Methane Hydrate Formation Research Articles

NMR Investigation of Methane Hydrate Formation and Dissociation Behavior Induced by Heat Flow in Sandy Porous Media

NMR Investigation of Methane Hydrate Formation and Dissociation Behavior Induced by Heat Flow in Sandy Porous Media

Branched sulfonated promoter: Achieving high methane uptake and foam-free gas recovery for solidified gas storage

Gas hydrates offer a promising solution for clean and low-carbon energy storage and the transportation of natural gas. However, their slow formation kinetics and dissociation-induced foaming hinder their practical application. This study investigates a novel branched sulfonated promoter (BSP) to address these challenges. The effectiveness of BSP in promoting methane hydrate formation was evaluated by measuring the conversion degree, methane consumption, storage capacity, hydrate growth rate, and reaction rate constant. Molecular dynamics (MD) simulations provided insights into BSP's interaction with methane and water molecules, its self-aggregation, adsorption, and its role in hydrate cage formation. BSP demonstrated comparable performance to SDS in accelerating methane hydrate formation. At a concentration of 500 ppm, BSP achieved a water-to-hydrate conversion rate of 89.54 %, methane consumption of 432.16 mmol, and a storage capacity of 165.1 v/v after 450 min. BSP effectively suppressed foam formation during methane hydrate dissociation, and all the hydrates melted within 15 min. Moreover, BSP promotes the formation of dense and solid hydrates, unlike SDS, which favors hydrate growth on reactor walls. MD simulations revealed that BSP molecules do not form micelles but interact with water molecules through their hydrophilic chains, facilitating methane accumulation around their hydrophobic tails. This behavior promotes methane aggregation and hydrate formation. BSP surpasses SDS in terms of foam-free dissociation, making it a promising candidate for practical hydrate-based energy storage and transportation technologies. The combined experimental and computational approach provides valuable insights into the mechanisms underlying BSP's promotional effect, challenging the long-held belief that long alkyl chains are essential for hydrate promotion. This paves the way for further development of effective and environmentally friendly hydrate promoters.

Pore-scale investigation on the morphology evolution and micro-mechanism of methane hydrate formed from free gas and dissolved gas

The distribution characteristics of gas hydrates in the pores of sediments are critical to predict the macroscopic properties of hydrate reservoirs and the efficient production of gas hydrates. In this study, the experiments of methane hydrate formation were conducted in a glass micromodel, and the morphology evolution of hydrate formed from the free gas and dissolved gas in the pores were observed through a video microscope. Observation results showed that the hydrate formed from free gas grew preferentially along the gas–water interface and subsequently toward the center of the gas phase. For the hydrate formed from dissolved gas, it was preferentially occurred on the surface of the hydrate crust formed from free gas and gradually grew toward the water phase. The hydrate formation rate was determined by the concentration of methane molecules in surroundings water. The hydrate formed from free gas was porous structure and composed of many tiny hydrate crystals, and the hydrate formed from dissolved gas was smooth and transparent polyhedral hydrate crystal. For the hydrate formed by free gas, the occurrence pattern of hydrate in the pores might change from the grain-cementing to the contact-cementing or the patchy. The occurrence pattern of the hydrate formed from dissolved gas could be the pore-filling or the load-bearing. This study could be helpful for explaining the phenomenon of macro-experiments, the model construction for the macro-properties of hydrate-bearing sediments, and the exploring of gas hydrates reservoirs.

Freshwater Recovery and Removal of Cesium and Strontium from Radioactive Wastewater by Methane Hydrate Formation.

