Phase Equilibrium Conditions Research Articles

3D model of a stable triangle LiF–NaBr–KBr four-component reciprocal system Li+, Na+, K+ || F-, Вr-

A 3D model of the phase equilibrium states of the quasi-three-component system LiF–NaBr–KBr, which is a stable triangle of the four-component reciprocal system Li+, Na+, K+ || F-, Br-, has been constructed. Based on the 3D-model, polythermal, isothermal sections and the polytherm of phase crystallization were constructed for the first time. Two polythermal sections contain wide areas of boundary solid solutions based on sodium and potassium bromide. In an isothermal section at 650 оC, the fields of the liquid phase and the coexisting two and three phases are delimited. The crystallization polytherm is represented by three fields. In the crystallization field of lithium fluoride, the area of separation of two liquids is limited. The direction of the ion exchange reaction 2LiBr + NaF + KF = 2LiF + NaBr + KBr was confirmed by thermodynamic calculations at temperatures of 400, 600, 800, 1000K. The exothermic nature of the exchange reaction is confirmed by taking a DTA heating curve for a mixture of powders from 50% LiBr + 25% NaF + 25% KF, and the phase composition of the reaction products LiF + NaBr(OTR) + KBr(OTR) is confirmed by X-ray phase analysis data, where OTR is limited solid solution.

Assessment of dissociation enthalpies of methane hydrates in the absence and presence of ionic liquids using the Clausius-Clapeyron approach

The Clausius-Clapeyron (CC) equation is generally preferred to obtain dissociation enthalpies (ΔH) of hydrate-forming systems due to its ease of use. The application of other direct and indirect methods becomes more problematic if complex additives such as ionic liquids (ILs) are also present in the system. In this work, around 400 equilibrium data points for methane hydrates in the presence of over 80 ILs were collected from the literature in the temperature and pressure ranges of (272.10 – 306.07) K and (2.48 – 100.34) MPa, respectively. The ΔH of methane hydrates in the absence and presence of ionic liquids (ILs) have been calculated using the CC equation. The compressibility factor (z), required to calculate ΔH at each phase equilibrium condition has been obtained from three different approaches viz., Peng-Robinson (PR) equation of state, Soave-Redlich-Kwong (SRK) equation of state and Pitzer (Pz) correlation. The results were compared to the experimentally reported dissociation enthalpy (54.5 ± 1.5 kJ.mol−1) of methane hydrates. The role of the compressibility factor along with the slope of the equilibrium data set and the temperature/pressure range in determining the outcome of the CC equation has been discussed. The effect of molar mass, molar volume, and hydrate suppression temperature of the ILs on the ΔH of methane hydrates has been explored. The tested ILs do not show a systematic and significant influence on enthalpies, rather they show a large scattering in the ΔH values, which might mask any existing subtle effect of the ILs on the dissociation enthalpies. Therefore, this approach should be dealt with care to obtain molecular-level insights.

Hydrogen purification via hydrate-based methods: Insights into H2-CO2-CO hydrate structures, thermodynamics, and kinetics

Hydrate-based H2 purification is promising for removing impurities owing to the cage-like structures formed by water molecules. Understanding the competition mechanism of multicomponent gas molecule in hydrate is critical for improving gas purification efficiency. This study investigated the hydrate structure, thermodynamics, and kinetics of ternary gas mixture (H2–CO2–CO) from natural gas reforming products. The results identified H2–CO2–CO hydrate as type sI and determined the lattice parameters using X-ray diffraction. Raman spectroscopy results confirmed the presence of H2, CO2, and CO gas molecules in the hydrate phase. Increasing pressure, compared to cooling, enhanced CO2 content in hydrate phase. The phase equilibrium conditions and average hydrate dissociation enthalpy (53.47 J/g) were determined using a high-pressure microcalorimeter. Gas chromatography identified that the content of CO2 in the hydrate was the highest, followed by H2, and CO was the least abundant. The molecule dynamics simulation results show CO2 molecule numbers reflected trends in 51262 cages, H2 numbers correlated with changes in 512 cages, while CO numbers showed insignificant variation. Under the gas composition studied, the ability of gas molecules to be incorporated within hydrates decreases in the following order: CO2, H2, and CO.

