Methane Hydrate Formation Research Articles

Development of explicit models to predict methane hydrate equilibrium conditions in pure water and brine solutions: A machine learning approach

An important phase in the design of processes involving gas hydrates is predicting the hydrate formation conditions. In this study, three explicit correlations based on machine learning techniques, gene expression programming (GEP), and optimizing two correlations with predetermined structures were developed for the prediction of methane hydrate formation temperature (HFT) in pure water and brines. The proposed correlations are based on the pressure and ionic strength (IS) of solutions. Compared to the literature, this is the first time that the effect of salinity has been considered in the development of explicit models to predict methane HFT. To achieve practical correlations, the least number of coefficients was used. The error analysis revealed an acceptable agreement with the experimental data. Among the models, GEP-based correlation provided the best performance with an R2 and AARD of 0.8860 and 0.087%, respectively. The developed correlations are easy-to-use and accurate for both academics and non-academics.

Kinetics behaviors of CH4 hydrate formation in porous sediments: Non-unidirectional influence of sediment particle size on hydrate formation

The kinetic characteristics governing methane conversion into solid hydrates within seabed sediments influence hydrate accumulation and resource distribution, which is significant for the evaluation of global natural gas hydrate reserves and the implication of hydrate development. However, the influence of sediment particle size on methane hydrate formation kinetics remains unclear. In this study, simulating in situ conditions of the seafloor, the kinetics behaviors of CH4 hydrate formation within saline porous sediments were investigated. The experimental results indicate that the methane hydrate formation rate does not exhibit a strictly unidirectional change with changed quartz sand particle size. The unidirectionality and magnitude of hydrate formation rate change are simultaneously influenced by both quartz sand particle size and water saturation levels. The different effective gas-liquid contact area is the primary factor underlying the occurrence of these phenomena. However, for more porous clay sediments with greater specific surface area, the theory of effective gas-liquid contact area becomes inapplicable. The addition of clay to quartz sand sediment inversely inhibits the methane hydrate formation, which is caused by water absorption. This work can advance the comprehension of the intricate interplay between hydrate growth kinetics and the attributes of sedimentary hosts.

Experimental study of methane hydrate formation and agglomeration in waxy oil-in-water emulsions

In deep-water multiphase flow pipelines, hydrate and wax agglomeration can cause blockages. To clarify the influence of wax and Tween 80 on hydrate formation and agglomeration in water-in-oil (W/O) emulsions, hydrate generation experiments were conducted in a high-pressure reactor, focusing on W/O emulsions both with and without wax and Tween 80. Additionally, the paper further explored the characteristics of hydrate formation and agglomeration in wax-containing W/O emulsions with Tween 80 under various initial pressure conditions. Results indicated that wax presence curtailed the Tween 80's dual role: inhibiting hydrate nucleation and promoting rapid hydrate growth. The interplay of waxes and Tween 80 had a synergistic impact on hydrate formation, elevating the cumulative gas consumption by 0.74 mol and augmenting the water conversion rate by 9 %. This intensifies the likelihood of hydrate blockages. Under higher initial pressures, a notable multi-step pressure decrease occurred during hydrate formation, attributed to a high water cut, wax/Tween 80 presence, and initial pressure. Torque evaluations indicate that wax-Tween 80 interactions diminish particle agglomeration, enhancing hydrate slurry liquidity.

Enhanced formation of methane hydrate from active ice with high gas uptake

Gas hydrates provide alternative solutions for gas storage & transportation and gas separation. However, slow formation rate of clathrate hydrate has hindered their commercial development. Here we report a form of porous ice containing an unfrozen solution layer of sodium dodecyl sulfate, here named active ice, which can significantly accelerate gas hydrate formation while generating little heat. It can be readily produced via forming gas hydrates with water containing very low dosage (0.06 wt% or 600 ppm) of surfactant like sodium dodecyl sulfate and dissociating it below the ice point, or by simply mixing ice powder or natural snow with the surfactant. We prove that the active ice can rapidly store gas with high storage capacity up to 185 VgVw−1 with heat release of ~18 kJ mol−1 CH4 and the active ice can be easily regenerated by depressurization below the ice point. The active ice undergoes cyclic ice−hydrate−ice phase changes during gas uptake/release, thus removing most critical drawbacks of hydrate-based technologies. Our work provides a green and economic approach to gas storage and gas separation and paves the way to industrial application of hydrate-based technologies.

