Eilis Rosenbaum

THERMAL PROPERTIES OF METHANE HYDRATE BY EXPERIMENT AND MODELING AND IMPACTS UPON TECHNOLOGY

Thermal properties of pure methane hydrate, under conditions similar to naturally occurring hydrate-bearing sediments being considered for potential production, have been determined both by a new experimental technique and by advanced molecular dynamics simulation (MDS). A novel single-sided, Transient Plane Source (TPS) technique has been developed and used to measure thermal conductivity and thermal diffusivity values of low-porosity methane hydrate formed in the laboratory. The experimental thermal conductivity data are closely matched by results from an equilibrium MDS method using in-plane polarization of the water molecules. MDS was also performed using a non-equilibrium model with a fully polarizable force field for water. The calculated thermal conductivity values from this latter approach were similar to the experimental data. The impact of thermal conductivity on gas production from a hydrate-bearing reservoir was also evaluated using the Tough+/Hydrate reservoir simulator.

Thermal conductivity measurements in unsaturated hydrate‐bearing sediments

Current database on the thermal properties of hydrate-bearing sediments remains limited and has not been able to capture their consequential changes during gas production where vigorous phase changes occur in this unsaturated system. This study uses the transient plane source (TPS) technique to measure the thermal conductivity of methane hydrate-bearing sediments with various hydrate/water/gas saturations. We propose a simplified method to obtain thermal properties from single-sided TPS signatures. Results reveal that both volume fraction and distribution of the pore constituents govern the thermal conductivity of unsaturated specimens. Thermal conductivity hysteresis is observed due to water redistribution and fabric change caused by hydrate formation and dissociation. Measured thermal conductivity increases evidently when hydrate saturation Sh > 30–40%, shifting upward from the geometric mean model prediction to a Pythagorean mixing model. These observations envisage a significant drop in sediment thermal conductivity when residual hydrate/water saturation falls below ~40%, hindering further gas production.

Thermal Property Measurements of Methane Hydrate Using a Transient Plane Source Technique

Knowledge of the thermal properties of gas hydrates and sediments containing gas hydrates is essential for assessing their commercial potential for natural gas recovery and their possible factors in sea-floor stability and climate change. Unlike phase equilibrium properties of hydrates, little information is available on their thermal properties. A major experimental challenge in thermal property measurement is determining the composition of the sample being measured. This chapter describes work being performed at the National Energy Technology Laboratory to develop a means to reliably measure the thermal properties of hydrate and hydrate-containing samples, while facilitating characterization of the sample with minimal decomposition or disturbance. A transient plane source (TPS) technique for simultaneously determining thermal conductivity and thermal diffusivity has been adapted for use at high pressure for this purpose. The TPS element is mounted inside a specially designed cup assembly that not only holds and contains the sample, but can also serve as a sample compaction device. The cup assembly is contained inside a high-pressure vessel that not only facilitates measurements at in-situ conditions, but can also be used to form hydrate or hydrate-containing samples in contact with the TPS element. The part of the cup containing the TPS element can simply be pulled away from the hydrate sample to permit subsequent characterization of the part of the sample that was measured. The formation of uncompacted methane hydrate in the cup and measurement of its thermal properties are described. The recovery of the sample and characterization by Raman spectroscopy are also presented.