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Shinya Nishio, Shimizu Corporation (Japan)
Tohru Abe, Shimizu Corporation (Japan)
Satoshi Yamashita, Kitami Institute of Technology (Japan)
Oleg Khlystov, Limnological Institute, RAS SB (Russian Federation)
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In Lake Baikal shallow gas hydrates have already been identified in six mud volcano/seep structures through joint Russian, Japanese and Belgian research. These mud volcano/seep structures are found at different water depths (from 1380 m to as shallow as 440 m) and contain shallow hydrates of both structure I and II. Bottom Simulating Reflectors (BSRs), indicative for the presence of deep-seated hydrates, has been observed on nearby seismic profiles. Production test of shallow gas hydrate in Lake Baikal is planed in cooperation with Japanese and Russian parties. The aim of this project is to develop technologies for recovering gas hydrate from the near surface sediments in the bottom of Lake Baikal, with the goal of establishing environmentally friendly and economical natural gas production technologies from gas hydrate layers. To produce gas from hydrate safely and without damaging the environment, we need to address many wide-ranging environmental issues. One of them is to assess sediment deformation during gas production. Gas hydrate acts as a binding agent that holds together the soil grains that make up the strata. It has been suggested that production may lead to settlement or landslides on the bottom of lake, as the strata becomes unstable following removal of this binding agent. The high quality strength parameters of hydrates bearing sediments are essential for a success of the production test of shallow gas hydrate. The cone penetration tests (CPTs) were conducted to estimate the strength of sediments under in-situ stress condition at the bottom of Lake Baikal. A new CPT probe for deep water (maximum depth 2,000m) has been developed. The results of CPTs around the mud volcano structures indicated that the cone tip resistance in hydrate bearing sediments strongly depends on the textures of hydrate in sediments, and that the ratio of CPT tip resistance to the shear strength obtained from the vane shear tests on core samples is 12.
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