Effective thermal conductivity changes of the hydrate-bearing quartz sands in depressurization and soaking

The effective thermal conductivity changes in the sediments during depressurization are significant for hydrate exploitation. But these changes cannot be measured directly because of the unavailable stable conditions during depressurization. In this work, in order to form the stable conditions for the measurements, soaking was designed to stabilize temperature and pressure in the sample after depressurization. Afterward, the effective thermal conductivity changes were measured by the transient hot-wire method. To define reasons for these changes, gaswater-hydrate distribution was inferred by the electrical resistance changes. The effective thermal conductivity changes were further analyzed from initial hydrate saturation, back pressure, water-gas production ratio, and gas-water-hydrate distribution, respectively. The results showed that the effective thermal conductivity changes were involved with hydrate dissociation closely. The effective thermal conductivity was increased with increasing initial hydrate saturation and back pressure. Moreover, the effective thermal conductivity was increased by the enlarged water distribution at the early period of hydrate dissociation and decreased by the enlarged gas distribution at the late period of hydrate dissociation. Gas slippage effect and gas-water gravity differentiation played important roles in these gas-water redistribution in the sample. Meanwhile, the sandy grain rearrangement was inferred to improve the contact quality among grains and thus also increased the effective thermal conductivity. Additionally, although there was hydrate dissociation rate of 0.36% during the measurements, the trends of the effective thermal conductivity were not supposed to change. This work may offer some reference to understand the mechanisms of heat transfer in the sediments during depressurization.