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Marine natural gas hydrate (NGH) is a promising substitutive low-carbon energy resource, whereas NGH-production induced geoengineering concerns remain challenging. Advanced forecast of possible geoengineering risks is the fundamental for eco-friendly NGH exploitation. Reservoir creep deformation is an early symptom of the geoengineering risks. However, whether the creep deformation behaviors of the NGH-bearing strata is predictable remains controversial. In this study, a series of multi-step loading creep test are conducted for sandy gas hydrate bearing sediment (GHBS) samples, during which the ultrasonic responses are recorded simultaneously. The acoustic velocity, compression-to-shear velocity ratio, Poission's ratio, main frequency, and main frequency amplitude are used to characterize creep failures of the GHBS for the first time. Combining analyses of the creep behaviors and acoustic responses yield the following conclusions. Firstly, the long-term strength derived from creeping test is 0.45–0.60 times of the shear strength derived from triaxial shearing. Ignoring the creep effect might underestimate the scale and intensity of possible geoengineering risks during long-term NGH exploitation. Secondly, the acoustic velocity increases gently and then decreases continuously during creeping. Once the accelerated creep appears, the acoustic velocity plummets significantly, together with a sudden decrease in the compression-to-shear velocity ratio, and fluctuations in the main frequency and its amplitude. Furthermore, the main frequency and its amplitude shall fluctuate abruptly prior to the emergence of the accelerated creep. Therefore, we anticipate that the combination of abnormal fluctuations of main frequency and its amplitude can be used as early-warning indicators for possible creep failure of the GHBS. The results might have great significance for in-situ detection and prediction of possible reservoir failure during long-term NGH exploitation. [ABSTRACT FROM AUTHOR]

The high pressure in some gas wells, such as those in the Xushen gas field in Daqing, China, makes them susceptible to freezing and hydrate blockages. Downhole throttling technology is widely used to reduce costs during well construction, however, due to the limitations of temperature, pressure and depth structure, this technology is sometime applied independently in some gas wells in which freezing and blockages are a frequent problem that can seriously affect production capacity. Moreover, artificial alcohol injection of 'passive plugging' to prevent hydrate formation not only consumes significant amounts of methanol but its efficiency is also dependent on factors such as weather, personnel and equipment, so it is not a continuous solution. In order to solve the above problems, the mechanism of hydrate formation was analyzed in this study, from which a combined mechanical and chemical hydrate control process was developed. OLGA software was used to design the process parameters of the novel mechanical and chemical inhibition technology for hydrate prevention and control, and also to simulate and analyze the wellhead temperature, pressure and hydrate generation once the process was implemented. Based on the results of the parameters calculation, the downhole throttle and hydrate inhibitor automatic filling device are used to realize the functions of downhole throttle depressurization and hydrate inhibitor continuous filling, reduce the wellhead pressure and hydrate generation temperature, and ensure the continuous production of gas well. This novel combination process was subsequently tested in three wells in the Daqing gas oilfield. Measurements showed that the average daily gas increase from a single well was 0.5×104m3, methanol consumption was reduced from the original maximum daily amount of 1750 kg to just 60 kg, the manual maintenance workload was reduced by 80%, and the rate of the well openings was increased from 45% to 100%. These results proved that this technology is feasible and efficient for applications in gas wells with high downhole pressure and low wellhead temperature, and, thus, provides important technical support for the prevention of gas hydrate and improvement of gas well production. [ABSTRACT FROM AUTHOR]

The conditions for the formation of gas hydrates associated with subsea permafrost in the Kara Sea have been predicted based on numerical modeling. The forecast of the distribution of the relic submarine permafrost and related methane hydrate stability zone is given on the basis of solving the equation of thermal conductivity. According to modeling data, an extensive thermobaric relic submarine permafrost zone is predicted within the Kara Sea shelf. The greatest thickness (up to 600 m) of the permafrost is confined to the Taimyr shelf. Based on the results of the analysis of our model, drilling and seismic data, the southwestern shelf of the Kara Sea has insular or sporadic permafrost. In the northeastern part, the nature of the permafrost is also discontinuous, despite the greater thickness of the frozen strata. For the first time, accumulations of cryogenic gas hydrates on the Taimyr shelf have been characterized. The latest drilling data, seismic data reinterpretation, and numerical modeling have shown that the gas hydrate reservoir is confined to unconformably occurring Silurian–Devonian and underlying Triassic–Jurassic strata. The thickness of the gas hydrate reservoir varies from 800 to 1100 m. Based on the interpretation of CDP data and their comparison with model calculations, frozen deposits, and sub-permafrost traps of stratigraphic, anticline and anticline-stratigraphic types were identified for the first time. These pioneering studies allowed us to characterize the thickness and morphology of the gas hydrate reservoir, give a preliminary seismostratigraphic reference, and identify potentially gas hydrate-bearing structures. Due to the favorable thermobaric and permafrost-geothermal conditions, most of the identified traps may turn out to be sub-permafrost accumulations of gas hydrates. In total, at least five potential accumulations of gas hydrates were discovered, confined to structural depressions; the Uedineniya Trough and its side included the Egiazarov Step and North Mikhailovskaya Depression. [ABSTRACT FROM AUTHOR]

Efficient integration of the carbon capture and storage (CCS) process in power generation plants can help reduce global CO2 emissions. Hydrate technology has emerged as one of the most promising technologies for the separation and sequestration of CO2. This paper compares the process energy consumption of different CO2 capture techniques, gas transportation, and sequestration methods integrated into a pre-combustion power plant. Process modeling of a conceptualized hydrate technology-based CCS process is simulated using a coupled TRNSYS simulation software and engineering equation solver. The performance in efficiency, energy consumption, and potential energy penalty is evaluated and analyzed for three study cases. Furthermore, the energy requirement for transporting and sequestrating CO2 in hydrate as hydrate slurry is evaluated and compared to supercritical transportation and sequestration. The results obtained show that the energy consumption of hydrate-based gas separation amounts to 70 % of the total energy consumption for hydrate-based CO2 capture, transportation, and sequestration. [ABSTRACT FROM AUTHOR]

In this paper, four lithological parameters, that is, thermal conductivity, particle size, porosity, and saturation, are investigated by combining experimental observations with numerical simulations to study the influence laws and mechanisms of action on the combustion process of methane hydrate sediments. The variations in combustion characteristics parameters such as flame height, effective combustion ratio, and dimensionless discharge water mass with the lithological parameters are studied. In addition, the combustion mechanism of lithologic parameters on methane hydrate deposits is revealed. Combining the experimental results and simulation calculations to optimize the combustion of methane hydrate sediments, it is recommended to use methane hydrate sediment samples with high saturation and low thermal conductivity, while the oxidant concentration and porosity of methane hydrate sediment samples should be increased. [ABSTRACT FROM AUTHOR]

