Phase Equilibrium Condition for Pore Hydrate: Theoretical Formulation and Experimental Validation

Abstract

Based on the chemical potential equilibrium of water, a generalized equation of phase equilibrium is presented for pore hydrate, which relates the temperature depression of hydrate to the capillary pressure and osmotic pressure. The relationship between capillary pressure and unhydrated water content can be characterized by a soil‐water characteristic curve (SWCC). Uniting the SWCC and the phase equilibrium equation yields the equation of soil hydration characteristic curve (SHCC), which expresses the relationship between the unhydrated water content and temperature depression of pore hydrate. A series of experiments are performed, validating the phase equilibrium equation and the concept of SHCC. From the SHCC, the phase equilibrium surface can be determined in the space of temperature, pressure, and unhydrated water content. The thermodynamic state of pore hydrate moves on the equilibrium surface when the hydrate forms or dissociates. The projections of the equilibrium surface indicate the dissociation process of pore hydrate caused by thermal stimulation or depressurization. The salt solution changes the equilibrium surface to the direction that requires lower temperature and higher pressure and slows down the dissociation rates of hydrate to temperature and pressure.

A Simplified Model for the Phase Composition Curve of Saline Soils Considering the Second Phase Transition

“… where s u is the dissolved salt content (%) and w u the liquid or unfrozen water content (%). The freezing point depression induced by solute is correlated with the concentration of solute (Bing & Ma, 2011; Xu et al, 1995; Zhou et al, 2019). Thus, it is defined as follows.…”

Dissociation‐Induced Deformation of Hydrate‐Bearing Silty Sand During Depressurization Under Constant Effective Stress

“…The unhydrated water content (the ratio of unhydrated water mass to sediment particle mass) w u is correlated with P c via the soil-water characteristic curve. As P c is related to (T b −T) via Equation 2, w u can also be correlated to (T b −T), plotted as the soil hydration characteristic curve (Liang et al, 2021;Zhou et al, 2019Zhou et al, , 2021, as shown in Figure 3c.…”

Influence of Hydrate-Forming Gas Pressure on Equilibrium Pore Water Content in Soils

“…This model gives the value of the temperature shift of the hydrate formation curve 2 of 17 depending on capillary radius (the shift is increased while decreasing the capillary radius). This was followed by numerous attempts of experimental study on gas hydrate conditions in different porous media [2][3][4][5][6][7][8][9][10][11][12][13][14], as well as attempts to present theoretical estimations for the description of size distribution and its influence on phase equilibrium in a porous medium [14][15][16][17][18][19][20][21][22][23][24][25][26][27].…”