Maheswar Ojha

Gas-hydrates in Krishna-Godavari and Mahanadi basins: New data

KALACHAND SAIN, MAHESWAR OJHA, NITTALA SATYAVANI, G.A. RAMADASS, T. RAMPRASAD, S. K. DAS and HARSH GUPTA CSIR National Geophysical Research Institute, Uppal Road, Hyderabad 500 007 National Institute of Ocean Technology, Velachery-Tambaram Main Road, Chennai 600 100 CSIR-National Institute of Oceanography, Dona Paula, Goa 403 004 Ministry of Earth Sciences, Prithvi Bhavan, Lodhi Road, New Delhi 110 003 Email: kalachandsain@yahoo.com

Velocity-porosity and velocity-density relationship for shallow sediments in the Kerala-Konkan basin of western Indian margin

During the expedition 01 of the National Gas Hydrate Program (NGHP), drilling and coring were carried out at one site in the Kerala-Konkan basin on the west cost of India to validate gas hydrate. Drilling/coring results show a homogenous sequence of oozes and explains that the reflector, which was identified as a bottom-simulating reflector (BSR) on seismic section, is mainly due to changes in formation density because of less clay content in carbonate-rich sediment. Downhole logs collected at this site are of good quality and have been used to establish empirical relationship between the P-wave velocity (VP), S-wave velocity (VS), density (ρ) and porosity (ϕ). The established relations show very good fit with high R2 value (>0.73), and can be used for further studies in this region. Well known existing empirical formulas between VP, VS, ρ and ϕ deviate significantly from our established relations.

Azimuthal anisotropy from OBS observations in Mahanadi offshore, India

AbstractWe have carried out an ocean bottom seismometer (OBS) survey in a grid along with multichannel seismic survey for gas hydrate exploration in the Mahanadi offshore, India. Here, we report on some interesting observations in seismic waveform data and their interpretations. These include sudden amplitude dimming in the multichannel data that is azimuth- and space-dependent and a clear manifestation of seismic anisotropy in the region. We observe significant patterns of shear wave splitting in the azimuthal gathers in the OBS data, clearly isolating the fast (S1) and slow (S2) axes of propagation in the radial azimuthal gathers. Further, amplitude nulls and amplitude maxima are observed in the transverse azimuthal gathers. These two features are diagnostic of the existence and orientation of anisotropy which is also modeled by generating full waveform synthetic seismograms. We interpret the occurrence of anisotropy to be due to the presence of fractures. The strike of this fracture set is inferred to ...