Ryndin, Alexander (2009) Mechanisms Controlling Gas Fractionation of Hydro-Thermally Derived Natural Gas Emissions in the Okinawa Trough. (Master thesis), University of Bremen ; [St. Petersburg State University], Bremen ; St. Petersburg, Russia, 57 pp.

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Abstract

Climate change is already happening and represents one of the greatest environmental, social and economic threats facing the planet. The main cause of climate change or global warming effects is believed to be the accumulation of manmade carbon dioxide (CO2) gas in the atmosphere.
Discharge of CO2 into the ocean is considered as a possibility to reduce CO2 emissions into the atmosphere. Creation of liquid CO2 lakes on the sea bottom and disposal of liquid CO2 in sediments of the deep ocean, including formation of hydrates are amongst the scenarios discussed for accurate, economically effective, and safe CO2 storage.
The rationale of this work is to characterize a natural analogue for proposed scenarios of CO2 deposition in the ocean, which offers. Natural examples of carbon dioxide and water interactions, with its gaseous, liquid and solid hydrate phases. Hydrothermal vents, often associated with mid-ocean-ridge systems, often release CO2-rich fluids into the ocean and can be used to study CO2 behavior and effects. One of the most unique areas for this kind of field studies is the Okinawa Trough, which hydrothermal sites, rich in carbon dioxide and emitting even condensed, liquid CO2, might be ideally suited for the investigation of deliberate carbon dioxide ocean disposal and storage.
The main scientific problem of this work is the investigation of complicated mechanisms controlling gas fractionation of hydro-thermally derived natural gas emissions and gas hydrate formation in the area of Okinawa Trough, driven by the observation of large differences of the composition of gas emissions immediate vicinity. This work is based on data gathered during a joint research expedition of the German Research Vessel SONNE in March 2008, with partners from the National Institute of Advanced Science and Technology Tsukuba (Japan), IFM-GEOMAR (Kiel, Germany), Baltic Sea Research Institute Warnemünde (Warnemünde, Germany), JAMSTEC Japan Marine Science and Technology Center (Japan) and others.
The majority of calculations were produced using the INFOCHEM Software Multiflash, Version 3.1.27 (Infochem Computer Service Ltd.). Multiflash is an advanced software package for performing equilibrium calculations.
Based on Multiflash calculations, an analysis of different compositions of hydrothermally derived natural gas emissions, from pure carbon dioxide to pure methane was performed. Gas fractionation calculations were performed for gas mixtures under high-temperature conditions, related to seismic activity, as well as under conditions related to extreme cooling on the contact boundary with ambient sea water. Another problem addressed in this work is the estimation of thermodynamic conditions of different phase transitions – including gaseous, aqueous, liquid, and solid hydrate phases – related to different initial ratio of CO2 and CH4 in the gas mixture. Data and information about phase behavior of carbon dioxide in seawater and gas fractionation processes calculated in this work can be an important base for the research of future scenarios for industrial carbon dioxide storage in the ocean environment.

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