Correction of Hydrate Dissociation in Shale Media via Correlation of Kim's Model

• Published in: Oil & gas science and technology 2009-03, Vol.64 (2), p.133-140
• Main Authors: Mokhtari, B., Enayati, M., Pourabdollah, K.
• Format: Article
• Language: English
• Subjects: Applied sciences; Crude oil, natural gas and petroleum products; Energy; Exact sciences and technology; Fuels; Physics
• ISSN: 1294-4475; 1953-8189
• DOI: 10.2516/ogst/2009008

Deep-sea gas hydrates are ice-like crystalline substances in which hydrocarbon and non-hydrocarbon gases of specific molecular diameters are held by hydrogen bonding within rigid cages of water molecules. Sudden release of 1100-2100 Gt of carbon from dissociation of up to 10% of the global hydrate reservoir has been suggested as the cause of both the C-isotope excursion and coeval global atmospheric warming through an enhanced greenhouse effect. Kim's model assumed that, at a constant temperature, a two-step process could describe gas hydrate decomposition, including destruction of the clathrate host lattice at the surface of a particle and desorption of the guest molecule from the surface. In this paper, first, the thermodynamics and the kinetics of gas hydrate decomposition via Kim's model in the seafloors was reviewed; then, by a stainless steel test cell reactor and Omega Data Acquisition software, their correlation to sandy environments was formulated via numerical fitting of experimental data. The correlation of the conventional Kim's model is that the configuration of gas hydrate formation as a type of surface coating around sand grains was assumed. In the first stage of new mechanism dissociation, when the rate-controlling factor is dissociation heat, the formulation of the correlated dissociation rate was expressed. In the second stage of the mechanism, when the rate-controlling factor is mass transfer, the modified rate constant factor instead of Kim's constant factor was determined. The coefficient of correlation between the results of the estimation and experiment was more than 0.98 for both 85 and 216-μm sands. Les hydrates de gaz des fonds océaniques sont des substances cristallines semblables à de la glace dans lesquelles des gaz hydrocarbonés et non hydrocarbonés ayant des diamètres moléculaires spécifiques sont maintenus par des liaisons hydrogène à l'intérieur de cages rigides faites de molécules d'eau. Il a été suggéré que la libération soudaine de 1100 à 2100 Gt de carbone causée par la dissociation de jusqu'à 10% du stock mondial d'hydrates est la cause à la fois d'une anomalie positive de l'isotope C et d'un réchauffement atmosphérique mondial contemporain par l'intermédiaire d'un accroissement de l'effet de serre. Le modèle de Kim suppose que, à température constante, la décomposition des hydrates de gaz peut être décrite par un processus en deux étapes : destruction du réseau hôte du clathrate à la surface d'une particule et désorpt