Dissociation Conditions of Methane Hydrate in Mesoporous Silica Gels in Wide Ranges of Pressure and Water Content

Abstract

The temperature of methane hydrate dissociation in silica mesopores has been monitored within a wide range of pressures from 10 MPa to 1 GPa. Because the determination of pore size appears to be crucial for the studied phenomenon, several methods of calculation have been applied. According to our findings, the size that corresponds to the mean size of the most representative pores is to be considered as the most reliable. It was concluded that the shape of hydrate particles replicates a host space of pores and may have a complex (e.g., fractal) shape. An attempt to simulate the curvature of hydrate particles by globular (quasi-spherical), elongated (quasi-cylindrical), or any intermediate models has been done. The quasi-spherical model seems to be more adequate for hydrate particles in small pores (<8 nm), while the quasi-cylindrical model fits better the experimental data for hydrate particles in larger pores. According to our experimental results, the hydrate can be formed in pores only by capillary condensate, without involving the water layers tightly bound by the surface, and pressure has an insignificant effect on the decrease of the dissociation temperature of the confined hydrate. A new effect of the formation of hydrates at a temperature higher than the bulk hydrate dissociation temperature has been observed for silica gels with the narrowest pores studied.

Mechanisms of Methane Hydrate Formation in Geological Systems

“…Theoretical studies indicate that the gas-liquid capillary pressure has an opposite effect on the methane hydrate phase boundary as it inhibits the formation of gas bubbles and thus makes methane hydrate more stable in pores (Buffett & Zatsepina, 1999;Henry et al, 1999;Liu & Flemings, 2011;Yagasaki et al, 2014). The net effect of gas-liquid and hydrate-liquid capillary pressure is to shift the methane hydrate phase boundary toward higher temperature/lower pressure (Liu & Flemings, 2011), which was observed by Aladko et al (2004) in pores with radius less than 5 nm. However, experiments that include both the gasliquid and hydrate-liquid capillary pressure are rare in literatures.…”

Methane Hydrate Formation and Dissociation in the Presence of Silica Sand and Bentonite Clay

“…3). Earlier studies also showed that silica particles exhibit thermodynamic inhibition during methane and natural gas hydrate formation [18,19].…”

The influence of temperature, pressure, salinity and capillary force on the formation of methane hydrate

“…Evidence shows that the pore sizes (Ruppel, 1997;Clennell et al, 1999), surface structure and mineral composition of the medium may influence the three-phase equilibrium conditions of gas hydrate. Recent workers have done many experiments to determine the three-phase equilibrium conditions of gas hydrate in porous medium (Handa and Stupin, 1992;Uchida et al, 1999Uchida et al, , 2002Seshadri et al, 2001;Seo et al, 2002;Smith et al, 2002a,b;Zhang et al, 2002;Seo and Lee, 2003;Anderson et al, 2003b;Aladko et al, 2004). These studies indicate that the capillary force can inhibit the formation of gas hydrate in small pores.…”