Waves in porous media containing gas hydrate

Abstract

The propagation of pressure waves in porous medium containing a gas hydrate is numerically investigated. The study was performed in the framework of the three-phase model of a porous medium (the skeleton, hydrate and fluid). The porous medium is saturated with methane gas and partially filled with methane hydrate. The transmission and reflection of waves at the boundaries between the gas containing and the hydrate containing porous media is studied. It is established that in a partially filled hydrate porous medium an acoustic pulse propagates without distortion, with some attenuation. By increasing hydrate fraction and decreasing gas fraction the acoustic impedance of the porous medium increases. The characteristics of pressure wave propagation in a cylindrical cavity in a porous medium with hydrate-containing layer are studied in the linear approximation. The two-phase model of a porous medium with effective parameters of the skeleton is used for the mathematical description of porous media containing gas hydrate. Skeleton is considered as a homogeneous mixture of solid and hydrate grains. The dispersion relation for the main acoustic mode in a cylindrical cavity for each layer constituting the porous medium is obtained. The reflection and transmission coefficients of waves passing through the boundary of layers inside the cavity are calculated. The influence of rock properties, frequency, and length of layer containing hydrate on the total reflection coefficient from the layer is studied.