediments in a large volume pressure vessel through temperature and pressure data, as well as visual observations. Observations of hydrate growth suggest that accumulation of gas bubbles within void spaces and at sediment interfaces likely results in the formation of massive hydrate deposits. Methane hydrate was first observed as a thin film forming at the gas/water interface of methane bubbles trapped within sediment void spaces. As bubbles accumulated, massive hydrate growth occurred. These experiments suggest that in systems containing free methane gas, bubble pathways and accumulation points likely control the location and habit of massive hydrate deposits.  相似文献   

Experimental impact cratering: A summary of the major results of the MEMIN research unit     

Thomas Kenkmann  Alex Deutsch  Klaus Thoma  Matthias Ebert  Michael H. Poelchau  Elmar Buhl  Eva-Regine Carl  Andreas N. Danilewsky  Georg Dresen  Anja Dufresne  Nathanaël Durr  Lars Ehm  Christian Grosse  Max Gulde  Nicole Güldemeister  Christopher Hamann  Lutz Hecht  Stefan Hiermaier  Tobias Hoerth  Astrid Kowitz  Falko Langenhorst  Bernd Lexow  Hanns-Peter Liermann  Robert Luther  Ulrich Mansfeld  Dorothee Moser  Manuel Raith  Wolf Uwe Reimold  Martin Sauer  Frank Schäfer  Ralf Thomas Schmitt  Frank Sommer  Jakob Wilk  Rebecca Winkler  Kai Wünnemann 《Meteoritics & planetary science》2018,53(8):1543-1568

This paper reviews major findings of the Multidisciplinary Experimental and Modeling Impact Crater Research Network (MEMIN). MEMIN is a consortium, funded from 2009 till 2017 by the German Research Foundation, and is aimed at investigating impact cratering processes by experimental and modeling approaches. The vision of this network has been to comprehensively quantify impact processes by conducting a strictly controlled experimental campaign at the laboratory scale, together with a multidisciplinary analytical approach. Central to MEMIN has been the use of powerful two-stage light-gas accelerators capable of producing impact craters in the decimeter size range in solid rocks that allowed detailed spatial analyses of petrophysical, structural, and geochemical changes in target rocks and ejecta. In addition, explosive setups, membrane-driven diamond anvil cells, as well as laser irradiation and split Hopkinson pressure bar technologies have been used to study the response of minerals and rocks to shock and dynamic loading as well as high-temperature conditions. We used Seeberger sandstone, Taunus quartzite, Carrara marble, and Weibern tuff as major target rock types. In concert with the experiments we conducted mesoscale numerical simulations of shock wave propagation in heterogeneous rocks resolving the complex response of grains and pores to compressive, shear, and tensile loading and macroscale modeling of crater formation and fracturing. Major results comprise (1) projectile–target interaction, (2) various aspects of shock metamorphism with special focus on low shock pressures and effects of target porosity and water saturation, (3) crater morphologies and cratering efficiencies in various nonporous and porous lithologies, (4) in situ target damage, (5) ejecta dynamics, and (6) geophysical survey of experimental craters.  相似文献   

High‐pressure phase transitions of α‐quartz under nonhydrostatic dynamic conditions: A reconnaissance study at PETRA III          下载免费PDF全文

Eva‐Regine Carl  Ulrich Mansfeld  Hanns‐Peter Liermann  Andreas Danilewsky  Falko Langenhorst  Lars Ehm  Ghislain Trullenque  Thomas Kenkmann 《Meteoritics & planetary science》2017,52(7):1465-1474

Hypervelocity collisions of solid bodies occur frequently in the solar system and affect rocks by shock waves and dynamic loading. A range of shock metamorphic effects and high‐pressure polymorphs in rock‐forming minerals are known from meteorites and terrestrial impact craters. Here, we investigate the formation of high‐pressure polymorphs of α‐quartz under dynamic and nonhydrostatic conditions and compare these disequilibrium states with those predicted by phase diagrams derived from static experiments under equilibrium conditions. We create highly dynamic conditions utilizing a mDAC and study the phase transformations in α‐quartz in situ by synchrotron powder X‐ray diffraction. Phase transitions of α‐quartz are studied at pressures up to 66.1 and different loading rates. At compression rates between 0.14 and 1.96 GPa s^?1, experiments reveal that α‐quartz is amorphized and partially converted to stishovite between 20.7 GPa and 28.0 GPa. Therefore, coesite is not formed as would be expected from equilibrium conditions. With the increasing compression rate, a slight increase in the transition pressure occurs. The experiments show that dynamic compression causes an instantaneous formation of structures consisting only of SiO₆ octahedra rather than the rearrangement of the SiO₄ tetrahedra to form a coesite. Although shock compression rates are orders of magnitude faster, a similar mechanism could operate in impact events.  相似文献   

