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• An anisotropy of gas hydrate growth was in-situ characterized through X-ray technique. • Themotactic habit of hydrate growth towards a low temperature region was proposed. • The hydrate morphology can be controlled via regulating the heat transfer scheme. Promoting hydrate formation kinetics is considered a major challenge hindering the application of hydrate-based techniques. Surfactants are thus widely used for a better gas solution and water conversion. Yet significant issues involving an uncontrolled morphology and foaming are encountered. In this work, a unique anisotropic behavior of gas hydrate formation was identified through in-situ X-ray technique with the rate of vertical growth 5 times higher than the lateral. This was ascribed to the varying driving force of hydrate nucleation at the wall surface where the reaction heat could be more easily dissipated. Consequently, a thermotactic habit of gas hydrate growth was proposed: the nucleation and growth would preferentially proceed towards a low temperature region to release the reaction heat. Hence through regulating the temperature and thereby the heat transfer scheme one can design the behavior and morphology of hydrate formation. Specifically, a surprisingly fast hydrate formation was observed when freezing the surfactant-containing solution prior to warming-up and pressurization. The melting ice consuming large amount of heat enabled a sequential transformation of water into hydrate tracing the thawing front. This thermotactic behavior was also consolidated in a more macroscopic process. The findings could provide new insights into the kinetics of gas hydrate formation coupling the heat-associated phase transition; the results could also be of help in the up-scale of the hydrate-based techniques where a concentrated transformation is highly required. [ABSTRACT FROM AUTHOR]

• Presence of fine particle could block the pores and hinder gas production. • Water content determines the behavior of fine particle aggregation. • Distribution pattern of fine particles directly affects the gas production efficiency. Natural gas hydrates are widely distributed in silty marine sediments containing fine particles less than 75 μm in size. The effects of WC (water content) on the behavior of fine particle migration and their role in gas and water production do not appear well understood. This work found that the WC slightly affected the gas production pattern in uniform sandy reservoirs. Yet upon a mixture of coarse and fine particles, the fine particles would instantly aggregate at the nearby pore throat reducing the reservoir permeability and prolonging the production by more than 3 times. Surprisingly, 16% of the fine particles at the edge and 19% at the middle were found to migrate with the fluid flow upon increasing water content, resulting in a less hindered initial gas production but a following more complete blockage or even production failure. This behavior can be consolidated in the scenario of a sand-kaolin mixture. The findings could provide new knowledge on the particle migration behavior upon gas and especially water production and guide the strategy design on dealing with the sand problem in the field test. [ABSTRACT FROM AUTHOR]

• Aerogels with tunable surface properties significantly promoted hydrate formation. • C O and –OH were found to dominate nucleation and growth of hydrate. • The finely tuned oxygen-containing groups lead to the enhanced kinetics. • Aerogels exhibit high storage capacity and excellent cycling stability. • Aerogels can be prepared in a large scale for hydrate-based applications. Gas hydrate, composed of water molecule cages, is promising for safe and sustainable gas storage with minor energy consumption. However, the practical utilization of hydrate-based technologies is hindered by the sluggish formation kinetics of gas hydrate. Central to the challenge of utilizing hydrate-based gas storage is developing effective promoters and improving the understanding of the complicated interplay between a promoter's structure and chemical composition. Herein, we reported a simple and scalable strategy to produce pyrolytic composite aerogels assembled from vermiculite nanosheets and sodium alginate as efficient promoters for the methane hydrate formation. Benefiting from the high specific surface area and finely tuned surface functional groups, the as-made aerogels significantly improve methane hydrate formation kinetics with high storage capacity and excellent cycling stability. It is found that the phase change process of water to methane hydrate conversion can be controlled by adjusting the content of carbonyl and hydroxyl groups of the as-made aerogels. Raman spectra were used to elucidate the molecular mechanisms for the enhanced methane hydrate formation due to the interaction between oxygen-containing surface functional groups and water molecules close to used aerogels. This work not only provides an effective way to fabricate aerogel-based promoters for methane hydrate formation but also sheds light on the underlying mechanism of the surface composition dependent performance for improving gas hydrate formation. [ABSTRACT FROM AUTHOR]