The absorption/desorption of water vapor by bambus[6]uril (Bu[6]) has been studied. According to kinetic experiments, the absorption capacity of Bu[6] is 4 moles of water per 1 mole of Bu[6] with the absorption duration of 20 min and the complete desorption duration of 100 min. Experimental rate constants for water vapor absorption and desorption by Bu[6] have been determined to be 0.166 min−1 and 0.0221 min−1, respectively. The obtained results are in agreement with theoretical calculations using the DFT method. A hypothetical structure of bambus[6]uril tetrahydrate (Bu[6]·4H2O) has been proposed based on the experimental and DFT data. [ABSTRACT FROM AUTHOR]

The dissociation of gas hydrate leads to the accumulation of excess pore pressure and the decrease of sediment strength, which may cause the instability of submarine slopes. Aiming at the risk caused by gas hydrate dissociation in offshore engineering, this study is conducted to propose a novel excess pore pressure model by improving the Grozic-Nixon model. Combined with the actual seismic and topographic data of the submarine slope in the northern South China Sea, the proposed excess pore pressure model is employed to numerically investigate the submarine landslide induced by gas hydrate dissociation. The corresponding safety factor is also obtained with the strength reduction method. The effects of water depth and the total amount of hydrate dissociation are discussed in detail on the stability of submarine slopes. The results show that the excess pore pressure caused by hydrate dissociation increases rapidly at the beginning, then increases slowly, and finally dissipates gradually. The hydrate re-formation of hydrate blocks the pore channels and slows down the dissipation of excess pore pressure to a certain extent. Hydrate dissociation amount, water depth, and sediment depth are crucial factors affecting the stability of submarine slopes. [ABSTRACT FROM AUTHOR]

The crystal structure of potassium guaninate hydrate, K+·C5H4N5O−·H2O, was studied in the pressure range of 1 atm to 7.3 GPa by single‐crystal diffraction using synchrotron radiation and a laboratory X‐ray diffraction source. Structural strain was compared to that of the same salt hydrate on cooling, and in 2Na+·C5H3N5O2−·7H2O under hydrostatic compression and on cooling. A polymorphic transition into a new, incommensurately modulated, phase was observed at ∼4–5 GPa. The transition was reversible with a hysteresis: the satellite reflections disappeared on decompression to ∼1.4 GPa. [ABSTRACT FROM AUTHOR]

The decomposition of hydrates can cause serious sand production and collapse problems, hindering the long-term effective production of hydrates. This study proposes a theory for framework reconstruction and reinforcement for deep-water hydrate layers based on grouting fracturing technology and chemical sand control principles. The setting liquid was injected via fracturing and grouting to form several cracks with a certain depth and width. The setting liquid remains in the fracture and solidifies to form a "reconstruction body." Simultaneously, the setting liquid permeates and diffuses from the cracks to the surrounding hydrate layer, bonding with the sediment and forming a gradient solidification zone to achieve solidification and reinforcement of the hydrate layer. To achieve effective production of hydrates, the reconstruction body must consider internal reinforcement, sand control, and good permeability. The parameters of the reconstruction body were designed based on the geological characteristics of hydrate formation in a certain area. In order to effectively support the hydrate layer, the reconstruction body was designed with a 24 h compressive strength of at least 3.20 MPa and a long-term compressive strength of at least 17.70 MPa. To ensure that the permeability characteristics of the reconstructed body meet production needs, the permeability of the reconstructed body must be greater than that of the hydrate layer. The maximum concentrated pore size of the skeleton reconstruction body is designed to be 9 μm based on the particle characteristics of shale sand in hydrate reservoirs. This study provides a new approach to solving sand production and collapse. [ABSTRACT FROM AUTHOR]

Composites based on mineral binders are highly concentrated polydisperse systems. These systems consist of a dispersed phase in the form of particles of filler and binder, hydration products, as well as a dispersion medium in the form of a porous electrolyte (mixing water). The properties of such systems are determined by the action of forces that manifest themselves in interfacial interactions and act within each phase between atoms, ions, or molecules. To increase the strength and water resistance of materials, it is necessary to ensure the formation of contacts in which electrostatic attraction with the maximum interaction energy is realized. A significant role is played by the electric charges and potentials of the surface of the particles of the components of the structure. The introduction of chemical additives provides the synthesis of additional crystalline hydrates with certain surface properties, which contributes to an increase in the number of electroheterogeneous contacts in the system. The introduction of polydisperse mineral fillers, taking into account their surface charges, ensures the formation of a dense structure of a composite material with a large number of electroheterogeneous contacts. Based on the research results, composite materials based on mineral binders of various functional purposes with specified physical‐mechanical, hydrophysical, electrophysical properties have been developed. The use of these materials made it possible to increase the reliability and durability of building structures. [ABSTRACT FROM AUTHOR]

The reaction coordinate (RC) is the principal collective variable or feature that determines the progress along an activated or reactive process. In a molecular simulation using enhanced sampling, a good description of the RC is crucial for generating sufficient statistics. Moreover, the RC provides invaluable atomistic insight into the process under study. The optimal RC is the committor, which represents the likelihood of a system to evolve toward a given state based on the coordinates of all its particles. As the interpretability of such a high dimensional function is low, a more practical approach is to describe the RC by some low-dimensional molecular collective variables or order parameters. While several methods can perform this dimensionality reduction, they usually require a preselection of these low-dimension collective variables (CVs). Here, we propose to automate this dimensionality reduction using an extended autoencoder, which maps the input (many CVs) onto a lower-dimensional latent space, which is subsequently used for the reconstruction of the input as well as the prediction of the committor function. As a consequence, the latent space is optimized for both reconstruction and committor prediction and is likely to yield the best non-linear low-dimensional representation of the committor. We test our extended autoencoder model on simple but nontrivial toy systems, as well as extensive molecular simulation data of methane hydrate nucleation. The extended autoencoder model can effectively extract the underlying mechanism of a reaction, make reliable predictions about the committor of a given configuration, and potentially even generate new paths representative for a reaction. [ABSTRACT FROM AUTHOR]

We use a novel hybrid method to explore the temperature dependence of the solid–liquid interfacial tension of a system that consists of solid methane hydrate and liquid water. The calculated values along the three-phase (hydrate–liquid water–vapor) equilibrium line are obtained through the combination of available experimental measurements and computational results that are based on approaches at the atomistic scale, including molecular dynamics and Monte Carlo. An extensive comparison with available experimental and computational studies is performed, and a critical assessment and re-evaluation of previously reported data is presented. [ABSTRACT FROM AUTHOR]

