Since pure gas hydrates have much higher resistivity than that of host sediments, their presence in the sediments increases the resistivity of the formation, which can be used for the delineation and assessment of gas hydrates. As characterization of gas hydrate reservoir from seismic data assumes homogeneous distribution of gas hydrates, it leads to overestimation of gas-hydrate saturation. To overcome this problem, earlier we demonstrated estimation of gas hydrates from simulated 2-D heterogeneous velocity and density models (Jana et al., Geophys. Jour. International, 2015). Now we propose a method for the estimation of gas hydrates from 3-D heterogeneous resistivity model simulated using 1-D resistivity log data. A 3-D heterogeneous resistivity model has been constructed from 1-D resistivity log in the KG basin in eastern Indian offshore. The simulated resistivity model contains small scale variation of the reservoir and maintains all properties associated with covariance, like root mean square fluctuation, characteristic scales and fractal dimension of the observed log. We have estimated volumetric gas hydrate saturation using the simulated 3-D resistivity model. The porosity used for the estimation of gas hydrates is calculated from simulated density field generated using the observed density log data. The average gas hydrates is estimated as 9.84% of pore volume over a 1000 x 1000 x 131 cubic meter volume (Fig.1).
Fig.1. Left - 3-D cross-sectional view of gas hydrate saturation (left) calculated from simulated heterogeneous resistivity and density. Right - A 3-D volumetric view (1000 m x 1000 m x 131 m) of gas hydrate saturation model over gas hydrate bearing zone around the borehole NGHP-01-10A.
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1. S. Jana, M. Ojha, & K. Sain, 2015. Gas hydrate saturation from heterogeneous model constructed from well log in Krishna-Godavari basin, eastern Indian offshore, Geophys. Jour. Internat., 203, 246-256.
2. S. Jana, M. Ojha, K. Sain & Shalivahan, 2017. An approach to estimate gas hydrate saturation from 3-D heterogeneous resistivity model: a study from Krishna-Godavari Basin, eastern Indian offshore, Jour. Mar. & Petrol. Geol., 79, 99-107.