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

Depressurization combined with heat (mainly hot water) injection is an important technique for exploiting natural gas hydrate (NGH). To overcome the problems of pore water intrusion and hot water energy loss in the technique, this paper employs a method of setting sealing boundaries in permeable overburden and underburden to exploit NGH. The influence of the presence of sealing boundaries on NGH exploitation performances was numerically investigated. The results indicate that the sealing boundaries in permeable overburden and underburden can inhibit water intrusion and reduce heat loss, significantly improving the efficiency of hydrate dissociation and gas production. Specifically, the hydrate dissociation and gas production efficiency increased by 22.0–30.1% and 63.9–85.1%, respectively. Moreover, there is an optimal sealing vertical distance within the range of 0–15 m, maximizing the mining efficiency of NGH at the end of production. On the other hand, the presence of sealing boundaries effectively limits the escape range of CH4 in the permeable overburden and underburden, resulting in an increasing gas-to-water ratio and an increasing energy efficiency. These findings provide theoretical and technical support for the mining of NGH by depressurization combined with heat injection. [ABSTRACT FROM AUTHOR]

The exploitation of natural gas hydrates by the pressure reduction method is affected by the decomposition heat absorption effect, and the range of the formation temperature reduction area is expanding. At the same time, the temperature reduction phenomenon is more significant around the production wells under the influence of gas throttling and expansion effects, and hydrate formation will occur under certain temperature and pressure conditions, leading to blockage of effective seepage channels in the reservoir in the region and elevation of seepage resistance, which may affect the output of hydrate decomposition gas. A numerical simulation model is constructed for the purpose of studying the secondary hydrate generation pattern around the well, analyzing the impact of secondary hydrates around wells on the production capacity, and assessing the effectiveness of prevention methods to inform the actual production of hydrates. The results demonstrate that secondary hydrate is typically formed in the near-well area of the upper part of the production well, and the secondary hydrate around the upper part of the production well is the first to be formed, exhibiting the highest saturation peak and the latest decomposition. The formation of the secondary hydrate can be predicted based on the observed change in temperature and pressure, and the rate of secondary hydrate formation is markedly rapid, whereas the decomposition rate, approximately 0.285 mole/d, is relatively slow. Additionally, the impact of secondary hydrates on cumulative gas production is insignificant, and the effect of secondary hydrates on capacity can be ignored. Hot water injection, wellbore heating, and reservoir reconstruction can effectively eliminate secondary hydrates around the well. Reservoir reconstruction represents a superior approach to the elimination of secondary hydrates, which can effectively enhance production capacity while preventing the generation of secondary hydrates. [ABSTRACT FROM AUTHOR]

The efficient utilization of methane, a vital component of natural gas, shale gas and methane hydrate, holds significant importance for global energy security and environmental sustainability. However, converting methane into value-added oxygenates presents a formidable challenge due to its inert nature. Direct selective oxidation of methane (DSOM) under mild conditions is essential for reducing energy consumption and carbon emissions compared with traditional indirect routes. Achieving total selectivity in methane hydroxylation remains elusive due to the competitive CO2 formation. This feature article highlights recent advancements in methane hydroxylation using thermo-, photo-, and electro-catalytic systems. Through strategically designing the structure of catalysts to control the reactive oxygen species and optimizing reaction parameters, significant progress has been made in enhancing oxygenate selectivity and minimizing overoxidation. A comprehensive understanding of the mechanisms underlying methane hydroxylation with total selectivity offers insights for improving catalyst design and reaction parameter optimization, promoting sustainable methane utilization. [ABSTRACT FROM AUTHOR]

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

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Copyright of Low-Carbon Chemistry & Chemical Engineering is the property of Low-Carbon Chemistry & Chemical Engineering Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The accurate prediction of Darcy‐scale permeability (absolute permeability and gas‐water relative permeability) of hydrate‐bearing sediments (HBS) plays a crucial role in assessing reservoir potential and optimizing recovery strategies. However, the challenges of field coring, the rigorous conditions encountered in laboratory permeability tests, and the multi‐scale pore structure characteristics of HBS complicate the understanding of the relationship between pore structures and Darcy‐scale permeability of HBS. In this study, we propose an innovative upscaling method that integrates flow properties of typical regions, such as coarse, medium, and fine regions, to predict the Darcy‐scale permeability of HBS from the pore‐scale. This method considers two hydrate habits (pore‐filling and grain‐coating hydrates), heterogeneity and anisotropy of HBS, and multi‐scale pore structures. Taking the absolute permeability of hydrate‐free sediments in the y direction for example, the permeability values for the fine region, the medium region, the coarse region, and the equivalent HBS are 9.43 D, 13.59 D, 18.87 D, and 14.06 D, respectively. Thus, the predicted permeability (14.06 D) is much closer to the experimental data (15.44 D), which validates the efficacy of our upscaling method in estimating Darcy‐scale permeability. Moreover, the characteristics of our predicted Darcy‐scale permeability align with those reported in previous literature. This approach introduces a groundbreaking perspective for predicting permeability in HBS from pore‐scale to Darcy‐scale. It offers essential insights into predicting permeability in HBS while effectively preserving the impact of pore‐scale structural variations caused by local heterogeneity and facilitating numerical simulations of gas production from hydrate reservoirs. Key Points: An innovative upscaling method is proposed to predict the Darcy‐scale permeability of hydrate‐bearing sedimentsThe predicted permeability exhibits good agreement with test dataThe proposed method allows predicting Darcy‐scale permeability while preserving the effects of micro‐pore structure variation [ABSTRACT FROM AUTHOR]

The saturation of natural gas hydrates is a key parameter for characterizing hydrate reservoirs, estimating hydrate reserves, and developing hydrate as an energy resource. Several methods have been proposed to estimate hydrate saturation, although most of these studies rely on logging and seismic data. However, the methods for estimating hydrate saturation from recovered core sediments have not been thoroughly reviewed, which hinders a deeper understanding, proper application, and the use of these experimental data to integrate geophysical and numerical model results with the actual geological conditions. In this paper, the methods widely used for estimating natural gas hydrate saturation from core sediments, including those based on pore water chemistry (Cl− concentration, δD, and δ18O values), gas volumetric analysis, and temperature anomaly, have been summarized in terms of the principle, estimation strategy, and issues to be considered of each method. The applicability, advantages and disadvantages, and scope of application of each method are also compared and discussed. All methods for estimating gas hydrate saturation have certain limitations. A comprehensive application of results from multiple methods could lead to a better understanding of the amount of gas hydrate in sediments, although the chlorinity of pore water is the most commonly used method of estimation. [ABSTRACT FROM AUTHOR]

