Effective thermal conductivity of methane hydrate-bearing sediments: Experiments and correlations

Thermal properties of gas hydrate-bearing sediments directly govern the heat transfer process during hydrate decomposition which couples with phase transitions and multiphase flows. The effective thermal conductivity of a multiphase system represents the composite capacity to conduct heat. Here we report on point heat source measurements of the effective thermal conductivity of methane hydrate-bearing sediments through a thermistor-based method combining with X-ray CT observations. Methane hydrates were formed at different saturations, with various initial water contents, and in porous matrices simulated by grains with differing thermal conductivities. It is indicated that the effective thermal conductivity of sediments negatively correlated with the hydrate saturation, while an increase of initial water contents and thermal conductivity of grains has a positive impact on the elevation of the effective thermal conductivity. Moreover, the effective thermal conductivity was found to slightly increase with the proceeding of hydrate decomposition. Typical effective medium models were evaluated with the measurements of this study, and a hybrid fitting model combining three forms of self-consistent models was proposed, with the optimal weighting parameters determined via the genetic algorithm. The effective prediction of the measurements in this work and results in literatures corroborates the feasibility of the model. This study could help in understanding the evolutions of sediment thermal properties during gas production and their effects on large-scale hydrate decomposition when expanded to field scale tests. (C) 2016 Elsevier Ltd. All rights reserved.