Experimental Study of the Rate of Methane Hydrate Formation: Influence of Simultaneous Utilization of Tetra n-Butylammonium Fluoride and Sodium Dodecyl Sulfate

Experimental Study of the Rate of Methane Hydrate Formation: Influence of Simultaneous Utilization of Tetra n-Butylammonium Fluoride and Sodium Dodecyl Sulfate

Natural self-assembled supramolecules as green inhibitors against methane hydrate formation

Environmentally friendly hydrate inhibitors are the most promising method to solve the environmental pollution of inhibitors, among which Safranine O (SO) with antifreeze protein properties shows excellent application prospects. SO will self-assemble into macromolecules under hydrogen bonding and electrostatic action in an aqueous solution. The assembled macromolecules' hydrophobic and hydrophilic functional groups are regularly arranged with the properties of an antifreeze protein. In the crystal growth inhibition (CGI) test, the supercooling degree of the complete inhibition region (CIR) of 1.0 wt% SO solution for SI hydrate was significantly higher than that of 1.0 wt% PVP solution. Further, the acidic environment did not affect the inhibitory effect of SO on hydrate. The complete inhibition range of 1.0 wt% SO solution on SI hydrate at pH 1.4 and 7.1 was 7.41 °C and 8.35 °C, respectively. These results suggest that SO-based KHIs may provide new ideas for developing highly efficient acid-resistant hydrate inhibitors.

Influence of silt sand on the characteristics of methane hydrate equilibrium and formation

Influence of silt sand on the characteristics of methane hydrate equilibrium and formation

Effect of asphaltenes on growth behavior of methane hydrate film at the oil-water interface

Investigation of the effect of asphaltenes, the natural surfactant in crude oil, on the methane hydrate formation is crucial for flow assurance in deep-water oil and gas field. However, most of recent studies on hydrate growth mainly focused on the impact of artificial and commercial surfactants. Limited attention has been given to the effect of the important natural surfactants presented in crude oil on hydrate film growth, such as asphaltenes. In this study, the influences of dissolved asphaltenes on the properties of oil-water interface and the growth of methane hydrate film were investigated. The morphology of methane hydrate film on the water droplet in the oil phase with different asphaltene concentrations was in-situ visualized in a visual autoclave equipped with microscopic imaging, and the lateral growth rate of the methane hydrate film was measured. The results showed that the addition of asphaltenes could increase the hydrophobicity of the methane hydrate film, inhibit the growth of hydrate, and change the morphology of the hydrate film. The growth rate of the hydrate film was negatively correlated with the asphaltene concentration (0–200 ppm), but stabilized above 200 ppm. In addition, this inhibition effect on the lateral growth rate was negatively correlated with temperature.

Driving sustainable energy storage: A multi-scale investigation of methane hydrate formation with green promoters and innovative reactor design

Synthetic Gas hydrates are promising materials for safe and compact energy storage but their wide-scale application is hindered by slow formation kinetics. We investigated the effect of green kinetic promoters of H-SSZ-13 zeolite, L-tryptophan, L-leucine, and L-methionine in a novel reactor design to accelerate hydrate formation at 6 MPa. In (NSR), H-SSZ-13 and L-tryptophan showed superior performance over L-leucine and L-methionine. While H-SSZ-13 showed the lowest average (t90) of 286 mins and the highest volumetric capacity of 115 V/V at 283 K, its kinetic performance, along with other promoters, dropped significantly at 293 K. We introduced a new (FBR) equipped with light (MFP) to increase gas diffusion and thermal conductivity. The combined effect of (FBR)-(MFP) reactor with zeolite significantly improved the kinetics overcoming (NSR) drawbacks. At 293.15 K, H-SSZ-13 zeolite promoter showed superior performance reducing the induction time and (t90) to 3 and 154 mins, respectively. Furthermore, it exploited 88.6%, and 96% of the sII clathrates volumetric storage capacity at 293 K and 283 K, respectively. Finally, we showed that the synthesized hydrates can be stored at atmospheric pressure for 4 months without significant methane loss. This multi-scale approach is paving the way for scaling up green and economical gas hydrate technology.

