Thermal Conductivity Characteristics of Porous Media in Marine Natural Gas Hydrate Reservoirs

Abstract

As a new type of clean energy, the exploitation of natural gas hydrate resources is key in global energy development of the future. A fundamental understanding of the heat transfer characteristics of natural gas hydrate reservoirs is critical for effective natural gas hydrate exploitation. In this work, the heat transfer characteristics of the sediments on marine natural gas hydrate reservoirs were investigated by using experiments and machine learning algorithms. The thermal conductivities of natural marine sediments from the marine natural gas hydrate reservoir and their primary porous media (quartz sand, Illite, and montmorillonite) were measured. The effects of the porous media component, the water content, the salt concentration, and the phase state change on the thermal conductivity of the reservoir were discussed. The experimental results show that the thermal conductivity of the reservoir depends not only on the inherent thermal conductivity of the porous media but also on the heat transfer mode between the components. The effective thermal conductivity of the porous media system is proportional to the water content and inversely proportional to the salt concentration in porous media. The swelling characteristics of porous media affect the heat transfer mode of the system, thus affecting the extent of change in the effective thermal conductivity with variations in the water content and salt concentration. During the phase transition process, the swelling characteristics of the porous media slow down the heat transfer process, an effect that can be mitigated by the swelling inhibition caused by salt. Additionally, the performances of six machine learning algorithms were evaluated using four evaluation indicators. Results show that the gradient boosted decision trees (GBDT) can yield good predicted values of the thermal conductivity of porous media in a marine natural gas hydrate. A feature importance analysis further reveals that the salt concentration and porous media components are the essential factors influencing the thermal conductivity of marine gas hydrate reservoirs.