As human society has advanced, nuclear energy has provided energy security while also offering low carbon emissions and reduced dependence on fossil fuels, whereas nuclear power plants have produced large amounts of radioactive wastewater, which threatens human health and the sustainability of water resources. Here, we demonstrate a hydrate-based desalination (HBD) technology that uses methane as a hydrate former for freshwater recovery and for the removal of radioactive chemicals from wastewater, specifically from Cs- and Sr-containing wastewater. The complete exclusion of radioactive ions from solid methane hydrates was confirmed by a close examination using phase equilibria, spectroscopic investigations, thermal analyses, and theoretical calculations, enabling simultaneous freshwater recovery and the removal of radioactive chemicals from wastewater by the methane hydrate formation process described in this study. More importantly, the proposed HBD technology is applicable to radioactive wastewater containing Cs+ and Sr2+ across a broad concentration range of low percentages to hundreds of parts per million (ppm) and even subppm levels, with high removal efficiency of radioactive chemicals. This study highlights the potential of environmentally sustainable technologies to address the challenges posed by radioactive wastewater generated by nuclear technology, providing new insights for future research and development efforts.

Hydrate Formation with the Memory Effect Using Classical Nucleation Theory

Methane hydrate formation is analytically studied in the presence of the water memory effect using the classical nucleation theory. The memory effect is introduced as a change in nucleation site from a three-dimensional heterogenous nucleation on a solid surface with cap-shaped hydrate clusters (3D-HEN) to a two-dimensional nucleation on the solid hydrate residue surface with monolayer disk-shaped hydrate clusters (2D-NOH). The analysis on the stationary nucleation of methane hydrate under isobaric conditions shows that the memory effect caused an average decrease of 4.4 K in metastable zone width, or subcooling. This decrease can be erased at higher dissociation temperatures (ΔT > 17.2 K) due to a decrease in the concentration of 2D-NOH nucleation sites. Moreover, the probability of hydrate formation is estimated for the purpose of quantifying risk associated with methane hydrate formation in the presence of the memory effect.

Affecting Mechanism of Natural Sandstone Porous Media on the Formation and Phase Equilibrium of Methane Hydrate

Affecting Mechanism of Natural Sandstone Porous Media on the Formation and Phase Equilibrium of Methane Hydrate

Enhanced methane hydrate formation using a newly synthesized biosurfactant: Application to solidified gas storage

Surfactants are considered the most influential promoters for accelerating the formation of gas hydrates in gas storage applications. However, their promotion mechanism remains unclear, and the formation of foam during the hydrate dissociation step severely limits hydrate-based gas storage technology. Oleic acid was used as a renewable biomass source in this study to develop a novel biosurfactant capable of enhancing methane hydrate formation. Oleic acid-based promoter (OAP) significantly improved kinetics of methane hydrate formation, and enhanced growth of hydrate crystals. A maximum conversion of 81 % and storage capacity of ∼151 v/v were achieved in a solution containing 1000 ppm OAP at 9 MPa. Additionally, OAP showed good promotion activity at a lower driving force (7 MPa), resulting in conversion and storage capacity 4.2 times greater than pure water. Moreover, molecular dynamics simulations revealed that the primary mechanism action of OAP is to increase the solubility of methane in an aqueous solution by forming promoter micelles. A gas release simulation for sodium dodecyl sulfate (SDS) solution generated significant foam, whereas no foam formed when OAP was present. The obtained findings are useful for developing efficient biosurfactants based on vegetable oils and can shed light on the promotion mechanism of promoters.

Novel core–shell and recyclable gas hydrate promoter for efficient solidified natural gas storage