The present work intends to join and respond to the excellent and thoroughly documented rovibrational study of X. G. Wang and T. Carrington, Jr. [J. Chem. Phys. 154, 124112 (2021)] that used an approach tailored for floppy dimers with an analytic dimer Hamiltonian and a non-product basis set including Wigner D functions. It is shown in the present work that the GENIUSH black-box-type rovibrational method can approach the performance of the tailor-made computation for the example of the floppy methane–water dimer. Rovibrational transition energies and intensities are obtained in the black-box-type computation with a twice as large basis set and in excellent numerical agreement in comparison with the more efficient tailor-made approach. [ABSTRACT FROM AUTHOR]

The main purpose of this study is investigating a reliable and convenient model based on Dickens and Quinby-Hunt approach to predict CH4/CO2 gas hydrate equilibrium temperature in presence of organic inhibitors (e.g., methanol, ethanol, ethylene glycol, triethylene glycol, glycerol), and electrolyte inhibitors (e.g., NaCl, KCl, NaBr, KBr, CaCl2, CaBr2, MgCl2, EMIM-Cl, BMIM-Cl, BMIM-Br, BMIM-I, BMIM-DCA, EMIM-HSO4, EMIM-EtSO4, and EMIM-MeSO4). This model named as Dickens' model is an activity-based model and to calculate water activity of organic solutions the nonrandom two-liquid (NRTL) and Margules was used. Also, Pitzer model was employed to calculate activity of water in electrolyte solutions. A correlation was suggested to determine enthalpy of hydrate dissociation in terms of inhibitor weight percent and equilibrium pressure. Due to no data in open literature, the virial coefficients of Pitzer model in ionic liquid solutions were adjusted. The model results were compared with available experimental data from open literature and observed to be in good agreement with the reported literature. [ABSTRACT FROM AUTHOR]

The development of methane hydrate extraction technology remains constrained due to the limited physical understanding of hydrate dissociation dynamics. While recent breakthroughs in pore-scale visualization techniques offer intuitive insights into the dissociation process, obtaining a profound grasp of the underlying mechanisms necessitates more than mere experimental observations. In this research, we introduce a two-phase micro-continuum model that facilitates the numerical simulation of methane hydrate dissociation at both single- and multiscale levels. We employed this numerical model to simulate microfluidic experiments and determined the kinetic parameters of methane hydrate dissociation based on experimental data under various dissociation scenarios. The simulations, once calibrated, correspond closely to experimental results. By comprehensively comparing the simulated results with experimental data, the rate constant and the effective diffusion coefficient were reliably determined to be kd = 1.5 × 108 kmol2/(J·s·m2) and Dl = 0.8 × 10−7 m2/s, respectively. Notably, the multiscale model not only matches the precision of the single-scale model but also presents considerable promise for streamlining the simulation of hydrate dissociation across multiscale porous media. Moreover, we contrast hydrate dissociation under isothermal versus adiabatic conditions, wherein the dissociation rate is significantly reduced under adiabatic conditions due to the shifted thermodynamic condition. This comparison highlights the disparities between microfluidic experiments and real-world extraction environments. [ABSTRACT FROM AUTHOR]

Fluid sources and flow rates at methane seeps control gas hydrate formation, and are potentially archived in authigenic carbonates. Lithium (Li) in seeping fluids exhibits a broad range of isotopic fractionation during its ascent to the seafloor, providing information on temperatures and flow rates of the fluids. To test the applicability of Li isotopes as a fluid tracer in authigenic carbonates, this study investigates the element and Li isotope composition of methane-seep carbonates collected from the Black Sea and the Japan Sea. The Li/Ca ratios and δ7Li values of the aragonite-rich and calcite-rich samples (10–60 μmol mol−1 and 3.5–15.6‰; 21–142 μmol mol−1 and 8.3–24.4‰, respectively) are distinct from those in carbonates precipitated from seawater, and indicate an input of deep-seated fluids enriched in 6Li. After correcting for a minor admixture of clay-bound Li, the Li/Ca ratios and δ7Li values of the parent fluids were estimated to be 2400–11 000 μmol mol−1 and 17.2–34.5‰, respectively. Variations in the estimated values cannot be explained by fluid mixing alone, but rather reflect the isotopic fractionation caused by interaction of the deep fluids with secondary minerals during fluid ascent. The δ7Li fluid values as low as 17.2‰ for the Japan Sea carbonates indicate a deep fluid source with estimated temperatures of >26 °C derived from >250 m below the seafloor. Reaction-transport modeling shows that the deep fluid was transported to the zone of carbonate precipitation with advection rates of ≥10−2 cm yr−1. Higher advection rates were indicated for the Japan Sea fluids than for Black Sea fluids, probably due to a larger contribution of dissolved methane to hydrate formation. Spatiotemporal variations in fluid sources and advection rates were indicated by distinct (Li/Ca) fluid and δ7Li fluid values between the carbonates and pore fluids. The Li isotope systematics of seep carbonates are a potent indicator of the origin and flow rate of deep-seated fluids and their spatiotemporal variability, which is explored herein in detail for the first time. [ABSTRACT FROM AUTHOR]

Rutin hydrate has some pharmacological properties and is widely available in human food and household samples. Although many methods based on large-scale instruments have been established for the detection of rutin hydrate, a simple, rapid and in situ measurement strategy was rarely reported up to now. In this work, a fluorescent sensor based on the cyanostilbene macrocycle (BCM) was developed for detecting rutin hydrate with high selectivity and sensitivity. BCM is a bis-cyanostilbene macrocycle with a bridging thiourea chain prepared by "1 + 1" condensation in 75% yield. BCM possessed a good fluorescence emission at 475 nm with an absolute fluorescence quantum yield of 0.26 in DMSO–H2O (5 : 95). It exhibited good selective detection for rutin hydrate among a series of normal ions and biomolecules with a "turn-off" fluorescence response. The binding constant of BCM for rutin hydrate was 2.4 × 104 M−1 and the detection limit attained 1.16 × 10−7 M. The 1 : 1 sensing mechanism was clarified using Job's plot, and 1H NMR and MS binding spectra. The sensing ability of BCM for rutin hydrate was successfully applied in detecting rutin hydrate in a test paper, three fruits and experiments of standard addition recovery with the recoveries of 90–95%, implying the simple, rapid and in situ detecting potential of BCM for rutin hydrate in real samples and the environment. [ABSTRACT FROM AUTHOR]