Methane gas hydrates (MGH), which are hosted in gas hydrate-bearing sediments (GHBS) located beneath the ocean bed and permafrost regions, are considered a panacea to meet the huge energy requirements of present-day society. GHBS are a multiphase system that comprises gas hydrates and ice crystals (in permafrost regions) apart from the soil minerals, water and gas. It is worth realising that the production of methane gas from GHBS is a complex process that couples phase transition (MGH to water and methane gas), multiphase, multi-component heat flow and mass flow and their mechanical stability. Hence, establishing the thermo-hydro-mechanical properties of GHBS is paramount for the safe and efficient production of methane gas from GHBS. As the formation of hydrates deals with exposure of the sediments to low temperatures and high pressures, needs-based laboratory setups and instrumentation were developed, and their utility has been demonstrated in this paper for establishing the soil freezing characteristics curve, thermal and shear strength characteristics, and synthesising gas hydrates. A critical synthesis of these results reveals that temperature and volumetric ice content influence the thermal and shear strength properties and volumetric ice content of the fine-grained sands. At the same time, the compression and shear wave velocities of gas hydrate-bearing fine-sands were found to depend on the hydrate saturation. Efforts have also been made to model the methane gas production from a typical turbidite reservoir of Krishna Godavari Basin, India, by employing vertical and horizontal wellbores. [ABSTRACT FROM AUTHOR]

Natural gas production from reservoirs is often associated with water, which poses numerous challenges, such as methane hydrate formation, sludge, corrosion and flow assurance issues in gas processing plants and sales gas transmission pipelines. To effectively remove water from natural gas, there is a need to design, compare and modify dehydration plants. This study investigated the performance difference between a conventional triethylene glycol (TEG)‐based dehydration system with a cooler at the TEG inlet to the contactor, and a newly proposed TEG‐based dehydration system with a heat exchanger replacing the cooler at the TEG inlet with the contactor. The advanced process simulation software Aspen HYSYS was used to design and compare two dehydration system configurations. The modified design configuration exhibited better performance in terms of energy conservation and water‐removal capability. The material balance of molar flow, mass flow and volume flow of dry gas produced in the absorber/contactor column showed a higher volume of dry gas produced in the modified system configuration, indicating that it is a better design. The modified design configuration also produced dry gas within the recommended temperature range for underground storage and transmission. There was a significant difference in the percentage difference of 64% between the conventional and modified designs in terms of energy consumption, whereas the percentage differences of 0% and 0.6% showed nonsignificant and significant differences between the two plant design configurations. Both plant design configurations showed a significant reduction (from 0.005 to 0.0002 mol%) in the water composition of natural gas after the simulation. [ABSTRACT FROM AUTHOR]

Active and relic marine methane‐seep sites are widely distributed globally and are distinguished by distinctive geology, biogeochemistry, and ecosystems. The discovery of methane‐seep sites in the Krishna‐Godavari (K‐G) basin has created exciting new opportunities for methane‐seep research in the Bay of Bengal. In this study, we document the occurrence of authigenic carbonates, including micro‐crystalline aragonite crust (arg‐crusts) admixed with chemosynthetic shells and high‐magnesium carbonate tubular structures (HMC‐tube), from the methane‐seep site SSD‐045/4 in the K‐G basin. The δ13C values of HMC‐tubes (−54.5 to −46.2‰) and arg‐crusts (−57.6 to −34.8‰) indicate biogenic methane as the likely carbon source. Enhanced porewater alkalinity driving carbonate precipitation may be attributed to microbial‐mediated SO₄2−‐AOM processes. Additionally, δ13C values (−35.2 ± 8‰) of the residual organic matter within the carbonates suggest a contribution of methanotrophic bacterial biomass. The δ18Ocarb values of HMC and aragonite indicate methane hydrate degassing and crystallization pathways, respectively. Pelloid‐filled burrows suggest the reworking of shallow HMC deposit by burrowing organisms, whereas the polyphase cementations (aragonite and HMC) within burrows indicate early and burial diagenetic pathways. The wide range in ΣLREE/ΣHREE ratios and Ceanom values in arg‐crusts reflect micro‐spatial variations in redox conditions, likely due to cementation occurring in both open and closed diagenetic systems. In contrast, more constrained Ceanom values and ΣLREE/ΣHREE ratios in HMC tubes suggest persistent sulfidic conditions. Overall, these findings provide insights into the pathways of carbonate formation at the K‐G basin methane‐seep site, highlighting the complex interplay of microbial processes, fluid dynamics, and diagenetic alterations. Plain Language Summary: Methane cold‐seeps are regions on the seabed where methane (CH4) gas oozes out across the sediment‐water interface into the water column. Both active and inactive seepage sites are known across the oceans. Active methane seep sites expel significant quantities of methane into the seawater which influences the oceanic methane budget as well as the carbon cycle. In contrast, the preserved authigenic carbonate deposits and chemosynthetic fauna at the relic seep sites are archives of past seepage activities. The seep ecosystem comprises a variety of chemosynthetic and non‐chemosynthetic organisms, whereas the geological features include mounds, mud volcanoes, carbonate crusts, chimneys, etc. formed due to methane expulsion processes. Here, we investigate the origin of calcium carbonate structures formed in a cold seep region off the east coast of India. The carbonate structures include tubular‐shaped high magnesian carbonates (HMC) and crusts composed of aragonite minerals. These tubes and crusts archive biological and geological processes, including past variations in methane effusion and diffusion through the sediment. Tubular structures are formed by gas flow through the sediments as chimneys and by burrowing activities of benthic organisms. On the other hand, the aragonite crusts are formed where methane flow is high across the seabed. Key Points: Relics of methanogenic high magnesian calcite tubes and aragonite crust recovered from cold seep site K‐G basin east coast of IndiaHMC precipitation is confined to sulfidic conditions in contrast to a wider redox range for aragonite precipitationReworking of unconsolidated HMC produced the pelloid rich tubular structures, whereas aragonite crust formed at high CH4 flow conditions [ABSTRACT FROM AUTHOR]