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

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

Comparison of methods for calculating the enthalpy of vaporization of binary azeotropic mixtures

Objectives. To calculate the molar enthalpy of vaporization of binary homogeneous mixtures based on isothermal and isobaric vapor–liquid equilibrium data, and to compare the results of calculation of molar enthalpy of vaporization by different methods with experimental data.Methods. Simulation of the vapor–liquid equilibrium of binary systems according to the Non-Random Two Liquid “local compositions” equation and thermodynamic calculations of molar vaporization enthalpies of binary mixtures at different conditions of vapor–liquid equilibrium were used.Results. Arrays of calculated data were obtained with regard to molar enthalpies of vaporization for 25 compositions of binary azeotropes (isothermal, isobaric conditions of phase equilibrium), and the full range of compositions of the benzene–ethanol system at atmospheric pressure.Conclusions. The accuracy of thermodynamic methods for calculating the vaporization enthalpy of binary azeotropic mixtures according to vapor–liquid equilibrium data is higher in 85% of cases for isothermal, and in 75% of cases for isobaric conditions. By taking into account the influence of temperature on the activity coefficients of components in the liquid phase, the values of excess molar enthalpy both for azeotrope compositions and for the full concentration range of the benzene–ethanol system under isobaric conditions of liquid–vapor phase equilibrium can be accurately reproduced.

Phase equilibrium data for semiclathrate hydrates formed with n-propyl, tri-n-butylammonium bromide and tri-n-butyl, n-pentylammonium bromide under methane, carbon dioxide and nitrogen gas pressure

Semiclathrate hydrates are water-based materials formed from aqueous solutions of ionic substances. To enhance the gas capture performance of these materials, it is necessary to direct focus on the cation, which is a key part of construction of the hydrogen-bonding framework. In this paper, we focus on the partly-asymmetric cations, i.e., the n-propyl, tri-n-butylammonium bromide (N3444Br) and tri-n‑butyl, n-pentylammonium bromide (N4445Br), which are yet to be subjected to gas hydrate formation. The three phase equilibrium (gas–hydrate–liquid) conditions for the systems of (N3444Br or N4445Br) + H2O + (CH4, CO2 or N2) in the range of the pressure and mass fractions of the aqueous solutions between 1 and 11 MPa and 0.10–0.40, respectively, are reported. In all the systems, the semiclathrate hydrates were successfully formed under gas pressure. It was demonstrated that both the N3444Br and N4445Br salts promoted hydrate formation under these gases, while in the case with lean aqueous solutions N3444Br acted as an inhibitor of methane hydrate formation in pure water system. The present data are compared with the literature data, and the effect of the side chain length on the phase behavior of the semiclathrate hydrate phase is discussed.

Effect of organic matter with various carbon chain lengths on methane hydrate formation: Kinetic, thermodynamic, and microstructural studies

Organic matter is a pivotal component in methane hydrate (MH) deposition and plays a crucial role in the MH formation process due to its intricate chain structures. In this study, organic matters (OMs) with varying carbon chain lengths, including glycine, alanine, phenylalanine, 12-amino dodecanoic acid, dodecyl amine, and dodecanoic acid, were selected to investigate their impacts on the kinetics, thermodynamics, and microstructure of MH. Kinetic experimental findings reveal that long carbon chain OMs and OMs containing hydrophobic functional groups promote MH formation, with a more pronounced effect at higher concentrations. Conversely, short carbon chain OMs and OMs with hydrophilic functional groups exhibit kinetic inhibition of MH. Thermodynamic experiments show that the effect of OMs on the thermodynamics of MH at low concentrations (<1 wt%) is negligible. At higher concentrations, 12-aminododecanoic acid and dodecyl amine at 5 wt% make the phase equilibrium conditions of MH more moderate, while glycine at 3 wt% shows an inhibiting effect. Furthermore, the interaction between OMs functional groups, water and methane molecules influences MH crystals, alters crystal size and increases the proportion of large and small cages of MH. This study helps to understand the role of OMs in MH formation and promots an in-depth understanding and utilization of MH resources.