Subglacial environments provide conditions suitable for the microbial production of methane, an important greenhouse gas, which can be released from beneath the ice as a result of glacial melting. High gaseous methane emissions have recently been discovered at Russell Glacier, an outlet of the southwestern margin of the Greenland Ice Sheet, acting not only as a potential climate amplifier but also as a substrate for methane consuming microorganisms. Here, we describe the composition of the microbial assemblage exported in meltwater from the methane release hotspot at Russell Glacier and its changes over the melt season and as it travels downstream. We found that a substantial part (relative abundance 27.2% across the whole dataset) of the exported assemblage was made up of methylotrophs and that the relative abundance of methylotrophs increased as the melt season progressed, likely due to the seasonal development of the glacial drainage system. The methylotrophs were dominated by representatives of type I methanotrophs from the Gammaproteobacteria; however, their relative abundance decreased with increasing distance from the ice margin at the expense of type II methanotrophs and/or methylotrophs from the Alphaproteobacteria and Betaproteobacteria. Our results show that subglacial methane release hotspot sites can be colonized by microorganisms that can potentially reduce methane emissions. [ABSTRACT FROM AUTHOR]

As pipeline transportation operation moves into deep seas, the formation of hydrate has become a major flow assurance challenge for transmission pipelines. Some nonionic surfactants can play emulsification and anti-agglomeration effects in the oil-water two-phase system. Studying the mechanism of surfactants is helpful to solve the problem of hydrate blocking pipelines and ensuring good fluidity in the pipelines. This study investigated the influence of HLB of nonionic surfactants on the types of emulsions and the formation kinetics of methane hydrate. The experimental results showed that with the increase of the hydrophilic-lipophilic balance (HLB), low water content emulsion successively formed water/oil (W/O) and oil/water (O/W) emulsions, as well as a phase transition zone. The increase in the hydrophilic component had an inhibitory effect on the kinetics of hydrate formation. Under the low water content system, the anti-agglomeration effect of the composite surfactant was better than that of the single surfactant. The slurry-like hydrate generated by the 65% Span 80 + 35% Tween 80 compound system ensures good fluidity in the pipeline. [ABSTRACT FROM AUTHOR]

The Total Organic Carbon (TOC) content plays a crucial role in gas hydrate exploration because a higher TOC content signifies a greater potential for buried gas hydrates. The regulatory mechanisms governing organic matter in sediment are intricate and influenced by various predominant factors unique to different regions. Notably, the Shenhu area in the South China Sea stands as a pioneering region for methane hydrate research. Despite its significance, limited research has focused on the burial patterns of TOC, resulting in an insufficient dataset to draw definitive conclusions. Consequently, a comprehensive understanding of the burial patterns and controlling factors of TOC within this area remains elusive. This study examines the pore-water characteristics, mineral composition, geochemistry, and sedimentary factors of four distinct sites within the Shenhu region of the South China Sea. The current depths of the Sulfate-Methane Interface (SMI) for sites CL54, CL56, CL57, and CL60 are identified as 28.6, 8.5, 31.9, and 8.1 m below the seafloor (mbsf), respectively. It's noteworthy that these SMI depths align with locations known to harbor underlying gas hydrates. Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD) analyses reveal that the primary sediment sources within this region encompass microbial shells (such as foraminifera and diatoms), clay, and terrestrial detritus. In addition, marine productivity exhibits a reverse correlation with TOC content, and both TOC content and Ce/Ce* ratios exhibit synchronous fluctuations with sedimentation rate. Drawing from the sedimentation rate, TOC content, as well as indicators of redox conditions (MoEF, Ce/Ce*, Mo/U) and productivity proxies (Ba/Al, P/Al) within the sampled sites, it becomes apparent that high sedimentation rate coupled with 'anaerobic' conditions foster favorable conditions for TOC accumulation. This comprehensive investigation not only provides valuable datasets but also offers insights into the intricate processes governing TOC accumulation. [ABSTRACT FROM AUTHOR]

[Display omitted] Clathrate hydrates form and grow at interfaces. Understanding the relevant molecular processes is crucial for developing hydrate-based technologies. Many computational studies focus on hydrate growth within the aqueous phase using the 'direct coexistence method', which is limited in its ability to investigate hydrate film growth at hydrocarbon-water interfaces. To overcome this shortcoming, a new simulation setup is presented here, which allows us to study the growth of a methane hydrate nucleus in a system where oil–water, hydrate-water, and hydrate-oil interfaces are all simultaneously present, thereby mimicking experimental setups. Using this setup, hydrate growth is studied here under the influence of two additives, a polyvinylcaprolactam oligomer and sodium dodecyl sulfate, at varying concentrations. Our results confirm that hydrate films grow along the oil–water interface, in general agreement with visual experimental observations; growth, albeit slower, also occurs at the hydrate-water interface, the interface most often interrogated via simulations. The results obtained demonstrate that the additives present within curved interfaces control the solubility of methane in the aqueous phase, which correlates with hydrate growth rate. Building on our simulation insights, we suggest that by combining data for the potential of mean force profile for methane transport across the oil–water interface and for the average free energy required to perturb a flat interface, it is possible to predict the performance of additives used to control hydrate growth. These insights could be helpful to achieve optimal methane storage in hydrates, one of many applications which are attracting significant fundamental and applied interests. [ABSTRACT FROM AUTHOR]

Given the increasing demand for clean natural gas energy, solidified natural gas (SNG) is regarded as a potential natural gas storage technology owing to its numerous advantages. In this work, the effects of the concentration of graphite nanoparticles (GNs) on the rate of hydrate formation, gas consumption, induction time, and morphology of methane hydrates under different pressures were studied. The results showed that under lower pressure, the low concentration of GNs increased the gas consumption of hydrates, but the hydrate formation rate decreased by 50% and the induction time increased. The addition of high concentration GNs decreased the hydrate formation rate significantly, there was no obvious induction period, and the final gas consumption changed little. At the same time, only a small amount of hydrate was formed, accompanied by a considerable volume of foam. Under higher pressure, the addition of GNs promoted the formation of hydrates, increased the rate of hydrate formation. Among them, the 0.3 wt% concentration of GNs showed the best promotion effect, and the final gas consumption was higher than that of other metal and oxide nanofluids. Therefore, under the proper pressure, using cheap GNs as promoters can not only effectively promote hydrate formation, but also save costs. [ABSTRACT FROM AUTHOR]