Mysterious craters, with anomalously high concentrations of methane, have formed in the Yamal and Taymyr peninsulas of Siberia since 2014. While thawing permafrost owing to climate warming promotes methane releases, it is unknown how such release might be associated with explosion and crater formation. A significant volume of surface ice‐melt water can migrate downward driven by osmotic pressure associated with a cryopeg, a lens of salty water below. Overpressure reached at depth may lead to the cracking of the soil and subsequent decomposition of methane hydrates, with implications for the climate. Plain Language Summary: We show how osmosis drives explosions and methane release in Siberian permafrost. We anticipate that as well as being of direct relevance to permafrost researchers, this work will be of interest to a large number of people involved in climate change research, because the mechanism we uncover of osmotic pumping leading to permafrost explosions has potentially grave consequences involving the release of methane presently locked up in hydrates. Key Points: Surface ice‐melt water can migrate downward driven by the osmotic pressure associated with a cryopeg, a lens of salty water belowOverpressure can cause the frozen soil to crack resulting in mechanical explosion [ABSTRACT FROM AUTHOR]

A study was carried out on the effect of copolymers derived from maleic anhydride and isopropylacrylamide on the formation of the methane-propane hydrate. The polymerization was carried out in petroleum ether and dimethylformamide. The maleic anhydride ring was then opened by dibutylaminopropylamine. Some of the resultant polymers at concentration 0.5 mass % demonstrated a reduction in the temperature for the onset hydrate formation and in the conversion of gas into hydrate resembling commercial kinetic hydrate formation inhibitors Luvicap EG and PNIPAM. The best supercooling results were found for the sample with an enhanced content of isopropylacrylamide fragments. The least conversion of gas to hydrate was observed for the system containing maleic anhydride homopolymer modified with dibutylaminopropylamine. [ABSTRACT FROM AUTHOR]

A differential thermal analysis study was carried out on the formation and decomposition of hydrates in systems containing natural gas, sand, and 5 mass % aqueous NaHCO3 as well as natural gas, sand, and 5 mass % aqueous NaCl with initial gas pressures from 3 to 9 MPa. Equilibrium conditions, enthalpy of dissociation, and the kinetic parameters of hydrate formation were determined. Hydrate formation in the system containing aqueous sodium bicarbonate proceeds at higher temperatures and lower pressures and has higher kinetic parameters than in the system with aqueous sodium chloride of the same concentration. Composition of the solutions is one of the factors affecting hydrate formation in the studied systems. The HCO3– ion is found to have a greater structure-making effect than the Cl– ion, which leads to differences in the thermodynamic conditions and kinetic parameters of natural gas hydrate formation in a porous medium. [ABSTRACT FROM AUTHOR]

Results are given for a study of the thermodynamic conditions of the natural gas hydrates formation in a dispersed medium saturated with water, polymer solutions and their mixtures with aqueous CaCl2 as well as the gas composition in the resultant hydrates. Natural gas in all studied systems is found to form a mixture of hydrates of methane (first-stage hydrates with cubic structure I) and of natural gas (second-stage hydrates with cubic structure II). The equilibrium conditions of the second-stage hydrates formation are shifted toward higher temperatures by 0.5-1°C relative to the calculated equilibrium curve, this is probably caused by the concentration of C2-C4 hydrocarbons in the hydrate. The presence of CaCl2 leads to a shift of the equilibrium conditions of the second-stage hydrates formation in comparison to the calculated curves toward higher temperatures and lower pressures with an increase of C2-C4 components in the hydrates. No specific effect was found for CaCl2 on the thermodynamic conditions of natural gas hydrate formation in a dispersed medium in a mixture with polymer solutions since these data obtained for the equilibrium conditions of the natural gas hydrates formation are identical with the data obtained upon hydrate formation in solutions of CaCl2 and water. [ABSTRACT FROM AUTHOR]

In this work, we studied new citric acid derivatives of some amino acids, which improve the formation kinetics of methane hydrate at low concentrations. These compounds hold potential as efficient promoters of hydrate formation with the advantage that they do not foam upon release of the gas from the hydrates. The modification of the amino acids by citric acid enhances their efficiency as kinetic promoters of methane hydrate formation relative to the unmodified amino acids. This leads to shortening of the induction time and time to achieve maximal conversion of water to hydrate as well as to enhancing the methane uptake. The amide of norleucine and citric acid enhances the conversion of water to hydrate relative to the unmodified amino acid. For 0.05 mass % solutions, the conversion is increased by 5% to 89%, which corresponds to the absorption of 0.148 mole of methane per 1 mole of water. This modification of norleucine also leads to shortening of the induction time by a factor of 1.6 and of the time to reach maximal conversion by a factor of 2.8 relative to unmodified norleucine. [ABSTRACT FROM AUTHOR]

This paper introduces a laboratory setup designed to produce gas hydrate under static conditions and to compress hydrate pellets directly within the reactor. The setup is intended to facilitate development of effective methods for obtaining and storing gas hydrates. The paper discusses the design specifics of the setup, outlines the sequence of operations for producing methane hydrate and granules from it, and provides examples of experimental data related to accelerated production and compression of methane hydrate from a kinetic promoter solution. [ABSTRACT FROM AUTHOR]

The kinetics of hydrate formation in powder hydrogel systems saturated with aqueous surfactant solutions and stabilized with hydrophobic nanoparticles was studied. The systems were also studied for stability in multiple hydrate formation and dissociation cycles, i.e., for their capacity to maintain the original rate and degree of conversion of water to hydrate in the second and subsequent cycles. [ABSTRACT FROM AUTHOR]

Results are given for a study of the thermobaric conditions and kinetics of the methane hydrate formation in bulk solutions with 0.5 mass % soy lecithin obtained in distilled water and aqueous salt solutions (containing 1 and 3 mass % NaCl) at 273.2 K and driving force 4 MPa without stirring. The addition of soy lecithin was found not to lead to a shift in the water‑hydrate‑methane phase equilibrium diagram. The presence of NaCl was found to lead to a 50% decrease in the absorption of methane into the hydrate in comparison with the soy lecithin solutions without NaCl. This finding can be attributed to precipitation of the soy lecithin in the salt solutions. [ABSTRACT FROM AUTHOR]

This study examined the stability of methane hydrate at a concentration of 20 mass % in aqueous solutions of allyl and propargyl alcohols. The research determined the position of the three-phase equilibrium «alcohol solution - hydrate - gas» in the pressure range of 3.68 to 9.53 MPa. A comparison of the data revealed that the equilibrium conditions for hydrate formation for both alcohols are the same at lower pressures. However, at higher pressures, the curve for allyl alcohol deviates towards lower temperatures by 0.6°C. The study found that these alcohols act as thermodynamic inhibitors of hydrate formation. From a practical viewpoint, these systems can be used in the gas industry to prevent hydrate formation and address issues related to formed hydrates. [ABSTRACT FROM AUTHOR]

