gas hydrate forming fluids on the ne sakhalin slope, sea ... · of gas hydrates present in marine...

Gas hydrate forming fluids on the NE Sakhalin slope, Sea of Okhotsk L. L. MAZURENKO'~, T. V. MATVEEVA1*, E. M. PRASOLOV',2, H. SHOJ13, A. I. OBZHIROV4, Y. K. JINS,J. POORT6, E. A. LOGVINA1, H. MINAMI" H. SAKAGAM13, A. HACHIKUBO" A. S. SALOMATIN4, A. N. SALYUK4, E. B. PRILEPSKIY2 & CHAOS 2003 SCIENTIFIC TEAM '~11-~ussia Research Institute for Geology and Mineral Resources of the World Ocean, 1, Angliyskiy prospect, 190121 St Petersburg, Russia 'centre of Isotopic Research of VSEGEI, 190 136, 74, Srednii prospect V.O., St Petersburg, Russia k i t a m i Institute of Technology, New Energy Research Center, 165 Koen-cho, 090-8507 Kitami, Japan 4~~.~lyichev's PaciJic Oceanographical Institute, Baltiyskaya Street, 690041, Vladivostok, Russia '~orea Polar Research Institute (KOPRI), 1903 Get-Pearl Tower, Songdo Technopark, 7-50 Songdo-dong, Yunsu-ku Incheon, 406-840, Korea benard Centre of Marine Geology, Ghent University, Krijgslaan 281, S8, B-9000 Ghent, Belgium t~eonid Mazurenko died in July 2007 *Corresponding author (e-mail: &-ma&[email protected]) 215888 Abstract: An area of focused fluid venting off NE Sakhalin, Sea of Okhotsk, was investigated in 2003 during the 3 1 st and 32nd international expeditions of R/V Akademik M. A. Lavrenryev within the framework of the CHAOS Project. More than 40 structures related to seafloor gas venting were discovered and gas hydrates were sampled from three of these: CHAOS, Hieroglyph and Kitami. Geochemical analyses were used to define the mechanisms of gas hydrate accumulation and the sources of fluids involved. Chemical and isotopic analyses of the interstitial and hydrate waters suggest that hydrates were formed from seawater (or in-situ pore water) and an ascending fluid enriched in salts. Hydrate formation occurs at locations of the most intensive saline water upflow, and this is probably a function of the gas solubility in water in equilibrium with hydrate. The water involved in gas hydrate formation consists of about 70% pore water derived from the host sediment and 30% from the ascending fluid. The overall isotopic composition of the 'fluid' taking part in hydrate formation was calculated as 6 '~ -- -I 1% and 6180 - -1.5%0. Gas hydrates in marine sediments are considered as a potential hydrocarbon energy resource and as an important matter of concern regarding the impact of their dissociation upon global climate change. In both cases, it is essential to estimate the quantities of gas hydrates present in marine sediments and to understand the processes leading to gas hydrate accumulation and decomposition. Of particular interest are shallow gas hydrates associated with fluid venting structures. These gas hydrates are capable of forming geochemical barriers to the gas flux, and therefore reducing the amount of gas enter- ing the hydrosphere from the seafloor. To calculate the global methane budget in marine sediments, an evaluation has to be made of the different processes involved, such as gas diffusion, oxidation and formation of methane-derived carbonates and hydrates. The composition of the original gas and of the gas locked up in carbonates or hydrates is often rather different, and understanding the gas origin is important in evaluating the role of methane hydrate in the carbon cycle (Dickens 1999). Although the origin and composition of fluids discharging at the venting locations have been the subject of numerous studies (Luff & Wallmann 2003; Aloisi et al. 2004; Hensen et al. 2007), the From: LONG. D., LOVELL, M. A., REES, J. G. & ROCHELLE, C. A. (eds) Sediment-Hosted Gas Hydrates: New Insights on Natural and Synthetic Sjstems. The Geological Society, London, Special Publications, 319, 5 1-72. DOI: 10.1144/SP319.5 0305-8719/09/$15.00 C) The Geological Society of London 2009.