The storage and transportation of gases, including hydrogen, methane, and carbon dioxide in the form of gas hydrates, have recently garnered considerable attention. The practical implementation of gas hydrates crucially depends on the development of efficient and reusable promoters. In this study, novel core–shell magnetic nanoparticles (CSNs) developed as recyclable promoter to enhance gas uptake. Hydrate formation experiments indicated that the storage capacity can reach up to 132.7 ± 1.4 v/v and 160.6 ± 2.5 v/v in CSNs and CSNs + SDS solutions, respectively. Compared to pure water and SDS solution, the initial methane consumption rate (0.5972 mol/h) of CSNs increased by 12.2 times and 1.08 times at 3000 ppm, respectively. CSNs exhibited favorable characteristics in terms of cycling ability and preventing foam formation during repeated methane hydrate formation and dissociation experiments. Furthermore, the combination of CSNs and SDS resulted in a 72 % reduction in hydrate nucleation induction time and a 58.3 % decrease in foam formation ability compared to the sole use of SDS. In comparison to pure water, the addition of CSNs increased the onset temperature of hydrate formation by 4 °C and reduced the driving force required for methane hydrate formation. Additionally, molecular dynamics simulation studies revealed that CSNs effectively improved the amount of the ordered water structure, hydrate cage formation, and the growth state of methane hydrates. These properties make CSNs promising for potential use in the storage and transportation of gas, considering the economic and environmental advantages associated with the use of promoters.

Experimental Study on Permeability and Gas Production Characteristics of Montmorillonite Hydrate Sediments Considering the Effective Stress and Gas Slippage Effect

Summary Gas permeability in hydrate reservoirs is the decisive parameter in determining the gas production efficiency and gas production of hydrate. In the South China Sea (SCS), the gas flow in tight natural gas hydrate (NGH) silty clay reservoirs is significantly affected by the gas slippage effect and the effective stress (ES) of overlying rock. To improve the effectiveness of hydrate exploitation, it is necessary to understand the influence of gas slippage in hydrate reservoirs on the permeability evolution law. For this paper, the gas permeability characteristics and methane production of hydrate montmorillonite sediments were studied at different pore pressures and ESs. Experimental data revealed that the gas permeability of montmorillonite samples before methane hydrate (MH) formation is seriously affected by the Klinkenberg effect. The gas permeability of montmorillonite sediments before hydrate formation is generally smaller than that after hydrate formation, and the gas slippage effect in the sediments after hydrate formation is weaker than that before hydrate formation. With the change in ES, the intrinsic permeability of sediment has a power law relationship with the simple ES. The ES law coefficient n was determined using the response surface method to eliminate the influence of gas slip on gas permeability. As pore pressure decreases and MH decomposes, montmorillonite swelling seriously affects gas permeability. However, the gas slippage effect has a good compensation effect on the permeability of montmorillonite sediments after MH decomposition under low pore pressure. The multistage depressurization-producing process of MH in montmorillonite sediments is mainly 3 MPa depressurization-producing stage and 2 MPa depressurization-producing stage. In this paper, the influence mechanism of gas slippage effect of hydrate reservoir is studied, which is conducive to improving the prediction accuracy of gas content in the process of hydrate exploitation and exploring the best pressure reduction method to increase the gas production of hydrate in the process of exploitation.

Eco-friendly hydrogels serving as water carriers for improving methane hydrate formation and dissociation processes

Natural gas hydrate (NGH) technology has broad application prospects in natural gas storage & transportation. In this work, we used eco-friendly hydrogel-based carriers to retain water, which were biodegradable polyvinyl alcohol-co-acrylic acid (PVA-co-PAA) hydrogels, and to react with methane gas and form hydrates. Results indicated that hydrates could be formed in the presences of swollen hydrogel particles without stirring or promoter adding, which might be owed to the enlarged gas–liquid interface and bulk of hydrophilic groups. When mass ratio of PVA to AA (MR) was 1:4, hydrogels performed best in improving hydrate formation kinetics: the induction time was 20.3 ± 20 min, the hydrate growth rate was 0.0217 ± 0.0088 mmol mL−1 min−1, and the methane uptake was 75.84 ± 4.70 mmol mol−1 water. Morphological observations revealed the water retaining behaviors of hydrogels during hydrate formation-dissociation process: a part of absorbed water transferred out of hydrogels to participate in hydrate formation, and afterwards hydrogels could re-absorbed the water released by hydrate dissociation. Moreover, hydrogels kept excellent recycling performance in seven repeated hydrate formation-dissociation cycles. Collectively, PVA-co-PAA hydrogels used as water carriers could improve mass transfer and reaction efficiency during methane hydrate formation-dissociation process, and meanwhile exhibited good recyclability due to strong water absorbing and retaining capabilities, implying that PVA-co-PAA hydrogels might potentially have broad applications in NGH technology.