The heat transfer and stability of methane hydrate in reservoirs have a direct impact on the drilling and production efficiency of hydrate resources, especially in complex stress environments caused by formation subsidence. In this study, we investigated the thermal transport and structural stability of methane hydrate under triaxial compression using molecular dynamics simulations. The results suggest that the thermal conductivity of methane hydrate increases with increasing compression strain. Two phonon transport mechanisms were identified as factors enhancing thermal conductivity. At low compressive strains, a low-frequency phonon transport channel was established due to the overlap of phonon vibration peaks between methane and water molecules. At high compressive strains, the filling of larger phonon bandgaps facilitated the opening of more phonon transport channels. Additionally, we found that a strain of −0.04 is a watershed point, where methane hydrate transitions from stable to unstable. Furthermore, a strain of −0.06 marks the threshold at which the diffusion capacities of methane and water molecules are at their peaks. At a higher strain of −0.08, the increased volume compression reduces the available space, limiting the diffusion ability of water and methane molecules within the hydrate. The synergistic effect of the strong diffusion ability and high probability of collision between atoms increases the thermal conductivity of hydrates during the unstable period compared to the stable period. Our findings offer valuable theoretical insights into the thermal conductivity and stability of methane hydrates in reservoir stress environments. [ABSTRACT FROM AUTHOR]

In ultra-deep water drilling, the formation of natural gas hydrates aways endanger the safety of drilling and production. The development of excellent kinetic hydrate inhibitors (KHI) which are compounded with thermodynamic is of great importance to the effective inhibition of gas hydrates in ultra-deep water drilling. Using 4-acryloyl morpholine and N-vinylpyrrolidone to copolymerize in different molar ratios to produce kinetic gas hydrate inhibitor ACNs. The reaction conditions are optimized through single-factor method, the reaction products are analyzed by IR, SEM and gel permeation chromatograph, and the properties of the products are evaluated by methane-hydrate simulation (MHS) test and tetrahydrofuran (THF) inhibition performance test. Through the evaluation and test, the best ACN is selected, and is compared with other KHIs. The best ACN is then compounded with thermodynamic gas hydrate inhibitors to produce a gas hydrate inhibitor for use in drilling fluids for drilling in areas with water depth of more than 2,000 m and with narrow safe drilling windows. XXXX found in studies that the best ACN can be obtained when AIBN is used as the reaction initiator and let the monomers react under 65 ℃ for 6 h, and 2% ACN (4∶6) has the optimum inhibition. The formulation of the gas hydrate inhibitor is 2%ACN + 1%KHI-1 + 35%glycol + 5%NaCl. The density of the gas hydrate inhibitor is 1.078 g/cm³, and the initial crystallization time of the gas hydrate inhibitor measured at −25 ℃with THF method is 32 min. The drilling fluid tested has a density of 1.150 g/cm³, a high temperature high pressure filtration rate of less than 17 mL, and a percent shale cuttings recovery in hot rolling test of greater than 82%, satisfying the relevant requirements for the drilling fluid. [ABSTRACT FROM AUTHOR]

Most of the implemented marine gas hydrate test exploitation in the world adopt the depressurization method to break down the hydrate in the reservoir into natural gas and then extract it, but because the gas production results are still a certain distance away from the commercial exploitation, and it mainly stays in the stage of theoretical research and trial exploitation. Based on two trial productions in the Shenhu area of the South China Sea, this study established a model for hydrate exploitation and investigated the impact of different well types on the recovery rates of hydrates and free gas in different development layers during depressurization. For the Class 1 hydrate reservoirs, horizontal wells are the optimal solution to extract hydrate and free gas simultaneously when exploiting the hydrate three-phase layer. Meanwhile, the effect of different well spacing in vertical wells on the recovery rate of hydrate and free gas was studied. It is found that the best recovery efficiency is achieved when the spacing between two wells is 80 m. The lower the bottom flow pressure of the well, the higher the production capacity, but its influence is limited. [ABSTRACT FROM AUTHOR]

The behavior of low concentrations of methanol (0.5 and 1.0 wt% of water) as a promoter for hydrate formation in seawater or pure water metastable solutions of methane was investigated using the classical molecular dynamics method at moderate temperature and pressure. The influence of methanol on the dynamics of the re-arrangement of the hydrogen bond network in seawater and pure water solutions of methane was studied by calculating order parameters of the tetrahedral environment and intermolecular torsion angles for water molecules, as well as by calculating the number of hydrogen bonds, hydrate, and hydrate-like cavities. It was found that hydrate nucleation can be considered a collective process in which the rate of hydrate growth is faster in systems with low concentrations of methanol, and confident hydrate growth begins earlier in a metastable solution without sea salt with a small amount of methanol than in systems without methanol. [ABSTRACT FROM AUTHOR]

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

We investigate the effect of pressure on the carbon dioxide (CO2) hydrate–water interfacial free energy along its dissociation line using advanced computer simulation techniques. In previous works, we have determined the interfacial energy of the hydrate at 400 bars using the TIP4P/Ice and TraPPE molecular models for water and CO2, respectively, in combination with two different extensions of the Mold Integration technique [J. Colloid Interface Sci. 623, 354 (2022) and J. Chem. Phys. 157, 134709 (2022)]. Results obtained from computer simulation, 29(2) and 30(2) mJ/m2, are found to be in excellent agreement with the only two measurements that exist in the literature, 28(6) mJ/m2 determined by Uchida et al. [J. Phys. Chem. B 106, 8202 (2002)] and 30(3) mJ/m2 determined by Anderson et al. [J. Phys. Chem. B 107, 3507 (2002)]. Since the experiments do not allow to obtain the variation of the interfacial energy along the dissociation line of the hydrate, we extend our previous studies to quantify the effect of pressure on the interfacial energy at different pressures. Our results suggest that there exists a correlation between the interfacial free energy values and the pressure, i.e., it decreases with the pressure between 100 and 1000 bars. We expect that the combination of reliable molecular models and advanced simulation techniques could help to improve our knowledge of the thermodynamic parameters that control the interfacial free energy of hydrates from a molecular perspective. [ABSTRACT FROM AUTHOR]

