Influence of the Particle Size of Porous Media on the Formation of Natural Gas Hydrate: A Review

Abstract

As a new source of energy with great potential, natural gas hydrate (NGH) will play an indispensable and important strategic role in the future because of its tremendous reserves and wide application prospects in industry. It is of great significance to study the factors affecting the formation and occurrence of NGH for its exploration and exploitation under natural conditions and its application in industry. Since the sediments where NGH are mostly found are in porous media, the impact of porous media on the formation and occurrence of NGH has always been a research focus. This review focuses on the effects of the particle size of porous media on hydrate nucleation, growth, the conversion of water to hydrate, and phase equilibrium by summarizing previous studies. And occurrence characteristics of hydrates in porous media and the application of hydrate-based technologies are reviewed. A thorough analysis of the existing literature suggests that there is no consistent conclusion on the influence of the particle size and surface characteristics of porous media on hydrate formation. There is some debate, and the existence of a critical size of porous media needs further exploration. In addition, the interaction mechanism between the complex pore structure of porous media and the joint effects of particle size and initial water saturation on the hydrate formation process is still not clear. Thus, the influence of different initial water saturation conditions and pore structures on the formation and occurrence of NGH under different particle size conditions should be studied in the future to provide a reference for understanding the mineralization mechanism of NGH under natural conditions. Finally, some suggestions are put forward for studies of gas hydrate formation.

Formation Behaviors of Methane Hydrate in Partially Water-Saturated Porous Media with Different Particle Sizes

“…As a whole, the gas consumption rate in the water conversion range of 0–40% in 2.30 μm silicon dioxide powder is higher than that in 5.54 μm silicon dioxide powder. For the porous media with a smaller particle size, the pores in porous media are smaller and the specific surface area is larger, providing a larger contact area of gas and water and reaction interface. , Therefore, the hydrate formation rate is higher in the early stage in 2.30 μm silicon dioxide powder. When the water conversion is higher than 50%, the gas consumption in 2.30 μm silicon dioxide powder becomes lower than that in 5.54 μm silicon dioxide powder.…”

“…From Figure , it also can be found that the hydrate formation rate at 7 °C is higher than that at 3 and 5 °C, indicating that the hydrate formation in 229.90 μm silica sand has stronger randomness than those in 2.30 and 5.40 μm silicon powders. Qin et al analyzed that the water is less bound in the unsaturated bed with a larger sand particle size as a result of the smaller specific surface area. , Therefore, in 229.90 μm silica sand, a larger amount of water will accumulate at the bottom under the action of gravity, resulting in the uneven distribution of water in the bed and the randomness of the hydrate formation rate in the early stage. At the same time, it should be pointed out that the accumulation and uneven distribution of water caused by gravity should be more significant in the reactor with a larger inner volume, the randomness of the hydrate formation would be more notable, and the effect of water distribution on the hydrate formation rate should be taken into account.…”

“…From Figure 13, it also can be found that the hydrate formation rate at 7 °C is higher than that at 3 and 5 °C, indicating that the hydrate formation in 229.90 μm silica sand has stronger randomness than those in 2.30 and 5.40 μm silicon powders. Qin et al 22 analyzed that the water is less bound in the unsaturated bed with a larger sand particle size as a result of the smaller specific surface area. 31,32 Therefore, in 229.90 μm silica sand, a larger amount of water will accumulate at the bottom under the action of gravity, resulting in the uneven distribution of water in the bed and the randomness of the hydrate formation rate in the early stage.…”

“…In summary, previous research shows that the pore space, mass transfer, and liquid−gas contact area are significantly affected by grain sizes and water saturation in sediments, which further affect the hydrate formation process, the hydrate morphology, and the hydrate distribution. 13,14,18 As reviewed by Qin et al, 22 the particle size and surface characteristics of porous media have important influence on hydrate formation, but the conclusion in different studies is still not consistent. The influence of initial water saturation and pore structures in porous media with different particle sizes still needs further studies to obtain an in-depth understanding of the hydrate formation mechanism.…”

Advances in Characterizing Gas Hydrate Formation in Sediments with NMR Transverse Relaxation Time

“…Natural gas hydrate occurs in continental margin sediments [4,12,13,18]. The hydrate-bearing sediment has complex pore structures, unique interfacial properties, and various mineral compositions, prompting huge contrasts between the formation of gas hydrates in the confined space and that in the free space [19][20][21][22][23]. The formation process, structure, and distribution of natural gas hydrates in sediments have become focal points of exploring natural gas hydrates [24][25][26].…”