Metastable structure II methane hydrate: A bridge to obtain high methane uptake in the presence of thermodynamic promoter

The addition of thermodynamic promoters is a promising and perhaps the only effective method to reduce hydrate formation conditions. However, this is achieved at the cost of the gas storage capacity reduction since the thermodynamic promoter will occupy some hydrate cages. To date, there is no effective method that can simultaneously limit this negative effect and obtain high water-to-hydrate conversion. In this work, we determine the methane (CH4) hydrate formation mechanism in the presence of a thermodynamics promoter, Cyclopentane (CP), and find that structure II (Str.II) CH4 hydrate, as a metastable intermediate structure of the reaction, plays a quite significant role in encapsulating CH4 molecules in some 51264 cages (Str.II hydrates) and facilitating structure I CH4 hydrate formation, thereby increasing gas uptake significantly. A CH4 uptake, as high as 141.21 mmol/molH2O, is obtained from this work. Relative to the acknowledged limit of CH4 uptake of Str.II hydrates formed commonly in the presence of same mole fractions of thermodynamics promoter (8(Promoter)·16(CH4)·136H2O)), the highest increase in CH4 uptake is up to 232.75 %. These results would stimulate the development of the hydrate reaction theory and provide a new direction for promoter design.

Insights into behaviors of guest and host molecules in methane hydrate formation process in the presence of kinetic inhibitors via in-situ micro-Raman spectroscopy

In-situ microscopic observation on methane hydrate formation in the presence of kinetic hydrate inhibitor, poly (vinyl caprolactam) (PVCap) or poly (N-isopropyl acrylamide) (PNIPAM), is conducted with a confocal Raman imaging microscope, and the behaviors of CH4 molecules and water molecules in hydrate formation process are studied to understand the inhibition mechanism. It is found that both PVCap and PNIPAM have influences on hydrate formation, but their interactions with host and guest molecules are different. PVCap with cyclic pendant groups works better on preventing hydrate formation from the gas–liquid interface into the bulk solution, while PNIPAM with acyclic pendant groups is more effectively on inhibiting hydrate growth to well-ordered clathrate structures. Those are caused by the difference in the prominent inhibition mechanism of the two types of kinetic hydrate inhibitors, lactam-based PVCap mainly limiting the diffusion of CH4 molecules from the gaseous phase to the liquid phase, while non-lactam PNIPAM undermining hydrate growth by retarding the rearrangement of water molecules to form clathrate structures.

Structure I methane hydrate confined in C8-grafted SBA-15: A highly efficient storage system enabling ultrafast methane loading and unloading

Confinement of water and methane in mesopores of hydrophobized SBA-15 is demonstrated to promote methane hydrate formation. In comparison to as-synthesized SBA-15, hydrophobization by C8 grafting accelerates the kinetics of methane storage in and delivery from the hydrate. C8 grafting density was determined at 0.5 groups nm−2 based on TGA and quantitative NMR spectroscopy. Multinuclear 1H-1H DQSQ and 1H-1H RFDR NMR provided spectroscopic evidence for the occurrence of C8 chains inside the mesopores of SBA-15, by showcasing close spatial proximity between the grafted C8 chains and pore-intruded water species. X-ray diffraction demonstrates formation of Structure I hydrate on SBA-15 C8. At 7.0 MPa and 248 K, the water-to-hydrate conversion on hydrophobized SBA-15 C8 reaches 96% as compared to only 71% on a pristine SBA-15 sample with comparable pore size, pore volume and surface area. The clathrate loading amounted to 14.8 g/g. 2D correlation NMR spectroscopy (1H-13C CP-HETCOR, 1H-1H RFDR) reveals hydrate formation occurs within pores of SBA-15 C8 as well as in interparticle volumes. Following the initial crystallization of SBA-15 C8-supported methane hydrate taking several hours, a pressure swing process at 248 K allows to desorb and re-adsorb methane from the structure within minutes and without thawing the frozen water structure. Fast loading and unloading of methane was achieved in 19 subsequent cycles without losses in kinetics. The ability to harvest the gas and regenerate the structure without the need to re-freeze the water represents a 50% energy gain with respect to melting and subsequently recrystallizing the hydrate at 298 K and 248 K, respectively. After methane desorption, a small amount of residual methane hydrate in combination with an amorphous yet locally ordered ice phase is observed using 13C and 2H NMR spectroscopy. This effect offers an explanation for the enhanced hydrate formation kinetics in adsorption-desorption cycles. These findings open new perspectives for clathrate hydrate-based methane storage.

