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Kumar P.,Oil and Natural Gas Corporation | Collett T.S.,U.S. Geological Survey | Boswell R.,U.S. National Energy Technology Laboratory | Cochran J.R.,Lamont Doherty Earth Observatory | And 9 more authors.
Marine and Petroleum Geology | Year: 2014

Gas hydrate resource assessments that indicate enormous global volumes of gas present within hydrate accumulations have been one of the primary driving forces behind the growing interest in gas hydrates. Gas hydrate volumetric estimates in recent years have focused on documenting the geologic parameters in the "gas hydrate petroleum system" that control the occurrence of gas hydrates in nature. The primary goals of this report are to review our present understanding of the geologic controls on the occurrence of gas hydrate in the offshore of India and to document the application of the petroleum system approach to the study of gas hydrates.National Gas Hydrate Program of India executed the National Gas Hydrate Program Expedition 01 (NGHP-01) in 2006 in four areas located on the eastern and western margins of the Indian Peninsula and in the Andaman Sea. These areas have experienced very different tectonic and depositional histories. The peninsular margins are passive continental margins resulting from a series of rifting episodes during the breakup and dispersion of Gondwanaland to form the present Indian Ocean. The Andaman Sea is bounded on its western side by a convergent margin where the Indian plate lithosphere is being subducted beneath southeast Asia.NGHP-01 drilled, logged, and/or cored 15 sites (31 holes) in the Krishna-Godavari Basin, 4 sites (5 holes) in the Mahanadi Basin, 1 site (2 holes) in the Andaman Sea, and 1 site (1 hole) in the Kerala-Konkan Basin. Holes were drilled using standard drilling methods for the purpose of logging-while-drilling and dedicated wireline logging; as well as through the use of a variety of standard coring systems and specialized pressure coring systems.NGHP-01 yielded evidence of gas hydrate from downhole log and core data obtained from all the sites in the Krishna-Godavari Basin, the Mahanadi Basin, and in the Andaman Sea. The site drilled in the Kerala-Konkan Basin during NGHP-01 did not yield any evidence of gas hydrate. Most of the downhole log-inferred gas hydrate and core-recovered gas hydrate were characterized as either fracture-filling in clay-dominated sediments or as pore-filling or grain-displacement particles disseminated in both fine- and coarse-grained sediments. Geochemical analyses of gases obtained from sediment cores recovered during NGHP-01 indicated that the gas in most all of the hydrates in the offshore of India is derived from microbial sources; only one site in the Andaman Sea exhibited limited evidence of a thermogenic gas source. The gas hydrate petroleum system concept has been used to effectively characterize the geologic controls on the occurrence of gas hydrates in the offshore of India. © 2014.


Collett T.S.,U.S. Geological Survey | Boswell R.,U.S. National Energy Technology Laboratory | Cochran J.R.,Lamont Doherty Earth Observatory | Kumar P.,Oil and Natural Gas Corporation | And 8 more authors.
Marine and Petroleum Geology | Year: 2014

The Indian National Gas Hydrate Program Expedition 01 (NGHP-01) is 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 the Krishna-Godavari and Mahanadi Basins, and the Andaman Sea. The expedition discovered in the Krishna-Godavari Basin one of the thickest gas hydrate accumulations ever 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. This was done 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 (1 site in Kerala-Konkan, 15 sites in Krishna-Godavari, 4 sites in Mahanadi, and 1 site in the Andaman deep offshore area), penetrated more than 9250m of sedimentary section, and recovered nearly 2850m 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 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, physical and sedimentological properties, thermal images of the recovered cores, and downhole measured logging data (LWD and/or conventional wireline log data), were obtained from most of the drill sites established during NGHP-01. Almost all of the drill sites yielded evidence for the occurrence of gas hydrate; however, the inferred in situ concentration of gas hydrate varied substantially from site to site. For the most part, the interpretation of downhole logging data, core thermal images, interstitial water analyses, and pressure core images from the sites drilled during NGHP-01 indicate that the occurrence of concentrated gas hydrate is mostly associated with the presence of fractures in the sediments, and in some limited cases, by coarser grained (mostly sand-rich) sediments. © 2014.