Schematic diagram for N 2 /CO 2 gas enrichment process during hydrate growth process. Blue sticks and spheres: N 2 in the gas phase; yellow spheres: CO 2 in the gas phase or hydrate phase; red sticks: hydrate seeds. [Display omitted] • Proper subcooling can improve the hydrate growth rate and final occupancy of CO 2 molecules. • Mass transfer process could impact the hydrate growth rate, with a higher pressure improving the concentrations of N 2 and CO 2 in the free water. • Higher pressure decreased the selectivity of CO 2 for 51262, and lower subcooling assisted CO 2 in entering 51262 cages easily. The climate system is changing and becoming warmer due to the consumption of fossil energy, which results in a large quantity of CO 2 emitted into the atmosphere. The hydrate formation process can encapsulate guest molecules in hydrate cages, enabling a promising storage of CO 2 in the form of hydrate under the seafloor. Here, we performed molecular dynamics (MD) simulations to validate the hydrate-based gas storage method for low-concentration flue gas. The direct phase method was applied at four target pressures to obtain the melting temperature of mixed gas hydrate in the presence of SI hydrate seeds that are fully occupied by CO 2 molecules. Hydrate growth simulations showed that a proper subcooling can improve the hydrate growth rate and final occupancy of CO 2 molecules in newly formed hydrate cages. The mass transfer process could impact the hydrate growth rate, with a higher pressure improving the concentrations of N 2 and CO 2 in the free water. This enhanced the hydrate growth at both 260 K and low subcooling temperatures. The influence of pressure and subcooling on cage selectivity presented a different tendency for CO 2 and N 2. A higher pressure decreased the selectivity of CO 2 for 51262, and lower subcooling assisted CO 2 in entering 51262 cages easily. Interestingly, the CO 2 occupancy at 260 K is larger than that of the simulations at the melting temperature. The results could be of help in revealing the behavior of case filling during hydrate formation from a gas mixture. [ABSTRACT FROM AUTHOR]

• Observed hydrate formation of pure water system in fully visual flow loop. • Analyzed the effect of wet agglomeration on hydrate in flow. • Proposed hydrate formation to blockage conceptual model in pure water system. • Developed two machine learning hydrate blockage prediction models. Gas hydrate blockage is a major challenge in flow assurance. The mechanisms underlying hydrate formation and blockage are still not well understood, and appropriate forecasting methods are needed. In this study, using a high-pressure fully visual flow loop to simulate multiphase flow conditions, hydrate formation and blockage were evaluated in a pure water system. The effects of liquid loading and pump speeds on the pressure difference and water conversion rate were investigated. Three regions and two critical transition points (i.e., "action point" and "blockage point") in the hydrate formation process were defined. Based on analysis, it is believed the wet agglomeration results in increased pressure difference and hydrate blockage. An underlying mechanism in the pure water system was proposed. By applying machine learning methods, two prediction models for hydrate blockage were established, with accuracies of 99% and 71%, respectively. Data-driven machine learning models with high flexibility could be an effective method for hydrate blockage management in future. [ABSTRACT FROM AUTHOR]

Conceptually a new method to promote rapid nucleation and growth of hydrates was proposed and investigated to deal with the existing condition of complex hydrate growth and nucleation. It is based on self-circulation of tetrafluoroethane boiling-condensation process in enclosed water volume. Under this cyclic system, hydrate formation interface increased from two to four, which included the water–gas tetrafluoroethane, water–liquid tetrafluoroethane, water–bubble, and water–droplet interfaces. A number of nucleation sites provided by bubbles and droplets accompanied by energy disturbance effectively strengthened the hydrate nucleation. Thus, the accumulation of hydrates can be completed efficiently and rapidly by an order of magnitude at non-additive and non-mechanical conditions. The experimental results indicate that 1.703 mol of hydrate was generated within 35 min, and the rate of hydrates increased by 4000 times. Furthermore, the hydrate reformation presented a different nucleation and growth morphology and promoted the hydrate conversion amount. The experiments also obtained the optimum hydrate formation condition by comparing the hydrate conversion amount and induction time at different circulating water bath temperatures and thermal stimulation temperatures. Thus, the new method of boiling–condensing has greatly accelerated the application of gas hydrates in cold storage, seawater desalination, and gas separation. • A rapid hydrate nucleation and growth method was developed by boiling–condensation. • The formation rate of hydrate increased nearly 4000 times at 2.919 mol/h. • Hydrate-forming interfaces increased by an order of magnitude. • The boiling-condensation cycle can be applied to hydrate production efficiently. [ABSTRACT FROM AUTHOR]

