[M-IS26] Gas hydrates in environmental-resource sciences

[MIS26-08] High resolution X-ray CT observation of natural methane hydrate

*Satoshi Takeya¹, Akihiro Hachikubo², Satoshi Yamashita², Hirotsugu Minami², Hirotoshi Sakagami², Akio Yoneyama³ (1.National Institute of Advanced Industrial Science and Technology, 2.Kitami Institute of Technology, 3.SAGA Light Source)

Keywords:clathrate hydrate, natural gas hydarte, Hydrate sediment, X-ray CT

X-ray computed tomography (CT) is an effective nondestructive inspection method to visualize the microstructure in gas hydrate sediments and the formation and decomposition processes of the hydrates. Although many studies of gas hydrates using X-ray CT have been reported, the spatial resolution of the inhouse X-ray CT system is as low as 0.1 mm-1 mm, and little is known about the microstructure and its time evolution. In contrast, the latest synchrotron radiation-based X-ray CT has achieved spatial resolutions of several hundred nanometers (100 nm) to several micrometers at room temperature. We show that synchrotron radiation X-ray CT using a cryogenic system is suitable for the analysis of natural gas hydrate samples from natural sediments and outperforms conventional X-ray CT. The obtained X-ray CT images show the feasibility of this method for various missing information related to pores and gas hydrates, such as the occurrence of micropores and the amount of each individual gas hydrate.
In this study, three-dimensional microstructural analysis of natural gas hydrate collected from marine sediments is reported. The samples were characterized by synchrotron radiation using a low-temperature CT system with a SAGA light source (SAGA-LS). It was demonstrated that synchrotron radiation X-ray CT can reveal microscopic features of marine hydrates such as crystal size and pore network of gas hydrates with a spatial resolution of several micrometers. Pores with a diameter of several micrometers are formed around gas hydrates due to hydrate decomposition. The volume of the gas hydrate to water ratio was also estimated by powder X-ray diffraction analysis. These results reveal the ability of synchrotron X-ray CT to enable three-dimensional microstructure, which is of fundamental importance in modeling the physical and kinetic properties of natural gas hydrates.