Experimental study of the velocity and resistivity variations along with methane hydrate saturation in unconsolidated sediments

A new experimental method and a new instrument system were designed to laboratorially simulate the growth process of dispersed gas hydrate in unconsolidated marine sediments. Under brine-saturated and macroscopically undrained condition, the methane hydrate was formed from pore brine and dissolved methane. During methane hydrate formation, we in-situ measured the important geophysical properties of compressional and shear wave velocities (VP and VS) and resistivity. The experimental results also showed that the influence of free methane gas in sediment pore space on VP and resistivity of sediment can not be neglected. An acoustic-electrical combined rock physical model was developed with the granular media contact theory, Gassmann's relation and Archie's law. With the qualitative analysis of experimental data and the quantitative prediction of the rock physical model, the major occurrence state of methane hydrate in sediment pore space could be estimated.