Microstructure Observations of Natural Gas Hydrate Occurrence in Porous Media Using Microfocus X-ray Computed Tomography

Natural gas hydrates are globally considered a potential alternative form of energy suitable for sustainable development. The microstructure of natural gas hydrates in sediments governs their seismic and acoustic exploration, stability of seafloors, and gas production from hydrate deposits. To investigate the microstructure and occurrence of natural gas hydrates in pores, natural gas hydrate-bearing porous media were directly observed using microfocus X-ray computed tomography (CT). The spatial distributions of free gas, natural gas hydrates, water, and grains were identified. The results indicated the preference of natural gas hydrates to form primarily within pore spaces and not to cement the adjacent grains, which was described by the floating model. Moreover, the migration of gas and water within pore spaces during hydrate formation appeared random, and natural gas hydrates were found to nucleate preferentially at the gas water interface. The values of porosity and hydrate saturation obtained via reconstruction of CT images agreed well with the conventional methods, indicating that X-ray CT is effective in microstructural studies on natural gas hydrate-bearing sediments. These findings could have implications for both understanding of natural gas hydrate existence within deposits and future gas production from hydrate-bearing sediments.