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We report some main results of multidisciplinary investigations carried out within the framework of the Indian National Gas Hydrate Program in [2002][2003] in the Krishna-Godavari Basin offshore sector, east coast of India, to explore indicators of likely gas hydrate occurrence suggested by preliminary multi-channel seismic reflection data and estimates of gas hydrate stability zone thickness. Swath bathymetry data reveal new evidence of three distinct geomorphic units representing (1) a delta front incised by several narrow valleys and mass flows, (2) a deep fan in the east and (3) a WNW-ESE-trending sedimentary ridge in the south.Deep-tow digital side-scan sonar, multi-frequency chirp sonar, and sub-bottom profiler records indicate several surface and subsurface gas-escape features with a highly resolved stratification within the upper 50 m sedimentary strata. Multi-channel seismic reflection data show the presence of bottom simulating reflections of continuous to discrete character. Textural analyses of 76 gravity cores indicate that the sediments are mostly silty clay. Geochemical analyses reveal decreasing downcore pore water sulphate (SO 4 2− ) concentrations (28.7 to <4 mM), increasing downcore methane (CH 4 ) concentrations (0-20 nM) and relatively high total organic carbon contents (1-2.5%), and microbial analyses a high abundance of microbes in top core sediments and a low abundance of sulphate-reducing bacteria in bottom core sediments.Methane-derived authigenic carbonates were identified in some cores. Combined with evidence of gasescape features in association with bottom simulating reflections, the findings strongly suggest that the physicochemical conditions prevailing in the study area are highly conducive to methane generation and gas hydrate occurrence. Deep drilling from aboard the JOIDES Resolution during 2006 has indeed confirmed the presence of gas hydrate in the KrishnaGodavari Basin offshore.

This report is part of a two-report series that summarizes the results of the Indian National Gas Hydrate Program Expedition 01 (NGHP-01). This first report (Collett et al., this issue) in this series summarizes the overall operational and scientific accomplishments of NGHP-01, while the second report reviews the occurrence and geologic controls on gas hydrates in the Krishna-Godavari Basin, the Mahanadi Basin, the Andaman Sea, and the Kerala-Konkan Basin (Kumar et al., this issue). AbstractThe Indian National Gas Hydrate Program Expedition 01 (NGHP-01) was designed to study the occurrence of gas hydrate along the passive continental margin of the Indian Peninsula and in the Andaman convergent margin with special emphasis on understanding the geologic and geochemical controls on the occurrence of gas hydrate in these two diverse settings. The NGHP-01 expedition established the presence of gas hydrates in Krishna-Godavari, Mahanadi and Andaman basins. The expedition discovered in the Krishna-Godavari Basin one of the thickest gas hydrate accumulations yet documented, in the Andaman Sea one of the thickest and deepest gas hydrate stability zones in the world, and established the existence of a fully-developed gas hydrate petroleum system in all three basins.The primary goal of NGHP-01 was to conduct scientific ocean drilling/coring, logging, and analytical activities to assess the geologic occurrence, regional context, and characteristics of gas hydrate deposits along the continental margins of India in order to meet the long term goal of exploiting gas hydrate as a potential energy resource in a cost effective and safe manner. During its 113.5-day voyage, the D/V JOIDES Resolution cored and/or drilled 39 holes at 21 sites (one site in Kerala-Konkan, 15 sites in Krishna-Godavari, four sites in Mahanadi and one site in Andaman deep offshore area), penetrated more than 9,250 m of sedimentary section and recovered nearly 2,850 m of core. Twelve holes were logged with logging-while-drilling (LWD) tools and an additional 13 holes were wireline logged. The science team utilized extensive on-board laboratory facilities to examine and prepare preliminary reports on the physical properties, geochemistry, and sedimentology of all the data collected prior to the end of the expedition. Samples were also analyzed in additional post-expedition shore-based studies conducted in leading laboratories around the world.One of the specific sets of objectives of this expedition was to test gas hydrate formation models and constrain model parameters, especially those that account for the formation of concentrated gas hydrate accumulations. The necessary data for characterizing the occurrence of in-situ gas hydrate such as interstitial water chlorinities, core-derived gas chemistry, core physical and sedimentological properties, thermal images of the recovered core, and downhole measured logging data (LWD and/or conventional wireline log data) were obtained from most of the research sites established during NGHP-01. Almost all of the sit...

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