Phase equilibria and crystallographic structure of clathrate hydrate formed with carbon dioxide and cyclohexanone

This paper reports the phase equilibrium and crystallographic data of the hydrate formed in the CO2 + cyclohexanone + water system. We measured the phase equilibrium condition and conducted the powder X-ray diffraction measurements. The formation of the structure II hydrate in the system of CO2 + cyclohexanone + water was observed at the temperature from 270.0 K to 275.6 K, under the pressure from 0.62 MPa to 1.70 MPa.At 270.0 K – 275.6 K and 0.62 MPa – 1.70 MPa, the structure II hydrate formed, and the phase equilibrium condition alleviated in the system of CO2 + cyclohexanone + water, while the hydrate formed at 276.5 K - 280.7 K and 2.02 MPa – 3.33 MPa, displayed structure I and cyclohexanone acted as an inhibitor. Equilibrium conditions were measured using the isochoric method, revealing different p-T slopes at high and low temperatures. The high-temperature slope closely resembled that of structure I CO2 hydrate reported previously. We continuously monitored temperature and pressure during the structural phase transition, resulting in a slope change. To directly determine the hydrate structure, PXRD measurements were conducted on two samples: one from the high-temperature side and the other from the low-temperature side. The sample from the high-temperature side exhibited structure I with a lattice constant of 11.8749 (9) Å at 153 K, while the low-temperature sample displayed structure II with a lattice constant of 17.443(1) Å at 153 K.

CO2/H2 Separation by Synergistic Enhanced Hydrate Method with SDS and R134a.

The synergistic effect of thermodynamic promoter tetrafluoroethane (R134a) and kinetic promoter sodium dodecyl sulfate (SDS) can significantly improve the phase equilibrium conditions required for CO2 hydrate formation and promote rapid generation of CO2 hydrate. Based on this, this study investigates the influence of SDS and R134a synergy on the separation of CO2/H2 mixed gas using the hydrate method. The research reveals that without SDS addition, R134a hydrate forms first at the gas-liquid interface before CO2 hydrate induction, hindering gas-liquid exchange. The addition of SDS can inhibit the formation of the hydrate film, enhance the initiator effect of R134a in the CO2 hydrate formation process, accelerate the nucleation of CO2 hydrate, and thus synergistically strengthen the separation of CO2/H2 mixed gases. Hydrate formation can be achieved at a concentration of 100 ppm of SDS solution, and the synergistic growth effect of R134a and CO2 hydrate becomes more significant with increasing SDS concentration. Optimal separation efficiency and maximum H2 concentration are achieved at 500 ppm of SDS, with 42.29 and 54.88% separation efficiency and H2 concentration, respectively. Decreasing the initial charge temperature has little impact on separation efficiency but significantly reduces the induction time, reducing it to 3 min at 12 °C. This study improved the separation efficiency of CO2 and H2 mixed gas, providing a better reference for hydrogen purification by the hydrate method.

Experimental and modeling investigations on CH4 hydrate phase equilibria in multi-ion “Haima” cold seep environment

CH4 hydrate formation represents a primary pathway for CH4 transformation within the deep-sea CH4 seepage environment, holding utmost significance for global carbon budget and marine hydrate resources distribution. As a typical active CH4 seeping, however, the influence characteristics of various ions in in-situ “Haima” cold seep on CH4 hydrate stability remains unclear. In this study, founded on the multiple ion components from the seawater of the “Haima” cold seep, the effects of salt ion categories and concentrations on CH4 hydrate phase equilibrium were investigated, and a thermodynamic model suitable for high-salinity deep-sea environment was proposed. Results indicated that, in higher concentration salt solutions (>3.45 wt%), hydrate stability was no longer solely governed by salinity, and significant differences among ion types were observed. The inhibitory strength of the ions on CH4 hydrate stability followed the order of Mg2+>Na+>Ca2+>Mn2+≈K+>Sr2+>Ba2+. The predicted CH4 hydrate phase equilibrium conditions from the proposed model exhibited strong agreement with both experimental results and data reported in the literature. The average absolute deviation of pressure (AADP) from the model prediction was 2.7% and 4.3% compared to the experimental and published literature data, respectively, which outperformed those of the CSMHYD model, Chen-Guo model and Hu-Lee-Sum correlation (4.7%–6.2%). In light of the marine temperature gradient and prediction results, it is estimated that CH4 hydrate could maintain stably below 600 m depth of the seawater in the cold seep area.