Coesite in suevite from the Ries impact structure (Germany): From formation to postshock evolution          下载免费PDF全文

Agnese Fazio  Ulrich Mansfeld  Falko Langenhorst 《Meteoritics & planetary science》2017,52(7):1437-1448

Coesite is one of the most common and abundant high‐pressure phases occurring in impactites. The mechanism of formation of coesite and its postshock evolution is revisited in this paper based on Raman microspectroscopy, and scanning and transmission electron microscopy of a coesite‐bearing suevite from the Ries impact structure. Our data indicate that coesite forms through a single process, i.e., by crystallization from high‐pressure silica melt, and that its formation is related to fluid inclusions in precursor quartz. During the postshock phase, coesite aggregates are partially modified by annealing and interactions with fluids. In an early stage of the postshock evolution, coesite is back‐transformed to quartz and the surrounding diaplectic glass devitrifies into β‐cristobalite, which transforms into α‐cristobalite and then into microcrystalline quartz during subsequent stages of the postshock evolution. Altogether these postshock modifications result in a significant volume loss and extensional fracturing. During a late postshock stage, the fractures are filled with clay minerals due to circulation of hydrothermal fluids.  相似文献   

Revealing hydrocarbon migration pathways     

Ulrich Mann 《International Journal of Earth Sciences》1989,78(1):337-348

In this paper a general concept for revealing hydrocarbon migration pathways in rock sequences is introduced. The concept uses a multidisciplinary approach based on a geochemical and a petrophysical (or mineralogical) index. These two indices provide together the migration plot which shows the direction of hydrocarbon movement.With the help of this technique, serrerai hydrocarbon migration effects were established for a sequence of continous cores from the Upper Carboniferous. The results were verified by comparing gradients of hydrocarbon concentrations relative to pore volume. In this way the relative importance of individual migration pathways were recognized, as well as presently or formerly active migration pathways.The strong influence of permeability changes on hydrocarbon movement in source beds requires the use of the »atypical pore network« model to supplement the kerogen network model. Both models help in understanding the mechanisms of primary migration, but in certain stiuations, one might be more effective than the other.

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Zusammenfassung In diesem Aufsatz wird ein Konzept vorgestellt zur Erkennung von Erdölmigrationsbahnen in Gesteinsabfolgen. Das Konzept ist multidisziplinär ausgerichtet und beruht auf der Anwendung eines geochemischen und eines petrophysikalischen (oder mineralogischen) Parameters. Beide zusammen genommen erlauben die Erstellung eines Migrationsdiagramms, das angibt in welche Richtung sich die Kohlenwasserstoffe bewegen.Mittels dieser Methode wurden in einer fortlaufenden Abfolge von Bohrkernen aus dem Oberkarbon mehrere Trends für die Migrationsrichtung von Erdöl erkannt. Diese Trends wurden durch Vergleich mit Kohlenwasserstoffkonzentrationsgradienten, bezogen auf das Porenvolumen des Gesteins, verifiziert. Auf diese Art und Weise ließ sich sowohl die Bedeutung der einzelnen Migrationsbahnen relativieren als auch zwischen jetzigen und früheren Migrationswegen unterscheiden.Der starke Einfluß von Permeabilitätsänderungen auf die Bewegung von Kohlenwasserstoffen auch in Erdölmuttergesteinen fordert die Anwendung des »Atypischen Porennetzwerk-Modells« als Ergänzung zum Kerogennetzwerk-Modell. Beide Modelle tragen wesentlich zum Verständnis der Mechanismen der primären Migration von Erdöl bei, jedoch kann im Einzelfall die Verwendung des einen Modells effektiver sein als die des anderen.

