Permeability estimation of gas hydrate-bearing sediments from well log data in the Krishna-Godavari basin

Absolute and effective permeability are two very important petrophysical parameters that govern the production of gas from hydrate-bearing sediments. In the present study, an attempt is made to estimate the permeability from well log data using a theoretical approach, which is validated by comparing the obtained results with the core-derived values. The log data of the well NGHP-02-16B in Krishna-Godavari basin is used for the purpose of computing the permeability, and the core data from the same site are used for validation. The absolute permeability in the reservoir estimated using the Timur method ranges from 0.1 to 100 mD, and matches well with the core sample permeability. It is also demonstrated that the hydrate saturation and the existing hydrate morphology in pore spaces of the sediments play a significant role in the computation of effective permeability. The computed P-wave velocities reveal that the hydrates occur within the pore spaces of the sediments with hydrate saturation of 44-90%. The effective permeability of the hydrate-bearing sediments obtained by the Masuda model with a permeability reduction exponent (N = 2.5) agrees well with the core-derived permeability. The coating of the grain surfaces by the interspace hydrate within the pore is confirmed by comparison and normalization of effective permeability obtained from the Masuda model. The present study infers that the Masuda model is the most accurate and can be reliably used in the absence of core data for the computation of permeability of hydrate-bearing sediments in the vicinity of the study area.