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Estimation of gas hydrate saturation using isotropic and anisotropic modelling in the Mahanadi basin

  • Uma ShankarEmail author
  • Ashok Kumar Pandey
Article
  • 34 Downloads

Abstract

A base of gas hydrate stability zone was established after coring and drilling under the National Gas Hydrate Program (NGHP) Expedition-01 in the Mahanadi basin. At two sites, logging-while-drilling log data, and, at one site, wireline log data, were acquired during the NGHP Expedition-01. Gas hydrate reservoirs modelling can be performed in two different ways. One way is isotropic (load bearing) and, on the other hand, anisotropic media (fracture filling with gas hydrate). Here, we have performed anisotropic modelling and estimated gas hydrate saturation using P-wave velocity, assuming an incidence angle of 75\(^{\circ }\) represents the vertical fracture. The estimated gas hydrate saturation at sites NGHP-01-08 and NGHP-01-09, assuming anisotropic media, reduces the estimate by half compared to the saturation estimation by assuming isotropic media. The saturation at site NGHP-01-19 estimated from the isotropic and anisotropic P-wave velocity models are more or less similar except in the zone (175–210 m) just above the bottom simulating reflector depth, and this zone shows similar reduction in saturation as estimated at sites NGHP-01-08 and NGHP-01-09. Observations show that average gas hydrate saturations are relatively low (up to 5% of the pore space). The saturation of a gas hydrate estimated from an isotropic P-wave model varies from 5% to 20%. However, the saturation estimated from the anisotropic P-wave model shows a variation up to 10% of the pore spaces at three sites.

Keywords

Gas hydrate Mahanadi basin well logs rock physics modelling saturation anisotropy 

Notes

Acknowledgements

We would like to thank DGH and ONGC for their fruitful collaboration, especially by making the seismic and log data sets available for extended studies on the gas hydrate in the Mahanadi basin. We would like to thank the anonymous reviewer for the constructive review.

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Copyright information

© Indian Academy of Sciences 2019

Authors and Affiliations

  1. 1.Department of Geophysics, Institute of ScienceBanaras Hindu UniversityVaranasiIndia

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