[1] Methane gas hydrates, crystalline inclusion compounds formed from methane and water, are found in marine continental margin and permafrost sediments worldwide. This article reviews the current understanding of phenomena involved in gas hydrate formation and the physical properties of hydrate-bearing sediments. Formation phenomena include pore-scale habit, solubility, spatial variability, and host sediment aggregate properties. Physical properties include thermal properties, permeability, electrical conductivity and permittivity, small-strain elastic P and S wave velocities, shear strength, and volume changes resulting from hydrate dissociation. The magnitudes and interdependencies of these properties are critically important for predicting and quantifying macroscale responses of hydrate-bearing sediments to changes in mechanical, thermal, or chemical boundary conditions. These predictions are vital for mitigating borehole, local, and regional slope stability hazards; optimizing recovery techniques for extracting methane from hydrate-bearing sediments or sequestering carbon dioxide in gas hydrate; and evaluating the role of gas hydrate in the global carbon cycle.

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Physical properties of hydrate-bearing sediments

Experimental data on the kinetics of methane gas hydrate decomposition are reported. The isothermal/isobaric semi-batch stirred-tank reactor, used by Kim et al. (1987), was modified to include an on-line particle size analyzer. The experiments were conducted at temperatures ranging from 274.65 K to 281.15 K and at pressures between 3.1 and 6.1 MPa. The model of Clarke and Bishnoi (1999, 2000) was used to determine the intrinsic rate constant. It was found that the activation energy for methane hydrate decomposition is 81 kJ/mol and the intrinsic rate constant of decomposition is 3.6 × 104 mol/m2 Pa.s.



Des donnees experimentales sur la cinetique de la decomposition des hydrates de gaz de methane sont presentees. Le reacteur a reservoir agite semi-continu isotherme/isobare utilise par Kim et al. (1987) a ete modified de facon a y inclure un dispositif d'analyse des particules en continu. Les experiences ont ete menees a des temperatures comprises entre 374,65 et 281,15 K et des pressions allant de 3,1 a 6,1 MPa. On a utilise le modele de Clarke et Bishnoi (1999, 2000) afin de determiner la constante de vitesse intrinseque. On a trouve que l'energie d'activation pour la decomposition des hydrates de methane etait de 81 kJ/mol et la constante de vitesse intrinseque de decomposition de 3,6 × 104 mol/m2 Pa.s.

Determination of the activation energy and intrinsic rate constant of methane gas hydrate decomposition

Review of gas hydrate dissociation kinetic models for energy recovery

Formation and decomposition of gas hydrates

Effects of dissociation on the shear strength and deformation behavior of methane hydrate-bearing sediments

Experimental data on the rate of dissociation of methane hydrates are presented. The data were obtained from hydrate mass loss measurements using an electrobalance. A resistance heater with a known heat flux was used in the dissociation experiments. A mathematical model describing the dissociation process is also presented. The model, based upon first principles, assumes that the water formed during dissociation is blown away by the methane gas produced so that the dissociation process may be regarded as a moving-boundary ablation problem. Agreement between the model and the data is within 10%.

J. W. Ullerich

Papers

Theory and measurement of hydrate dissociation