It is not easy to obtain hydrate samples from actual marine reservoirs, and a large number of basic experiments in laboratory are still needed to support their resource exploitation. In order to accurately prepare representative hydrate reservoir samples, the laboratory developed a set of three-dimensional experimental device for natural gas hydrates. By multiple-times water injections, the saturation of gas, water and hydrates in target samples and the temperature and pressure conditions of the generated system were controlled, and the parameter characteristics of pressure, temperature and resistivity in system during the formation of methane hydrates were analyzed. The results show that multiple-times water injections can effectively control the saturation of each phase in the sample. It is difficult to observe the induction period of hydrate formation when the driving pressure and the degree of supercooling are large enough. Under the good heat transfer of the surrounding water bath, the temperature rise caused by the exothermic formation of hydrates could be eliminated. The resistivity change shows that there may be "wall climbing effect" in the formation of hydrates in porous media, but there are many factors affecting the resistivity change, which is difficult to accurately judge the formation of hydrates in porous media. In addition, the increase of the initial gas-liquid ratio can promote the increase of the hydrate formation rate. [ABSTRACT FROM AUTHOR]

In order to mitigate the issues caused by hydrate blockage in flow assurance, experimental data on natural gas hydrate formation was collected to construct a Probabilistic Neural Network (PNN) model. By improving the Aquila Optimizer (AO) algorithm through adaptive weights and hyperbolic tangent function, optimization of smoothing parameters was achieved, resulting in the establishment of an IAO-PNN-based hydrate formation prediction model. A comparison with thermodynamic models and machine learning models validated the superiority of the algorithm. The results show that the improved AO algorithm (IAO) exhibits significantly higher optimization precision and convergence speed compared to intelligent algorithms such as AO, PSO and SSA. The IAO-PNN model exhibits the highest consistency with experimental data, making it suitable for predicting hydrate formation conditions in binary systems, multicomponent systems, acid systems and alcohol-salt systems, and it demonstrates good predictive performance in high- pressure environments. Compared to thermodynamic models and machine learning models, the IAO-PNN model shows excellent generalization performance, with an root mean square error (RMSE) of 0.6176 and an coefficient of determination (R²) of 0.9994 on the training set, and an RMSE of 0.7624 and an R² of 0.9991 on the test set. Through on-site verification, the IAO-PNN model displays good applicability and can provide reference for formulating on-site remediation measures. [ABSTRACT FROM AUTHOR]

Spectral observations of Neptune made in 2019 with the Multi Unit Spectroscopic Explorer (MUSE) instrument at the Very Large Telescope (VLT) in Chile have been analyzed to determine the spatial variation of aerosol scattering properties and methane abundance in Neptune's atmosphere. The darkening of the South Polar Wave at ∼60°S, and dark spots such as the Voyager 2 Great Dark Spot is concluded to be due to a spectrally dependent darkening (λ < 650 nm) of particles in a deep aerosol layer at ∼5 bar and presumed to be composed of a mixture of photochemically generated haze and H2S ice. We also note a regular latitudinal variation of reflectivity at wavelengths of very low methane absorption longer than ∼650 nm, with bright zones latitudinally separated by ∼25°. This feature, which has similar spectral characteristics to a discrete deep bright spot DBS‐2019 found in our data, is found to be consistent with a brightening of the particles in the same ∼5‐bar aerosol layer at λ > 650 nm. We find the properties of an overlying methane/haze aerosol layer at ∼2 bar are, to first‐order, invariant with latitude, while variations in the opacity of an upper tropospheric haze layer reproduce the observed reflectivity at methane‐absorbing wavelengths, with higher abundances found at the equator and also in a narrow "zone" at 80°S. Finally, we find the mean abundance of methane below its condensation level to be 6%–7% at the equator reducing to ∼3% south of ∼25°S, although the absolute abundances are model dependent. Plain Language Summary: Observations of Neptune in visible light, made with the Multi Unit Spectroscopic Explorer (MUSE) instrument at ESO's Very Large Telescope, reveal the different layers of clouds and gases within this Ice Giant atmosphere, and how they change with height and latitude. The properties of the 1–2‐bar layer of methane ice and haze are found to be roughly constant with latitude. However, a diffuse upper layer is thickest at the equator and near the south pole, indicating air rising at mid‐latitudes and descending near the equator and poles. Conversely, the distribution of methane between the deep 5‐bar clouds (hydrogen sulphide ice and haze) and the middle layers decreases from 6% to 7% at the equator to ∼3% near the south pole, suggesting instead that air is rising at the equator and descending elsewhere. Finally, a blue‐green darkening of the particles in the deep layer can explain Neptune's dark spots and the dark "South Polar Wave" at 60°S, whereas a brightening of the same particles at red and infrared wavelengths matches occasional discrete deep bright spots and a set of previously unnoticed bright "zones", separated by 25° latitude. All this is evidence that the atmospheric circulation changes as a function of height and latitude in complex and surprising ways. Key Points: Neptune Multi Unit Spectroscopic Explorer (MUSE) visible/near‐infrared spectra are well fitted by a simple aerosol model comprised of three distinct layersA darkening of particles at blue‐green wavelengths in a deep aerosol layer near 5 bar can explain dark spots and the dark "South Polar Wave"A brightening of the same particles at red‐infrared wavelengths can explain bright zones and spots seen in longwave narrow reflectance peaks [ABSTRACT FROM AUTHOR]

Rapid corrosion of steel bars in marine and complex saline environments has become a serious concern, and corrosion inhibitor for steel bar has proved to be one of the main protective measures to prevent the corrosion. In this paper, a new organic composite anti-corrosion agent (HTCI) was synthesised by hydrazine hydrate and tartaric acid for the preventing reinforced concrete from corrosion in marine engineering. The inhibition behaviors of HTCI for Q235 steel in saturated Ca(OH)2 solution with 3.0 wt.% NaCl were studied by weight loss, electrochemical measurement and surface analysis. All these techniques revealed that inhibition efficiency increased with increasing HTCI concentration and the inhibitor showed 84.37% inhibition efficiency at a concentration of 500 mg·L-1. Potentiodynamic polarization studies indicated the HTCI with mixed-type inhibitor properties. Scan analysis demonstrated that the depth of the pitting crater decreased with increasing HTCI concentration. Kinetically and thermodynamically simulated that the adsorption of HTCI on mild steel obeys Langmuir adsorption isotherm, and the mechanisms of this corrosion inhibitor were based on physical and chemical adsorption. [ABSTRACT FROM AUTHOR]

Aiming at the problem of natural gas hydrate blockage in oil and gas pipelines. The key to rationally inhibiting the formation of hydrates in pipelines is to find the factors that lead to the rapid coalescence of hydrates. We studied the effect of 0.2 wt% graphite particles and Fe2O3 particles (20 nm and 1 μm) as solid dispersants on hydrate formation in a W/O emulsion system at 275.15 K and 7 MPa. The results showed that 0.2 wt% solid dispersants could be adsorbed on the interface of Pickering emulsion to inhibit the binding of particles. In addition, solid dispersants improve the mass and heat transfer capacity of the reaction system and increase the final gas consumption. The 20 nm Fe2O3 particle reaction system had the largest gas consumption and the highest reaction rate. A three-dimensional network mechanism was proposed to explain the rapid formation of hydrate particles from the perspective of kinetics. Our experimental results and suggested mechanisms provided a reference for the promotion or inhibition of hydrate growth. [ABSTRACT FROM AUTHOR]

