Pattern Variety of Tetrahydrofuran Clathrate Hydrates Formed in Porous Media

We observed the pattern formation of tetrahydrofuran (THF) clathrate hydrates in a mixture of a THF-17H(2)O solution and glass beads (2 and 50 mu m diameter). The overall hydrate growth rate, V, was controlled using a directional growth apparatus. We are the first to successfully obtain a variety of hydrate patterns: a disseminated type at higher V values, a nodular type in the middle range of V, and massive and layer types at lower V values. The hydrate images obtained were analyzed by several methods to quantitatively characterize the patterns. Image processing retaining the relatively large hydrate regions (90% of the total hydrate area formed by segregated growth) was suitable for evaluating the number density of the hydrate grains and the average hydrate area, which dominated the total hydrate area. The segregated growth area of the hydrates was one of the most useful indices for quantitatively categorizing the hydrate types. The image analysis results showed that the segregated growth area of the hydrates and the average hydrate area increased and the number density of hydrate grains decreased with decreasing V. These results are qualitatively consistent with the theoretical frost heave model.