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

Abstract

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.

Microscopic measurements on the decomposition behaviour of methane hydrates formed in natural sands

“…The formed hydrate bearing sediments were quickly shied and preserved in liquid nitrogen. The calculation of the values of hydrate saturation was described by Chong et al 17 and Zhan et al 38 The initial saturation of hydrates in sediments was given in ESI (Table S1 †). The sample was placed in the sample cell of the cryo-SEM (S-4800, Hitachi, Japan) and wrapped with tinfoil (in the sample process liquid nitrogen), then it was transferred to the sample preparation room at 133 K. Aer sublimation deicing, the sample was transferred to the electron microscope sample chamber 133 K cold plate so that we could observe the changes of the sample and shoot electronic images.…”

“…In addition to the pressure and temperature changes, factors such as sediment type, 10,11 salinity, 12-14 permeability, 15 particle size, [16][17][18][19][20] and pore effect. 21 can also affect the kinetics of hydrates decomposition in porous media.…”

“…However, at the laboratory level, to more closely investigate the hydrate decomposition characteristics of sediments in the natural world, it is generally better to use natural sand or quartz as the porous medium. 17 Liu et al used a multistep decomposition method to study hydrate stability under different systems (aqueous solution, quartz sand, and marine sediment). They found that the capillary effect of pores in ne-grained (<35 mm) quartz sands was signicant, and the stability temperature of methane hydrates was reduced by 1.5 K at the maximum.…”

“…23,24 Chong et al selected siliceous sand ranging from silt (0.063 mm) to granular pebbles (3 mm) to study changes in macro-basic parameters such as sand layer changes and gas production. 17 Saw et al found that sand size had no signicant effect on hydrate enthalpy. 19 The hydrate decomposition enthalpy was estimated from the measured phase equilibrium data using the Clausius-Clapeyron equation.…”

Biopromoters for Gas Hydrate Formation: A Mini Review of Current Status

“…Kinetic promoters can improve the hydrate formation rate with very small doses and do not affect gas storage capacity (He et al, 2019 ). Researchers have used various kinetic promoters for gas hydrate formation, such as synthetic surfactants, activated carbon, porous silica, metal nanoparticles, graphene, carbon nanotubes, glass beads, sand grains, and dry water (Siangsai et al, 2015 ; Chong et al, 2016 ; He et al, 2019 ). However, most of the promoters above are non-renewable, petrochemical-derived, non-degradable materials, which will inevitably lead to resource waste and environmental pollution.…”