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Page 1: Gas hydrate forming fluids on the NE Sakhalin slope, Sea ... · of gas hydrates present in marine sediments and to understand the processes leading to gas hydrate accumulation and

Gas hydrate forming fluids on the NE Sakhalin slope, Sea of Okhotsk

L. L. MAZURENKO'~, T. V. MATVEEVA1*, E. M. PRASOLOV',2, H. SHOJ13, A. I. OBZHIROV4, Y. K. JINS, J. POORT6, E. A. LOGVINA1, H. MINAMI" H. SAKAGAM13, A. HACHIKUBO" A. S. SALOMATIN4, A. N. SALYUK4, E. B. PRILEPSKIY2 & CHAOS

2003 SCIENTIFIC TEAM

' ~11 -~us s ia Research Institute for Geology and Mineral Resources of the World Ocean, 1, Angliyskiy prospect, 190121 St Petersburg, Russia

'centre of Isotopic Research of VSEGEI, 190 136, 74, Srednii prospect V.O., St Petersburg, Russia

k i tami Institute of Technology, New Energy Research Center, 165 Koen-cho, 090-8507 Kitami, Japan

4 ~ ~ . ~ l y i c h e v ' s PaciJic Oceanographical Institute, Baltiyskaya Street, 690041, Vladivostok, Russia

' ~ o r e a Polar Research Institute (KOPRI), 1903 Get-Pearl Tower, Songdo Technopark, 7-50 Songdo-dong, Yunsu-ku Incheon, 406-840, Korea

benard Centre of Marine Geology, Ghent University, Krijgslaan 281, S8, B-9000 Ghent, Belgium

t~eonid Mazurenko died in July 2007

*Corresponding author (e-mail: &-ma&[email protected]) 2 1 5 8 8 8

Abstract: An area of focused fluid venting off NE Sakhalin, Sea of Okhotsk, was investigated in 2003 during the 3 1 st and 32nd international expeditions of R/V Akademik M. A. Lavrenryev within the framework of the CHAOS Project. More than 40 structures related to seafloor gas venting were discovered and gas hydrates were sampled from three of these: CHAOS, Hieroglyph and Kitami. Geochemical analyses were used to define the mechanisms of gas hydrate accumulation and the sources of fluids involved. Chemical and isotopic analyses of the interstitial and hydrate waters suggest that hydrates were formed from seawater (or in-situ pore water) and an ascending fluid enriched in salts. Hydrate formation occurs at locations of the most intensive saline water upflow, and this is probably a function of the gas solubility in water in equilibrium with hydrate. The water involved in gas hydrate formation consists of about 70% pore water derived from the host sediment and 30% from the ascending fluid. The overall isotopic composition of the 'fluid' taking part in hydrate formation was calculated as 6 ' ~ -- -I 1% and 6180 - -1.5%0.

Gas hydrates in marine sediments are considered as a potential hydrocarbon energy resource and as an important matter of concern regarding the impact of their dissociation upon global climate change. In both cases, it is essential to estimate the quantities of gas hydrates present in marine sediments and to understand the processes leading to gas hydrate accumulation and decomposition. Of particular interest are shallow gas hydrates associated with fluid venting structures. These gas hydrates are capable of forming geochemical barriers to the gas flux, and therefore reducing the amount of gas enter- ing the hydrosphere from the seafloor. To calculate

the global methane budget in marine sediments, an evaluation has to be made of the different processes involved, such as gas diffusion, oxidation and formation of methane-derived carbonates and hydrates. The composition of the original gas and of the gas locked up in carbonates or hydrates is often rather different, and understanding the gas origin is important in evaluating the role of methane hydrate in the carbon cycle (Dickens 1999).

Although the origin and composition of fluids discharging at the venting locations have been the subject of numerous studies (Luff & Wallmann 2003; Aloisi et al. 2004; Hensen et al. 2007), the

From: LONG. D., LOVELL, M. A., REES, J. G. & ROCHELLE, C. A. (eds) Sediment-Hosted Gas Hydrates: New Insights on Natural and Synthetic Sjstems. The Geological Society, London, Special Publications, 319, 5 1-72. DOI: 10.1 144/SP319.5 0305-8719/09/$15.00 C) The Geological Society of London 2009.