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Multi-channel seismic reflection data from the western continental margin of India (WCMI) have been analyzed to construct a plausible model for gas hydrate formation. A reflector at 2950 ms two way travel time (TWT) on one of the sections is interpreted to represent the base of the layer of the methane hydrate, identified by a bottom simulating reflector (BSR) that lies almost 500 ms beneath the sea floor. BSRs of similar origin are common world wide, where they are usually interpreted to mark the base of gas hydrate bearing clastic sediment, with or without underlying free gas. In this study we present a model with the contrasting physical properties that produce synthetic wavelets that match with the observed BSR amplitude and waveforms for varying source-receiver offsets of multi-channel seismic reflection data. The preliminary results presented here put important constraints on models that predict the distribution and formation of hydrate. Offset-dependent amplitude recovery also gives an appropriate response for hydrate characterization. 相似文献
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N. Satyavani 《Marine Georesources & Geotechnology》2013,31(3):191-201
The multichannel seismic data along one long-offset survey line from Krishna-Godavari (K-G) basin in the eastern margin of India were analyzed to define the seismic character of the gas hydrate/free gas bearing sediments. The discontinuous nature of bottom simulating reflection (BSR) was carefully examined. The presence of active faults and possible upward fluid circulation explain the discontinuous nature and low amplitude of the BSR. The study reveals free gas below gas hydrates, which is also indicated by enhancement of seismic amplitudes with offsets from BSR. These findings were characterized by computing seismic attributes such as the reflection strength and instantaneous frequency along the line. Geothermal gradients were computed for 18°C and 20°C temperature at the depth of BSR to understand the geothermal anomaly that can explain the dispersed nature of BSR. The estimated geothermal gradient shows an increase from 32°C/km in the slope region to 41°C/km in the deeper part, where free gas is present. The ray-based travel time inversion of identifiable reflected phases was also carried out along the line. The result of velocity tomography delineates the high-velocity (1.85–2.0 km/s) gas hydrate bearing sediments and low-velocity (1.45–1.5 km/s) free gas bearing sediments across the BSR. 相似文献
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N. Satyavani Kalachand Sain Malcolm Lall B. J. P. Kumar 《Marine Geophysical Researches》2008,29(3):167-175
Seismic data from the Andaman offshore region has been examined to investigate for the presence of gas hydrates. The seismic
data displays reflection characteristics such as blanking, enhanced reflection patterns, shadows in instantaneous frequency,
and increase in amplitude with the offset, which are indicative of gas hydrates and underlying free gas. A prominent bottom-simulating
reflection, BSR, coupled with reverse polarity is observed around 650–700 ms. Seismic attributes such as the reflection strength
and instantaneous frequency are computed along this reflector in order to probe for the presence of gas hydrates or free gas
in this region. The reflection plot shows a strong reflector paralleling the seafloor. In addition, attenuation of the high
frequency signal is noticed, indicating the presence of free gas below the BSR. 相似文献
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Kalachand Sain V. Rajesh N. Satyavani K.V. Subbarao C. Subrahmanyam 《Marine and Petroleum Geology》2011,28(10):1779-1786
The gas-hydrate stability thickness (GHST) map along the Indian continental margin is prepared from available bathymetry, sea-bottom temperature and geothermal gradient data. The bottom-simulating reflector (BSR) often marks the base of gas-hydrate stability zone. The prior information about the stability thickness in a particular area will help in identifying BSR on seismic data. The map is also useful to the exploration scientists to set a depth window within which proxies for gas-hydrate can be looked into. A GHST map was initially prepared in 1998 based on the-then available data. A lot of new data has been generated by various organizations under the Indian National Gas Hydrate Programs for the advancement of exploration and exploitation activities. By incorporating the new data from the published and available documents, we have modified the GHST map along the Indian margin. Besides filling the data gap, the new map shows the gas-hydrate stability zone in the Andaman offshore. In addition, we show maps of sea-bottom temperature, sediment thickness, geothermal gradient and heat flow to provide a bird’s eye view of these parameters along the continental margin of India. 相似文献
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