Methane hydrate formation in slit-shaped pores: Impacts of surface hydrophilicity

Gas hydrate accumulation and hydrate-based gas storage and transportation technology are intimately linked to the formation process of hydrates in the pore space. However, the molecular mechanism underlying this process remains unclear. Here, we employ molecular simulations to investigate methane hydrate formation in surface-modified silica pores, with specific emphasis on the impact of pore surface characteristics. Our results show that under the same thermodynamic conditions, methane hydrate shows no preference towards either the hydrophobic or hydrophilic pore surface, and tends to nucleate in the central part of the hydrophilic slit. It means that whilst the surface properties can impact the dynamics and structure of the molecules on it, thus affecting methane concentration and, as a result, the probability of cage formation, the confinement effect ultimately controls the nucleation process. Furthermore, the pre-filling of the pores with methane can significantly accelerate hydrate formation. This is because methane bubbles adsorbed in the pores can noticeably elevate methane concentration in solution. Moreover, the hydrophobic surface can help with methane dissolution in water, which can both promote the transportation of molecules between methane bubbles and enhance methane hydrate nucleation. This study enhances understanding of the hydrate formation process in pores, which can aid in the design of gas hydrate promoters or inhibitors that meet the demands of hydrate technologies.

Effect of Silica Nanoparticles to Span 80 and Cocamidopropyl Dimethylamine in Methane Hydrate Formation and Agglomeration in Water–Oil System

Effect of Silica Nanoparticles to Span 80 and Cocamidopropyl Dimethylamine in Methane Hydrate Formation and Agglomeration in Water–Oil System

Inhibition on methane hydrate formation by polyacrylate superabsorbent hydrogel

Hydrate blockage in submarine oil and gas transport pipelines has always been the focus of attention in the oil and gas industry. Using superabsorbent hydrogels (SAHs), three-dimensional network structures with numerous hydrophilic groups, to prevent hydrate formation in gas/oil pipeline has been endowed with theoretical potential. In this work, the inhibition of traditional polyacrylate SAHs on methane hydrate formation was systematically studied via both numerical and morphological analysis. In methane hydrate formation from SDS solution (1 mmol/L), SAHs at relatively low swelling ratio of 10 and 5 produced obvious inhibition on hydrate nucleation, prolonging the induction time from 27.6 ± 14.5 min to 155.5 ± 157.1 and 334.2 ± 126.6 min, respectively. And the water fixation effects of SAHs could prevent methane hydrate growth from efficiently, with the inhibition efficiency reaching 65.83 ± 1.82 %, 81.82 ± 1.83 %, and 87.96 ± 1.66 % at swelling ratio of 20, 10, and 5, respectively. When used in simulated DI water/decane (W/O) mixture, at water content of 30 %, SAHs performed well at swelling ratio of 50 (mass ratio of 0.6 %), preventing methane hydrate formation by 94 % and keeping the mixture with low viscosity and good fluidity; at water content of 70 %, SAHs produced excellent performance at swelling ratio of 50–100 (mass ratio of 1.4%–0.7 %), preventing methane hydrate formation by 80 % and avoiding increasing the viscosity of the mixture. The results in this work confirmed the promising application potential of SAHs in gas/oil pipeline flow assurance.

