Methane Hydrate Formation and Dissociation in Sand Media: Effect of Water Saturation, Gas Flowrate and Particle Size

Abstract

Assessing the influence of key parameters governing the formation of hydrates and determining the capacity of the latter to store gaseous molecules is needed to improve our understanding of the role of natural gas hydrates in the oceanic methane cycle. Such knowledge will also support the development of new industrial processes and technologies such as those related to thermal energy storage. In this study, high-pressure laboratory methane hydrate formation and dissociation experiments were carried out in a sandy matrix at a temperature around 276.65 K. Methane was continuously injected at constant flowrate to allow hydrate formation over the course of the injection step. The influence of water saturation, methane injection flowrate and particle size on hydrate formation kinetics and methane storage capacity were investigated. Six water saturations (10.8%, 21.6%, 33%, 43.9%, 55% and 66.3%), three gas flowrates (29, 58 and 78 mLn·min−1) and three classes of particle size (80–140, 315–450 and 80–450 µm) were tested, and the resulting data were tabulated. Overall, the measured induction time obtained at 53–57% water saturation has an average value of 58 ± 14 min minutes with clear discrepancies that express the stochastic nature of hydrate nucleation, and/or results from the heterogeneity in the porosity and permeability fields of the sandy core due to heterogeneous particles. Besides, the results emphasize a clear link between the gas injection flowrate and the induction time whatever the particle size and water saturation. An increase in the gas flowrate from 29 to 78 mLn·min−1 is accompanied by a decrease in the induction time up to ~100 min (i.e., ~77% decrease). However, such clear behaviour is less conspicuous when varying either the particle size or the water saturation. Likewise, the volume of hydrate-bound methane increases with increasing water saturation. This study showed that water is not totally converted into hydrates and most of the calculated conversion ratios are around 74–84%, with the lowest value of 49.5% conversion at 54% of water saturation and the highest values of 97.8% for the lowest water saturation (10.8%). Comparison with similar experiments in the literature is also carried out herein.

Influence of Clay‐Containing Sediments on Methane Hydrate Formation: Impacts on Kinetic Behavior and Gas Storage Capacity

“…Figure 5a summarize the measured induction times for the first series of experiments performed at constant injected water volume in sand and clay/sand mixtures (experiments 1_1 to 5_5 in Table 4). The average induction time for hydrate formation within the sand is 50 ± 6 min, which is close to the value of 53 ± 5 min obtained by Benmesbah et al (2020) in a previous study using the same apparatus and operating conditions.…”

Influence of Water Saturation, Grain Size of Quartz Sand and Hydrate-Former on the Gas Hydrate Formation

“…According to the literature, particle size is one of key factors affecting the gas hydrates formation in a porous media [40,41]. It was shown [42] that media with a particle size of fewer than 4 µm are characterized by a significant shift in the equilibrium conditions of hydrate formation towards lower temperatures and higher pressure.…”

“…According to studies [43,44], the rate of hydrate formation is higher in quartz sand with smaller particles. Another relevant characteristic for hydrate formation in porous sediments is water saturation [35,40,41,45]. It was shown that an increase in water saturation resulted in a decrease in water to hydrate conversion while the addition of sodium dodecyl sulfate removing this restriction.…”

Dry Water as a Promoter for Gas Hydrate Formation: A Review

“…As a result, recent efforts have focused on improving the kinetics of hydrate formation through methods that enhance contact between the guest and the water molecules. A wide range of porous media has been investigated, including metal-organic frameworks (MOFs) [37], silica sands [38][39][40], silica gels [39,41], superabsorbent polymers (SAP) [42][43][44], glass beads [45], clay [46], activated carbon [47,48], nanotubes [49,50], and biological porous materials [51]. If we disregard the impact of porous media on the phase equilibrium of gas hydrates, it is commonly believed that such media can provide a greater number of nucleation sites [52,53], increase the gas-liquid contact areas [54], thus promoting hydrate formation kinetics.…”

“…The impact of factors, such as water saturation, gas flow rate, particle size, and the morphology of porous media on CO2 hydrate and methane hydrate formation and dissociation processes, has been extensively investigated in References [39] and [40], respectively. It is disappointing that the particle size of porous media has been found to have an opposite effect on hydrate formation kinetics and gas storage capacity [56].…”