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Abstract

Characterization of the relationship between the resistivity and gas hydrate concentration in the subsurface of mud volcanoes in Baratang island, Andaman through electromagnetic (Terra tem) Technique

Documentation of mud volcanoes owing to their role in global ethane budget, explosive expansion of trapped methane and as indicator of petroleum are made in Caspian Sea, Gulf of Mexico, Azerbaijan,Trinidad and Makran coast of Pakistan. Mud volcanoes located in the frontal thrust areas of Andaman active tectonic zone where seismic pumping enhance stress perturbation triggered methane mud volcano eruption after 2004 great Sumatra- Andaman earthquake with M9. Intend of the present study is to characterize the relationship between resistivity and gas hydrate concentration in the subsurface of mud volcanoes through Transient Electromagnetic technique. Pseudo sections by coincident loop of 90x90 m reveal the average resistivity values of 4.0Ωm; 3.5Ωm and 6.3Ωm for mud and host sedimentary formations, whereas gas hydrate accumulated in chambers and vertical pipes show very high resistivity values of 192.0 Ω m, 250.0 Ω m, and 1666.0 Ωm in three mud volcanoes at Pusi , Rajathgarh and Mirchitikiri respectively. The higher resistivity implies the higher gas hydrate concentration. Of the three mud volcanoes, Mirchitikiri is in dormant stage and consequently higher gas pressure accumulated in the pressure chamber and vertical pipe may be the cause for increasing of higher resistivity than the other two. Comparatively low resistivity values observed as in the case of other two mud volcanoes can be assigned due to hydrate dissociation where eruptions of mud volcanoes are in progress. Mud volcanoes in locations of Rajathgarh, Mirchtikiri and Pusi in Baratang Island are aligned to the deep seated faults in N-S direction. From Transient Electromagnetic (TEM) survey, it is evident that the zones containing gas hydrate are more resistive than the surrounding host sedimentary formation and also seen that the resistivity of the gas hydrate increases proportionately with increase of gas hydrate concentration. The characterization of the gas hydrate concentration through TEM technique is dependent on the true resistivity (conductivity) rather than apparent resistivity of the hydrated sediments. Keywords: Mud Volcano


Author(s): A. Vignesh, N. Ramanujam, P. Prasad, S. H. K. Murti, Qazi Akhter Rasool, Swapan Kumar Biswas, Chandrakanta Ojha and Janarthana Boobalan

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