In this paper, the solubility of carbon dioxide (CO2) in water along the isobar of 400 bar is determined by computer simulations using the well-known TIP4P/Ice force field for water and the TraPPE model for CO2. In particular, the solubility of CO2 in water when in contact with the CO2 liquid phase and the solubility of CO2 in water when in contact with the hydrate have been determined. The solubility of CO2 in a liquid–liquid system decreases as the temperature increases. The solubility of CO2 in a hydrate–liquid system increases with temperature. The two curves intersect at a certain temperature that determines the dissociation temperature of the hydrate at 400 bar (T3). We compare the predictions with T3 obtained using the direct coexistence technique in a previous work. The results of both methods agree, and we suggest 290(2) K as the value of T3 for this system using the same cutoff distance for dispersive interactions. We also propose a novel and alternative route to evaluate the change in chemical potential for the formation of hydrates along the isobar. The new approach is based on the use of the solubility curve of CO2 when the aqueous solution is in contact with the hydrate phase. It considers rigorously the non-ideality of the aqueous solution of CO2, providing reliable values for the driving force for nucleation of hydrates in good agreement with other thermodynamic routes used. It is shown that the driving force for hydrate nucleation at 400 bar is larger for the methane hydrate than for the carbon dioxide hydrate when compared at the same supercooling. We have also analyzed and discussed the effect of the cutoff distance of dispersive interactions and the occupancy of CO2 on the driving force for nucleation of the hydrate. [ABSTRACT FROM AUTHOR]

Clathrate hydrates are crystalline inclusion compounds wherein a water framework encages small guest atoms/molecules within its cavities. Among the others, methane clathrates are the largest fossil fuel resource still available. They can also be used to safely transport gases and can also form spontaneously under suitable conditions plugging pipelines. Understanding the crystallization mechanism is very important, and given the impossibility of experimentally identifying the atomistic path, simulations played an important role in this field. Given the large computational cost of these simulations, in addition to all-atom force fields, scientists considered coarse-grained water models. Here, we have investigated the effect of coarse-graining, as implemented in the water model mW, on the crystallization characteristics of methane clathrate in comparison with the all-atom TIP4P force field. Our analyses revealed that although the characteristics directly depending on the energetics of the water models are well reproduced, dynamical properties are off by the orders of magnitude. Being crystallization a non-equilibrium process, the altered kinetics of the process results in different characteristics of crystalline nuclei. Both TIP4P and mW water models produce methane clathrate nuclei with some amount of the less stable (in the given thermodynamic conditions) structure II phase and an excess of pentagonal dodecahedral cages over the tetrakaidecahedral ones regarding the ideal ratio in structure I. However, the dependence of this excess on the methane concentration in solution is higher with the former water model, whereas with the latter, the methane concentration in solution dependence is reduced and within the statistical error. [ABSTRACT FROM AUTHOR]

In this work, we shall estimate via computer simulations the homogeneous nucleation rate for the methane hydrate at 400 bars for a supercooling of about 35 K. The TIP4P/ICE model and a Lennard-Jones center were used for water and methane, respectively. To estimate the nucleation rate, the seeding technique was employed. Clusters of the methane hydrate of different sizes were inserted into the aqueous phase of a two-phase gas–liquid equilibrium system at 260 K and 400 bars. Using these systems, we determined the size at which the cluster of the hydrate is critical (i.e., it has 50% probability of either growing or melting). Since nucleation rates estimated from the seeding technique are sensitive to the choice of the order parameter used to determine the size of the cluster of the solid, we considered several possibilities. We performed brute force simulations of an aqueous solution of methane in water in which the concentration of methane was several times higher than the equilibrium concentration (i.e., the solution was supersaturated). From brute force runs, we infer the value of the nucleation rate for this system rigorously. Subsequently, seeding runs were carried out for this system, and it was found that only two of the considered order parameters were able to reproduce the value of the nucleation rate obtained from brute force simulations. By using these two order parameters, we estimated the nucleation rate under experimental conditions (400 bars and 260 K) to be of the order of log10 (J/(m3 s)) = −7(5). [ABSTRACT FROM AUTHOR]

The interactions between molecules and electrode surfaces play a key role in electrochemical processes and are a subject of extensive research, both experimental and theoretical. In this paper, we address the water dissociation reaction on a Pd(111) electrode surface, modeled as a slab embedded in an external electric field. We aim at unraveling the relationship between surface charge and zero-point energy in aiding or hindering this reaction. We calculate the energy barriers with dispersion-corrected density-functional theory and an efficient parallel implementation of the nudged-elastic-band method. We show that the lowest dissociation barrier and consequently the highest reaction rate take place when the field reaches a strength where two different geometries of the water molecule in the reactant state are equally stable. The zero-point energy contributions to this reaction, on the other hand, remain nearly constant across a wide range of electric field strengths, despite significant changes in the reactant state. Interestingly, we show that the application of electric fields that induce a negative charge on the surface can make nuclear tunneling more significant for these reactions. [ABSTRACT FROM AUTHOR]

Methane hydrates are important from a scientific and industrial perspective, and form by nucleation and growth from a supersaturated aqueous solution of methane. Molecular simulation is able to shed light on the process of homogeneous nucleation of hydrates, using straightforward molecular dynamics or rare event enhanced sampling techniques with atomistic and coarse grained force fields. In our previous work [Arjun, T. A. Berendsen, and P. G. Bolhuis, Proc. Natl. Acad. Sci. U. S. A. 116, 19305 (2019)], we performed transition path sampling (TPS) simulations using all atom force fields under moderate driving forces at high pressure, which enabled unbiased atomistic insight into the formation of methane hydrates. The supersaturation in these simulations was influenced by the Laplace pressure induced by the spherical gas reservoir. Here, we investigate the effect of removing this influence. Focusing on the supercooled, supersaturated regime to keep the system size tractable, our TPS simulations indicate that nuclei form amorphous structures below roughly 260 K and crystalline sI structures above 260 K. For these temperatures, the average transition path lengths are significantly longer than in our previous study, pushing the boundaries of what can be achieved with TPS. The temperature to observe a critical nucleus of certain size was roughly 20 K lower compared to a spherical reservoir due to the lower concentration of methane in the solution, yielding a reduced driving force. We analyze the TPS results using a model based on classical nucleation theory. The corresponding free energy barriers are estimated and found to be consistent with previous predictions, thus adding to the overall picture of the hydrate formation process. [ABSTRACT FROM AUTHOR]

This document is a summary of a special issue titled "Macroscopic and Microscopic Thermodynamics: From Fundamentals to Present Applications, 2nd Edition." It explores the broad field of thermodynamics and its applications in various scientific disciplines. The article discusses the historical development of thermodynamics and its expansion into fields such as cosmology, information science, and social sciences. It also highlights the importance of molecular thermodynamics in chemical engineering and the use of computational methods in solving thermodynamic problems. The document provides a list of the contributions included in the special issue, which cover topics such as vapor-liquid equilibrium, clathrate hydrates, binary mixtures, and surface tension. The authors emphasize the importance of thermodynamics in addressing theoretical and practical problems and highlight its potential for further research in fields like process engineering, human health, and environmental preservation. [Extracted from the article]

