Magnetic Resonance Imaging of Gas Hydrate Formation in a Bed of Silica Sand Particles

The formation process of gas hydrates in sedimentary matrices is of crucial importance for the physical and transport properties of the resulting aggregates. This process has never been observed in situ at submicron resolution. Here we report on synchrotron-based microtomographic studies by which the nucleation and growth processes of gas hydrate were observed at 276 K in various sedimentary matrices such as natural quartz (with and without admixtures of montmorillonite type clay) or glass beads with different surface properties, at varying water saturation. Both juvenile water and metastably gas-enriched water obtained from gas hydrate decomposition was used. Xenon gas was employed to enhance the density contrast between gas hydrate and the fluid phases involved. The nucleation sites can be easily identified and the various growth patterns are clearly established. In sediments under-saturated with juvenile water, nucleation starts at the water-gas interface resulting in an initially several micrometer thick gas hydrate film; further growth proceeds to form isometric single crystals of 10-20 mm size. The growth of gas hydrate from gas-enriched water follows a different pattern, via the nucleation in the bulk of liquid producing polyhedral single crystals. A striking feature in both cases is the systematic appearance of a fluid phase film of up to several micron thickness between gas hydrates and the surface of the quartz grains. These microstructural findings are relevant for future efforts of quantitative rock physics modeling of gas hydrates in sedimentary matrices and explain the anomalous attenuation of seismic/sonic waves.

show abstract

“…Similar observations have been reported by e.g., Bagherzadeh et al . [], Dai et al . [], Kerkar et al .…”

Section: Nucleation and Growthmentioning

confidence: 99%

Microstructural evolution of gas hydrates in sedimentary matrices observed with synchrotron X‐ray computed tomographic microscopy

Chaouachi

Falenty

Sell

et al. 2015

Geochem Geophys Geosyst

224

210

View full text Add to dashboard Cite

show abstract

“…Because hydrate formation in a fully initial water saturation and a low initial saturation is not easy to occur. The causes of the phenomenon may be the difficulty of methane dissolving into the water, the small gas‐liquid contact area, and the randomness of nucleation can be the reasons, so it is not reported here. Figure shows the lognormal distribution of CH 4 hydrate induction time in BZ‐06 with different initial water saturations at 6.00 MPa and 275.15 K. The distributions of induction time are close with 50% and 80% water saturation, and the lognormal distributions are more positively skewed with the decrease in initial water saturation from less than 70%.…”

Section: Resultsmentioning

confidence: 99%

Experimental Analysis on the Probability Density Distribution of Methane Hydrate Induction Times in Porous Media

Wang

Yang

2018

ChemistrySelect

View full text Add to dashboard Cite

Hydrate‐based natural‐gas transport and storage have been proposed and developed because of the high safety and low cost, and hydrate reformation is a serious barrier for high‐efficiency natural‐gas hydrate exploitation. The hydrate formation induction time is a crucial kinetic parameter for both of the two fields. To clarify the hydrate formation and/or reformation induction characteristics, the effects of sub‐cooling, particle size, initial water saturation and memory effect on the stochastic induction time patterns are experimentally investigated. In total, 22 cases were performed, and each case was repeated in 20–30 runs under identical conditions. The experimental results show that the distribution of CH4 hydrate induction times can be properly fitted to a lognormal distribution function. Larger sub‐cooling leads to shorter induction time and more repeatable experimental results. It is also found that shorter induction time and repeatable results can be obtained with bigger particle size. The experimental results show that 70% water saturation can be considered a critical value for hydrate formation. Memory effect of water is existed in the experiments, which can help reducing the induction time and its stochastic nature. It can be considered that the memory effect on the induction time is dominant compared with the other factors (sub‐cooling, particle size and initial water saturation).

show abstract

“…[, ]. Magnetic resonance imaging and X‐Ray computed topography can be used to observe gas hydrate distribution and reorganization in sediment samples in the laboratory [e.g., Kneafsey et al ., ; Stevens et al ., ; Bagherzadeh et al ., ; Rees et al ., ; Seol and Kneafsey , ; Kneafsey et al ., ]. In recent years, many laboratory experiments were conducted to study hydrate growth kinetics [e.g., Bagherzadeh et al ., ; Linga et al ., , ] and the gas production behavior from natural or synthetic hydrate‐bearing sediments using thermal stimulation, depressurization, or inhibitor injection [e.g., Linga et al ., ; Pang et al ., ; Tang et al ., ; Yang et al ., , ; Yuan et al ., , ].…”

Section: Introductionmentioning

confidence: 99%

Salinity‐buffered methane hydrate formation and dissociation in gas‐rich systems

et al. 2015

View full text Add to dashboard Cite

Methane hydrate formation and dissociation are buffered by salinity in a closed system. During hydrate formation, salt excluded from hydrate increases salinity, drives the system to three-phase (gas, water, and hydrate phases) equilibrium, and limits further hydrate formation and dissociation. We developed a zero-dimensional local thermodynamic equilibrium-based model to explain this concept. We demonstrated this concept by forming and melting methane hydrate from a partially brine-saturated sand sample in a controlled laboratory experiment by holding pressure constant (6.94 MPa) and changing temperature stepwise. The modeled methane gas consumptions and hydrate saturations agreed well with the experimental measurements after hydrate nucleation. Hydrate dissociation occurred synchronously with temperature increase. The exception to this behavior is that substantial subcooling (6.4°C in this study) was observed for hydrate nucleation. X-ray computed tomography scanning images showed that core-scale hydrate distribution was heterogeneous. This implied core-scale water and salt transport induced by hydrate formation. Bulk resistivity increased sharply with initial hydrate formation and then decreased as the hydrate ripened. This study reproduced the salinity-buffered hydrate behavior interpreted for natural gas-rich hydrate systems by allowing methane gas to freely enter/leave the sample in response to volume changes associated with hydrate formation and dissociation. It provides insights into observations made at the core scale and log scale of salinity elevation to three-phase equilibrium in natural hydrate systems.

show abstract

Magnetic Resonance Imaging of Gas Hydrate Formation in a Bed of Silica Sand Particles

Cited by 168 publications

References 33 publications

Microstructural evolution of gas hydrates in sedimentary matrices observed with synchrotron X‐ray computed tomographic microscopy

Microstructural evolution of gas hydrates in sedimentary matrices observed with synchrotron X‐ray computed tomographic microscopy

Experimental Analysis on the Probability Density Distribution of Methane Hydrate Induction Times in Porous Media

Salinity‐buffered methane hydrate formation and dissociation in gas‐rich systems

Contact Info

Product

Resources

About