Dependence of thermal conductivity on the phase transition of gas hydrate in clay sediments

Abstract

The insufficient heat supply during gas production from hydrate reservoir significantly hinders the efficiency of hydrate exploitation. The effective thermal conductivity (ETC) of hydrate bearing sediment has been recognized as an effective indicator of the heat transfer process. Yet its evaluation could be coupled with the phase transition and components migration; the relevant knowledge on its dependence on the phase transition of gas hydrate in clay sediments still remains limited. Here in this work, a point-heat-source based instrument was used to investigate the change of ETC in fine-grained sediment during ice melting, hydrate formation and decomposition. The result shows that the ETC declined during ice melting and hydrate decomposition; hydrate formation could result in an increase of ETC. The decomposition water in pores could partly facilitate the heat transfer in porous media. Samples with the initial water saturation higher than 18% were more easily affected by hydrate formation and decomposition; this indicates that hydrate reservoir with a high water saturation could face a more varying capacity of heat transfer. The hydrate samples of deionized water and brine water system with similar saturation of nongaseous phase shows a similar behavior of ETC during phase transition. Moreover, typical effective medium model was evaluated with our measured data. A thermal resistance model based on the real distribution of phases in hydrate bearing sediment was proposed; its feasibility was verified by our measured data and those of in-house and field tests in the literature. This study could provide some insight into the energy supply during hydrate exploitation and the enhancement of the gas production process.