Dielectric behaviors of marine sediments for reliable estimation of gas hydrate saturation based on numerical simulation

Abstract

The accurate evaluation of hydrate saturation, in marine sediments, not only can provide references for hydrate resources assessment but also help to monitor hydrate decomposition that might cause disasters. The dielectric properties can be employed to efficiently estimate hydrate saturation. However, the correlations between dielectric properties and hydrate saturation are still poorly understood. To obtain such a reliable relationship, we first adopt a numerical simulation method based on the three-dimensional finite difference model and digital core technology to calculate the dielectric properties of hydrate-bearing marine sediments. After testing and validating the numerical method by comparing the simulation results with published experimental data, we further apply the simulation technique to calculating the dielectric properties of hydrate-bearing sediments with varying porosities, hydrate saturations and micro-distributions in a broaden frequency. It is found that the dependence of dielectric behaviors on hydrate saturation is significantly affected by hydrate micro-distributions, especially in lower frequency range. We also find that relative permittivity at the frequency of 1 GHz decreases exponentially with increasing hydrate saturation, and the two coefficients that determine the exponential correlation are both dependent on the porosity of the sediments. Using the established relationships, the hydrate saturation in the Mount Elbert Well is successfully estimated from the measured dielectric data. The study provides a reliable tool for the accurate estimation of hydrate saturation in marine sediments.