In tests of marine hydrate depressurization production in many countries, accidents such as collapse and failure of boreholes have occurred, which caused by the evolution of the effective stress field have motivated further attention. However, in existing effective stress models, the pressure of the fluid in the wellbore is taken as the boundary condition, which did not account for the effects of the wellbore on the effective stress distribution. This paper is aimed at proposing a methodology to research the spatio-temporal evolution of the effective stress during the hydrate depressurization production, in order to provide a theoretical benchmark against which to analyze the borehole stability. We derived a mathematical model of the effective stress by taking into account the interaction between the wellbore and the reservoir on the basis of the theory of elasticity, and coupled with deposited infiltration using fluid-structure interaction theory, a coupled multiple field model considering the kinetic effects of hydrate decomposition was then established. And a solver was developed independently. A case study shows that the wellbore has significant effect on the effective stress within the radius of 0.5 m of the reservoir. At the borehole wall, the radial effective stress is 23.58 MPa, whereas the circumferential effective stress is 7.31 MPa, such nonuniformity of the effective stress lead to the risk of borehole failure. As the production progresses, the effective stress increases rapidly at first and then slowly. The effective stress is slightly affected by the size of the wellbore, it is found that when the outside diameter of the wellbore is increased from 100 mm to 500 mm, the change is less than 3.04 %. [Display omitted] • A novel methodology to research the evolution of effective stress was proposed. • A multi-field coupled analytical model of effective stress was established. • The evolution of effective stress during hydrate depressurization was revealed. • The influence of geological factors on the effective stress was identified. [ABSTRACT FROM AUTHOR]

As ice-like crystals and non-stoichiometric compounds comprising gas and water, natural gas hydrates have drawn significant attention as a potential alternative energy source. This work focuses on holistically reviewing theoretical modeling and numerical studies conducted on the production of gas from natural gas hydrates. Firstly, fundamental models for the dissociation of a hydrate in a porous sediment are summarized in terms of the phase equilibrium and dissociation kinetics. The main features of different models and improvements for them are identified by clarifying crucial driving mechanisms and kinetic parameters. Subsequently, various numerical works addressing the dissociation of a hydrate in a porous sediment and the flow characteristics in a wellbore are reviewed, including aspects such as the theoretical background, computational scheme, and the physics involved. In general, profiting from a significant capacity to solve nonlinear differential equations, numerical simulations have contributed to great progress in fundamentally understanding the mechanism driving gas production and in developing effective exploitation methods. Owing to the substantial fundamental physics involved in the exploitation of natural gas hydrates, existing challenges, alternative strategies, and future directions are provided correspondingly from a practical application perspective. [ABSTRACT FROM AUTHOR]

In this work, methane (CH4) dissociation on Pt(111) surface dissociation was studied based on density functional theory (DFT) calculations to evaluate the nature of adsorption and to calculate the rate constant. The most stable configurations for H and CH3 were tested on the surface of Pt(111), and the results displayed that H tends to be adsorbed at the fcc site while CH3 tends to be adsorbed at the top site. The energy of barrier and rate constant of reaction were calculated and found to be (2.28 eV) and (3.21007E−08 s−1) respectively. In addition, the adsorption energy for the reactant and products to investigate the nature of adsorption of the reactant and products on Pt(111) surface either physisorption or chemisorption. The results showed that the kind of adsorption of CH4 adsorbed on the surface of Pt(111) at top site is physisorption, while CH3 and H species adsorption on the Pt(111) surface is chemisorption. [ABSTRACT FROM AUTHOR]

Four salts, namely, 2,4,6‐triaminopyrimidinium 6‐chloronicotinate dihydrate, C4H8N5+·C6H3ClNO2−·2H2O, (I), 2,4,6‐triaminopyrimidinediium pyridine‐2,6‐dicarboxylate dihydrate, C4H9N52+·C7H3NO42−·2H2O, (II), 2,4,6‐triaminopyrimidinediium sulfate monohydrate, C4H9N52+·SO42−·H2O, (III), and 2,4,6‐triaminopyrimidinium 3,5‐dinitrobenzoate dihydrate, C4H8N5+·C7H3N2O6−·2H2O, (IV), were synthesized and characterized by X‐ray diffraction techniques. Proton transfer from the corresponding acid to the pyrimidine base has occurred in all four crystal structures. Of the four salts, two [(I) and (IV)] exist as monoprotonated bases and two [(II) and (III)] exist as diprotonated bases. In all four crystal structures, the acid interacts with the pyrimidine base through N—H...O hydrogen bonds, generating an R22(8) ring motif. The sulfate group mimics the role of the carboxylate anions. The water molecules present in compounds (I)–(IV) form water‐mediated large ring motifs. The formation of water‐mediated interactions in these crystal structures can be used as a model in the study of the hydration of nucleobases. Water molecules play an important role in building supramolecular structures. In addition to these strong hydrogen‐bonding interactions, some of the crystal structures are further enriched by aromatic π–π stacking interactions [(I) and (II)]. [ABSTRACT FROM AUTHOR]

The article provides an overview of the PMEL Earth-Ocean Interactions (EOI) program and its research on seafloor and subseafloor processes in relation to ocean health, biogeochemical cycles, ecosystem diversity, and climate change. The program has made significant contributions to the study of methane seeps, hydrothermal vents, and submarine volcanoes. It emphasizes the need for better observational data on global ocean processes and highlights the importance of understanding hydrothermal iron sources and transport mechanisms. The article also mentions the discovery of hydrothermal activity on the Australian-Antarctic Ridge and the planned expedition to investigate hydrothermal venting and primary productivity in the Southern Ocean. Overall, the article underscores the significance of deep-sea exploration in understanding seafloor processes and their impact on ocean biogeochemistry, sustainable resources, and greenhouse gas accumulation. [Extracted from the article]

The purpose of this study is to investigate the composition of the gas, liquid and hydrate phases during gas hydrate formation. The kinetics of gas hydrate formation from a CO2/C3H8 gas mixture (initial molar ratio 80/20) under isochoric and isothermal (2, 4 and 6 °C) conditions from pure and saline water has been investigated. Experimental measurement of gas composition was performed by gas chromatography and that of the liquid phase by conductivity analysis. The main and novel finding of the present study is that at early times, the gas hydrate is supersaturated with CO2, following an equilibrium concentration of CO2 and C3H8 molecules at later times. Initially, the occupancy of the 51264 cages of the SII structure by the CO2 molecules exceeds the equilibrium plateau. A gradual egress of CO2 to the liquid/gas phase occurs afterward, eventually resulting in the decrease in CO2 and increase in C3H8 apparent mass transfer coefficients. [ABSTRACT FROM AUTHOR]

