Experimental study on the mechanical properties and the microstructure of methane hydrate-bearing sandy sediments

• Main Author: Le, Thi Xiu
• Other Authors: Laboratoire Navier (navier umr 8205), École des Ponts ParisTech (ENPC)-Centre National de la Recherche Scientifique (CNRS)-Institut Français des Sciences et Technologies des Transports, de l'Aménagement et des Réseaux (IFSTTAR), Université Paris-Est, Anh-Minh Tang
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2019
• Subjects: Mechanical properties; Gas hydrate distribution; Gas hydrate morphology; Gas hydrate formation/dissociation; Sandy sediments; Gas hydrates; Propriétés mécaniques; Distribution des hydrates; Morphologie des hydrates; Formation/Dissociation d'hydrates; Sédiments sableux; Hydrates de méthane; [SPI.MAT]Engineering Sciences [physics]/Materials; Ice; Methane hydrate; permafrost
• Online Access: https://pastel.archives-ouvertes.fr/tel-02884782; https://pastel.archives-ouvertes.fr/tel-02884782v2/document; https://pastel.archives-ouvertes.fr/tel-02884782v2/file/TH2019PESC1039.pdf

Methane hydrates (MHs), being solid ice-like compounds of methane gas and water, form naturally at high pressure and low temperature in marine or permafrost settings. They are being considered as an alternative energy resource (mainly methane hydrate-bearing sand, MHBS) but also a source of geo-hazards and climate change (MHs in both coarse and fine sediments). Knowledge of physical/mechanical properties of sediments containing MHs, depending considerably on hydrate morphologies and pore-habits, is of the importance to minimize the environmental impacts of future exploitations of methane gas from MHBS. Existing experimental works mainly focus on synthetic samples due to challenges to get cored intact methane hydrate-bearing sediment samples. Various methods have been proposed for MH formation in sandy sediments to mimic natural MHBS, but without much success. The main interests of this thesis are to investigate morphologies and pore-habits of MHs formed in synthetic MHBS at various scales and to study the effects of MHs (MH morphology and MH saturation) on the mechanical properties of MHBS.Two MH formation methods (modified from two methods existing in the literature) have been first proposed to create MHs in sandy sediments at different pore-habits. At the macroscopic scale, MH pore-habits have been predicted via comparisons between sonic wave velocities, measured and that calculated based on rock physic models. The effects of MHs formed following the two proposed methods (at different hydrate saturations) on the mechanical properties of MHBS were investigated by triaxial tests. Furthermore, Magnetic Resonance Imaging (MRI) has been used to investigate the kinetics of MH formation, MH distribution along with sample height and also MH dissociation following the depressurization method which has been considered as the most economical method for MH production from MHBS. A temperature cycle in undrained conditions was supposed to not only complete MH redistribution in pore space after the water saturation of the ...