Study on formation of methane hydrate in rotating packed bed

Offshore oilfield development process often carries a large amount of associated gas, most of it needs to be emptied or burned, resulting in a large amount of waste and environmental pollution. Hydrate storage and transportation technology has the advantages of simple process treatment, good offshore adaptability, good safety and relatively low investment. It is one of the important recovery technologies for associated gas in offshore oil fields. However, the long induction period of hydrate formation, the difficulty of gas dissolution, and the difficulty of continuous formation hinder the improvement of hydrate formation rate and gas storage density, and hinder the development of hydrate storage and transportation technology. High-gravity technology may be one of the development directions of new hydrate rapid formation reactors due to its small size and high mass transfer capacity. In this paper, a small-scale RPB was designed independently, and the effects of high-gravity factor, initial pressure, and packing type on hydrate formation were assessed by calculating the gas consumption, gas consumption rate, gas storage density, and gas conversion rate of hydrate formation under each experimental condition. The results show that in the range of high-gravity factor and pressure tested in the experiment, the increase of high-gravity factor and pressure can significantly accelerate the hydrate formation rate, which can be increased by up to 177 %, and the maximum gas storage density can reach 148.88 V/V. The type of packing has a strong influence on the rate of hydrate formation, and the principle of packing selection changes when dealing with solid-containing systems, and the rate of hydrate formation can be increased by 20 % with the proper selection of packing type. This study can provide a basis for subsequent high-gravity hydrate experiments and industrial applications.

Molecular dynamics simulation study of the cosine oscillation electric field's effect on methane hydrate growth

Cosine oscillation electric field could be a promising option to fasten methane hydrate formation in pure water. Molecular dynamics simulation was employed to examine the performance of cosine oscillation electric field in the intensity range of (0.5–2.0) V•nm−1 and frequency range of (0.2–1.0) THz. The hydrate growth time and the hydrate growth rate were firstly defined and obtained by calculating the four-body structure order parameter for different systems at different x positions. The results showed that the added electric field with appropriate parameters could promote methane hydrate formation significantly, represented by shorter hydrate growth time and higher hydrate growth rate. In all studied systems, system with 1.5 V•nm−1 intensity and 0.4 THz field intensity was recommended for fast hydrate growth rate, which could be three times higher than that of system without electric field. It was noteworthy that there was an electric field frequency boundary, lower than which the effect of cosine oscillation electric field on methane hydrate formation could be totally different. The electric field frequency boundary for systems with different electric field intensities was identified and fitted with two exponential growth functions.

Methane hydrate efficient formation in a 3D-rGO/SDBS composite.

The optimization of storage space and material composition can significantly improve the generation rate and storage capacity of methane hydrate, which is important for the industrial application of solidified natural gas (SNG) technology. In our report, the effects of the presence of SDBS (sodium dodecylbenzene sulfonate), GO (graphene oxide), 3D-rGO (3D-reduced graphene oxide) and 3D-rGO/SDBS (3D-reduced graphene oxide/sodium dodecylbenzene sulfonate) on the methane hydrate generation process are investigated. The results show that the heterogeneous effect on the solid-phase surface of 3D-rGO/SDBS and its interconnected three-dimensional (3D) structure can achieve rapid nucleation. In addition, the presence of 3D-rGO/SDBS can increase the dissolution and dispersion of gas in solution and further enhance the gas-liquid mass transfer, thus realizing efficient methane storage. The maximum methane storage capacity of 188 v/vw is obtained with 600 ppm of 3D-rGO/SDBS in water, reaching 87% of the theoretical maximum storage capacity. The addition of 3D-rGO/SDBS also significantly reduces the induction time and accelerates the formation rate of methane hydrate. This study reveals that 3D graphene materials have excellent kinetic promotion effects on methane hydrate formation, explores and enriches the hydrate-promoting mechanism, and provides essential data and theoretical basis for the research of new promoters in the field of SNG technology.

Experimental Study of the Influence of Water Mass on the Process of Hydrate Formation by the Method of Explosive Boiling Using Freon 32

The paper presents a study of the effect of the ratio of water and hydrate-forming gas on the process of hydrate formation by explosive boiling of liquefied hydrate-forming gas in a volume of water. Freon 32 is used as a hydrate-forming gas, which has a high specific heat of vaporization, a lower density compared to water, and also forms a hydrate structure with sI. The studied gas looks particularly promising for gas hydrate cold accumulation technologies, as well as for modelling the processes of methane or carbon dioxide hydrate formation.

Investigation of Hydrate Formation and Stability of Mixed Methane-THF Hydrates: Effects of Tetrahydrofuran Concentration.

Effects of tetrahydrofuran (THF) concentration on the mixed methane hydrate formation, dissociation, and stability were investigated. The experiment was conducted at 286.2 K and 6 MPa in a quiescent reactor. The presence of THF below 2.5 mol% did not show the evidence of hydrate formation. However, the concentration above 2.5 mol% enhanced the methane formation rate and the methane consumption. Increasing the THF concentration decreased the induction time as the result of the decrease in the surface tension. Moreover, the methane uptake and formation rate increased with the THF concentration due to the higher degree of hydrate nucleation. The methane recovery after the dissociation experiment showed up to 96%. Furthermore, the hydrate stability increased, and the hydrate dissociation kinetics decreased with the increase in the THF concentration. The optimum THF concentration to enhance and improve the hydrate formation kinetics and stability is its stoichiometric concentration.

Mechanical behaviour and microstructure of methane hydrate-bearing sandy sediment observed at various spatial scales

Methane hydrates (MHs) are considered an alternative energy resource but also a potential source of geo-hazards and climate change. The physical/mechanical properties of gas hydrate-bearing sandy sediments are strongly dependent on the distribution of hydrates within the pore space. The purpose of this study is to investigate morphologies and pore-habits of MHs formed in sandy sediments by means of experiments that probe a wide range of scales, from the pore scale – using Synchrotron X-Ray Computed Tomography (SXRCT) and optical microscopy – to the core scale, through mechanical property measurements. The same synthetic sands are used, in which MHs are generated successively under excess gas and excess water conditions. At the macroscopic (core) scale, MH pore habits are inferred by comparing the measured sonic wave velocities to velocities calculated from rock physics models and further assessed via triaxial compression tests. Furthermore, Magnetic Resonance Imaging is used to investigate the kinetics of MH formation and distribution along the core height. The pore habits and MH morphologies are directly visualized at the pore (grain) scale by SXRCT and, with still better spatial and temporal resolution, by transmission optical microscopy, revealing some more complex morphologies than in the hydrate pore habits commonly admitted.

Methane hydrate formation enhanced by thermally expanded graphite with multi-sized pores

Methane hydrate has been endowed with great potential in energy storage and transportation, but the sluggish formation kinetics restrict its industrial application. Herein the thermally expanded graphite (EG), with multi-sized pore structure that can be effectively controlled by expanding and grinding processes, is used to promote the nucleation and growth of methane hydrates. The results demonstrate that the EG exhibits a remarkable promotion in the formation of methane hydrate from water, with high gas storage capacity of 143 V/V, short induction time of 10 min, and rapid gas storage rate of 1 V·V·min−1, which are attributed to its well-designed multi-sized pore structure. Thereinto, the nano-sized pores can effectively adsorb guest molecules, increasing the guest–host contact area; meanwhile, the micron-sized pores with moderate scale not only provide abundant channels for mass transfer of reactants but also enable good thermal conductivity for heat transfer to soundings. This work provides an insight into the promotion effect of multi-sized porous medium in hydrate formation, and offers an effective strategy for fabricating high-performance promotors through pore designing.

Accelerated formation of methane hydrates in porous metal foams and leucine

Three kinds of porous metal foam, alumnium foam(AF), ion foam(IF) and copper foam(CF), were immersed into the aqueous phase, expecting to increase the equilibrium temperature, accelerate the CH4 hydrates nucleation, reduce the induction time and enhance gas consumption. CF was verified to be an optimal porous medium for CH4 hydrates due to its equilibrium temperature of 279.26 K with an induction time of 66 min around 5.0 MPa, and the accelerated gas consuming rate, showing an excellent thermodynamic-kinetic dual promotion ability. In order to enhance CH4 consumption, 0.3 wt% leucine was added as a kinetic promoter, increasing the CH4 consumption to be around 0.15 mol per mole of water, nearly 3–4 times more than that of pure water and those without leucine.

Kinetics of methane hydrate formation from stirred aqueous NaCl solutions

We experimentally studied the kinetics of methane hydrate formation from stirred aqueous NaCl solutions. The studies were carried out with pure water and aqueous solutions in which the mass fractions of NaCl were 0.2%, 0.5%, 1.5%, 3.0%, 5.0%, and 7.0%. In all our kinetic experiments, there was the same initial mass of liquid water, a similar temperature, and a similar driving force for gas hydrate formation in terms of pressure. Under these conditions, the values of the rate of change in the mass of liquid water during the initial stage of methane hydrate formation from stirred aqueous NaCl solutions were determined. It has been found that if the mass fraction of NaCl in an aqueous solution is less than 1.0%, then methane hydrate is formed more rapidly from this solution compared to pure water, and if the mass fraction of NaCl in an aqueous solution is greater than 1.0%, then methane hydrate is formed more slowly from this solution compared to pure water. It has also been found that the presence of NaCl in an aqueous solution has little effect on the kinetics of methane hydrate formation from this solution. Additionally, we experimentally determined the phase equilibrium points for methane hydrate in the pure water–methane and 3.0 wt% NaCl solution–methane systems.

Enhanced formation of methane hydrates via graphene oxide: Machine learning insights from molecular dynamics simulations

Gas hydrates, with their significant applications in energy and environment sectors, have emerged as promising technologies for gas separation, natural gas and energy storage. The formation of methane hydrates occurs in substrate-contact conditions, where the properties of the substrate surfaces play a crucial role in determining hydrate formation pathways. Herein, the influence of the hydroxyl group (-OH) content on the graphene surface on methane hydrate formation in confined systems using molecular dynamics (MD) simulations with machine learning (ML) technique. The MD results show that increasing the oxidation degree effectively enhances the formation of methane hydrate within the oxidation degree of 10 %–40 %. This enhancement is attributed to the hydrophilicity of the (GO) surfaces. When the oxidation degree reaches 50 %, however, the formation rate of methane hydrates slows down compared to the GO-40 system. This deceleration can be attributed to the formation of dense water layers that adhere to the GO surfaces, resulting in impeding the hydrate formation process. Markov State Model (MSM) is employed to analyze the induction time of GO on methane hydrate formation, highlighting the important role of GO in the formation of methane hydrates. Additionally, an eXtreme Gradient Boosting (XGboost) ML model is developed to predict the formation behaviors of methane hydrates. Ternary water-ring aggregations (TWRAs) are adopted as indicators to understand to the formation behaviors, and the XGboost ML model facilitate the identification of key TWRAs associated with the formation process. This work provides molecular-level insights into the influence of –OH group on formation of methane hydrates, and offers a predictive framework for understanding and characterizing the formation clathrate hydrates in confined systems.