Benedict–Webb–Rubin–Starling Equation of State + Hydrate Thermodynamic Theories: An Enhanced Prediction Method for CO2 Solubility and CO2 Hydrate Phase Equilibrium in Pure Water/NaCl Aqueous Solution System

Accurately predicting the phase behavior and physical properties of carbon dioxide (CO2) in pure water/NaCl mixtures is crucial for the design and implementation of carbon capture, utilization, and storage (CCUS) technology. However, the prediction task is complicated by CO2 liquefaction, CO2 hydrate formation, multicomponent and multiphase coexistence, etc. In this study, an improved method that combines Benedict–Webb–Rubin–Starling equation of state (BWRS EOS) + hydrate thermodynamic theories was proposed to predict CO2 solubility and phase equilibrium conditions for a mixed system across various temperature and pressure conditions. By modifying the interaction coefficients in BWRS EOS and the Van der Waals–Platteeuw model, this new method is applicable to complex systems containing two liquid phases and a CO2 hydrate phase, and its high prediction accuracy was verified through a comparative evaluation with a large number of reported experimental data. Furthermore, based on the calculation results, the characteristics of CO2 solubility and the variation of phase equilibrium conditions of the mixture system were discussed. These findings highlight the influence of hydrates and NaCl on CO2 solubility characteristics and clearly demonstrate the hindrance of NaCl to the formation of CO2 hydrates. This study provides valuable insights and fundamental data for designing and implementing CCUS technology that contribute to addressing global climate change and environmental challenges.

Permeability anisotropy analysis of two-phase flow during hydrate dissociation process

Natural gas hydrate (NGH) is a versatile and energy source. But in the actual extraction process, NGH in the reservoir will be out of phase equilibrium conditions and dissociate. This will induce alterations in permeability characteristics of reservoir and will exert a significant influence on the assessment of hydrate reservoir capacity. In the research, an innovative CT triaxial system was used to obtain the micro-structure of sediment specimen during hydrate dissociation. The anisotropy of absolute permeability (k), capillary pressure (Pc) and relative permeability (kr) were also analyzed using the pore network model (PNM). As demonstrated by the results, k increases gradually in all three directions during the dissociation. Pc gradually decreases. The degree of anisotropy of both Pc and gas-water relative permeability (krg and krw) gradually decreases. The impact of hydrate dissociation on the kr anisotropy during primary gas flooding surpasses that observed during secondary water flooding. As hydrate saturation decreases, the krw increases and the krg decreases in the horizontal directions. The krw does not change significantly and the krg increases in the vertical direction. Along the length of the sample, the distribution of hydrate and pore space exhibits heterogeneity across the sections. This inhomogeneous distribution will lead to anisotropy in permeability.

A novel model to predict phase equilibrium state of hydrates from the relationship of gas solubility

The study of hydrate phase equilibrium is crucial for ensuring the safety of natural gas pipeline transportation and the process of hydrate recovery. While scientists typically focus on the chemical potential of hydrates, the role of gas solubility in hydrate phase equilibrium remains unclear, and this study fills this gap. This work investigated the solubility of gas at the equilibrium point of the hydrate phase through model calculations. Additionally, a new model of hydrate phase equilibrium is established based on the relationship between solubility. Firstly, a solubility model based on gas-liquid equilibrium theory showed higher prediction accuracy in comparison to the PR equation and Duan model and was then used to calculate gas solubility under hydrate phase equilibrium conditions. Afterwards, a novel model was developed to predict hydrate equilibrium state based on the relationship between gas solubility and hydrate phase equilibrium temperature, and it was further compared with the Chen–Guo model and CSMGem in terms of prediction accuracy under pure water and brine settings. The results showed: (a) The calculation deviation of the solubility model was 0.7–8.7% in pure water settings and 2.6–11.7% in brine settings; (b) A strong linear correlation between the phase equilibrium temperature of hydrates and gas solubility was also found; (c) This proposed model achieved over 10 times the accuracy of the Chen–Guo model and the CSMGem in predicting the phase equilibrium state of N2 and CO2 hydrates, and 3–10 times higher accuracy than that of the Chen–Guo model and CSMGem in brine. This work suggests that the gas solubility equilibrium theory can provide a more accurate prediction of hydrate states.

