Combining spectroscopy, diffraction and imaging (Raman, neutron) for investigating synthetic and natural gas hydrates in marine clay media : formation kinetics, composition and spatial distribution.

• Main Author: Guimpier, Charlène
• Other Authors: Institut des Sciences Moléculaires (ISM), Université Montesquieu - Bordeaux 4-Université Sciences et Technologies - Bordeaux 1 (UB)-École Nationale Supérieure de Chimie et de Physique de Bordeaux (ENSCPB)-Institut de Chimie - CNRS Chimie (INC-CNRS)-Centre National de la Recherche Scientifique (CNRS), Université de Bordeaux, Arnaud Desmedt
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: HAL CCSD 2022
• Subjects: Gas hydrates; Neutron diffraction; Raman and neutron spectroscopy; Formation kinetics; Spatial distribution; Clays; Hydrates de gaz; Diffraction des neutrons; Spectroscopie Raman et neutronique; Cinétique de formation; Distribution spatiale; Argiles; [CHIM.OTHE]Chemical Sciences/Other; Methane hydrate; permafrost
• Online Access: https://theses.hal.science/tel-04220513; https://theses.hal.science/tel-04220513/document; https://theses.hal.science/tel-04220513/file/GUIMPIER_CHARLENE_2022.pdf

Gas hydrates are crystalline materials in which water molecules form cages, which can trap gaseous molecules. In nature, gas hydrates exist in the permafrost of polar regions and in the marine sediments of continental margins. These hydrates have a very large gas storage capacity and constitute the largest methane reservoir on Earth. In their natural environment, marine hydrates are mainly found in clay-rich sediments - multi-scale porosity systems. However, the assessment of the amount of gas stored in sedimentary hydrates is based on geophysical models assuming on one hand, a constant and homogeneous methane filling within the aqueous cages of the hydrate and on the other hand, a macroscopic distribution of hydrates in the sediments, not taking into account the potential formation in the micrometric or nanometric spaces of clays. Some studies (mainly theoretical) dedicated to methane hydrates in swelling clays suggest a potential formation in nanometric spaces (interlayer) of clays, with a variability of the filling rate of aqueous cages. This PhD work offers an experimental study of the physicochemical factors influencing the formation of gas hydrates in natural media. This work is based on a multi-scale approach where laboratory experiments are compared with measurements of natural samples collected in the Black Sea.Natural and synthetic gas hydrates mimicking the natural environment (gas composition, salinity and sediment mineralogy) were characterized at the microscopic and nanoscopic scales by Raman spectroscopy, neutron diffraction and inelastic neutron scattering. The influence of the natural environment on the resulting structures, cage occupancy, formation kinetics and dissociation mechanisms have been studied. Considering a wide range of gas mixtures encountered in the Marmara Sea, the spectral signatures of the gas hydrates (forming the so-called sI and sII structures) are reported. Studies of methane hydrate formation kinetics in swelling (Montmorillonite), non-swelling (Illite) clays and natural ...