Empirical expressions for gas hydrate stability law, its volume fraction and mass-density at temperatures 273.15K to 290.15K

Abstract

A series of empirical expressions for predicting gas hydrate stability, its volume fraction out of pore space and gas hydrate mass-density were established in different systems in consideration of gas composition (CH 4 , C 2 H 6 , H 2 S) and salinity (NaCl, seawater), and pore size at temperature between 273.15 and 300 K, based on our gas hydrate thermodynamic model (Sultan et al., 2004b, c). Six of the developed expressions for predicting gas hydrate stability were validated against the available published experimental data and they were also compared with other models. At temperature 273.15 to 290.15 K, the ARDPs (Average Relative Deviation of Pressures between the prediction and the experimental data) have shown that these empirical expressions are in agreement with the experimental data as well as other models, indicating their reliability of predicting gas hydrate stability for these systems. At higher temperatures, the empirical predictions for gas hydrate stability do not well reproduce the experimental data, because they are based on van der Waals model. The empirical expressions for predicting gas hydrate stability in the systems of CH 4 + H 2 S + H 2 O, CH 4 + seawater + poresize, CH 4 + H 2 S + NaCl and CH 4 + CO 2 + NaCl, and for evaluating gas hydrate fraction and its density need further validation due to lack of available published experimental data. However, the empirical expressions for gas hydrate fraction and its density show that the effects of pore size and salinity are negligible; gas hydrate fraction will increase if methane concentration continuously increases relatively in excess of methane solubility and decreases with pressure within gas hydrate stability zone, which is well consistent with data of natural gas hydrates in Cascadia; gas hydrate density tends to increase with ethane percentage and decrease with pressure. Keywords: gas hydrate, stability law, fraction out of pore space, mass-density, empirical expressionsIn recent years, numerous theoretical models are proposed about the gas hydrate stability (Handa, 1990;

The challenges of quantifying the carbon stored in Arctic marine gas hydrate

“…B) Change in the volume of the GHSZ and in the mass of carbon due to ocean warming. Notation: P 0 seabed pressure; T 0 , seabed temperature; TG, thermal gradient; K th, thermal conductivity; calculated using six different methane hydrate phase boundaries Quinby-Hunt, 1994, 1997;Distribution Coefficient Method or K vsi -Method, Sloan and Koh, 2008;Moridis et al, 2008;Tischenko et al, 2005;Lu and Sultan, 2008) and assuming 3.5 wt% salinity and steady state conditions. B) Holocene sedimentation rate calculated using the water depth vs sediment accumulation relationship from Burwicz et al (2011).…”

“…with six different methane hydrate phase boundaries: (1) and (2) Dickens and Quinby-Hunt (1994;, (3) Distribution Coefficient Method or K vsi -Method (Sloan and Koh, 2008), (4) Moridis et al (2008), (5) Tischenko et al (2005) and (6) Lu and Sultan (2008). Water depth was converted to hydrostatic pressure assuming a constant water density of 1046 kg m 3 (Giustiniani et al, 2013).…”

Bottom‐simulating reflector dynamics at Arctic thermogenic gas provinces: An example from Vestnesa Ridge, offshore west Svalbard

“…Global estimates of gas hydrate concentrations rely on the prediction of the extent of the GHSZ at specific geological settings [e.g., Klauda and Sandler , ]. The GHSZ extent can be predicted using thermodynamic models [e.g., Bale et al ., ; Dickens and Quinby‐Hunt , ; Lu and Sultan , ; Sloan and Koh , ] together with constraints from direct sampling and indirect evidence from both geophysical and geochemical data. Several numerical models have been proposed that emphasize controls on hydrate stability by specific parameters [ Bale et al ., , and references therein; Peszynska et al ., ].…”

Modeling Effects of Gas Sources on Gas Hydrate Formation in the Northern South China Sea

“…Considering that the theory model of formation condition of gas hydrate is complex in calculation, based on the above theory model, the empirical models for different systems consisting of gas composition, pure water/pore water and pore size were established and applied [32] : where units of P and T are respectively kPa and K; parameters a, b, c, d, and e are determined by the certain gas composition (requiring R 2 > 0.98). Comparing the empirical model and experimental data, the difference between them is generally below 5% [32] . It indicates that the empirical model is applicable.…”