Data/hora: 03/06/2024 11:07:02

Provedor de dados: | 5
País: | France
Título: | Caractérisation physique et géochimique d'hydrates de gaz d'environnements géologiques différents. Apport des techniques de Diffraction X Synchrotron et de Spectroscopie Raman. Contribution à l'étude de leur origine, formation et stabilité sur les marges
Autores: | Bourry, Christophe.
Data: | 2008-12-10
Ano: | 2008
Palavras-chave: | X Ray synchrotron diffraction; Raman spectroscopy; Geochemistry; Gas hydrate; Eau interstitielle; Diffraction X synchrotron; Spectroscopie Raman; Géochimie; Hydrate de gaz.
Resumo: | Clathrate hydrates are inclusion compounds consisting of an ice-like network of water cages surrounding occluded guest molecules. They occur beneath the oceans and in polar regions, where low temperature and high pressure conditions prevail. Natural gas hydrates, mainly composed of methane occur worldwide and may contain huge natural gas amount, but they can also play an important role in continental slope stability or climate change, due to the potentially enormous "greenhouse" feedback effect of methane. The knowledge of their occurrence in the natural environment, their physical, chemical or thermodynamical properties is essential to prevent geohazards, to anticipate their role in climate change or to develop technologies to take advantage of this energy resource. To this purpose, this work reports a physical and chemical characterization of four natural gas hydrates for documenting their origin, formation and stability. The gas hydrate natural samples were collected from contrasted geological environments such as pockmarks on the Congo-Angola and Nigeria African margins, the Hakon Mosby Mud Volcano or the active fault system in the sea of Marmara. Physical properties of gas hydrates have been measured by X-ray synchrotron diffraction and Raman spectroscopy. Samples from African and Norwegian margins crystallize in type I structure. This observation is in agreement with their biogenic origin, confirmed by low o13CCH4 values. On the other hand, hydrate samples from the sea of Marmara, characterized by a thermogenic origin, exhibit a type II structure. Raman spectroscopy was also used to investigate the dissociation processes of natural gas hydrates. These results indicate that there is no preferential dissociation of large or small cages. This conclusion is in contrast with processes observed during hydrate formation. A difference in the rate of formation of hydrate cages may be attributed to the relatively large stability of the small cages compared to the large cages. Thermodynamical modeling let us evaluate the highly variable gas hydrate stability fields in sediments from the Hakon Mosby Mud Volcano, whereas it let us assert that only thermogenic gas hydrates can crystallize in the sea of Marmara. In a last chapter, geochemical data obtained from porewaters, gases, and gas hydrates collected during the Vicking cruise (2006) – HERMES Program – permitted to characterize the processes controlling the fluid circulation in the Hakon Mosby Mud Volcano where gas hydrates are present in great quantity.
Tipo: | Text
Idioma: | Francês
Identificador: | http://archimer.ifremer.fr/doc/2008/these-6236.pdf
Editor: | Université de Bretagne Occidentale
Relação: | http://archimer.ifremer.fr/doc/00000/6236/
Formato: | application/pdf