Inversion of gas hydrate saturation and solid frame permeability in a gas hydrate-bearing sediment by Stoneley wave attenuation

Abstract

Natural gas hydrate is a potential novel energy resource that is widely distributed globally. Acoustic logging can effectively provide information on the surrounding reservoir and plays an important guiding role in gas hydrate exploration and development. Natural gas hydrate-bearing sediments are composed of a solid frame with natural gas hydrates and water-filled pores. The borehole mode wave characteristics of two-phase porous media cannot be used to evaluate the parameters of such a multiphase porous medium. We explore factors that influence the monopole Stoneley wave in a borehole embedded in a multiphase porous medium containing two solids and one fluid and analyze the influence of each factor on monopole Stoneley wave attenuation systematically. The sensitivity analysis results indicate that the Stoneley wave attenuation is highly sensitive to solid frame permeability and gas hydrate saturation. Building upon this foundation, a method to invert for gas hydrate saturation and solid frame permeability is first developed using Stoneley wave attenuation. Synthetic logging data are used to demonstrate the feasibility of this method for inverting for gas hydrate-bearing sediment properties. Even in the presence of considerable noise added to the receiver signal arrays, the inversion method is stable, and reliably evaluates gas hydrate saturation and solid frame permeability.