There have been several field tests worldwide to recover natural gas from marine gas hydrate reservoirs. The resulting intrinsic characteristics of the sediments are recognized as the major challenge hindering the large-scale gas production; of particular interest is the heterogeneous spatial distribution of natural gas hydrates in the sediments. Open issues still remain on mimicking the locally varying reservoir and revealing its role in the production process. Here in this work, reservoirs with a heterogeneous distribution of gas hydrates were prepared by controlling the uneven distribution of moisture in the fine natural sediments drilled from the South China Sea; special interest was put in the effects of the well location and depressurization schemes on the gas production performance. The results showed that the production efficiency in the heterogeneous reservoirs was significantly weakened compared with the homogeneous case; this was ascribed to the ununiform distribution of methane hydrates and pore fluids and a resulting locally different energy demand. Consequently, the production behavior showed a strong dependence on the depressurization location. A wellbore arranged in the layer with a high permeability can help improve the gas production efficiency by up to 38.25%. This yet resulted in an uneven temperature distribution; the rapid gas production and methane hydrate dissociation decreased the reservoir temperature to −3.33 °C. Further applying a cycling and step-wise depressurization could raise the minimum reservoir temperature up to 1.12 °C. Whereas, relieving temperature decline only through consuming the sensible heat in the reservoir and the surroundings was found to seriously weaken the gas production rate; an external heat supply was thus suggested in the hydrate-abundant regions for efficient gas production. Our findings expand the understanding of the spatially varying gas production behavior from the vertically heterogeneous hydrate-bearing fine marine sediments and may guide the operation of well location and depressurization schemes for field production in similar reservoirs. [Display omitted] • Heterogeneous hydrate samples were prepared by unevenly distributing the moisture. • Production behavior from the vertically heterogeneous hydrate reservoir was studied. • The optimized wellbore location would increase the production efficiency by 38.25%. • Heat supply was suggested in the hydrate-rich area to compensate the sensible heat. [ABSTRACT FROM AUTHOR]

• The long-term joint production from hydrate and shallow gas layer provides a 4.1 times enhancement of the cumulative gas yield. • The regulated layer-dependent scheme effectively alleviated the interbedded pressure difference by ∼70%, avoiding the interlayer instability. • An energy return on investment (EROI) analysis was carried out to evaluated the optimized joint production method. Recent field tests to recover natural gas from marine gas hydrate reservoirs in Japan and China have exhibited worldwide attention to this strategic energy form; significant challenges still remain in improving the accumulative gas yield for a better economic efficiency. According to the geological survey in marine hydrate reservoirs, there exists a concomitant free gas layer underlying the gas hydrate reservoir. Consequently, here we propose a new scheme to jointly produce the gases from hydrate layer and its underlying shallow gas layer. It was found that a dual horizontal well deployment respectively in the corresponding two layers could contribute to a 4.1 times cumulative gas yield comparing that of a single vertical well scenario. This implies a remarkable enhancement of gas productivity via making full use of the gases in the shallow gas layer. Notably, a potential risk of interlayer failure could occur upon the great interbedded pressure difference (maximum 10.7 MPa) arising from the varying behavior of pressure propagation in the layers. This can be effectively alleviated by separately controlling the depressurization scheme in different layers; a mild step-wise depressurization was suggested in the more permeable shallow gas layer while the hydrate layer with a lower permeability should experience a sharper pressure drop. This was found beneficial reducing the interbedded pressure difference by about 70% without intervening the gas production. An energy return on investment (EROI) analysis showed a promising positive energy harvest of our optimized layer-dependent pressure scheme. It could be therefore a potential method to be applied in the field tests in the South China Sea to improve the economic efficiency without disturbing the reservoir stability. [ABSTRACT FROM AUTHOR]