The degree and amount of sand production in hydrate reservoirs is related to the selection of stable production processes, but there is currently a lack of quantitative sand production prediction research using real logging data and formation samples from hydrate reservoirs. To reveal the dynamic change characteristics of in-situ reservoirs during hydrate decomposition, and explore quantitative prediction methods for guiding production practice, it is conducted a series of numerical simulations and quantitative prediction experiments. The numerical simulations are carried out using different sand-out prediction methods by using hydrate logging data during drilling, while quantitative prediction experiments of water production and sand-out are carried out based on in-situ reservoir samples. Our experiments indicate that hydrate mining is facing a serious risk of sand-out. The particle transport in the reservoir changes from "large-channel seepage" to "umbrella seepage" and then to "uniform fine flow" as the replacement flow rate decreases. A quantitative prediction model for water and sand production is also established. As a result, our study can provide support for the advancement of technology for long-term stable production and sand control of hydrates, laying the groundwork for developing a stable production plan for natural gas hydrates in offshore areas and determining the optimal depressurisation method. [ABSTRACT FROM AUTHOR]

Due to high energy density, clean combustion products and abundant resources, natural gas hydrates (NGHs) have been regarded as an important clean energy source with the potential for large-scale development and utilization. However, pilot tests in NGHs show that their production rates are far below commercial needs. Multilateral well technology may lead to a solution to this problem because it can dramatically expand the drainage area of production wells. This paper presents the practical rate transient analysis for multilateral horizontal wells in NGHs. In developing solution to the diffusivity equation of multilateral horizontal wells in NGHs, the superposition principle and reciprocity are applied. We wrote the governing equation in cylindrical coordinates to describe the NGH flow process. We used the moving boundaries and dissociation coefficients to model the solid-to-gas transition process in hydrates. To obtain solutions for flow in hydrate reservoirs, we used Laplace transforms and the Stehfest numerical inversion method. Superposition principle and Gaussian elimination are applied to obtain the desired solution for multilateral horizontal wells. We validated our proposed model with a commercial numerical simulator. By performing sensitivity analyses, effects on production behavior of the number of branches, dissociation coefficient, radius of the region with dissociated hydrate, and dispersion ratio are determined. A synthetic case study is conducted to show the typical production behaviors. [ABSTRACT FROM AUTHOR]

Accurate estimation of gas hydrate formation condition is crucial for many reasons. In one hand, the gas hydrate formation is a promising approach for gas separation, cold energy storage, seawater desalination, etc. On the other hand, in some industries, this phenomenon may cause some challenges, such as pipelines blockage. The current study was undertaken to develop trustworthy predictive tools for methane hydrate formation temperature (MHFT) in the presence of brines. To achieve this target, 1051 experimental data pertinent to the methane hydrate equilibrium in 26 single and multiple brines over an extensive range of operating conditions were amassed from published studies. Four simple factors, including pressure, brine concentration, salt molecular weight and salt melting temperature were defined as the input variables, and the black-box intelligent techniques, including gaussian process regression (GPR), multilayer perceptron (MLP) and radial basis function (RBF) were employed to link MHFT to the mentioned factors. A plethora of graphical and statistically-based assessments were performed to determine the accuracy level of the proposed models. While all intelligent models had excellent performances, the one established by the GPR method showed the best agreements with experimental data, and gave the AARE and R2 values of 0.14% and 99.17%, respectively, in the testing step. The foregoing model was capable of predicting MHFT over a broad range of conditions with relative deviations mostly below 0.10%. Additionally, it showed an excellent performance in describing the physical variations of MHFT versus operating factors. The authority of the analyzed databank and the presented model was asserted via the William's plot investigation. Moreover, a sensitivity analysis was undertaken in order to determine the most fundamental factors in controlling MHFT. Eventually, a simple mathematical correlation was also derived based on the white-box intelligent approach of gene expression programming (GEP), which allowed the accurate estimation of MHFT with an AARE of 0.56%. [Display omitted] • Smart predictive models were presented for methane hydrate formation condition. • 1051 methane hydrate equilibrium data in the presence of 26 brines were analyzed. • The GPR method presented the best predictions with the testing AARE of 0.14%. • The models favorably described the physical variations of MHFT. • A simple and accurate MHFT correlation was derived by the GEP approach. [ABSTRACT FROM AUTHOR]

The aim of this study was to determine the influence of four inorganic salts, KCl, NaCl, KBr and NaBr, on the thermodynamic conditions of methane hydrate formation. In order to achieve this, the vapor–liquid water-hydrate (VLWH) equilibrium conditions of methane (CH4) hydrate were measured in the temperature range of 274.15 K–282.15 K by the isothermal pressure search method. The results demonstrated that, in comparison with deionized water, the four inorganic salts exhibited a significant thermodynamic inhibition on CH4 hydrate. Furthermore, the inhibitory effect of Na+ on methane hydrate is more pronounced than that of K+, where there is no discernible difference between Cl− and Br−. The dissociation enthalpy ( ∆ H d i s s ) of CH4 hydrate in the four inorganic salt solutions is comparable to that of deionized water, indicating that the inorganic salt does not participate in the formation of hydrate crystals. The Chen–Guo hydrate model and N–NRTL–NRF activity model were employed to forecast the equilibrium conditions of CH4 hydrate in electrolyte solution. The absolute relative deviation (AARD) between the predicted and experimental values were 1.24%, 1.08%, 1.18% and 1.21%, respectively. The model demonstrated satisfactory universality and accuracy. This study presents a novel approach to elucidating the mechanism and model prediction of inorganic salt inhibition of hydrate. [ABSTRACT FROM AUTHOR]

The thermodynamic effect of octyl-β-D-glucopyranoside (OGP) on the formation of methane-1,3-dimethylcyclohexane (DMCH) hydrate was studied in this work. The thermodynamic equilibrium hydrate formation pressures between 275.15 K and 283.15 K were measured by the isothermal pressure search method. Different OGP aqueous solutions (0, 0.1, and 1 wt%) were used in this work. The experimental results show that OGP had no obvious thermodynamic inhibition on methane-DMCH hydrate formation when its concentration was low (0.1 wt%), whereas it had an inhibition on methane-DMCH hydrate formation when its concentration was high (1 wt%). The phase equilibrium hydrate formation pressure of the methane-DMCH-OGP system is about 0.1 MPa higher than that of the methane-DMCH system. The dissociation enthalpies of methane hydrate in different solutions remained uniform, which indicates that OGP was not involved in methane-DMCH hydrate formation. This phenomenon is explained from the perspective of the molecular structure of OGP. As a renewable and biological nonionic surfactant, the concentration of OGP in the liquid phase is low, so OGP can be added to the methane-DMCH system without significant thermodynamic inhibition. [ABSTRACT FROM AUTHOR]