Prediction of Phase Equilibrium Conditions and Thermodynamic Stability of CO2-CH4 Gas Hydrate

With the large-scale promotion and application of CO2 flooding, more and more engineering problems have emerged. Due to the high CO2 mole fraction, the associated gas of CO2 flooding very easily forms solid hydrates, compared to conventional natural gas. This has resulted in production decline or shutdown. Understanding the phase equilibrium conditions for hydrate formation in production fluids is crucial for hydrate prevention and control. In this study, accurate predictions of CO2-CH4 mixed gas hydrate formation conditions were performed using theoretical models. The temperature and pressure ranges for hydrate formation were calculated for different CO2 mole fraction, ranging from −11.5 °C to 20.85 °C and from 0.81 MPa to −28.1 MPa, respectively. Based on the calculated phase equilibrium data, a multi-parameter empirical model was developed using polynomial fitting. The calculation errors for the multi-parameter empirical model were 3.09%. The multi-parameter empirical model established in this study can avoid complex thermodynamic equilibrium calculations and has the advantages of simplicity, high accuracy, and wide coverage of downhole conditions. Based on the calculated phase equilibrium data, the dissociation enthalpy of CO2-CH4 hydrate below and above the freezing point of water was calculated. The results showed that an increase in CO2 mole fraction led to an increase in hydrate dissociation enthalpy and enhanced thermodynamic stability, making hydrate prevention more challenging. Our work can contribute to the optimization of CO2 production fluid treatment processes and the development of hydrate prevention and control technologies.

Intrinsic correlation between the generalized phase equilibrium condition and mechanical behaviors in hydrate-bearing sediments

The phase equilibrium and mechanical behaviors of natural gas hydrate-bearing sediment are essential for gas recovery from hydrate reservoirs. In heating closed systems, the temperature-pressure path of hydrate-bearing sediment deviates from that of pure bulk hydrate, reflecting the porous media effect in phase equilibrium. A generalized phase equilibrium equation was established for hydrate-bearing sediments, which indicates that both capillary and osmotic pressures cause the phase equilibrium curve to shift leftward on the temperature-pressure plane. In contrast to bulk hydrate, hydrate-bearing sediment always contains a certain amount of unhydrated water, which keeps phase equilibrium with the hydrate within the hydrate stability field. With changes in temperature and pressure, a portion of pore hydrate and unhydrated water may transform into each other, affecting the shear strength of hydrate-bearing sediment. A shear strength model is proposed to consider not only hydrate saturation but also the change in temperature and pressure of hydrate-bearing sediment. The model is validated by experimental data with various hydrate saturation, temperature and pressure conditions. The deformation induced by partial dissociation was studied through depressurization tests under constant effective stress. The reduction in gas pressure within the hydrate stability field indeed caused sediment deformation. The dissociation-induced deformation can be reasonably estimated as the difference in volume between hydrate-bearing and hydrate-free sediments from the compression curves.

FEATURES OF DECOMPOSITION OF GAS HYDRATE IN NONEQUILIBRIUM MODE IN A POROUS MEDIUM

The paper presents a mathematical model of the nonequilibrium decomposition of a gas hydrate contained in a porous reservoir of finite extent. The system of basic equations, which includes the law of conservation of mass, the heat inflow equation and Darcy’s law, also contains an equation describing the kinetics of nonequilibrium hydrate decomposition, which is determined by pressure, temperature and surface area of particles. On the basis of the numerical solution of the problem, dependences are obtained that allow us to identify the regularities of the process of nonequilibrium decomposition of gas hydrate in a natural reservoir when warm gas is injected into a porous reservoir. It is shown that at the initial moments of time after the start of injection, the extent of the region saturated with gas, hydrate and water is very small compared to the extent of the formation, which corresponds to the mode of hydrate decomposition on the frontal surface. At long injection times, the nonequilibrium hydrate decomposition process is characterized by the formation of three characteristic zones: the near one, where the pores are saturated with gas and water, the far one, saturated with methane and its gas hydrate, and the intermediate one, where gas, hydrate and water are located. It is established that the pressure and temperature in the extended region are connected by the condition of phase equilibrium. The influence of the main parameters of the system on the distributions of pressure, temperature, water saturation and hydrate saturation, as well as on the dynamics of their changes over time, is analyzed. It is shown that injection pressure, as well as reservoir permeability and porosity have a significant effect on the decomposition rate of gas hydrate. An increase in the values of these parameters contributes to an increase in the rate of nonequilibrium hydrate decomposition. An increase in the injection temperature leads only to an increase in the extent of the area containing methane and water.

