Abstract
The porous microstructure of hydrates governs the mechanical strength of the hydrate-bearing sediment. To investigate the growth law and microstructure of hydrates in porous media, the growth process of tetrahydrofuran (THF) hydrate under different concentration of THF solution is directly observed using Magnetic Resonance Imaging (MRI). The images show that the THF hydrate grows as different models under different concentration of THF solution (19%, 11.4% and 5.7% by weight) at 1 °C. When the concentration is 19% (stoichiometric molar ratio of THF/H2O = 1:17), the THF hydrate grows as cementing model. However, with the decreasing concentration of THF, the growth model transfers from cementing model to floating model. The results show that the growth of the THF hydrate was influenced by the dissolved quantity of THF in the water. The extension of the observed behavior to methane hydrate could have implications in understanding their role in seafloor and permafrost stability.
Highlights
Multi kinds of gas and volatile liquid, such as methane, carbon dioxide, tetrahydrofuran, can transform clathrate hydrates through the interaction with water [1,2]
While in the pore space scale, the hydrates are concluded as four microstructures, cementing at grain contacts, grain coating, grain supporting and free floating [8]
The images show that the position where the hydrate forms is stochastic, while the position is at the grain contact
Summary
Multi kinds of gas and volatile liquid, such as methane, carbon dioxide, tetrahydrofuran, can transform clathrate hydrates through the interaction with water [1,2]. Natural gas hydrates exist in permafrost regions and beneath sediments of the seafloor, where high pressure and low temperature conditions naturally coexist [6]. Hydrates can (a) be free floating in the sediment matrix; (b) contact, but do not cement, existing sediment grains; (c) cement and stiffen the bulk sediment [7]. While in the pore space scale, the hydrates are concluded as four microstructures, cementing at grain contacts, grain coating, grain supporting and free floating [8]. The microstructure of hydrates in the pore space of the sediment determines the velocity and attenuation of compression and shear waves, which are the important parameters of hydrate exploration. The microstructure of the hydrates in sediment is crucial in the field of exploitation, because it governs the mechanical strength and hydraulic permeability of the hydrate-bearing sediment [9]
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