Figure TOC Comparison of methane hydrate nucleation process (a) without or (b) with EG molecules. Critical nucleus size increase under the influence of Thermodynamic hydrate inhibitors. [Display omitted] • Hydrophobic groups from the alcohols could approach the initial hydrate cages and destroy initial clusters. • The –OH groups were observed to form hydrogen bonds with the cage clusters and even initiate a new hydrate cage. • Alcohols can increase the critical nucleus size of gas hydrate. Thermodynamic inhibitors are intensively used in oil and gas pipelines to modify the formation conditions of gas hydrate, preventing the blockage of pipelines. However, their kinetic performance in hydrate nucleation is largely unclear. Herein, the molecular interactions of the small molecules of ethylene glycol and methanol with hydrate clusters were investigated. It was found that the hydrophobic groups from the glycols could approach the initial hydrate cages, thereby constricting the regional distribution of adjacent water molecules; thus, they functioned in the same way as the guest molecules that transiently helped to stabilize the water framework. However, these glycols would eventually dissolve into the solution to stay at the water/nanobubble interface; this would consequently destroy the initial cages upon losing the constraint from the surrounding hydrophobic molecules. In addition, the –OH groups were observed to form hydrogen bonds with the cage clusters and even initiate a new hydrate cage; however, they cannot stably reside there due to different atom coordination. Notably, these glycols can increase the critical nucleus size, which is considered the intrinsic mechanism of thermodynamic inhibition. Our results provide atomistic insights into the performance of glycols in the kinetic nucleation of gas hydrates and can help understand the interactions between guest and host molecules in the presence of hydrophobic and hydrophilic functional groups. [ABSTRACT FROM AUTHOR]

[Display omitted] • A magnetically recoverable nanoparticle inhibitor was synthesized. • The induction time with inhibitors was 3 times longer than pure water case. • The inhibitors exhibit good cycling performance and magnetic separation efficiency. • The inhibition mechanism based on in-situ Raman was proposed. Current schemes dealing with hydrate blockage problems in gas pipelines suffer a high dosage of inhibitors and thus are associated with a significant risk of environmental damage. Overcoming these issues requires the development of novel recoverable inhibitors with persistent cycle performance. In this work, a new approach involving coating poly(vinylcaprolactam) (PVCap) and poly(vinylpyrrolidone) (PVP) onto the surface of γ-methacryloxypropyltrimethoxy silane (MPS)-modified Fe 3 O 4 nanoparticles was proposed; this procedure enables the magnetic recovery of the inhibitory particles. It was found that the onset time of hydrate formation was extended 3 times compared to pure water with the help of the synthesized inhibitors showing better performance than commercial inhibitors. Excellent magnetic separation from sandy matrices in solution was achieved with a recovery efficiency of 86%. This was followed by a good cycle performance: the induction time remained still over 2 times longer than the pure water case after 5 cycles of recovery. The in-situ Raman spectra revealed that the recyclable inhibitors functioned through disturbing the construction of the large cages; a resulting mechanism was proposed with nanoparticles isolating the early hydrate patches preventing their further explosive bulk growth. In addition, the simple synthesis method makes it possible to coat various polymer inhibitors onto recovery particles. The results indicate that magnetically recovering the inhibitory particles and reusing them to hinder hydrate generation could be an alternative method to tackle the environmental and economic problems associated with current flow assurance procedures. [ABSTRACT FROM AUTHOR]

