Thermal conductivity data and the presence of gas hydrates in near-bottom sediments of Lake Baikal
Kaulio, V.; Poort, J.; Klerkx, J.; Morozov, S.; De Batist, M. (2001). Thermal conductivity data and the presence of gas hydrates in near-bottom sediments of Lake Baikal. Geophys. Res. Abstr. 3(773)
In: Geophysical Research Abstracts. Copernicus: Katlenburg-Lindau. ISSN 1029-7006; e-ISSN 1607-7962, more
The thermal conductivity of sediments in which natural hydrates have been formed, may be altered in two ways: by the particular conductivity of the hydrates itself, and as a result of water segregation caused by nearby hydrate accumulation processes. We will discuss particular features related to the measurement of the thermal conductivity of the near-bottom sediments that may be indicative for the presence of gas hydrates. The thermal conductivity measurements have been performed on cores and in-situ in an area in Lake Baikal were gas hydrates in the near-bottom have recently been evidenced.Thermal conductivity was measured on 10 cores (up to 90 cm in length) using the Lithos needle probe (PALS, Samara). Cores not containing gas hydrates returned normal thermal conductivity for diatomeous mud. Some cores, however, have a thermal conductivity that shows a decreasing trend with depth with values even smaller than 0.6 W/m/K. This is the result of large gas content in the cores released from the hydrates after uplift. A second particularity are the high thermal conductivities (0.9-1.1 W/m/K) that correspond to a very dense layer of silty clay. In some cores it was clearly observed that this layer is formed just above a hydrate bearing zone. We interpret that this dense layer is formed as a result of the withdrawal of water used for the formation of hydrates below.In-situ thermal conductivity measurements were performed with the GEOS-T probe (PALS Samara) which applies the continuous heating method. Of the 22 succesful derterminations, 6 stations showed a particlar behaviour never observed before. After about 1 minute of heating when an temperature of about 9 C has been reached the normal heating evolution is shortly interrupted by a proces that absorbs part of the heat. The occurrence of this signal consistantly near the same heating time for all observations suggests that the infiltration of cold water is not the source of noise.We propose that it is more appropriate to explain it as a result of the dissociation of a small amount of hydrates in the sediments. Due to the these finger prints of hydrate presence, the thermal conductivity measurement potentially offers an interesting tool for the prospection of gas hydrates in the near-bottom sediments.
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