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and available online here Cet article fait partie du dossier thématique ci-dessous publié dans la revue OGST, Vol. 70, n°6, pp. 909-1132 et téléchargeable ici D o s s i e rOil & Gas Science and Technology -Rev. IFP Energies nouvelles, Vol. 70 (2015), No. 6, pp. 909-1132 Copyright © 2015, IFP Energies nouvelles > Editorial -Enhanced Oil Recovery (EOR), Asphaltenes and HydratesÉditorial -EOR «récupération assistée du pétrole», Asphaltènes et Hydrates D. Langevin and F. Baudin ENHANCED OIL RECOVERY (EOR) > HP-HT Drilling Mud Based on Environmently-Friendly Fluorinated ChemicalsBoues de forage HP/HT à base de composés fluorés respectueux de l'environnement Abstract -The formation and dissociation of methane hydrates in a porous media containing silica sand of different sizes and bentonite clay were studied in the presence of synthetic seawater with 3.55 wt% salinity. The phase equilibrium of methane hydrate under different experimental conditions was investigated. The effects of the particle size of silica sand as well as a mixture of bentonite clay and silica sand on methane hydrate formation and its dissociation were studied. The kinetics of hydrate formation was studied under different subcooling conditions to observe its effects on the induction time of hydrate formation. The amount of methane gas encapsulated in hydrate was computed using a real gas equation. The Clausius-Clapeyron equation is used to estimate the enthalpy of hydrate dissociation with measured phase equilibrium data.

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Natural gas hydrate creates a lot of problems during its transportation and production by plugging gas pipelines and process equipment. This work envisages the effect of electrolytes (NaCl and CaCl 2 ) at different concentrations on methane hydrate formation and dissociation. Extensive observations on equilibrium pressure and temperature during hydrate formation and dissociation have been made. The experiments were conducted in the temperature range of 261 to 270 K and pressure range of 2.6 to 3.0 MPa. Both sodium chloride and calcium chloride salts were found to have significant inhibiting effects on hydrate formation and dissociation with the latter having stronger effects. Gas consumption was found to vary with the progress of the hydrate formation as well as the concentration of salts in the hydrate cell. The dissociation enthalpies of methane hydrates in the presence of the above salts were also determined using the Clausius-Clapeyron equation based on the phase equilibrium data.

The present work reports the effect of bentonite clay on methane hydrate formation and dissociation in synthetic seawater of salinity 3.55 % of total dissolved salts. Extensive observations of pressure-temperature equilibrium during formation and decomposition of methane hydrate under different conditions have been made. It is observed that phase equilibrium conditions of hydrate are affected on changing the concentration of bentonite clay in synthetic seawater. Induction time for hydrate nucleation has been measured under different concentrations of clay and subcooling conditions. The presence of bentonite clay in synthetic seawater reduces the induction time of hydrate formation. Enthalpy of hydrate dissociation is calculated by Clausius-Clapeyron equation using measured phase equilibrium data. The amount of gas consumed during hydrate formation has been calculated using real gas equation. It is found that a larger amount of gas is consumed upon addition of bentonite clay in synthetic seawater.