Desa M.A.,National Institute of Oceanography of India | Ramana M.V.,National Institute of Oceanography of India | Ramprasad T.,National Institute of Oceanography of India | Anuradha M.,National Institute of Oceanography of India | And 2 more authors.
Journal of Asian Earth Sciences | Year: 2013

The nature and origin of the subsurface 85°E Ridge in the Bay of Bengal has remained enigmatic till date despite several theories proposed by earlier researchers. We reinterpreted the recently acquired high quality multichannel seismic reflection data over the northern segment of the ridge that traverses through the Mahanadi offshore, Eastern Continental Margin of India and mapped the ridge boundary and its northward continuity. The ridge is characterized by complex topography, multilayer composition, intrusive bodies and discrete nature of underlying crust. The ridge is associated with large amplitude negative magnetic and gravity anomalies. The negative gravity response across the ridge is probably due to emplacement of relatively low density material as well as ~2-3. km flexure of the Moho. The observed broad shelf margin basin gravity anomaly in the northern Mahanadi offshore is due to the amalgamation of the 85°E Ridge material with that of continental and oceanic crust. The negative magnetic anomaly signature over the ridge indicates its evolution in the southern hemisphere when the Earth's magnetic field was normally polarized. The presence of ~5. s TWT thick sediments over the acoustic basement west of the ridge indicates that the underlying crust is relatively old, Early Cretaceous age.The present study indicates that the probable palaeo-location of Elan Bank is not between the Krishna-Godavari and Mahanadi offshores, but north of Mahanadi. Further, the study suggests that the northern segment of the 85°E Ridge may have emplaced along a pseudo fault during the Mid Cretaceous due to Kerguelen mantle plume activity. The shallow basement east of the ridge may have formed due to the later movement of the microcontinents Elan Bank and Southern Kerguelen Plateau along with the Antarctica plate. © 2013 Elsevier Ltd.


Mandal R.,National Institute of Oceanography of India | Dewangan P.,National Institute of Oceanography of India | Ramprasad T.,National Institute of Oceanography of India | Kumar B.J.P.,Directorate General of Hydrocarbons | Vishwanath K.,Directorate General of Hydrocarbons
Marine and Petroleum Geology | Year: 2014

The seafloor and bottom simulating reflectors (BSRs) are interpreted from the 3D seismic data acquired in Krishna-Godavari (KG) offshore basin in the vicinity of sites drilled/cored during National Gas Hydrate Program (NGHP) Expedition-01. The shallow structures such as inner toe-thrust fault system, regional and local linear fault systems and mass transport deposits are inferred from attributes of seafloor time structure as well as from the seismic profiles. The geothermal gradient is estimated from the depths and temperatures of the seafloor and the BSR. The temperature at the BSR depth is estimated from the methane hydrate and seawater salinity phase boundary assuming that the BSR represents the base of the gas hydrate stability zone.The spatial variations in geothermal gradient (GTG) show a strong correlation with seafloor topography in the KG basin. The GTG decreases by ~13-30% over the topographic mounds formed due to inner toe-thrust faults and recent mass transport deposits. The GTG decreases by only 5-10% over the mounds, likely due to defocusing of heat flux based on one-dimensional topographic modeling. Hence, the GTG perturbation due to topography alone cannot explain the observed GTG anomaly. The temperature profile beneath these mounds may not be in equilibrium with the surroundings either due to the recent upliftment of sediments along the inner toe-thrust faults or rapid deposition of sediments due to slumping/sliding. In contrast, an increase in GTG by 10-15% is observed in the vicinity of major fault systems. We presume that the likely mechanism for the increase in GTG is fluid advection from a deeper part of the basin. A detailed thermal modeling involving the effect of surface topography, high sedimentation rates, fluid advection and sediment thickening due to tectonics is required to understand the thermal profile in KG offshore basin. © 2014 Elsevier Ltd.

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