Recently, it was found that mud flocculates, or flocs, coexist with methane hydrate within turbidite layers off the Japanese coast. There is a concern that mud flocs may be broken down by the flow of pure water generated from the dissociation of methane hydrate, causing sand troubles in the production wells. To clarify the characteristics of the flocs, in this study, the samples of mud flocs collected from natural cores having contained methane hydrate were observed before and after sonication in a pure-water ultrasonic bath. Then, these flocs were placed in distilled water flow to investigate their mechanical stability. As a result, it was confirmed that the flocs mainly consist of silt together with a little clay and fine sand. In addition, these flocs were found to be stable for flow rates on the order of magnitude of 10−3 m/s, which is expected inside the strata during gas production from methane hydrate. However, it was also found that, after the distilled water flow experiments, the flocs were decomposed into silt and clay particles when pressed with a handheld needle in the air, suggesting that the floc might be a source of the fine particles as underground stress conditions change, although not many flocs are likely to be immersed in pure water alone. [ABSTRACT FROM AUTHOR]

Understanding the acoustic characteristics of hydrates in various sediments is crucial for hydrate resource detection and safe and efficient exploitation, as hydrate occurrence patterns vary greatly in different sediments. In this work, sediments with different bentonite contents, water saturations, and types were prepared to investigate the characteristics of P-wave velocity (reflecting the magnitude of hydrate saturation in the sediment) and amplitude (reflecting the degree of hydrate-sediment cementation) during hydrate formation and depressurization. During hydrate formation, the P-wave velocity and amplitude have similar trends. As clay content increases, the P-wave velocity increase rates quickened. On the other hand, the increased rate of P-wave velocity slows down with the increase of water saturation in the clay-bearing sediments. Comparing various types of sediment shows that the water absorption and swelling of bentonite reduce the pore space, speeding up the cementation of the hydrate with the sediment and increasing P-wave velocity at a faster rate. Correspondence between P-wave velocity and hydrate saturation is strongly related to sediment type, clay content, and water saturation. The rapidly decreasing amplitude in the early stage of hydrate depressurization indicates that hydrate in clay-bearing sediments is weakly cemented to the sediments, which is prone to stratigraphic instability. The findings of this study offer guidance for hydrate resource assessments in clay-bearing sediments as well as geologic risk estimations during hydrate mining. [ABSTRACT FROM AUTHOR]

From December 2021 to January 2022, MH21-S conducted an exploratory drilling campaign using logging-while-drilling tools to confirm the methane hydrate concentrated zone (MHCZ) for future offshore production tests. In a preliminary screening study using seismic survey data, methane hydrate (MH) prospects have been extracted in The Hyuganada Sea, offshore Kyushu. In the exploration drilling site, a previous study had reported that MH prospects were inferred from four indices. We have selected two MH prospects: one with an anticlinal structure and another with a planus structure. As a result of drilling, a resistivity value higher than 3 Ω·m, which was a criterion for interpreting MHCZs from log data, was confirmed at a depth of 336–376 mBSF in the prospect with an anticlinal structure. The MH saturation calculated using Archie's formula was 12–95% (average saturation of 70%). The average density porosity at the same depth was 52%. P-wave velocities were faster than the upper layers. Compared with those of the MHCZ at Daini Atsumi Knoll, the MH saturation is expected to be higher, the spread of some strong-amplitude reflectors has been interpreted from seismic survey data, and the potential MH resources in this area can be sufficiently expected. [ABSTRACT FROM AUTHOR]

In this paper, a one-dimensional model of gas–water two-phase productivity for hydrate depressurization is established, which takes into account permeability variation and gas–water two-phase flow. By solving the coupled algebraic equations of dissociation front position, equilibrium temperature, and pressure in an iterative scheme, the movement law of the hydrate dissociation front and the evolution process of temperature and pressure near the well were obtained, and the effects of bottom hole pressure, reservoir temperature, and hydrate saturation on productivity were analyzed. The results show that the hydrate reservoir is divided into a decomposed zone and an undecomposed zone by the dissociation front, and the temperature and pressure gradients of the former are greater than those of the latter. Reducing bottom hole pressure, increasing reservoir temperature, and increasing hydrate saturation all lead to an increase in temperature and pressure gradient in the decomposed zone. Methane gas production is a sensitive function of bottom hole pressure, reservoir temperature, and hydrate saturation. The lower the bottom hole pressure, the higher the reservoir temperature, the lower the hydrate saturation (within a certain range), and the higher the gas production rate. The trend of the water production curve is the same as that of gas, but the value is 3–4 orders of magnitude smaller, which may be due to the large difference in the viscosity of gas and water, and the gas seepage speed is much larger than that of water. [ABSTRACT FROM AUTHOR]

Natural gas hydrate is a kind of low-carbon and clean new energy, so research on its efficient extraction in terms of theory and technology is particularly important. Combined thermal injection and depressurization is an effective method for extracting natural gas hydrate. In this study, the classical local heat equilibrium model was modified, and a pore-scale fully coupled unsteady heat transfer model for hydrate reservoirs was set up by considering multiple forms of heat flow accompanying hydrate's decomposition and gas–liquid flow. Based on this model and the basic geological information of the X2 hydrate reservoir in the western Pacific Ocean, a numerical model of gas hydrate extraction using combined heat injection and depressurization was constructed to simulate the production performance of the hydrate reservoir. The results were fully compared with the results obtained by the depressurization method alone. The results indicated the hydrate extraction via a combined heat injection and depressurization would have a cumulative gas production of 31.609 million m3 and a cumulative water production of 1.5219 million m3, which are 72.57% higher and 31.75% lower than those obtained by depressurization alone, respectively. These study results can provide theoretical support for the industrial extraction of gas hydrate in seas. [ABSTRACT FROM AUTHOR]