Self-assembly of two-dimensional (2D) nanosheets into three-dimensional (3D) aerogels, can solve the problems of recovery and re-stacking, and fully utilize the potential of high specific surface areas and easily accessible surface sites. However, organic binders have to be added to fabricate aerogels using 2D nanosheets as building blocks, which inevitably limit the performance of 2D nanosheets due to covered surfaces. Herein, we proposed a new strategy to fabricate vermiculite aerogels (VAs) assembled from delaminated vermiculite nanosheets (VNSs) via metal ion induced fast gelation. The cheap and earth-abundant vermiculite was used as the raw materials to produce high-quality nanosheets by high speed shear-mixing. VNSs with a concentration as high as 15 mg/mL were produced. The concentration-dependent gelation performance was studied and showed a critical concentration of 6 mg/mL for gelation and fabricating monolithic aerogels without cracks. It is also found metal ions played critical roles in formation mechanically stable and robust aerogels with trivalent cations, particularly Al3+ being most effective. The edge-surface intertwining VNSs induced by the Al3+ cross-linking endow the VAs good mechanical strength and excellent environmental stability. As fixed adsorbent beds, the VAs show promising performance in fast removing organic dyes from water due to the developed pore structures, large specific surface area, and exposed surface sites. [Display omitted] • Vermiculite aerogels were successfully assembled using a fast and scalable method. • Both nanosheet concentration and the ion type play critical roles in gelation. • Vermiculite aerogels have shown excellent performance in removing organic dyes. [ABSTRACT FROM AUTHOR]

Highlights: [•] The ultrasound had enhanced removal capacities for CODCr and nitrogen. [•] The removal efficiencies of nitrogen were inversely proportional to C/N ratios. [•] The C/N and ultrasound could influence the distribution of microbial populations. [Copyright &y& Elsevier]

• 3D morphologies and time-dependent parameters of the hydrate shell are obtained. • Water is more mobile than gas in hydrates in the diffusion-controlled growth stage. • Protrusions growth on the outer surface of a hydrate shell is due to water permeation. • Effective diffusion coefficients of gas and water in hydrate are determined. Understanding the transport properties of water and guest molecules in dense hydrate structures is pivotal in controlling their formation and stability; this is nevertheless hindered by challenges in characterizing the time-varying diffusion and permeation process. This paper reports experimental results on the mass-transfer characteristics of water and guest molecules across hydrate shells during their formation from water droplets. The time-dependent 3D morphologies and parameters of hydrate shells were in-situ obtained via X-ray computed tomography to reveal the transport mechanism in hydrates. It was found that in the mass-transfer-limited stage, hydrate growth occurred primarily at the hydrate-gas interface, indicating a more mobile characteristic of water molecules in those hydrate shells than gas. The resulting outward permeation of water led to the growth of hydrate protrusions on the outer surface of the hydrate shell, suggesting a transition of the water transport schema through the hydrate shell from diffusion to permeation. Consequently, a diffusion-based shell growth model was developed to quantify the diffusivity of gas and water molecules in hydrates. Combining the measurements in the temperature range of 275.15–283.15 K, the effective diffusion coefficient of gas through the hydrates was estimated to be in the range of 1.34 × 10−14 − 1.90 × 10−13 m2/s, with that of interstitial water in the range of 2.87 × 10−12 − 3.83 × 10−11 m2/s. These results are of fundamental value in developing an improved understanding of the kinetics of hydrate formation from gas-water interfaces, which is essential in the optimization of hydrate-based techniques. [ABSTRACT FROM AUTHOR]

[Display omitted] • Amorphous clusters could act as mass transfer barrier for solutes. • CO 2 molecules can replace methylene blue residing in the cage. • Chloride ions can participate in cage building during the exclusion process. Hydration-based techniques involve hydrate formation in complicated systems containing ions and organics. Consequently, it is necessary to understand the molecular behavior of hydrate nucleation and growth in such solutions. This work shows that the hydrate-growth rate in a system containing methylene blue molecules does not necessarily accelerate on increasing the subcooling. Unexpected amorphous cage clusters were observed at a lower temperature of 240 K. To the best of our knowledge, this is the first study to propose that these amorphous clusters act as mass transfer barriers disturbing the agglomeration of solutes. Herein, hydrate growth was accompanied with the exclusion of methylene blue molecules. Although methylene blue can instantaneously reside in the cavity a half-cage structure, they were subsequently replaced by CO 2 molecules. Notably, chloride ions were observed to participate in cage building (42510, 512, and 51262 cages) by bonding with the oxygen atoms of the surrounding water molecules. This phenomenon shows an interaction between the methylene blue molecules and hydrate cages during the exclusion process. These results support the current understanding on hydrate formation in the presence of ion-containing organics and could help improve kinetics-dependent applications in separation process. [ABSTRACT FROM AUTHOR]

