The Arctic Ocean

Natural gas hydrates are considered as a high-potential source of unconventional hydrocarbons. Economically viable and environmentally safe production of gas sequestered in hydrates requires estimating the amount of liquid pore water that resides in hydrate-bearing sediments, including one in permafrost. In this work, we present results of estimating the content of residual pore water in gas hydrate reservoirs using nuclear magnetic resonance relaxometry on a low-field NMR rock analyzer with a designed high-pressure core holder at pressures up to 8.0 MPa. The measurements are conducted on artificial samples of fine sand with inclusions of kaolinite and montmorillonite clay. The NMR results reveal the presence of liquid pore water in all hydrate-bearing samples, with its content decreasing under increasing gas pressure and cooling. The content of residual pore water approaches the calculated amount of nonclathrated water, the minimum for hydrate-bearing media, in samples exposed to repeated heating–cooling cycles. Results confirm that samples with higher percentages of clay (especially montmorillonite) contain more residual pore water, which varies from <0.2 wt % in pure sand to 5.0 or 6.8 wt % (at −5.5 and +2.5 °C, respectively) in a mixture of sand with 25 wt % of montmorillonite clay. It is also noted that the content of residual water is sensitive to initial moisture content and residual ice content in permafrost hydrate-bearing reservoirs.

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Estimation of Residual Pore Water Content in Hydrate-Bearing Sediments at Temperatures below and above 0 °C by NMR

Bukhanov

Chuvilin

Mukhametdinova

et al. 2022

Energy Fuels

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Findings of Pogonophores (Annelida: Siboglinidae) in the Kara Sea Associated with the Regions of Dissociation of Seafloor and Cryogenic Gas Hydrates

Malakhov,

Rimskaya-Korsakova,

Osadchiev

et al. 2023

Biologiya Morya

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The discovery of new occurrences of pogonophores Siboglinum sp. and Nereilinum sp. from the St. Anna Trough (northwestern portion of the Kara Sea) has been described in this paper. Previously, occurrences of pogonophores (Crispabrachia yenisey and Galathealinum karaense) were reported in the southern part of the Kara Sea, in the estuary of the Yenisei River. Two areas in the Kara Sea where pogonophores were found coincide with the regions of distribution of two types of gas hydrates: oceanic seafloor gas hydrates, and gas hydrates associated with permafrost. Gas hydrate deposits in the permafrost are confined to the coastal regions of the Kara Sea. A methane flux forms in areas of dissociation of gas hydrates under the influence of river runoff. This methane source is vital for the survival of pogonophores. The existence of pogonophores in the St. Anna Trough indicates the presence of a methane flux associated with the inflow of Atlantic water, which causes dissociation of seafloor gas hydrates. The possible role of Arctic warming is apparent in both processes.

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The Discovery of Pogonophores (Annelida, Siboglinidae) in the St. Anna Trough (Kara Sea) in the Area of Gas Hydrates Dissociation

Rimskaya-Korsakova,

Karaseva,

Osadchiev

et al. 2023

Doklady Rossijskoj akademii nauk. Nauki o žizni

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Representatives of pogonophores (Annelida, Siboglinidae), whose vital activity is provided by symbiotic chemoautotrophic bacteria that oxidize methane and hydrogen sulfide, were found in the St. Anna trough at depths of 539 m and 437 m. The discovery of pogonophores indicates high concentrations of methane, which can occur because of dissociation of bottom gas hydrates under the influence of the influx of warm Atlantic water penetrating into the Kara Sea along the St. Anna trough.

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The Arctic Ocean

Cited by 3 publications

References 15 publications

Estimation of Residual Pore Water Content in Hydrate-Bearing Sediments at Temperatures below and above 0 °C by NMR

Estimation of Residual Pore Water Content in Hydrate-Bearing Sediments at Temperatures below and above 0 °C by NMR

Findings of Pogonophores (Annelida: Siboglinidae) in the Kara Sea Associated with the Regions of Dissociation of Seafloor and Cryogenic Gas Hydrates

The Discovery of Pogonophores (Annelida, Siboglinidae) in the St. Anna Trough (Kara Sea) in the Area of Gas Hydrates Dissociation

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