The physical and consolidation properties of sediments were investigated using borehole cores collected from the Sakata Knoll, where shallow methane hydrate fields exist, and from nearby sites where methane hydrate is not present. The soil particle density, grain size distribution, liquid limit, plastic limit, and plasticity index were similar at all depths. The void ratio change with depth was approximately e=3 near the seafloor, decreased to approximately e =2 at approximately 20 meters below the seafloor, and remained almost unchanged until approximately 56 meters below the seafloor. This void ratio change was found to be similar to that of the seafloor in the Joetsu Basin, which has shallow methane hydrate fields. The degree of soil structure development was examined by performing incremental loading consolidation tests on the collected core samples. Structural coefficient A values indicated that structure developed with increasing depth in both cores, but the degree of structural development was small regardless of whether the cores were in the Methane hydrate bearing area or not. [ABSTRACT FROM AUTHOR]

Polyalanine (polyA) disease-causative proteins with an expansion of alanine repeats can be aggregated. Although curative treatments for polyA diseases have not been explored, the dissociation of polyA aggregates likely reduces the cytotoxicity of polyA. Mid-infrared free electron laser (FEL) successfully dissociated multiple aggregates. However, whether the FEL dissociates polyA aggregates like other aggregates has not been tested. Here, we show that FEL at 6.1 μm experimentally weakened the extent of aggregation of a peptide with 13 alanine repeats (13A), and the irradiated 13A exerted lesser cytotoxicity to neuron-like cells than non-irradiated 13A. Then, we applied molecular dynamics (MD) simulation to follow the dissociation process by FEL. We successfully observed how the intermolecular β-sheet of polyA aggregates was dissociated and separated into monomers with helix structures upon FEL irradiation. After the dissociation by FEL, water molecules inhibited the reformation of polyA aggregates. We recently verified the same dissociation process using FEL-treated amyloid-β aggregates. Thus, a common mechanism underlies the dissociation of different protein aggregates that cause different diseases, polyA disease and Alzheimer's disease. However, MD simulation indicated that polyA aggregates are less easily dissociated than amyloid-β aggregates and require longer laser irradiation due to hydrophobic alanine repeats. [ABSTRACT FROM AUTHOR]

Methane hydrates in natural geological settings are commonly distributed within sediments, with a variety of minerals (such as silica sand, talc, and montmorillonite). The mechanisms that control the influence of sediments on methane hydrate formation remain poorly understood. In this study, we performed experiments on methane hydrate formation in pure H2O with the addition of 3% sediments (montmorillonite, talc, and silica sand). A large-volume stirred reactor (80 mL) and a small-volume unstirred reactor (20 mL) were used. The results show that montmorillonite and talc severely inhibit methane hydrate formation. For experiments in the stirred reactor with pure H2O, normalized gas consumption is 30 (mmol/mol) after 1000 min. In contrast, normalized gas consumption in experiments with the addition of 3% montmorillonite and talc decreases greatly to <5 (mmol/mol) over the same period. The inhibiting effect of montmorillonite and talc is closely associated with the release of cations (Mg2+, Ca2+, K+, and Na+) into fluids, with higher concentrations of cations for slower rates of methane hydrate formation. The interaction of montmorillonite and talc with H2O consumes hydrogen ions (H+), resulting in alkaline solutions. It was found that alkaline solutions may not be favorable for methane hydrate formation. In contrast, silica sand slightly promotes methane hydrate formation in the unstirred reactor, which may be related to acidic solutions formed during the interaction of silica sand with H2O. The phase equilibrium temperatures and pressures of methane hydrate in the presence of 3% montmorillonite, talc, and silica sand are essentially the same as those in pure H2O, excluding the thermodynamic effect of minerals. The experiments of this study are important for understanding the formation of massive methane hydrates with low amounts of sediment (e.g., ≤3%). They suggest that methane hydrates may not be highly concentrated in sediments with abundant talc and montmorillonite. The experiments of this study may explain the close association of methane hydrates with silica sand. [ABSTRACT FROM AUTHOR]

Fast multi-phase processes in methane hydrate bearing samples pose a challenge for quantitative micro-computed tomography study and experiment steering due to complex tomographic data analysis involving time-consuming segmentation procedures. This is because of the sample's multi-scale structure, which changes over time, low contrast between solid and fluid materials, and the large amount of data acquired during dynamic processes. Here, a hybrid approach is proposed for the automatic segmentation of tomographic data from time-resolved imaging of methane gas-hydrate formation in sandy granular media, which includes a deep-learning 3D U-Net model. To prepare a training dataset for the 3D U-Net, a technique to automate data labeling based on sample-specific information about the mineral matrix immobility and occasional fluid movement in pores is proposed. Automatic segmentation allowed for studying properties of the hydrate growth in pores, as well as dynamic processes such as incremental flow and redistribution of pore brine. Results of the quantitative analysis showed that for typical gas-hydrate stability parameters (100 bar methane pressure, 7°C temperature) the rate of formation is slow (less than 1% per hour), after which the surface area of contact between brine and gas increases, resulting in faster formation (2.5% per hour). Hydrate growth reaches the saturation point after 11 h of the experiment. Finally, the efficacy of the proposed segmentation scheme in on-the-fly automatic data analysis and experiment steering with zooming to regions of interest is demonstrated. [ABSTRACT FROM AUTHOR]

The reactivity of bis(2‐chloroprop‐2‐enyl)sulfide in the system hydrazine hydrate/alkali has been studied using quantum‐chemical methods. The B2PLYP‐D2//B3LYP approach shows a good agreement between the relative values of activation barriers compared to high‐precision CBS//Q‐B3. The correction for the entropy change during the transition from the gas phase to the binary solvent hydrazine hydrate is calculated. The IEF PCM model was parameterized for hydrazine hydrate solvent. The studied reaction routes includes (i) a competition between migration of the C=C bond and dehydrochlorination of bis(2‐chloroprop‐2‐enyl)sulfide; (ii) 1,3‐prototropic rearrangements of bis (allenyl)sulfide resulting from a dehydrochlorination; (iii) the possible substitution of sulfur and chlorine atoms with hydrazine. The probable formation of the thiiranium and thiirenium cations formation in the above has also been evaluated. [ABSTRACT FROM AUTHOR]