• The micro-nano bubbles shorten the induction period of methane hydrate nucleation. • The nucleation rate of methane hydrate increased by 4.73 times. • Micro-nano bubbles of guest molecules with milder phase equilibrium conditions have more advantages in promoting methane hydrate nucleation. • The concentration of micro-nano bubbles affects the memory effect of hydrate, and the memory effect disappears when the concentration of micro bubbles decreases by 73.5%. Hydrate technology has significant application potential in the fields of phase-change cold storage, seawater desalination, gas separation, etc. The key factors influencing the development of hydrate technology are the reduction in the induction time and the promotion of nucleation and growth of hydrates. Micro-nano bubbles (MNBs) can significantly increase the nucleation rate of hydrates owing to their advantages of increasing the gas–liquid interface, enhancing mass transfer, and providing sites for nucleation. In this study, a visualization experimental system for in situ hydrate formation promoted by MNBs was developed. The induction time and the nucleation rate of methane hydrate under the action of MNBs, and the influence mechanism of different guest molecule bulk MNBs on the induction time of methane hydrate were studied. Furthermore, the effects of hydrate formation with injection of bulk MNBs and the reformation with dissociation solution were compared, and the mechanism of bulk MNBs on the memory effect of hydrates was analyzed. The results show that under the action of bulk MNBs (size 80–240 nm), the average induction time of hydrate nucleation is reduced by 80.9%, and the average nucleation rate is increased by 4.73 times. At the same time, by comparing the bulk MNBs of different guest molecules (CH 4 , N 2 , CO 2 , R134a), it was found that R134a has relatively mild phase equilibrium conditions and is easier to nucleate, which has an enhancement effect on the nucleation of methane hydrate. Finally, compared with the concentration changes of bulk MNBs in the dissociated solution, it was found that bulk MNBs play an important role in the hydrate memory effect. When the concentration of bulk MNBs in the dissociated solution decreases by 73.5%, the memory effect disappears, which quantitatively proves the mechanisms of bulk MNBs on memory effects. [ABSTRACT FROM AUTHOR]

Pressure oscillation controlled CH 4 /CO 2 replacement in methane hydrates to enhance CH 4 recovery and CO 2 storage. [Display omitted] • The oscillated pressure control is proposed to enhance CH 4 /CO 2 replacement. • Inner replacement cause CH 4 hydrate decomposition and mixed hydrate regeneration. • Optimized depressurization is crucial to improve CH 4 production and CO 2 storage. The recovery of CH 4 from natural gas hydrates via CH 4 /CO 2 replacement is a highly attractive method for achieving the recovery of CH 4 and storing CO 2. However, although extensive simulation and experimental studies have been conducted, applying CH 4 /CO 2 replacement is currently hampered by a lack of in-depth understanding about the replacement mechanism and the insufficient replacement efficiency and rate achieved. Therefore, to enhance CH 4 recovery and CO 2 storage, we propose a method that uses pressure oscillation during CH 4 /CO 2 replacement. The effects of depressurization pressure, depressurization time, and depressurization frequencies were analyzed in this study. The characteristics of pressure and temperature were analyzed during the depressurization process, and the decomposition and regeneration of hydrates relating to the oscillation pressure were observed on a macro level. The results show that this newly proposed combined method effectively improves CH 4 /CO 2 replacement, and the maximum amounts of CH 4 recovered and the CO 2 storage efficiency are nearly double than those achieved without pressure oscillation. CH 4 /CO 2 replacement is promoted by the pressure oscillation mechanism by breaking the balance of the hydrate layer, which results in the dissociation of CH 4 hydrates and finally forms a CO 2 /CH 4 mixed hydrate layer with free water. The results of this study provide a valuable method that can be used to enhance CH 4 recovery and CO 2 sequestration. [ABSTRACT FROM AUTHOR]

