Thermal Conductivity Of Methane Hydrate Research Articles

Enhanced phonon transport in sI-type methane hydrate under uniaxial compression strain: Unveiling the opening of an advantageous channel

Unveiling the thermal transport mechanisms of natural gas hydrate under strain conditions is fundamental to the heat transfer of the hydrate reservoir during drilling and production. This work investigated the structural stability and phonon transport mechanisms of methane hydrate using equilibrium molecular dynamics simulations subjected to uniaxial compression strain. The results indicate that the stability of large cages within methane hydrates weakens under strain. However, the presence of methane molecules effectively stabilizes the cage structure, enabling it to remain intact even under significant deformation. Furthermore, the thermal conductivity of methane hydrate demonstrates non-linear behavior, characterized by an initial increase followed by a subsequent decrease with increasing uniaxial compression strain. Particularly, the thermal conductivity of methane hydrate attains a maximum value of 0.87±0.018 W⋅m−1⋅K−1 at a strain of -0.04. The results suggest that the elevated spectral energy density and the prolonged phonon lifetime contribute to the enhanced thermal conductivity of methane hydrate. Interestingly, it was observed that the overlapping of phonon vibration modes between water and methane molecules results in the suppression of the peaks and valleys when the strain reaches -0.04. This overlap eliminates the gap and opens up an advantageous channel for phonon transport, thereby enhancing the heat transport capability of methane hydrate. The opening of an advantageous channel for phonon transport results in an extended phonon lifetime and a subsequent increase in thermal conductivity. This study presents a novel perspective for comprehending the unusual thermal conductivity of methane hydrate under strain conditions.

Study on the non‐in situ measurement method for hydrate thermal conductivity

A non-in situ measurement method for gas hydrate thermal conductivity was established, including the sample preparation, sample transfer, sample loading, and thermal conductivity measurement. Taking tetrahydrofuran (THF) hydrate and methane hydrate as examples, the detailed process was investigated by many experiments. THF hydrate samples were prepared by the combined method of THF aqueous solution + temperature oscillation + aging, while methane hydrate samples were prepared by the combined method of compacted ice powder + temperature oscillation + supplementary gas + aging. The sample box, quick-opening reactor, and sample mold were developed to improve the sample quality, shorten preparation time, and reduce exposure time. It was found that the time of sample transfer and loading can be controlled within 1 minute and 15 minutes for THF hydrate and methane hydrate, respectively. The thermal conductivities of THF hydrate and methane hydrate are 0.5200 ~ 0.5700 and 0.4803 ~ 0.6197 W•m−1•K−1 in the studied temperature range, respectively. The thermal conductivity of THF hydrate shows a positive dependence on temperature. The thermal conductivity of methane hydrate shows no dependence on temperature, but negative dependence on pressure. The errors of THF hydrate mainly come from the frost layer and micro airflow while the errors of methane hydrate mainly come from the ice film and micro gas flow. The precision, accuracy, and uncertainty of THF hydrate are 0.09% ~ 0.75%, 0.0450 ~ 0.0650 W•m−1•K−1 (absolute difference), 8.65% ~ 12.01% (relative error) and 0.00007 ~ 0.00017, respectively. Similarly, the precision, accuracy and uncertainty of methane hydrate are 0.04% ~ 5.98%, 0.005 ~ 0.0619 W•m−1•K−1(absolute difference), 1.02% ~ 12.12% (relative error) and 0.00016 ~ 0.00032, respectively. Based on the analysis, the established non-in situ measurement technique in this work is completely feasible and can be used to measure the obtained naturally occurring samples.