Natural gas hydrate is widely distributed, shallow-buried, clean, and pollution-free and has enormous reserves, it is regarded as the alternative clean energy source in the oil and gas field with the most potential. Pressure coring is the only way to drill for gas hydrate core on the surface under in situ conditions, which is of great value for analyzing its occurrence conditions and reserves comprehensively. Based on this, a new wireline pressure coring system (WPCS) with a ball valve seal was designed and developed in this paper; it was applied in the deep sea for the first time in the South China Sea hydrate survey voyage of the Guangzhou Marine Geological Survey (GMGS). A total of 15 runs of deep-sea gas hydrate drilling and coring applications were carried out, and they tested well. The experimental water depth was 1700–1800 m, and the coring depth below the seafloor was about 100–150 m. The formation consisted of sandy hydrate and argillaceous hydrate. The results showed the following. (1) The success rate of ball valve turn-over could reach almost 100% in the argillaceous hydrate reservoir, although there are some isolated cases of pressure relief. Meanwhile, drilling in the sandy hydrate reservoir, the success rate was only 54.55%. (2) When drilling in the argillaceous hydrate reservoir, the core recovery rate could reach 80%, while in the sandy hydrate reservoir, it was almost 0%. In practice, the sandy formation with gas hydrate is stiff to drill compared to the performance in argillaceous formations. After our analysis, it was believed that the ball valve and core tube could be easily plugged by sand debris during the sampling of sandy hydrate formation. Moreover, the sandy core is easily plugged into the core liner because of the high friction of sand grains in clearance. (3) The pressure-holding effect of the core drilling tool was related to the formation of hydrate, the sealing form of the ball valve, and the environmental pressure. Sandy hydrate formations often caused the ball valve to jam, while the muddy hydrate formation did not. The research results of this paper have reference value for the further optimization of the WPCS structure, the optimization of drilling parameters, and the design parameters of the ball valve structure, which could be better used for the pressure coring of gas hydrate and subsequent research work in the future. [ABSTRACT FROM AUTHOR]

The problem of hydrate plug, low efficiency of hydrate dissociation and short production time in hydrate exploitation processes have significantly hindered the commercial viability of gas hydrate extraction. This study investigated the inhibitory effects of ethylene glycol (EG), EG + polyvinyl pyrrolidone (PVP), and EG + PVP + sodium chloride (NaCl) on methane hydrate formation through experiment. The hydrate inhibitory performance is evaluated by using differential of pressure curve, the amount of hydrate, and pressure drop values, and the effects of different temperatures, pressures, inhibitors, and injection time on hydrate dissociation are further studied. The experiment results indicate that the rank of inhibitors combination in terms of effectiveness is 5%EG + 0.5 wt%PVP + 3 wt%Nacl > 10%EG + 1 wt%PVP > 30% EG. At low-temperature conditions, 30% EG exhibits good inhibition of hydrate synthesis but poor dissociation efficiency. As temperature increases, the hydrates dissociation rate with 30% EG also increases. For the combination inhibitor system of EG, PVP, and NaCl, PVP will reduce the dissociation efficiency of hydrates, while EG and Nacl will improve the hydrate dissociation performance. For low production pressure, it is found that 10% EG + 10% NaCl have a good promotion effect on hydrate dissociation, whereas under high production pressure, 20% EG + 10% NaCl is more effective. Furthermore, injecting the inhibitors earlier enhances the dissociation of hydrates more effectively. [ABSTRACT FROM AUTHOR]

As the understanding of natural gas hydrates as a vast potential resource deepens, their importance as a future clean energy source becomes increasingly evident. However, natural gas hydrates trend towards secondary generation during extraction and transportation, leading to safety issues such as pipeline blockages. Consequently, developing new and efficient natural gas hydrate inhibitors has become a focal point in hydrate research. Kinetic hydrate inhibitors (KHIs) offer an effective solution by disrupting the nucleation and growth processes of hydrates without altering their thermodynamic equilibrium conditions. This paper systematically reviews the latest research progress and development trends in KHIs for natural gas hydrates, covering their development history, classification, and inhibition mechanisms. It particularly focuses on the chemical properties, inhibition effects, and mechanisms of polymer inhibitors such as polyvinylpyrrolidone (PVP) and polyvinylcaprolactam (PVCap). Studies indicate that these polymer inhibitors provide an economical and efficient solution due to their low dosage and environmental friendliness. Additionally, this paper explores the environmental impact and biodegradability of these inhibitors, offering guidance for future research, including the development, optimization, and environmental assessment of new inhibitors. Through a comprehensive analysis of existing research, this work aims to provide a theoretical foundation and technical reference for the commercial development of natural gas hydrates, promoting their safe and efficient use as a clean energy resource. [ABSTRACT FROM AUTHOR]

The biological and technological importance of anion-mediated processes has made the development of improved methods for the selective recognition of anions one of the most relevant research topics today. The hydration sphere of anions plays an important role in the functions performed by anions by forming a variety of cluster complexes. Here we describe a supramolecular capsule that recognizes hydrated anion clusters. These clusters are most likely composed of three ions that form hydrated C3 symmetry complexes that are entrapped within the supramolecular capsule of the same symmetry. The capsule is made of self-assembled α,γ-cyclic peptide containing amino acid with by five-membered rings and equipped with a tris(triazolylethyl)amine cap. To recognise the hydrated anion clusters, the hexapeptide capsule must disassemble to entrap them between its two subunits. Due to the biological and technological importance of anion-mediated processes, the development of selective recognition methods which account for the hydration sphere of anions is highly relevant. Here, the authors describe a supramolecular capsule that recognizes hydrated anion clusters by disassembling to trap them between its two subunits. [ABSTRACT FROM AUTHOR]

In situ electric heating is an important method used to increase production capacity during the extraction of natural gas hydrates. This work numerically evaluated the sensitivity of different heating parameters on gas production behavior with a vertical well depressurization in the Shenhu Sea area hydrate reservoir, the production pressure difference of 4 MPa, and continuous depressurization for 1080 days. The results showed that the in situ electric heating method can effectively enhance production capability by promoting hydrate dissociation and eliminating secondary hydrates. Compared with scenarios without heating, implementing whole wellbore heating (100 W/m) increases cumulative gas production (Vg) by 118.56%. When intermittent heating is applied to the local wellbore (15 m) located in the three-phase layer (with an interval of 30 days) and stops heating in advance at 480 days, there is no significant difference in Vg compared to the whole wellbore heating case, and the cumulative heat input is only 4.76%. We recommend considering intermittent heating of the local wellbore and stopping heating in advance during vertical well depressurization as this approach significantly reduces heating energy consumption while simultaneously improving production capacity. [ABSTRACT FROM AUTHOR]