Open AccessMicrostructural evolution of gas hydrates in sedimentary matrices observed with synchrotron X ‐ray computed tomographic microscopy
Author(s) -
Chaouachi Marwen,
Falenty Andrzej,
Sell Kathleen,
Enzmann Frieder,
Kersten Michael,
Haberthür David,
Kuhs Werner F.
Publication year - 2015
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1002/2015gc005811
Subject(s) - clathrate hydrate , nucleation , mineralogy , saturation (graph theory) , hydrate , sedimentary rock , geology , quartz , micrometer , synchrotron , chemical physics , materials science , chemistry , composite material , geochemistry , optics , physics , mathematics , organic chemistry , combinatorics
The formation process of gas hydrates in sedimentary matrices is of crucial importance for the physical and transport properties of the resulting aggregates. This process has never been observed in situ at submicron resolution. Here we report on synchrotron‐based microtomographic studies by which the nucleation and growth processes of gas hydrate were observed at 276 K in various sedimentary matrices such as natural quartz (with and without admixtures of montmorillonite type clay) or glass beads with different surface properties, at varying water saturation. Both juvenile water and metastably gas‐enriched water obtained from gas hydrate decomposition was used. Xenon gas was employed to enhance the density contrast between gas hydrate and the fluid phases involved. The nucleation sites can be easily identified and the various growth patterns are clearly established. In sediments under‐saturated with juvenile water, nucleation starts at the water‐gas interface resulting in an initially several micrometer thick gas hydrate film; further growth proceeds to form isometric single crystals of 10–20 µm size. The growth of gas hydrate from gas‐enriched water follows a different pattern, via the nucleation in the bulk of liquid producing polyhedral single crystals. A striking feature in both cases is the systematic appearance of a fluid phase film of up to several micron thickness between gas hydrates and the surface of the quartz grains. These microstructural findings are relevant for future efforts of quantitative rock physics modeling of gas hydrates in sedimentary matrices and explain the anomalous attenuation of seismic/sonic waves.