Thermal conductivity of sediments within the gas-hydrate-bearing interval at the JAPEX/JNOC/GSC et al. Mallik 5L-38 gas hydrate production research well

Abstract

Three separate techniques were employed to investigate the thermal conductivity of unconsolidated sediments within the gas-hydrate-bearing reservoir at the Mallik gas hydrate production research site. A miniature needle probe was used to obtain thermal-conductivity measurements of quartz sand and a core specimen recovered from the Mallik reservoir. Measurements were obtained for various pore-water phases relevant to the Mallik geological setting, including pore occupancy by liquid water, gas hydrate, and ice. Measured thermal conductivities were compared to the predictions of an empirical model, which generates estimates of thermal conductivity based on the prescribed physical properties of sediments. Finally, calculations based on ground-temperature data and an estimate of the local geothermal heat flux identified distinct zonal variations in thermal conductivity within the broader gas-hydrate-bearing interval in the Mallik reservoir. These zonal variations are clearly related to variations in sediment character, rather than to the presence or absence of gas hydrate. Résumé : Nous avons employé trois méthodes différentes pour déterminer la conductivité thermique des sédiments non consolidés du réservoir d'hydrates de gaz qui a été mis à l'étude au site Mallik de recherche sur la production d'hydrates de gaz. Une sonde aiguille miniature a servi à effectuer des mesures de conductivité thermique sur du sable de quartz pur et sur un échantillon de carotte prélevé dans le réservoir Mallik. Ces mesures ont été obtenues pour diverses phases interstitielles pertinentes au cadre géologique du réservoir, dont l'eau liquide, les hydrates de gaz et la glace. Les conductivités thermiques mesurées ont été comparées à des prévisions obtenues au moyen d'un modèle empirique qui génère des estimations de la conductivité thermique à partir de spécifications des propriétés physiques des sédiments. Enfin, des calculs basés sur des données de température du sol et sur une estimation du flux géothermique local ont permis d'identifier des variations zonales distinctes de la conductivité thermique dans l'ensemble de l'intervalle renfermant des hydrates de gaz dans le réservoir Mallik. Il est clair que ces variations zonales sont reliées à des variations de la nature des sédiments plutôt qu'à la présence ou à l'absence d'hydrates de gaz.

Analysis and interpretation of the thermal test of gas hydrate dissociation in the JAPEX/JNOC/GSC et al. Mallik 5L-38 gas hydrate production research well

“…Note that the accuracy of the measurements is insufficient to resolve the minute temperature variation (estimated not to exceed 0.4°C) caused by the geothermal gradient across the gas hydrate deposit in the test zone. The average initial temperature in the perforated interval was 8°C, substantially lower than the equilibrium hydration temperature (T h ) of 12.6°C, corresponding to the prevailing pressure and a salinity of less than 10 ppt ('ppt' stands for 'parts per thousand') (as measured from core samples) at the site (Wright et al, 2005).…”

“…According to Wright et al (2005), salinity estimates near the base of the gas hydrate stability zone ranged between 35 and 45 ppt (based on chlorinity and temperature data), and 6 . Readings taken at 1 hour intervals.…”

Inferred gas hydrate and permafrost stability history models linked to climate change in the Beaufort-Mackenzie Basin, Arctic Canada

“…Neither do we generalize our models to the entire Arctic region, where variety of paleo-environmental conditions and geological settings, including ice sheet loading pressure effects may provide different results. One such specific condition can be the rapid change of temperature from cold terrestrial to warm sea bottom conditions that have been attributed to coastal IBP and GH destabilization in the Arctic Islands (Majorowicz, 1998;Wright et al, 2005).…”

“…Temperature also peaked 52-50 Myr ago, when atmospheric CO 2 concentrations were 1125-3000 parts per million, but by 20 Myr ago, atmospheric CO 2 concentration dropped to about 400 ppm (Polsson, 2007;Henninges et al, 2005a;Rath and Henninges, 2008). Following the Paleocene-early Eocene the climate cooled variably towards the Pleistocene glacial environment (Judge and Majorowicz, 1992;Henninges et al, 2005;Rath and Henninges, 2008). The Paleocene-Eocene Thermal Maximum (PETM) has itself been attributed to abrupt methane releases from oceanic GHs (Dickens et al, 1997).…”

“…It employs latent heat effects throughout the IBP and GH layers, which is an improvement upon previous models (Taylor et al, 2005). Deep heat flow is constrained by bottom hole temperatures from deep wells (Majorowicz et al, 1990;Taylor et al, 1982), and wellconstrained estimates of thermal conductivity, latent heat, present IBP thickness and observed GH thicknesses (Henninges et al, 2005b;Wright et al, 2005). The models consider the hydrostatic pressure-depth dependence of ice and GH thawing points over the entire expected extent of the model IBP and GH layers (Sloan, 1998) (Fig.…”