METHOD OF DETERMINING THE THERMAL CONDUCTIVITY OF DISPERSED GAS-SATURATED SEDIMENTS UNDER CONDITIONS OF HYDRATE AND ICE FORMATION

Evgeny Chuvilin, Boris Bukhanov, Gennagy Brovka

Dans les comptes rendus d’articles de la conférence: GeoQuébec 2015: 68th Canadian Geotechnical Conference & 7th Canadian Permafrost Conference

Session: Laboratory and Insitu Testing in Cold Regions / Essais en laboratoires et essais in situ pour les régions nordiques

ABSTRACT: This paper presents a new method of experimental investigation of thermal conductivity of fine-grained gas-saturated sediments during hydrate accumulation at temperatures above and below 0°C. The testing was conducted with a special gas hydrate experimental setup featuring an integrated measurement system for measuring thermal conductivity of the fine-grained sediments under high gas pressure. Measurements of soil thermal conductivity were carried out in steady-state thermal mode (the stationary thermal method). This method allows to quantify the impact of hydrate saturation and the extent of pore water to hydrate transition on the thermal conductivity of the fine-grained sediments.

RÉSUMÉ: Cet article présente une nouvelle méthode expérimentale d'investigation de la conductivité thermique des sédiments fins saturés en gaz lors de l™accumulation d'hydrates à des températures au-dessus et sous 0°C. Les essais ont été réalisés à partir d™un dispositif expérimental d'hydrate de gaz combiné à un système de mesure de conductivité thermique permettant l™étude des sédiments sous pression de gaz. La conductivité thermique des sédiments a été déterminée à partir de la méthode de flux de chaleur constant (régime thermique stationnaire). Cette méthode permet de quantifier l'impact de la saturation des hydrates et l'importance de l'eau interstitielle lors de la transition des hydrates sur la conductivité thermique des sédiments fins. 1. INTRODUCTION In nature, gas hydrates (mainly methane hydrates) are often formed in the offshore sediments at depths below 300 meters, and in permafrost ground areas (Sloan, 1998; Max, 2000). In the permafrost areas, gas hydrates are primarily formed in soils of subpermafrost horizons. Under long-term freezing conditions, the cooling effect in sediments is observed at great depths (hundreds of meters). This causes intersection of gas-bearing horizons and hydrate stability zone, which leads to formation of gas hydrate horizons ahead of the freezing front. It should be noted that increase in permafrost thickness, makes hydrate horizons undergo a process of freezing, which results in formation of naturally frozen hydrate-bearing soils. Despite the fact that most hydrate formations are observed at great depths, some could be found in permafrost areas at shallow depths (up to 250 meters) under close to 0°C negative temperatures. Such formations are subject to high pressure, generated by the process of water crystallization in pores (the crystallization factor) and by external load (the baric factor) applied to concentrated gas accumulations (gas pockets) in frozen sediments (Yakushev & Chuvilin, 2000; Chuvilin et al., 1998). The baric factor is mainly caused by two reasons: transgression of the Arctic seas, and development of glaciation (Romanovsky, 1993). As a result, gas accumulations at relatively shallow depths of permafrost enter the zone of hydrate stability and transform into gas hydrates (Chuvilin et al., 1998; Chuvilin & Lupachik 2011). Thus, the processes of hydrate accumulation can occur in sub-permafrost horizons at low positive temperatures and at temperatures below 0°C in permafrost. It is known that thermal conductivity of pore fluids water & ice are very different (0.6 and 2.23 W/(mŁK), respectively), but for water & gas hydrate they are similar (0.6 and 0.55-0.65 W/(m(Stoll & Bryan, 1979; Huang & Fan, 2004; Waite et al., 2007; Rosenbaum et al., 2007; Warzinski et al., 2008). Therefore, we can assume that thermal conductivity changes during hydrate formation will strongly depend on conditions of pore hydrates accumulation in sediments. Today, thermal conductivity of hydrate-bearing soils is investigated poorly in comparison to the thermal conductivity of pure gas hydrates (Chuvilin & Bukhanov, 2014a,b). There are some individual data of thermal conductivity of artificially hydrate-bearing sediments, given by (Groysman, 1985), (Asher, 1987), (Fan et al., 2005), (Waite et al., 2007) and (Duchkov et al., 2006; Permyakov et al., 2011). Experimental estimation of thermal conductivity of soil containing natural gas hydrates was

Please include this code when submitting a data update: GEO2015_305

Retrouver cet article:
Les membres de la Société canadienne de géotechnique peuvent accéder à cet article, ainsi qu'à tous les autres articles de la Conférence Géotechnique Canadienne, dans le Espace membre. Les comptes rendus d'articles sont également disponibles dans de nombreuses bibliothèques.

Citer cet article: