Methane Hydrate Research Articles

Methane hydrate formation between graphene oxide nanosheets: Insights from molecular dynamics simulations

This work focuses computationally on the role of graphene and graphene oxide nanosheets in improving the formation of methane gas hydrate and their potential as a promising alternative to traditional gas storage and transportation method. To evaluate methane gas mechanism storage between graphene and graphene oxide nanosheets including C8O-flat, C8O-polar, and C8(OH)2 surfaces, radial distribution function, mean squared displacement, number of hydrogen bonding, and coordination number were taken under consideration. Our results showed that methane hydrate is well formed between graphene, C8O-flat, and C8O-polar nanosheets. C8(OH)2 nanosheet has an inhibitory effect on the gas hydrate formation caused by the formation of hydrogen bonds between the hydroxyl functional groups of the sheets and water molecules. To further investigate the degree of hydrate formation, a four-body structural order (F4φ) was obtained. The values of the F4φ parameter for the C8O-flat, graphene, C8O-polar, and C8(OH)2 systems are 0.6, 0.55, 0.51, and −0.02, respectively. These values indicate the presence of an almost complete and regular network of methane hydrate between the first three mentioned sheets. However, the negative value of the F4φ parameter in the last one suggests the absence of significant hydrate formation by ice-like structure of water molecules. The effect of different temperatures on the formation of methane hydrate was also investigated. It is observed that the hydrate structure completely breaks down in the range of 300–400 K in the different structures.

Preparation of zwitterionic polymer and its application for dual-functional inhibition in deepwater drilling

During deep-water drilling operations, due to the conditions with low temperature and high pressure in the wellbore, methane hydrate can be easily formed in the presence of methane and plug the wellbore. In addition, the deep-water sediments are dominated by clay-silty with weak cementation, so well instability may be occurred due to clay hydration. In order to inhibit hydrate formation and clay hydration in deepwater drilling, a zwitterionic polymer AADV was synthesized through quaternary copolymerization of AM/AMPS/DMDAAV/VAC. The hydrate inhibition performance of AADV was evaluated in a high-pressure reactor chamber, and the results showed that AADV can delay the hydrate formation time from 330 min in pure water to 2204 min, indicating an excellent inhibition effect of hydrate formation. Meanwhile, 1 % AADV can significantly reduce the linear swelling rate of the calcium-based bentonite to 3.69 % for 10 h and increase the rolling recovery rate to 94.7 %, suggesting an excellent inhibition effect on clay hydration. The mechanism of dual-functional inhibition of AADV was further analyzed. The zwitterionic group in AADV and the hydrophilic amide group can strongly adsorb the water molecules through a strong hydration effect and the hydrogen bonding effect, respectively, which contributes to destroy the water molecules cage structure, and thus to suppress the hydrate formation. Besides, AADV can effectively obstruct mass transfer of methane molecules by increasing the viscosity of the aqueous phase and absorbing on the hydrate surface, leading to hydrate formation inhibition. For the inhibition of clay hydration, the SEM and XRD results proved that AADC inhibits the clay hydration through the film-forming effect. In addition, the contact angle of Na-Bent/AADC composite reached to 55.68° when the polymer concentration increased to 2 %, suggesting that the hydrophobicity of Na-Bent surface can be enhanced after AADC treatment. AADV can wrap around clay particles and form hydrophobic film through adsorption and intercalation, preventing the intrusion of external fluids and inhibiting clay hydration.

On the Significance of Hydrate Formation/Dissociation during CO2 Injection in Depleted Gas Reservoirs

Summary The study aims to quantitatively assess the risk of hydrate formation within the porous formation and its consequences on injectivity during storage of CO2 in depleted gas reservoirs considering low temperatures caused by the Joule-Thomson (JT) effect and hydrate kinetics. Hydrates formed during CO2 storage operation can occupy porous spaces in the reservoir rock, reducing the rock’s permeability and thus becoming a hindrance to the storage project. The aim was to understand which mechanisms can mitigate or prevent the formation of hydrates. The key mechanisms we studied included water dry-out, heat exchange with surrounding rock formation, and capillary pressure. A semicompositional thermal reservoir simulator is used to model the fluid and heat flow of CO2 through a reservoir initially composed of brine and methane. The simulator can model the formation and dissociation of both methane and CO2 hydrates using kinetic reactions. This approach has the advantage of computing the amount of hydrate deposited and estimating its effects on the porosity and permeability alteration. Sensitivity analyses are also carried out to investigate the impact of different parameters and mechanisms on the deposition of hydrates and the injectivity of CO2. Simulation results for a simplified model were verified with results from the literature. The key results of this work are as follows: (1) The JT effect strongly depends on the reservoir permeability and initial pressure and could lead to the formation of hydrates within the porous media even when the injected CO2 temperature was higher than the hydrate equilibrium temperature; (2) the heat gain from underburden and overburden rock formations could prevent hydrates formed at late time; (3) permeability reduction increased the formation of hydrates due to an increased JT cooling; and (4) water dry-out near the wellbore did not prevent hydrate formation. Finally, the role of capillary pressure was quite complex, as it reduced the formation of hydrates in certain cases and increased in other cases. Simulating this process with heat flow and hydrate reactions was also shown to present severe numerical issues. It was critical to select convergence criteria and linear system tolerances to avoid large material balance and numerical errors.

Biogeochemical Reconstruction of Authigenic Carbonate Deposits at Methane Seep Site off Krishna‐Godavari (K‐G) Basin, Bay of Bengal

AbstractActive and relic marine methane‐seep sites are widely distributed globally and are distinguished by distinctive geology, biogeochemistry, and ecosystems. The discovery of methane‐seep sites in the Krishna‐Godavari (K‐G) basin has created exciting new opportunities for methane‐seep research in the Bay of Bengal. In this study, we document the occurrence of authigenic carbonates, including micro‐crystalline aragonite crust (arg‐crusts) admixed with chemosynthetic shells and high‐magnesium carbonate tubular structures (HMC‐tube), from the methane‐seep site SSD‐045/4 in the K‐G basin. The δ13C values of HMC‐tubes (−54.5 to −46.2‰) and arg‐crusts (−57.6 to −34.8‰) indicate biogenic methane as the likely carbon source. Enhanced porewater alkalinity driving carbonate precipitation may be attributed to microbial‐mediated SO₄2−‐AOM processes. Additionally, δ13C values (−35.2 ± 8‰) of the residual organic matter within the carbonates suggest a contribution of methanotrophic bacterial biomass. The δ18Ocarb values of HMC and aragonite indicate methane hydrate degassing and crystallization pathways, respectively. Pelloid‐filled burrows suggest the reworking of shallow HMC deposit by burrowing organisms, whereas the polyphase cementations (aragonite and HMC) within burrows indicate early and burial diagenetic pathways. The wide range in ΣLREE/ΣHREE ratios and Ceanom values in arg‐crusts reflect micro‐spatial variations in redox conditions, likely due to cementation occurring in both open and closed diagenetic systems. In contrast, more constrained Ceanom values and ΣLREE/ΣHREE ratios in HMC tubes suggest persistent sulfidic conditions. Overall, these findings provide insights into the pathways of carbonate formation at the K‐G basin methane‐seep site, highlighting the complex interplay of microbial processes, fluid dynamics, and diagenetic alterations.

Metal plate-based promotion on methane hydrate nucleation: Insights into the influence of metal type and surface properties

Hydrate-based technologies hold significant promise in the fields of gas storage, water desalination and gas separation, but their application is restricted by the long induction time and high degree of randomness associated with hydrate nucleation. In this study, we conducted experimental investigations to access the influence of metal plates (Mg, Al and Zn) on methane hydrate nucleation under both pure water and acidic conditions. The results demonstrated that Mg plate exhibited the strongest promotion effect on methane hydrate nucleation. The presence of acid significantly accelerated hydrate nucleation in the Zn plate system, but conversely reduced the promotion effect of Al plate. In conjunction with the in-situ morphology evolution of hydrate nucleation, methane-liquid–metal interface was found to play a crucial role in the metal-induced promotion effect. Two nucleation modes were proposed accordingly: (i) in pure water, hydrate nucleation initiated exclusively at the methane-liquid–metal interface without extra nucleation site (Mode 1), and (ii) in acidic condition, hydrate nucleation occurred with evident multiple nucleation sites (Mode 2). Furthermore, SEM imaging, AFM and contact angle characterization revealed that the surface properties of metal plate (e.g., hydrophilicity and roughness) were the key factors in determining the effectiveness of the promotion effect. Liquid climbing upward along the metal plate surface was vital for metal plates to promote gas hydrate formation. Overall, this study provides new insights into hydrate nucleation promotion and suggests a straightforward way to enhance hydrate nucleation by modifying surface properties

Study on the dynamic characteristics of rising bubbles under the influence of viscosity based on VOF method

Abstract In order to study the buoyancy-driven rising bubbles in liquids in various types of problems such as oil pipeline transportation, combustible ice mining, ship drag reduction, and the use of bubbles to deliver drugs in blood, this paper establishes a model for the rising bubbles in liquids based on the Volume of Fluid Function (VOF) method, and investigates the change rule of the larger-size bubbles under the influence of viscosity in different viscous silicone oils. It provides theoretical and technical support for various natural and industrial processes such as deep-sea oil extraction and metal smelting.

Synthesis and performance evaluation of polymer-ceramic composite microcapsules as reservoir protectant for natural gas hydrate drilling.

Natural gas hydrate is a promising unconventional natural gas source due to its high energy density and huge global reserves. During exploitation, the drilling fluid may invade the hydrate formation and induce hydrate decomposition, causing reservoir damage. Herein, a novel reservoir protectant made by bio-degradable temporary plugging material (BDTPM) was developed in the form of polymer-ceramic composite microcapsules. As an additive to the drilling fluid, the BDTPM can minimize drilling fluid intrusion by plugging the reservoir during drilling and afterwards maximize permeability recovery by degrading the material. The particle size distribution was in the range of 1-130μm. The optimal mass ratio between modified ceramic particles, ethyl cellulose and epoxy resin was found to be 4:2:1. The plugging rate was 100% when ethyl cellulose and epoxy resin were mixed to coat the ceramic particles to form BDTPM, and the plugging performance was the best. At a temperature close to the typical hydrate reservoir environment (5°C), 0.02 wt% low-temperature complex enzyme can degrade BDTPM, and the permeability recovery rate is 64.66%. The efficient reservoir protectant developed in this work could play an important role in the successful drilling of natural gas hydrate reservoirs.

Experimental studies and pore-scale modeling of hydrate dissociation kinetics at different depressurization rates in a cubic hydrate simulator

Natural gas hydrate (NGH) is a promising energy resource that has triggered a race for scientific innovation in energy and environmental research. However, there still faces the challenges of low-efficiency hydrate dissociation and unstable gas production during the hydrate production. Clarifying the kinetic mechanism of hydrate dissociation is the key to improving the efficiency of “phase-transition to gas-supply” in hydrate-bearing sediment. This study successfully conducts hydrate dissociation experiments with different depressurization rates in the Cubic Hydrate Simulator (CHS). A novel dissociation kinetic model integrating the hydrate pore-scale morphology and its evolutions are established, and the sensitivities of the kinetic and thermal parameters are discussed in detail. The mathematical relationship between the hydrate saturation and reaction area is quantitatively analyzed for the hydrate formation and dissociation kinetics. The history matching simulation with the newly developed model achieves an excellent agreement with the experimental results. The full-lifecycle kinetic behaviors of the hydrate dissociation in the depressurization experiments are finely characterized. It is found that the evolutions of the hydrate saturation (SH) and temperature (T) spatial distributions exhibit strong heterogeneous characteristics in the vessel due to the phase transition and heat transfer effects. In addition, this reveals that the relatively high depressurization rate can lead to a more significant dissociation rate in the depressurization stage. This provides a new reliable and adaptable method for describing the hydrate dissociation kinetics in the porous media.

Study on the formation process of methane hydrates on the surface of wax crystals with pour point depressant

Molecular dynamics simulations were applied to clarify the kinetic pathways and mechanism in the process of methane hydrate formation on the wax crystal surface with ethylene–vinyl acetate copolymer (EVA). The simulation results showed that methane molecules near the surfaces would adsorb on the surfaces of wax-EVA eutectic, while hydrates formed in the bulk of the solution away from the surfaces. The VA side chains on the wax crystal surface inhibit/promote the growth of hydrates by influencing the growth and re-dissolution process of methane nano-bubbles on eutectic surface. When a small amount of VA side chains was introduced on the wax crystal surface, as the simulation proceeded, the generated hydrates would gradually decompose. However, when more VA side chains distribute on the surface of wax crystals, the growth rate of hydrates would increase. In addition, hydrates and wax crystals could connect through a semi-cage structure, in which the VA side chain served as the guest of this semi-cage, making the eutectic and hydrates form a whole and increasing the risk of co-deposition of wax crystals and hydrates.

Thermodynamic and Kinetic inhibition of Methane Hydrate with Organic Inhibitors

The present experimental work reports the impact of ethylene glycol, polyethylene glycol and glycerol on formation temperature, pressure and inhibition time of methane hydrate. The inhibition effects of hydroxyl functional group of inhibitors have been studied. It is evaluated in terms of temperature, pressure and induction time. Methane hydrate equilibrium temperature and pressure is also studied. Experimental results disclose that ethylene glycol is a strong candidate to hinder methane hydrate thermodynamically while glycerol is good competitor to discourage hydrate formation in both terms kinetic hindrance and thermodynamic hindrance.

Gas hydrate inhibition by urea and its blends with vinyl lactam polymer: Paving the way to green hybrid inhibitors

Urea is an environmentally benign substance considered a promising gas hydrate inhibitor in flow assurance. Nevertheless, its effect on gas hydrate formation kinetics remains poorly understood. This study investigates the impact of urea and hybrid urea/polymer KHI samples on the nucleation and growth kinetics of sII natural gas hydrates. Hydrate formation was observed at a lower onset temperature with increasing urea and polymer concentration. The nucleation of sII hydrate in aqueous urea solutions occurred at a higher subcooling (7.50 ± 0.58 K at 30 mass%) than in pure water (5.17 ± 0.69 K). These findings indicate that urea acts as a nucleation inhibitor of sII hydrates, although its capacity is not as potent as that of polymer KHI.The analysis of the hydrate nucleation probability distributions revealed that the sII hydrate nucleation rate exhibited a significant decline, approximately one order of magnitude, at subcooling of 5.3–6 K for 20 mass% urea compared to water. A similar behavior was noticed in an aqueous solution of polymer KHI. Urea has succeeded in providing a total benefit of up to 10 K in hydrate onset temperature due to a shift in the hydrate stability zone and nucleation retardation.Consequently, urea is a green dual-acting anti-hydrate chemical that inhibits the formation of sII hydrates by thermodynamic and kinetic mechanisms. Besides, adding 10 mass% urea increases the cloud point temperature of vinyl lactam polymer Luvicap 55W by 14 K. Urea is an additive that considerably augments the stability of the polymer in aqueous solutions at elevated temperatures. These findings make urea an effective and environmentally friendly top-up inhibitor that significantly enhances the anti-hydrate properties of polymer KHI.

Development and Evaluation of Insulation Materials for Deepwater Cementing.

Marine oil and gas resources are abundant in deepwater regions, where the shallow seabed harbors natural gas hydrate layers due to the cold temperature and high-pressure environment. Hydrates are prone to thermal decomposition, which can compromise the integrity of cement sealing and even lead to accidents like blowouts. While current low-hydrated heat cement systems mitigate hydrate decomposition from cement hydration heat during the waiting period for cementing, they do not address heat transfer from deep strata to shallow hydrate layers through fluid circulation in the tubing during deep oil and gas development. Rather than utilizing costly pipe insulation technology, adjusting the thermal conductivity of well cement emerges as a cost-effective approach to prevent heat loss in the wellbore to the hydrate layer and thus inhibit hydrate decomposition. The critical aspect lies in utilizing insulation functional materials. This study delves into the functional and structural design of insulation materials suitable for cement slurry systems in well cementing, outlining the preparation methods and processes for two insulation materials (SDBW and SDBW-II) tailored for deepwater well cementing. SDBW and SDBW-II are both nuclear shell structural materials. The core is made of high-strength hollow microspheres, produced by using a reverse suspension polymerization method to form spheres followed by high-temperature sintering. The shell consists of a wear-resistant BPA epoxy resin layer, with the surface of SDBW-II also containing highly reflective glass microspheres. Incorporating 20% of material SDBW into the cement reduces the thermal conductivity of the cement stone from 0.8 to 0.31 W·(m·K)-1 while achieving a compressive strength of 6 MPa after 24 h at 20 °C. Material SDBW-II offers both thermal resistance and reflection functions, increasing reflectivity (R) from 0.3 to 0.5. By adding 20% of this material to the cement, under the same conditions, although the compressive strength decreases to 4.2 MPa, the thermal conductivity can be reduced to 0.27 W·(m·K)-1. Furthermore, there is no significant change within 180 days, demonstrating long-term thermal insulation stability. These developed insulation materials can effectively improve the thermal insulation performance of the cement sheath, thereby maintaining the stability of the upper natural gas hydrate layer in the oil and gas production process of deepwater wells, providing an innovative solution for the long-term operation of deepwater oil and gas wells.

Kinetics of methane hydrate formation in a 1200 ml unstirred reactor for natural gas storage

Solidified natural gas (SNG) technology via clathrate hydrates, enhanced by promoters such as tetrahydrofuran (THF), promises large-scale natural gas storage due to its high volumetric capacity and mild storage conditions. Despite its potential for industrial scale-up, limited research exists on methane hydrate formation behaviors in large reactors (>1000 cm3), which is crucial for evaluating practical storage performance. In this study, methane hydrate formation kinetics were investigated in a scaled-up unstirred reactor (1200 cm3) at 288.15 K and 283.15 K, and 5.0 MPa. Methane uptake, system pressure, gas and liquid phase temperatures, and hydrate morphologies were analyzed to describe the dynamic hydrate formation process. Results reveal three effects of increased reactor size in contrast to smaller reactors: (i) heterogeneous distribution of THF-rich and methane-rich hydrates; (ii) hydrate bulk show a hollow inner structure with a cavity due to the wall-climbing behavior of hydrate growth; (iii) optimal THF concentration no longer always agrees with stoichiometric 5.56 mol%, which is case-dependent. These effects are attributed to higher diffusion resistances for methane molecules and more intensive heat accumulation. These findings provide some insight into the kinetics of methane hydrate formation in industrial reactors, which is critical for the commercialization of SNG technology.

Parameters Variation of Natural Gas Hydrate with Thermal Fluid Dissociation Based on Multi-Field Coupling under Pore-Scale Modeling

Parameters Variation of Natural Gas Hydrate with Thermal Fluid Dissociation Based on Multi-Field Coupling under Pore-Scale Modeling

Non-steady flow decomposition behaviors of heat and mass transfer on intrinsic kinetics for methane hydrate particles transported in pipelines

