Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

Uma Shankar ¹, Maheswar Ojha ¹, Kalachand Sain ¹, Ramesh Khanna ¹, M. Sudhakar ², Abhishek Tyagi ²

Affiliations
1 National Geophysical Research Institute, Hyderabad-500007, IN
2 National Center for Antarctic and Ocean Research, Headland Sada, Goa-403804, IN

Abstract

New data have been collected using the multibeam echosounder (Hydrosweep) and high resolution subbottom profiler (Parasound) systems in deep water of the Western Continental Margin of India (WCMI) during the 41^st cruise of R/V Academic Boris Petrov from 17 to 26 November, 2006. The six meters gravity coring along with CTD (Conductivity-Temperature-Depth) measurements are also carried out. Two sites in the Saurashtra and Kerala-Konkan offshore basins have been covered to find out features related to gas hydrates during this short cruise. High resolution multibeam echosounder and sub-Bottom profiling delineate the fine-Scale structure of the sedimentary layer of about 50-100 m thickness below the seafloor. Gravity corer is operated at five stations, out of which four gravity cores of more than 5 m length are recovered successfully. Gas and pore waters from cores have been collected for performing the laboratory studies. The Rosette system is used for temperature and salinity measurement in the water columns. The gravity cores collected on sites show the evidence of sediment fluidization and contain certain amount of gas. The gas is collected from sediments using the technique developed in the V.I.Vernadsky Institute of Geochemistry and Analytical Chemistry for the chemical and isotopic analysis for future research. The preliminary results show that the continental slope and rise of the oceanic margin of the Western India are prospective for exploration of gas hydrate. The more definite conclusion can be drawn after carrying out laboratory studies.

Keywords

WCMI, Gas Hydrates, Hydrosweep, Parasound, and CTD.

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Kalachand Sain ¹, Maheswar Ojha ¹, Nittala Satyavani ¹, G. A. Ramadass ², T. Ramprasad ³, S. K. Das ⁴, Harsh Gupta ¹

Affiliations
1 CSIR - National Geophysical Research Institute, Uppal Road, Hyderabad - 500 007, IN
2 National Institute of Ocean Technology, Velachery-Tambaram Main Road, Chennai - 600 100, IN
3 CSIR-National Institute of Oceanography, Dona Paula, Goa - 403 004, IN
4 Ministry of Earth Sciences, Prithvi Bhavan, Lodhi Road, New Delhi - 110 003, IN

Abstract

Gas-hydrates are crystalline substances consisting of mainly methane and water, and occur in shallow sediments of outer continental margins and permafrost regions. They are formed at high pressure and low temperature regime when supply of methane gas exceeds the solubility limit. Unlike natural gas, oil and minerals, gas-hydrates are not stable at standard temperature and pressure (STP). One volume of gas-hydrates, when dissociated, releases 164 volumes of methane at STP. Since methane is the lowest molecular weight hydrocarbon, use of gas-hydrates as fuel will cause less pollution to the environment. These have attracted the global attention due to their natural occurrences in abundance and huge energy potential. The methane locked as gas-hydrates is envisaged as 1-120 x 10¹⁵ m³ (Boswell and Collett, 2011). Only 15% recovery from this gigantic reserve may be sufficient to meet the global energy requirement for about 200 years (Makogon et al. 2007). Thus, gas-hydrates seem to be a viable major energy resource of future, and have been identified globally either by geophysical, geochemical and geological surveys or by drilling and coring (Boswell and Saeki, 2011; Ruppel, 2011; Sain and Gupta, 2012). Besides having the energy potential, the study of gas-hydrates is also important from natural hazards point of view related to seafloor subsidence, slumps and slides (Gupta and Sain, 2011).

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