Seismic Insights into Bottom Simulating Reflection (BSR) in the Krishna-Godavari Basin, Eastern Margin of India

Abstract

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.

Keywords:

• BSR
• gas hydrates
• heat flow
• K-G basin
• tomography

Acknowledgements

The authors wish to thank Director, NGRI, for his kind consent to publish this work. The Directorate General of Hydrocarbons (DGH), New Delhi, is thanked for providing the seismic data to the Gas Hydrate Group at NGRI. We thank Mr. Satendra Singh for his help in preparing the figures. This is a contribution to GEOSCAPE Project of NGRI under the 12th Five Year Plan Scientific Program of CSIR.

Notes

Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/umgt.