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Résumé L'auteur présente une méthode générale permettant de déterminer le chemin suivi par les hydrocarbures lors de leur migration à travers les roches. Cette méthode utilise une approche multidisciplinaire basée sur un indice géochimique et un indice pétrophysique (ou minéralogique). Ces deux indices combinés fournissent l'indice de migration, qui indique la direction du déplacement des hydrocarbures.Cette méthode a permis d'établir les effets de plusieurs migrations d'hydrocarbure dans une série continue de carottes du Carbonifère supérieur. Les résultats obtenus ont été vérifiés en comparant les gradients du rapport concentration d'hydrocarbure/volume des pores. On peut reconnaître, de cette manière, l'importance relative des voies individuelles de migration, ainsi que celle des voies de migration actives aujourd'hui ou dans le passé.Etant donné le rôle important joué par les différences de perméabilité dans le déplacement des hydrocarbures au sein des roches, on se réfère au modèle Atypical Pore Network, qui complète le modèle Kerogene Network. Les deux modèles sont utilisés de manière complémentaire pour comprendre les mécanismes de la migration primaire; dans des cas extrêmes, l'un d'eux peut être plus effectif que l'autre.Cette approche constitue un nouveau pas vers une meilleure identification et une meilleure quantification des effets de la migration; elle offre des avantages considérables en raison de la diversité des paramètres qui peuvent être utilisés. Comme n'importe quel autre outil d'exploration, elle ne peut être utilisée seule dans les travaux d'évaluation et d'interprétation. Pour porter tous ses fruits, elle doit être intégrée aux données géologiques, géophysiques et surtout hydrodynamiques.

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The long-term dynamics of crustacean communities in Lake Constance (Obersee, 1962–1986)     

Ulrich Einsle 《Aquatic Sciences - Research Across Boundaries》1988,50(2):136-165

The long-term development of crustacean associations in the Obersee of Lake Constance was studied at one central station from 1962 to 1986. In a simultaneously managed program with four additional stations from the eastern part (Bregenz Bay) to the western überlinger See mainly the differences in horizontal distribution were focussed. It was one aim of these investigations, to get an idea or an indication of a connexion between the recently observed eutrophication of the Obersee, and its crustacean communities. Due to the immigration of several species (cyclopids) or genotypes (Daphnia), the communities had changed in genetical structures, in reproduction rates and in predation or grazing impact. Dependent on the specific annual cycles, there resulted an extermination (Heterocope, Diaphanosoma), or a long-term decrease in annual means (Mesocyclops, Cyclops abyssorum) of the “old-settled” species. A general tendency was seen in an increase of annual averages until the middle of the seventies, and a following decrease of population density of most of the species. The horizontal differences in the species associations were remarkable. The Bregenz Bay showed an own aspect in its crustacean community with high total numbers and in earlier spring development. Most of the newcomers were concentrated in the eastern part of the lake.  相似文献   

A geomagnetic event recorded in loess deposits of the Tönchesberg (Germany): identification of the Blake magnetic polarity episode     

Jan Reinders  Ulrich Hambach 《Geophysical Journal International》1995,122(2):407-418

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Tertiary basalts and peridotite xenoliths from the Hessian Depression (NW Germany), reflecting mantle compositions low in radiogenic Nd and Sr     

Ulrich Kramm  K. Hans Wedepohl 《Contributions to Mineralogy and Petrology》1990,106(1):1-8

A total of 17 alkali basalts (alkali olivine basalt, limburgite, olivine nephelinite) and quartz tholeiites, and of 10 peridotite xenoliths (or their clinopyroxenes) were analyzed for Nd and Sr isotopes. ¹⁴³Nd/¹⁴⁴Nd ratios and ⁸⁷Sr/⁸⁶Sr ratios of all basalts and of the majority of ultramafic xenoliths plot below the mantle array with a large variation in Nd isotopes and a smaller variation in Sr isotopes. The tholeiites were less radiogenic in Nd than the alkali basalts. Volcanics from the Eifel and Massif Central regions contain Nd and Sr, which is more radiogenic than that of the basalts from the Hessian Depression. Nd and Sr isotopic compositions of all rocks from the latter area, with the exception of one tholeiite and one peridotite plot in the same field of isotope ratios as the Ronda ultramafic tectonite (SW Spain), which ranges in composition from garnet to plagioclase peridotite. The alkali basaltic rocks are products of smaller degrees of partial melting of depleted peridotite, which has undergone a larger metasomatic alteration compared with the source rock of tholeiitic magmas. For the peridotite xenoliths such metasomatic alteration is indicated by the correlation of their K contents and isotopic compositions. We assume that the upper mantle locally can acquire isotopic signatures low in radiogenic Nd and Sr from the introduction of delaminated crust. Such granulites low in radiogenic Nd and Sr are products of early REE fractionation and granite (Rb) separation.  相似文献   