The effective thermal conductivity of methane hydrate-bearing seasand

The thermal properties of hydrate-bearing sediments can help to evaluate the stability of hydrate reservoir and improve the safety of natural gas hydrate exploitation. In this work, the thermal conductivities of methane hydrate and methane hydrate-bearing seasand were investigated by the transient plane source (TPS) technique. The high-quality samples of hydrate were prepared by synergistic uses of a variety of methods, i.e., the “seeding” ice, simultaneous slowly heating and slowly supplying gas, temperature oscillation and aging method. The measured thermal conductivity of methane hydrate is 0.4877–0.5467 W·m−1·K−1 with the temperature 263.2–283.1 K and the pressure 4.0–9.5 MPa. The effective thermal conductivities of the saturated seasand sample, supersaturated seasand sample and unsaturated seasand sample (Here, the “saturated”, “unsaturated” and “supersaturated” refers to the three relationships between the pore volume of seasand and the volume of ice powder, respectively) are 1.1310–1.2703 W·m−1·K−1, 1.0070–1.1490 W·m−1·K−1, 0.9221–1.1980 W·m−1·K−1 with the pressure 8.0 MPa and the temperature 253.8–281.2 K, respectively. The effective thermal conductivities of the saturated sample, supersaturated sample and unsaturated sample are 1.1280–1.1402 W·m−1·K−1 (1.1331–1.5974 W·m−1·K−1), 1.0172–1.0252 W·m−1·K−1 (1.0181–1.2032 W·m−1·K−1), 0.9154–0.9388 W·m−1·K−1 (0.9401–1.1543 W·m−1·K−1) with the pressure 4.0–10.0 MPa and the temperature 263.2 K (275.2 K), respectively. The relationship between the effective thermal conductivity and methane hydrate saturation in the sample are λe,saturated > λe,supersaturated > λe,unsaturated. The results suggest that the thermal conductivities of methane hydrate and methane hydrate-bearing seasand are positively correlated with the temperature and the influence of the gas phase pressure is negligible. Besides, the effective thermal conductivity shows a sudden increase near to the phase equilibrium temperature. Due to the complex of actual samples, the same classic theory model cannot accurately predict three samples simultaneously.

Reconstruction of Intrinsic Thermal Parameters of Methane Hydrate and Thermal Contact Resistance by Freestanding 3ω Method**Supported by the National Natural Science Foundation of China under Grant No U1262112, and the Fundamental Research Funds for the Central Universities under Grant No 18CX06035A.

It is essential to obtain thermophysical properties of methane hydrate precisely with a freestanding probe for modeling and predicting thermal transport in gas hydrates. A method with a freestanding 3ω probe is presented to reconstruct the intrinsic thermal conductivity, thermal diffusivity, and thermal contact resistance of methane hydrate. Isolated from the thermal contact resistance, the intrinsic thermal conductivity of methane hydrate decreases between 250 K and 280 K and is 41% larger than the effective value at 253 K. More importantly, when the thermal contact resistance is isolated, the temperature dependence of intrinsic thermal conductivity shows a converse trend with the generally accepted glass-like feature at high temperature. Otherwise, thermal contact resistances measured in the experiment between the freestanding 3ω probe and the methane hydrate sample are extraordinary large. The freestanding 3ω method in this work is expected to measure the thermal property of methane hydrate more accurately.

Thermal conductivity and thermal diffusivity of methane hydrate formed from compacted granular ice

Thermal conductivity and thermal diffusivity of pure methane hydrate samples, formed from compacted granular ice (0–75 μm), and were measured simultaneously by the transient plane source (TPS) technique. The temperature dependence was measured between 263.15 and 283.05 K, and the gas-phase pressure dependence was measured between 2 and 10 MPa. It is revealed that the thermal conductivity of pure methane hydrate exhibits a positive trend with temperature and increases from 0.4877 to 0.5467 W·m−1·K−1. The thermal diffusivity of methane hydrate has inverse dependence on temperature and the values in the temperature range from 0.2940 to 0.3754 mm2·s−1, which is more than twice that of water. The experimental results show that the effects of gas-phase pressure on the thermal conductivity and thermal diffusivity are very small. Thermal conductivity of methane hydrate is found to have weakly positive gas-phase pressure dependence, whereas the thermal diffusivity has slightly negative trend with gas-phase pressure.

