Size Effect of Porous Media on Methane Hydrate Formation and Dissociation in an Excess Gas Environment

In this fundamental study, we examined the effect of silica sand grain size on methane hydrate formation under the excess gas formation approach method. The behavior of methane hydrate formation in four sizes of silica sands ranging from sand silt cut off size (0.063 mm) to granular pebble (3.0 mm) was examined to capture the particle size range found in natural hydrate samples. With the exception of the smallest grain size (0.063-0.18 mm), significant gas uptake was observed in all three sand sizes within the given experimental time of 70 h, and some unexpected formation behavior was seen in the coarse sands (0.56-1.3 mm) and granular samples (1.5-3.0 mm), where significant amounts of methane hydrate were observed to form on top of the porous media instead of dispersed within the porous media. This observation highlights the importance in selecting an appropriate porous medium and experimental approach to synthesize artificial methane hydrate in the laboratory for production tests, especially for reactors or crystallizers without viewing windows and relying on sparse temperature measuring points, as the gas consumption profile derived from pressure decrement could not depict the spatial dispersion of hydrates within the porous media.