A photoelectric detector for the measurement of photolysis frequencies of ozone and other atmospheric molecules     

Wolfgang Junkermann  Ulrich Platt  Andreas Volz-Thomas 《Journal of Atmospheric Chemistry》1989,8(3):203-227

Photoelectric detectors for the measurement of photolysis frequencies of different trace gases in the atmosphere are described. They exhibit uniform response characteristics over one hemisphere (2 sr) and wavelength characteristics closely matched to those of the photolysis frequencies J _O1D, J _NO2, and J _NO3, respectively. Absolute calibration of the J _O1D detector was performed by chemical actinometry with an accuracy of ±16 percent. Simultaneous measurements of J _NO2 and J _O1D are presented.  相似文献   

Towards the detection and attribution of an anthropogenic effect on climate   总被引：1，自引：0，他引：1  

Benjamin D. Santer  Karl E. Taylor  Tom M. L. Wigley  Joyce E. Penner  Philip D. Jones  Ulrich Cubasch 《Climate Dynamics》1995,12(2):77-100

It has been hypothesized recently that regional-scale cooling caused by anthropogenic sulfate aerosols may be partially obscuring a warming signal associated with changes in greenhouse gas concentrations. Here we use results from model experiments in which sulfate and carbon dioxide have been varied individually and in combination in order to test this hypothesis. We use centered [R (t)] and uncentered [C (t)] pattern similarity statistics to compare observed time-evolving surface temperature change patterns with the model-predicted equilibrium signal patterns. We show that in most cases, the C (t) statistic reduces to a measure of observed global-mean temperature changes, and is of limited use in attributing observed climate changes to a specific causal mechanism. We therefore focus on R (t), which is a more useful statistic for discriminating between forcing mechanisms with different pattern signatures but similar rates of global mean change. Our results indicate that over the last 50 years, the summer (JJA) and fall (SON) observed patterns of near-surface temperature change show increasing similarity to the model-simulated response to combined sulfate aerosol/CO₂ forcing. At least some of this increasing spatial congruence occurs in areas where the real world has cooled. To assess the significance of the most recent trends in R (t) and C (t), we use data from multi-century control integrations performed with two different coupled atmosphere-ocean models, which provide information on the statistical behavior of 'unforced' trends in the pattern correlation statistics. For the combined sulfate aerosol/CO₂ experiment, the 50-year R (t) trends for the JJA and SON signals are highly significant. Results are robust in that they do not depend on the choice of control run used to estimate natural variability noise properties. The R (t) trends for the CO₂-only signal are not significant in any season. C (t) trends for signals from both the CO₂-only and combined forcing experiments are highly significant in all seasons and for all trend lengths (except for trends over the last 10 years), indicating large global-mean changes relative to the two natural variability estimates used here. The caveats regarding the signals and natural variability noise which form the basis of this study are numerous. Nevertheless, we have provided first evidence that both the largest-scale (global-mean) and smaller-scale (spatial anomalies about the global mean) components of a combined CO₂/anthropogenic sulfate aerosol signal are identifiable in the observed near-surface air temperature data. If the coupled-model noise estimates used here are realistic, we can be highly confident that the anthropogenic signal that we have identified is distinctly different from internally generated natural variability noise. The fact that we have been able to detect the detailed spatial signature in response to combined CO₂ and sulfate aerosol forcing, but not in response to CO₂ forcing alone, suggests that some of the regional-scale background noise (against which we were trying to detect a CO₂-only signal) is in fact part of the signal of a sulfate aerosol effect on climate. The large effect of sulfate aerosols found in this study demonstrates the importance of their inclusion in experiments designed to simulate past and future climate change. Received: 10 November 1994 / Accepted: 19 July 1995  相似文献