Estimation of gas-hydrate concentration and free-gas saturation from log and seismic data

We propose a method to estimate the gas-hydrate concentration and free-gas saturation in marine sediments from log and seismic data. The method is based on a model that relates the concentrations to the P-wave velocity. We consider two different theoretical approaches: 1) a Biot-type three-phase theory and 2) Gassmann's equations. Both models consider the existence of two solids (grain and hydrate) and two fluids (water and free gas). A quantitative estimation is obtained by comparing the theoretical velocity profile for full-water saturated sediments to the experimental velocity profile. The deviations between the two curves are interpreted as presence of hydrates or free gas in the pore space. We considered the experimental data acquired during the Leg 164 of the Ocean Drilling Program.