The differential equations governing the decomposition rate and activation energy, convective mass transfer, methane diffusion and fugacity, as well as heat conduction and enthalpy change were derived by integrating thermal convection, heat conduction, mass transfer and intrinsic kinetics. Mathematical models for decomposition kinetics and thermodynamics in a non-steady field were solved using a radial logarithmic grid for node division and discretization of the equations. The study elucidated the heat and mass transfer processes as well as decomposition kinetics in pipelines by analyzing the impacts of particle size, temperature, pressure, flow rate and activation energy on decomposition rate. The results indicated that compared with the isothermal decomposition of the intrinsic kinetic model and static experimental decomposition, the complex non-steady multiphase flow model offers a more accurately simulation of hydrate decomposition as well as associated heat and mass transfer processes. Hydrate decomposition is characterized as a non-isothermal dynamic ablation process with heat transfer rate and intrinsic kinetics dominating during the preliminary stage and the stable stage, respectively. An increasing in the slurry temperature, temperature fluctuation and flow rate accelerated the heat transfer rate capacity, enhanced convective heat transfer capacity and facilitated hydrate decomposition, with the mass transfer rate exhibiting lesser influence. The particle surface area and slurry temperature exhibited the most significant influence on hydrate decomposition, which was followed by flow rate. Upon increasing particle size from 1 mm to 5 mm and the temperature from 293 K to 313 K, the decomposition rate increased by 20.7 times and 13.5 times, respectively. Furthermore, enhancing temperature and flow rate while decreasing particle size and pressure decreased both the decomposition time and the duration required for the decomposition rate to reach its peak. Additionally, the decomposition rate and its constant vary with the activation energy.

Insight into the micro-mechanism of hydrate-based methane storage from active ice

Gas hydrate formation in active ice holds significant potential for solidified natural gas storage, while the deep understanding of its micro-mechanism is required for the futural application of such a technology. In this study, the kinetics and micro-properties of methane hydrate formation enhanced by active ice (porous ice containing an unfrozen solution layer of sodium dodecyl sulfate) were investigated via experiments and molecular dynamics (MD) simulations. Raman spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray diffraction (XRD) differential scanning calorimetry (DSC) characterization, and in-situ visual observation confirmed the formation of sI methane hydrate in the active ice system and the occurrence of single-crystal hydrate, and also indicated the occurrence of active water near the surface of porous active ice during the active ice formation. A sensitivity analysis of the hydrate kinetics experiments suggested that temperature is the primary driver of rapid methane hydrate formation in the active ice system. The shortest induction time and t90 for hydrate formation were recorded at 5 s and 5.5 min, respectively. Furthermore, MD simulations indicated that the direct hydrate nucleation and growth in the active water, heat transfer from gas hydrate to ice, and the diffusion of active water (1.24 × 10-9 m2/s) and methane (7.10 × 10-8 m2/s) into the porous ice structure are the primary mechanism that enhances hydrate formation kinetics and methane storage capacity. This work provides an essential microscopic mechanism of the “active ice → active water → gas hydrate” circulation that contributes to the deep understanding and futural application of the efficient hydrate-based solidified methane storage in active ice system.

Hydrates production with gaseous CO2/C3H8 and CH4/C3H8 (90/10 vol%) mixtures and definition of the role of propane during CO2/CH4 replacement processes

Within the range of temperatures suitable for CO2/CH4 replacement, propane can form hydrates at widely milder conditions than those required for methane and carbon dioxide hydrates. Recent studies proved that the addition of minor quantities of propane to carbon dioxide strongly enhances replacement process, both in terms of methane recovery and carbon dioxide storage. At the same time, the capture of propane remains limited, even if the thermodynamic conditions are widely suitable for its capture. This study experimentally provided a coherent explanation of such a process. Hydrates were formed and dissociated on a lab-scale reactor with binary mixtures containing 90 vol% of CO2/CH4 and 10 vol% of C3H8; the results were compared with the phase equilibrium conditions of the pure species, obtained with the same procedure. The promoting/inhibiting effect of propane on the forming system was quantified and explained in terms of typology of hydrate structure formed and cage occupancy. Based on the results achieved in this study, the replacement mechanism, in presence of propane, was finally characterized and compared with the results obtained when replacement was carried out with the same procedure but with pure carbon dioxide and CO2/N2 mixtures.

