Experimental Study on the Effective Thermal Conductivity of Methane Hydrate-Bearing Sediments Using a Steady-State Method

The thermal conductivity of hydrate-bearing sediments is a key parameter used to evaluate the heat characteristics relevant to phase transformations during gas production. In this study, considering the dynamic evolution of hydrate saturation, a high-pressure experimental apparatus was designed, and the steady-state method was used to measure the effective thermal conductivity of hydrate-bearing sediments. The reliability of the experimental apparatus was verified through the effective thermal conductivity measurement using pure ice and agar gel as standard materials, and optimization of the experimental parameters was carried out. The effective thermal conductivity of hydrate-bearing sediments with the initial water saturation range of 20-60% and the hydrate saturation range of 7.43-48.74% was measured. The results reveal that the effective thermal conductivity of hydrate-bearing sediments increases with increasing hydrate saturation and shows a maximum value in the hydrate saturation range of 25-36%. Moreover, the effective thermal conductivity of the hydrate-bearing sediment is also strongly dependent on the hydrate occurrence patterns and growth habits. In sediments with a low water saturation (30%), gas is the initial main continuous phase, and the maximum difference in thermal conductivity between the sediment with and without hydrates is 40.15%. For a high water saturation in sediments (60%), water is the initial main continuous phase, and the maximum difference in thermal conductivity between the sediment with and without hydrates is 10.59%, indicating that the positive contribution of hydrate formation on effective thermal conductivity is decreased. In addition, a developed fitting model, considering the influence of hydrate saturation in sediments, was proposed. The calculated results of the model are in good agreement with the experimental data for different samples.