On Earth, natural hydrates are mostly encountered in clay‐rich sediments. Yet their formation processes in such matrices remain poorly understood. Achieving an in‐depth understanding of how methane hydrates accumulate on continental margins is key to accurately assess (a) their role in sustaining the development of some chemosynthetic communities at cold seeps, (b) their potential in terms of energy resources and geohazards, and (c) the fate of the methane releases, a powerful greenhouse gas, in this changing climate. This study investigated the formation of methane hydrates and their gas storage capacity (GSC) in clay‐rich sediments. A set of hydrate experiments were performed in matrices composed of sand, illite‐rich clay, and montmorillonite‐rich clay at different proportions aiming to determine the role of mineralogy on hydrate formation processes. The experiments demonstrate that a clay content of 10% in a partially water saturated sand/clay mixture increases the induction time by ∼60%, irrespective of the nature of the clay used. The increase in water saturation in the two matrices promotes hydrate formation. Micro‐Raman spectroscopic analyses reveal that increasing the clay content leads to a decrease in the hydrate small‐cage occupancy, with an impact on the storage capacity. Finally, the analyses of collected natural samples from the Black Sea (off Romania) enable us to estimate the GSC of the deposit. Our estimates is different from previous ones, and supports the importance of coupling multiscale properties, from the microscale to the geological scale, to accurately assess the total amount of methane hosts in hydrate deposits worldwide. Plain Language Summary: Natural gas hydrates are amongst the largest methane reservoirs on Earth. They are sensitive to temperature increase. Societal and environmental concerns surrounding natural gas hydrates pertain to their decomposition, and in particular to the amount of gas they may release and its fate: can it trigger geohazards, or jeopardize the development of unique chemosynthetic communities encountered on continental margins? In‐depth knowledge of hydrate formation processes and properties are essential to provide reliable answers to these questions. The majority of hydrate deposits are characterized by clay‐rich sediments. We led a comprehensive study coupling fine microstructural analyses of both natural and synthetic hydrate samples with macroscale laboratory experiments within different matrices to show how clays can affect their formation kinetics and storage capacity. We found that even a small amount of clay can significantly change the formation kinetics of hydrates, and the matrix mineralogy affects their storage capacity. This study is crucial with a view to accurately assessing the amount of methane trapped in hydrate deposits, and for improved prediction of the consequences of their decomposition on the environment in a changing climate. Key Points: Clay content and clay mineralogy significantly affect the induction time of methane hydrate formation as well as the hydrate morphologyIllite‐rich clays reduce the cage occupancy of hydrates and thus the resulting gas storage capacity (GSC)Microscale analyses underpins the need to characterize microscopic properties of hydrates to estimate GSC [ABSTRACT FROM AUTHOR]

Heavy metal pollution is an urgent challenge worldwide due to the acceleration of industrialization. While adsorption desalination is regarded as an innovative method for wastewater treatment, the current technologies have been impeded by high costs and intensive energy consumption. In this work, a novel low-temperature evaporation wastewater treatment apparatus based on hydrate adsorption was proposed. The water vapor from wastewater evaporation reacted with CO2 to form hydrate under the pressure of 3.3 MPa, constantly promoting wastewater evaporation due to the consumption of water vapor. The effect of feeding concentration on treatment effect was analyzed in terms of removal efficiency, water yield, and enrichment factor. Remarkably, a maximum removal efficiency of 97.4% can be achieved by treating an artificial solution with a Cu2+ concentration of 500 mg/L. Furthermore, compared with the control group that only depended on evaporation and condensation without forming hydrate, the maximum water yield of purified water in the experimental group increased to 310%. This innovative design concept for a low-temperature wastewater treatment apparatus based on hydrate adsorption presents a promising solution for the green and energy-efficient treatment of heavy metal wastewater. [ABSTRACT FROM AUTHOR]

A series of sulfosuccinate esters of cyclic alcohols was synthesized and we studied their effect on the kinetics of methane hydrate formation in high-pressure autoclaves. The effects of the structure of these compounds on foaming, induction time, and water-to-hydrate conversion were considered in comparison with sodium dodecyl sulfate. The preparation of these compounds was presented in detail. An increase in size of the cyclic fragment from C5 to C7 leads to some increase in the rates of nucleation and growth of the methane hydrate, while going to an eight-membered carbon ring leads to a decrease in the promotion effect. The effect of the synthesized compounds on the increase in rate of gas hydrates is comparable to the effect for sodium dodecyl sulfate. At the same time, the proposed reagents possess better performance characteristics (do not contribute to foaming). [ABSTRACT FROM AUTHOR]

This paper studied the process of methane hydrate formation from frozen solutions containing small amounts of promoters (sodium dodecyl sulfate and tri-sulfonated castor oil) under static conditions using differential scanning calorimetry (DSC). The research revealed regularities of phase transformations under the studied conditions (from ice and/or hydrate crystallization to joint ice melting and hydrate formation). Coupling the DSC tests with visualization of the forming hydrates allowed the factors affecting the growth rate of methane hydrate during ice melting to be established. These factors included the protocol for obtaining hydrates, which involved temperature and pressure control at different stages of the process, and the force of interaction of hydrate crystallites with each other and with cell walls. [ABSTRACT FROM AUTHOR]

A study was carried out on the effect of copolymers derived from maleic anhydride on the formation of a methane-propane hydrate. Isopropylacrylamide was selected as the co-monomer. The polymerization reaction was carried out in petroleum ether. The maleic acid ring was then opened using such nucleophiles as dibutylamine and diethanolamine. Some of the obtained polymers at concentration 0.5 mass % lower the temperature for the onset of hydrate formation similar to the commercial kinetic hydrate inhibitor Luvicap EG. However, the water-to-hydrate conversion was higher in the case of our proposed reagents. The best supercooling result was found for the sample with a higher content of isopropylacrylamide fragments when dibutylamine was used as the nucleophile. The lowest water-to-hydrate conversion was found for the polymer with a higher content of maleic fragments also opened by dibutylamine. [ABSTRACT FROM AUTHOR]

A study was carried out on the promoting activity of amides of ethylenediaminetetraacetic acid (EDTA) and amino acids in the formation of hydrates of methane and carbon dioxide. Most of the compounds studied in 0.05 mass % aqueous solution proved to be hydrate formation promoters in various stages of the formation process such as nucleation and growth. Foaming was not observed. The reagent derived from EDTA and leucine is a promoter of the formation of both methane and carbon dioxide hydrates. In the case of the carbon dioxide hydrate, the shortest induction time was found for the compounds of EDTA with asparagine (19±1 min) and with cysteic acid (29±1 min). The induction times were correspondingly 1.7 and 2.5 times shorter than for the system without additives. [ABSTRACT FROM AUTHOR]