S U M M A R YA LArge Reservoir Simulator (LARS) was equipped with an electrical resistivity tomography (ERT) array to monitor hydrate formation and dissociation experiments. During two hydrate formation experiments reaching 90 per cent bulk hydrate saturation, frequent measurements of the electrical properties within the sediment sample were performed. Subsequently, several common mixing rules, including two different interpretations of Archie's law, were tested to convert the obtained distribution of the electrical resistivity into the spatial distribution of local hydrate saturation. It turned out that the best results estimating values of local hydrate saturation were obtained using the Archie var-phi approach where the increasing hydrate phase is interpreted as part of the sediment grain framework reducing the sample's porosity. These values of local hydrate saturation were used to determine local permeabilities by applying the Carman-Kozeny relation. The formed hydrates were dissociated via depressurization. The decomposition onset as well as areas featuring hydrates and free gas were inferred from the ERT results. Supplemental consideration of temperature and pressure data granted information on discrete areas of hydrate dissociation.

Three 1200 m deep wells, spaced at 40 m, were equipped with permanent fibre-optic sensor cables. The variation of temperature within a continental, permafrost-associated gas hydrate occurrence was measured deploying the distributed temperature-sensing technology. Analysis of the transient temperature changes induced by the drilling and completion of the wells indicates that the base of the ice-bearing permafrost and the base of the gas hydrate occurrences is 604-609 ± 3.5 m, and 1108-1109 ± 3.5 m, respectively. Twenty-one months after the completion of the boreholes, the well temperatures are within ± 0.1°C of equilibrium with the formation temperature. The analysis of the geothermal gradient shows that high gas hydrate saturations within the pore space have only a minor effect on the bulk-rock thermal conductivity compared to changes in lithology. câbles-sondes permanents à fibres optiques permettant par détection thermique simultanée (distributed temperature sensing) de mesurer les variations de température dans une accumulation continentale d'hydrates de gaz associée à du pergélisol. L'analyse des changements transitoires de température occasionnés par le forage et l'achèvement des puits indique que la base du pergélisol contenant de la glace se situe entre 604 et 609 ± 3,5 m, alors que la base de la zone d'hydrates de gaz se trouve entre 1 108 et 1 109 ± 3,5 m. Vingt et un mois après l'achèvement des forages, les températures mesurées dans les puits s'écartaient d'un maximum de ± 0,1°C de l'équilibre avec la température des sédiments. L'analyse du gradient géothermique montre que, comparativement aux changements lithologiques, la forte saturation en hydrates de gaz de l'espace interstitiel a un effet mineur sur la conductivité thermique globale des formations.

Continuous‐temperature depth logs, especially when recorded in boreholes under thermal equilibrium conditions, provide detailed information of the subsurface thermal structure, which is necessary for the determination of reliable heat‐flow and rock thermal properties. In conjunction with independent thermal‐conductivity determinations, thermal logging data also allow the separation of heat conduction effects from thermal convection effects by fluid flow driven by various pressure differences such as pore fluid pressure. The Earth's thermal field is related intimately to geothermal resources and hydrocarbon resources. Therefore, the characterization of temperature in the subsurface and its relationship to lithology is of critical importance.

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