Molecular dynamics simulation of decomposition and thermal conductivity of methane hydrate in porous media**Project supported by the National Natural Science Foundation of Special Fund and Chinese Academy of Engineering (Grant No. L1322021).

The hydrate has characteristics of low thermal conductivity and temperature sensitivity. To further analysis the mechanism of thermal conductivity and provide method for the exploitation, transportation and utilization of hydrate, the effect of decomposition and thermal conductivity of methane hydrate in porous media has been studied by using the molecular dynamics simulation. In this study, the simulation is carried out under the condition of temperature 253.15 K–273.15 K and pressure 1 MPa. The results show that the thermal conductivity of methane hydrate increases with the increase of temperature and has a faster growth near freezing. With the addition of porous media, the thermal conductivity of the methane hydrate improves significantly. The methane hydrate-porous media system also has the characteristics of vitreous body. With the decrease of the pore size of the porous media, thermal conductivity of the system increases gradually at the same temperature. It can be ascertained that the porous media of different pore sizes have strengthened the role of the thermal conductivity of hydrates.

Kinetics and thermal analysis of methane hydrate formation in aluminum foam

Gas consumption experiments based on pressure–volume–temperature (PVT) measurements were conducted to study the formation kinetic behaviors of methane hydrate with sodium dodecyl sulfate (SDS) and open-cell aluminum foam (AF) in a stainless steel vessel without stirring under the pressure range of (4.2 to 8.3) MPa and 273.2K. The results demonstrated that porous AF played an acceleration role in the formation of methane hydrate by promoting hydrate nucleation and enhancing hydration heat transfer. AF can provide numerous natural micro vessels with excellent thermal conductivity wall for gas hydrates formation. A reliable heat conduction model based on two-phase materials with spherical inclusions has been applied to determine the effective thermal conductivity (ETC) of hydrate/AF composites. The predicted ETC of composites was 132 times higher than the thermal conductivity of methane hydrate. A heat transfer model based on multilayer cylindrical walls was built to investigate the hydration heat transfer between hydrate and vessel. The acceleration effect of AF on methane hydrate formation was concertedly concluded through experimental study on kinetics and theoretical analysis of heat transfer.

Molecular dynamics simulations of the mechanisms of thermal conduction in methane hydrates

The thermal conductivity of methane hydrate is an important physical parameter affecting the processes of methane hydrate exploration, mining, gas hydrate storage and transportation as well as other applications. Equilibrium molecular dynamics simulations and the Green-Kubo method have been employed for systems from fully occupied to vacant occupied sI methane hydrate in order to estimate their thermal conductivity. The estimations were carried out at temperatures from 203.15 to 263.15 K and at pressures from 3 to 100 MPa. Potential models selected for water were TIP4P, TIP4P-Ew, TIP4P/2005, TIP4P-FQ and TIP4P/Ice. The effects of varying the ratio of the host and guest molecules and the external thermobaric conditions on the thermal conductivity of methane hydrate were studied. The results indicated that the thermal conductivity of methane hydrate is essentially determined by the cage framework which constitutes the hydrate lattice and the cage framework has only slightly higher thermal conductivity in the presence of the guest molecules. Inclusion of more guest molecules in the cage improves the thermal conductivity of methane hydrate. It is also revealed that the thermal conductivity of the sI hydrate shows a similar variation with temperature. Pressure also has an effect on the thermal conductivity, particularly at higher pressures. As the pressure increases, slightly higher thermal conductivities result. Changes in density have little impact on the thermal conductivity of methane hydrate.

Measurement and modeling of the effective thermal conductivity for porous methane hydrate samples

The effective thermal conductivities of gas-saturated porous methane hydrates were measured by a single-sided transient plane source (TPS) technique and simulated by a generalized fractal model of porous media that based on self-similarity. The density of porous hydrate, measured by the volume of the sample in the experimental system, was used to evaluate the porosity of methane hydrate samples. The fractal model was based on Sierpinski carpet, a thermal-electrical analogy technique and one-dimensional heat flow assumption. Both the experimental and computational results show the effective thermal conductivity of methane hydrate decreases with the porosity increase. The porosity of 0.3 can reduce the thermal conductivity of the methane hydrate by 25%. By analysis of the experimental data and the simulative result, the optimized thermal conductivity of the zero-porosity methane hydrate is about 0.7 W m−1 K−1.