A comparison of the CPA equation of state and the Trebble-Bishnoi equation of state for use in correlating methane hydrate formation conditions in the presence of aqueous amino acids

A comparison of the CPA equation of state and the Trebble-Bishnoi equation of state for use in correlating methane hydrate formation conditions in the presence of aqueous amino acids

Application of Soy Lecithin as a Promoter of Methane Hydrate Formation

Application of Soy Lecithin as a Promoter of Methane Hydrate Formation

The effects of rhamnolipid on the formation of CH4 hydrate and separation of CH4/N2 via hydrate formation

Rhamnolipid (Rha) is an efficient green surfactant that is able to promote hydrate generation, it can be applied to the hydrate method of separating. However, the effect of rhamnolipid on the separation of methane and nitrogen by the hydrate method is not clear. Therefore, in this paper, we investigated the effect of rhamnolipid on methane hydrate formation and the separation between methane and nitrogen via hydrate method. Firstly, the effects of five concentrations (0 ppm, 200 ppm, 400 ppm, 600 ppm and 800 ppm), temperatures and pressures on methane hydrate formation were studied separately. The rate of methane hydrate formation was positively correlated with experimental pressure. The gas consumption increased rapidly with the rhamnolipid concentration, and then increased slowly to a steady state. The final gas consumption above 200 ppm rhamnolipid concentrations could be increased more than five times compared with pure water conditions. The promotion of methane hydrate production is most pronounced at 274.15 K, mainly depending on the diffusion of gas molecules in solution and the ease of hydrate nucleation. Then, the interfacial tension at different concentrations was measured by the suspension drop method, and the relationship between the interfacial tension and the rate of hydrate formation was studied. Hydrate formation rate shows a multiplicative power function with the interfacial tension. What’s more, the kinetics of hydrate formation and gas separation effect of 3:1 CH4/N2 at 274.15 K and 7 MPa were studied with five concentrations. And 200 ppm was found to be the optimum concentration for separation, the separation factor is 8.25. Finally, the kinetics and thermodynamics of hydrate formation and gas separation effect of 1:1 CH4/N2 at 274.15 K and 9 MPa were also investigated, and the separation factor reached a maximum of 12.7 at 800 ppm, and the methane gas recovery rate also reached the maximum at 40.46%. The results of this study can provide some theoretical guidance for the optimal selection of green surfactants in separation by hydrate method.

Improving Methane Hydrate Formation Kinetics and Gas Storage Capacity with a Promoter

Improving Methane Hydrate Formation Kinetics and Gas Storage Capacity with a Promoter

Effects of eco-friendly cyclodextrin on the methane hydrate formation in the complex systems

Due to the increasing demand for natural gas, solidified natural gas (SNG) technology provides an attractive option for natural gas storage and transportation. However, the use of sodium dodecyl sulfate (SDS) to promote hydrate formation will have a negative impact on the environment. To overcome this difficulty, the compounding system of environmentally friendly additives with SDS was intended to find the synergistic promotion effects aiming to reduce the usage of SDS in this study. Three kinds of cyclodextrins including αCD, βCD, hydroxypropyl-βCD (HPCD) with SDS were compounded to study the effect of their interaction on hydrate formation kinetics. The result showed that when used with SDS, the formation of hydrates was promoted by αCD and βCD but inhibited by HPCD. It is emphasized that the promoting effect depended on the water channel (completely hydrophilic zones) formed by H-bonds between cyclodextrin and SDS self-assembled channel-type complexes. Compared with 500 ppm SDS used along, it was possible to reduce the dosage of SDS by 40%. Finally, by observing the morphology of hydrate formation, it is found that the addition of cyclodextrins would affect the driving force for hydrate growth in the horizontal direction during hydrate formation. This study provides theoretical support for further understanding of cyclodextrin and surfactant compounding and shows an effective way for the application of SNG industry.