Hydrate phase equilibrium conditions for H2S and CO2 gas mixture removal from natural gas: modeling and optimization study

In this study, for the first time, a comprehensive mathematical modeling of the optimal conditions for the gas hydrates formation of hydrogen sulfide (H2S) and carbon dioxide (СО2) was carried out with the aim of them removing from natural gas. The study was carried out on a model gas mixture close to the natural gas composition: CH4 – C2H6 – С3Н8 – n-С4Н10 – СО2 – H2S – N2. A temperature range of 268.15–283.15 К and a pressure range of 2.00–8.00 MPa were investigated. The efficiency was assessed based on the gas hydrate distribution coefficients. It was found that the gas hydrate extraction of H2S is more significantly affected by the concentration of H2S in the initial gas mixture. The gas hydrate extraction of СО2 is more significantly affected by the temperature and pressure of the gas separation unit. The maximum gas hydrate distribution coefficient of H2S is 42.05 at T = 268.15 K, p = 8.00 MPa. The maximum gas hydrate distribution coefficient of СО2 is 0.49 at T = 283.15 K, p = 8.00 MPa. Due to the small amounts of CO2 entrapped in gas hydrates, a scheme that combines a multi-stage hydrate-based and membrane technology has been suggested to purify natural gas further.

Phase Equilibrium Conditions and Crystal Structure of Binary Hydrates Formed with 1-Methylpiperidine

Phase Equilibrium Conditions and Crystal Structure of Binary Hydrates Formed with 1-Methylpiperidine

EXPERIMENTAL STUDY AND THERMODYNAMIC SIMULATION OF CO2 HYDRATE PHASE EQUILIBRIUM CONDITIONS IN POROUS MEDIA

The phase equilibrium of CO&lt;sub&gt;2&lt;/sub&gt; hydrates on various types of porous media is studied by experiment and model. The experiments are conducted under controlled conditions to measure the hydrate equilibrium conditions. The proposed model is based on the Chen-Guo theory and incorporates the surface property parameters for each type of porous media. The predictions of model are validated by comparing them to experimental data, and the predicted temperature deviation is within 0.25 K. Furthermore, the accuracy of model is compared with other existing models, and the calculation accuracy of this model in glass beads with weak water absorption is 0.05 K higher than that of the existing model, and 0.09 K higher in sand with strong water absorption. The study contributes to a better understanding of CO&lt;sub&gt;2&lt;/sub&gt; hydrate formation on different porous media and provides a reliable model for predicting phase equilibrium conditions in such systems.

Influence mechanism of interfacial organic matter and salt system on carbon dioxide hydrate nucleation in porous media

CO2 carbon sequestration in marine gas hydrate occurrence areas is a potential way to mitigate the continued growth of CO2 in the atmosphere. The organic matters of marine sediment can affect the phase equilibrium conditions of CO2 hydrate in salt system, and the organic salt system in pore medium has effect on the nucleation growth of CO2 hydrate. The organic matters on the surface of the sediment is mainly composed of lipids, proteins, carbohydrates, and unsaturated hydrocarbon organic compounds, and these polar functional groups weaken the inhibitory effect of salt ions on hydrates through coordination bonds and Ca ion complexation. The nucleation kinetics of CO2 hydrate under organic salt system in pore medium in marine environment is an important parameter determining the carbon sequestration of hydrate. In addition, experimental results show that clay surface organic matters (CSOM) can reduce the surface tension of pore water, and thus pore water migration occurs during hydrate growth and expansion. The basic background in our findings will bring a much better recognition of phase equilibrium conditions among the offshore marine sediment CO2 sequestration process and further assess the location of potential marine CO2 storage sites.