Estimation of ultra-stability of methane hydrate at 1 atm by thermal conductivity measurement

Thermal conductivity of methane hydrate was measured in hydrate dissociation self-preservation zone by means of the transient plane source (TPS) technique developed by Gustafsson. The sample was formed from 99.9% (volume ratio) methane gas with 280 ppm sodium dodecyl sulfate (SDS) solution under 6.6 MPa and 273.15 K. The methane hydrate sample was taken out of the cell and moved into a low temperature chamber when the conversion ratio of water was more than 90%. In order to measure the thermal conductivity, the sample was compacted into two columnar parts by compact tool at 268.15 K. The measurements are carried out in the temperature ranging from 263.15 K to 271.15 K at atmospheric pressure. Additionally, the relationship between thermal conductivity and time is also investigated at 263.15 K and 268.15 K, respectively. In 24 h, thermal conductivity increases only 5.45% at 268.15 K, but thermal conductivity increases 196.29% at 263.15 K. Methane hydrates exhibit only minimal decomposition at 1 atm and the temperature ranging from 263.15 K to 271.15 K. At 1 atm and 268.15 K, the total gas that evolved after 24 h was amounted to less than 0.71% of the originally stored gas, and this ultra-stability was maintained if the test was lasted for more than two hundreds hours before terminating.

Molecular Dynamics Simulations of the Thermal Conductivity of Methane Hydrate

Nonequilibrium molecular dynamics simulations with the nonpolarizable SPC/E (Berendsen et al., J. Phys. Chem. 1987, 91, 6269) and the polarizable COS/G2 (Yu and van Gunsteren, J. Chem. Phys. 2004, 121, 9549) force fields have been employed to calculate the thermal conductivity and other associated properties of methane hydrate over a temperature range from 30 to 260 K. The calculated results are compared to experimental data over this same range. The values of the thermal conductivity calculated with the COS/G2 model are closer to the experimental values than are those calculated with the nonpolarizable SPC/E model. The calculations match the temperature trend in the experimental data at temperatures below 50 K; however, they exhibit a slight decrease in thermal conductivity at higher temperatures in comparison to an opposite trend in the experimental data. The calculated thermal conductivity values are found to be relatively insensitive to the occupancy of the cages except at low (T<or=50 K) temperatures, which indicates that the differences between the two lattice structures may have a more dominant role than generally thought in explaining the low thermal conductivity of methane hydrate compared to ice Ih. The introduction of defects into the water lattice is found to cause a reduction in the thermal conductivity but to have a negligible impact on its temperature dependence.

Thermal Conductivity of Methane Hydrate from Experiment and Molecular Simulation

A single-sided transient plane source technique has been used to determine the thermal conductivity and thermal diffusivity of a compacted methane hydrate sample over the temperature range of 261.5-277.4 K and at gas-phase pressures ranging from 3.8 to 14.2 MPa. The average thermal conductivity, 0.68 +/- 0.01 W/(m K), and thermal diffusivity, 2.04 x 10(-7) +/- 0.04 x 10(-7) m2/s, values are, respectively, higher and lower than previously reported values. Equilibrium molecular dynamics (MD) simulations of methane hydrate have also been performed in the NPT ensemble to estimate the thermal conductivity for methane compositions ranging from 80 to 100% of the maximum theoretical occupation, at 276 K and at pressures ranging from 0.1 to 100 MPa. Calculations were performed with three rigid potential models for water, namely, SPC/E, TIP4P-Ew, and TIP4P-FQ, the last of which includes the effects of polarizability. The thermal conductivities predicted from MD simulations were in reasonable agreement with experimental results, ranging from about 0.52 to 0.77 W/(m K) for the different potential models with the polarizable water model giving the best agreement with experiments. The MD simulation method was validated by comparing calculated and experimental thermal conductivity values for ice and liquid water. The simulations were in reasonable agreement with experimental data. The simulations predict a slight increase in the thermal conductivity with decreasing methane occupation of the hydrate cages. The thermal conductivity was found to be essentially independent of pressure in both simulations and experiments. Our experimental and simulation thermal conductivity results provide data to help predict gas hydrate stability in sediments for the purposes of production or estimating methane release into the environment due to gradual warming.