Experimental Study on the Transport Behavior of Micron-Sized Sand Particles in a Wellbore

In the process of natural gas hydrate extraction, especially in offshore hydrate extraction, the multiphase flow inside the wellbore is complex and prone to flow difficulties caused by reservoir sand production, leading to pipeline blockage accidents, posing a threat to the safety of hydrate extraction. This paper presents experimental research on the migration characteristics of micrometer-sized sand particles entering the wellbore, detailing the influence of key parameters such as sand particle size, sand ratio, wellbore deviation angle, fluid velocity, and fluid viscosity on the sand bed height. It establishes a predictive model for the deposition height of micrometer-sized sand particles. The model’s predicted results align well with experimental findings, and under the experimental conditions of this study, the model’s average prediction error for the sand bed height is 12.47%, indicating that the proposed model demonstrates a high level of accuracy in predicting the bed height. The research results can serve as a practical basis and engineering guidance for reducing the risk of natural gas hydrate and sand blockages, determining reasonable extraction procedures, and ensuring the safety of wellbore flow.

Quantum Chemical Molecular Dynamics Simulations for Methane‐Water Cages

ABSTRACTThe dynamic stability of various methane‐water clathrate‐like cages (CH4@(H2O)n, n = 16, 18, 20, 22), has been analyzed explicitly considering thermal effects by means of ab initio M06‐2X/6–31+G*/PCM calculations, which make use of Gaussian basis functions. Starting from the equilibrium filled cage structures, classical, dynamic reaction coordinate (DRC) on the Born–Oppenheimer surface, and semiclassical, Born–Oppenheimer plus harmonic zero‐point energy surface (BOMD), molecular dynamics have been carried out. Water molecules have a high tendency to orient covalent O–H bonds tangentially to the hydrophobic surface, thus clathrate‐like arrangements are an acceptable model to fully hydrate methane. If the cage size is such as to minimize core repulsion, due to electron cloud overlap, and to maximize host–guest van der Waals attractions, the clathrate‐like structures have a life‐time of two picoseconds in classical DRC simulations. The inclusion of quantum kinetic energy in BOMD simulations results in less structured cages with a reduced amount of hydrogen bond network. The preferential tangential orientation of the O‐H bonds is largely maintained, although few of them point toward the methane for a very short time in BOMD simulations. The reduced configurational space of water molecules hydrating hydrophobic moiety is highlighted, thus any satisfactory molecular modeling has to account for it.

Synergistic effect of alcohol polyoxyethylene ether sodium sulphate and copper foam on methane hydrate formation

AbstractNatural gas is the cleanest fossil energy source and its consumption is increasing rapidly, so an efficient natural gas way of storing and transporting is urgently needed. Solidified natural gas (SNG) technology is gaining traction because of its higher safety, lower cost, and flexible storage and transportation modes. To improve the methane uptake rate in SNG technology, this work investigated the growth of methane hydrate in fatty alcohol polyoxyethylene ether sodium sulphate (AES) solution with the addition of three different pores per inch (PPI) of copper foam (CF). The results showed that the addition of AES caused the hydrate to grow upwards along the wall, and the methane uptake in the 300 ppm AES solution was increased by 623% compared to pure water. CF not only provided more nucleation sites for hydrate but also transferred the heat generated during hydration. Moreover, there was a synergistic effect between AES and CF and the solution could continuously transport upward along the continuous metal skeleton to increase the gas–liquid contact area. Thus, the formation rate and induction time of methane hydrate improve. Hydrate had the highest methane uptake in the 20 PPI CF system and the lower the pressure, the greater the ability of CF to promote hydrate formation. The methane uptake improved by 27.6% and the induction time was reduced by 59.7% compared to the pure AES system at 6 MPa. This work is aimed at advancing SNG technology (especially at low pressure) and informs the theoretical foundation.