• 3D xenon hydrate shell meshes on water particle and ice sphere created from micro XCT. • Time-dependent hydrate shell thickness and inner/outer diameter were determined. • Novel 3D mesh method can quantify heterogeneous hydrate shell growth. Gas hydrates have gained increasing attention in energy and environmental fields and have potential applications in gas storage and transport, carbon dioxide sequestration, and flow assurance. Nevertheless, the kinetics of hydrate formation are still not well understood. In situ high-resolution X-ray computed tomography measurements were performed to monitor xenon hydrate formation on water droplets and ice spheres. For the first time, three-dimensional thickness meshes were used to quantify and visualize the kinetics of hydrate formation. The evolution of the hydrate morphology was investigated, and the time-dependent kinetic parameters were obtained, including the hydrate shell thickness and inner and outer diameters and the effective volume fraction of hydrate particles. The results indicate that the formation of gas hydrates undergoes an initial reaction-controlled stage followed by a mass-transfer-limited growth stage. For hydrate formation from a water droplet with an initial diameter of 1.66 mm, the hydrate shell thickness was approximately 30 μm and the effective volume fraction of hydrate particles was approximately 11% at 12 h after hydrate formation began. The standard deviation of the shell thickness, which indicates the surface roughness of the hydrate shell, increased with time for hydrate formation from water droplets. The results presented in this study renew our knowledge on the kinetics of hydrate formation, which is essential for their use in flow assurance and other hydrate-related technologies. [ABSTRACT FROM AUTHOR]

[Display omitted] • Inhibitors are used to prevent gas hydrates from clogging pipelines. • Effects of clay particles on polyvinylcaprolactam hydrate inhibition were studied. • Clay particles adsorbed the inhibitor, and the particle surface potential changed. • In the presence of clay particles, the inhibitory effects were weakened. Kinetic hydrate inhibitors are widely used during upstream activities in the oil industry to prevent gas hydrates from clogging pipelines. Yet their performance in the pipelines transporting natural gas from marine environment is largely veiled where clay particles and their adsorbability are generally present. In this study, it was found that the fine clay particles from a hydrate rich area in the South China Sea are majorly composed of layered silicate with a negative surface charge. Consequently, the clay particles would adsorb the inhibitor through Van der Waals attractions and ion–dipole interactions. The resulting weakened surface potential of the particles would trigger an aggregation of the clays together with the inhibitors attached on their surfaces. This will thereby result in less active components in the solution, significantly weakening the inhibition effect. It is therefore suggested that the effects of clay-rich conditions on the performance of the inhibitors should be carefully considered for an efficient dosage in the marine environments. [ABSTRACT FROM AUTHOR]

[Display omitted] • An improved model for hydrate particles removal from surface is proposed. • Hydrate particle diameter influencing the critical velocity than the initial liquid bridge volume. • Hydrate particles decomposition happening in the removal process. Understanding the critical velocity at which hydrate particles can be removed from a solid surface is crucial for flow assurance issues. An improved model is proposed to predict the critical velocity in hydrate particle removal process by considering a deformed liquid bridge. In situ experiments were performed for validation, and it was observed that hydrate particle decomposition occurred during the removal process. The particle diameter was determined to be a more dominant factor influencing the critical velocity than the initial liquid bridge volume. The resulting confidence level was 95% within a 30% error, showing its robust capability for engineering applications. [ABSTRACT FROM AUTHOR]

Owing to the substantial deposits and widespread applications of gas hydrates, research in gas hydrates has been increasing in recent decades. The inherent excellent physiochemical properties of gas hydrates determine the prominent roles that they play in a wide range of areas including energy and environment. Particularly, gas hydrates represent an attractive way for gas storage, gas separation, wastewater treatment, and other fields. The review summarizes the potential applications based on hydrate formation and dissociation. Challenges, limitation, and future visions of every application are discussed. The whole purpose of this paper is to give readers with a comprehensive understand of hydrate-based applications, stimulate further innovation application research using hydrate formation and dissociation, and give some useful guidance for their industrialization. • The excellent physiochemical properties of gas hydrates determine their great potential in industrial applications. • The potential applications including gas storage, gas separation, wastewater treatment, and other fields are reviewed. • Challenges, limitation, and future perspectives of each field are discussed. [ABSTRACT FROM AUTHOR]