Thermal Conductivity of Methane-Hydrate

The thermal conductivity of the methane hydrate CH4 (5.75 H2O) was measured in the interval 2-140 K using the steady-state technique. The thermal conductivity corresponding to a homogeneous substance was calculated from the measured effective thermal conductivity obtained in the experiment. The temperature dependence of the thermal conductivity is typical for the thermal conductivity of amorphous solids. It is shown that after separation of the hydrate into ice and methane, at 240 K, the thermal conductivity of the ice exhibits a dependence typical of heavily deformed fine-grain polycrystal. The reason for the glass-like behavior in the thermal conductivity of clathrate compounds has been discussed. The experimental results can be interpreted within the phenomenological soft-potential model with two fitting parameters.

Measuring and modeling thermal conductivity of gas hydrate‐bearing sand

Effective thermal conductivity (ETC) of both tetrahydrofuran (THF) and methane hydrate‐bearing sandy porous media was measured by the Hot Disk Thermal Constant Analyser. Thermal conductivity of methane hydrate is 0.575 W m−1K−1at 0°C and 6.6 MPa (methane gas pressure), which is close to THF hydrate's 0.51 W m−1K−1at 0°C and 0.1 MPa (atmosphere pressure). However, the measured 1 W m−1K−1ETC of methane hydrate‐bearing sand is significantly lower than that of THF hydrate‐bearing sand at ∼2 W m−1K−1. This is because the methane hydrate formed with a sodium dodecyl sulfate (SDS) solution in sand at our laboratory has a “wall creeping” growth characteristic and consequently a large part of the pores were filled with methane free gas. ETCs of sand containing gas hydrates were also calculated using a renormalization method. The process involves sample partitioning, labeling, initial value assignments, and renormalization calculations. A Monte Carlo analysis was applied to sample laboratory‐scale gas hydrate‐bearing sand assemblies. We found that the renormalization modeling results agreed well with measured ETCs when each photo of a 1.3 mm × 1.3 mm subsample was divided into 16 or more blocks.

Thermal Conductivity of Methane Hydrate Formed from Sodium Dodecyl Sulfate Solution

The thermal conductivity of methane hydrate was measured by means of Gustafsson's transient plane source (TPS) technique. The sample was formed from 99.9 vol % methane gas with a 0.9709 mol·m-3 aqueous sodium dodecyl sulfate (SDS) solution under 6.60 MPa and 273.15 K. The in-situ measurement was performed in the temperature range from (263.06 to 277.87) K, and the thermal conductivity of unimpacted sample was lower than that of the impacted, with values of (0.334 to 0.381) W·m-1·K-1 and (0.564 to 0.587) W·m-1·K-1, respectively. The results showed that the methane hydrate has glasslike thermal properties.

An exploratory study of the thermal conductivity of methane hydrate

Recent discoveries of natural gas hydrates in permafrost and sub‐oceanic environments have led us to measure the thermal conductivity of methane hydrate. A guarded hot‐plate cell was constructed and tested with various ice specimens. We find the conductivity of methane hydrate near −60°C is 0.45 W/mK, a value close to that obtained for other clathrate hydrates by us and others. It is much lower than for ice (by a factor of about 5), so that a logging tool based on this property should prove to be of use in identification of gas hydrates in permafrost zones.