Hydrate Process Research Articles

Cooperative effect of surfactant and porous media on CO2 hydrate formation and capacity of gas storage

Hydrate-based technology is considered to be a promising approach widely applied in the areas of industrial natural gas storage and transportation, CO2 capture and storage. The major technical issues related to this technology are enhancing the formation rate and gas storage capacity under different conditions. In this work, the formation characteristics of CO2 hydrate were investigated in porous media below the freezing point in the presence of SDS (Sodium Dodecyl Sulfate). The influence of cooperative effect of surfactant and porous media on hydrate formation was investigated at different concentration of SDS. The results indicated that surfactant could obviously promote the formation process of CO2 hydrate in porous media when the concentration of SDS was in the range of 0–1240 ppm and the temperature ranged from 268.15 K to 272.15 K. However, there was an optimal SDS concentration to promote the formation process of CO2 hydrate in porous media below the freezing point. When the SDS concentration was 240 ppm, the highest conversion rate of ice to hydrate and the largest gas storage capacity were obtained, which were 43.05% and 80.06 L/L, respectively. The results also indicated that, with or without SDS in porous media system, the higher the temperature was, the less time it brought to reach 90% of the CO2 gas absorption (t90). But the maximum gas storage capacity of CO2 hydrate was obtained at 270.15 K in porous media in the presence of SDS. In addition, the results demonstrated that the SDS concentration of 0.24 g/L could increase the gas storage capacity of hydrate and shorten the value of t90 at different temperature conditions. These results are helpful for comprehensively understanding the rapid formation of CO2 hydrate in industrial areas and providing an important theoretical guidance and reference for the CO2 capture and storage in the form of hydrate.

Investigation of the formation behaviors of CO2 hydrate in porous media below the freezing point

AbstractThe formation process of gas hydrate is a stochastic phenomenon considered to be significant for its application in the areas such as hydrate‐based technology and natural gas hydrate exploitation. The formation behaviors of CO2 hydrate were studied in porous media below the freezing point. In addition, the formation experiments were conducted in the high‐pressure vessel under different temperature and pressure conditions. The formation process of CO2 hydrate showed different formation behaviors in the porous media under different experimental conditions. The results showed that the formation rate was higher in earlier stage and the largest formation rate attained 7.18 × 10−4 mol h−1. The influence of initial pressure on the formation rate was indistinctive in porous media below the freezing point. Particle size of the porous media played an important role in affecting the formation characteristic of CO2 hydrate below the freezing point. The results indicated that, the smaller the particle size of porous media was, the larger the formation rate and the conversion rate of CO2 hydrate. The maximum conversion rate was attained 90.61%. The results also indicated that CO2 hydrate had a good gas storage capacity in porous media below the freezing point. The gas storage capacity was close to 160 L/L in frozen quartz sand with the particle size of 250 μm in the experiments. The relative results will provide some insight for sequestration and storage process of CO2 gas in the form of hydrates into sediments.

Experimental study on the effect of decomposition induction on the replacement process of CO2[sbnd]CH4 hydrate in hydrate-bearing sediments below the freezing point

The replacement technique of CH4 by CO2 is a promising strategy for natural gas hydrate exploitation, which has been regarded as a win-win situation for simultaneously achieving CO2 storage and CH4 recovery in permafrost region. How to improve the replacement efficiency is a fundamental issue related to the natural gas hydrate exploitation in permafrost region. In this work, the replacement process of CO2CH4 hydrate was carried out in the ice-sand mixture system and the replacement characteristics were further illustrated through experiment. The influence of different decomposition induction on the replacement process CO2CH4 hydrate was deeply analyzed, especially for the decompression driving force (ΔP) and thermal driving force (ΔT). The results showed that the ΔP has a significant inductive effect on the replacement process of CO2CH4 hydrate in porous media below the freezing point. The replacement efficiency attained 12.25% under condition of decomposition induction driven by ΔP with -0.1 MPa, which was raised 3.09% in comparison. However, the larger ΔP didn't mean that it was more favorable to the replacement process of CO2CH4 hydrate, and there was an optimal value in the experiment. Furthermore, an additional thermal drive (ΔT) is beneficial to the replacement efficiency of CH4 hydrate and the sequestration efficiency of CO2. It greatly improved the CH4 recovery and CO2 sequestration ratio during the replacement process of CO2CH4 hydrate. The replacement efficiency attained 20.34% under condition of depressurization drive combined with thermal drive. It was worth noting that the contribution of thermal drive (ΔT) was different on CH4 recovery and CO2 sequestration. There was an optimal value for the enhancement on the replacement process of CO2CH4 hydrate. These results are of significance for providing a theoretical guidance for natural gas hydrate exploitation in permafrost regions.

A Dual-Bed Cyclic Gas Hydrate Process (DB-CGHP) for Carbon Dioxide Capture and Other Gas Separations

A Dual-Bed Cyclic Gas Hydrate Process (DB-CGHP) for Carbon Dioxide Capture and Other Gas Separations

Nanoscale determination of calcium silicate hydrate (C-S-H) precursors crystallized at extreme early stage

The crystallization process of calcium silicate hydrate (C-S-H) is likely to follow a nonclassical crystallization pathway. However, the nanostructure of the C-S-H precursors (CPs) formed in the early crystallization stage remains unclear. This paper studied the nanostructure of chemical bonds and composition of nano-CPs by combining surface enhanced Raman scattering (SERS) and TEM-EDS correlative microscopy. The results show that the silicon tetrahedron chains in CPs are similar to fragments of tobermorite, jennite and xonotlite crystals. The formed CPs were amorphous and its Ca/Si ratios fluctuated from 0.75 to 2.0. The CPs formed in the early hydration process of the monoclinic tricalcium silicate (C3S) solution have SERS activity. The SERS enhancement factor related to the intensity of Raman peaks is in the range of 102–103. The findings enhance the understanding of early crystallization of C-S-H during cement hydration and provide a reference for obtaining the structure of other crystal precursors.

Effect of methanol as an amphiphile on water structuring around a hydrate forming gas molecule: Insights from molecular dynamics simulations

Gas hydrates (GH) are crystalline compounds composed of small hydrophobic molecules encapsulated within cavities formed by hydrogen bonded water molecules. These compounds are an important source of fuel and are of application in gas storage and transportation. Processes such as nucleation, crystal growth, stability and decomposition of GH are controlled by the introduction of molecules referred to as additives. A challenging aspect in the study of GH is to explain at a molecular level the influence of additives on these processes. An intriguing case of additives is that of amphiphilic molecules which influence hydrate processes through their complex effects on the organization of water as well as on gas solubility. In this study, we apply molecular dynamics simulations to examine the effect of CH3OH, the simplest amphiphile and the most commonly used additive, on the organization of H2O molecules in the hydration shell of CO2, a hydrate forming gas. The interface between methanol–water liquid mixture and CO2 is examined by applying the Identification of Truly Interfacial Molecules (ITIM) technique, thereby minimizing the errors due to molecular level roughness at the interface. The organizational order of hydration shell water (HSW) is examined by evaluating the F4 order parameter. The results show that the presence of CH3OH enhances the availability of aqueous CO2 near the interface which makes the arrangement of HSW in this region more hydrate-like, resulting in an increase in value of F4 on approaching the interface from the bulk. It is also observed that CH3OH molecules tend to orient their hydrophobic CH3 group towards aqueous CO2 thereby inducing hydrate-like ordering of water in the hydration shell. However, on approaching the liquid surface, hydrate-like organization of HSW is opposed by CH3OH molecules at the surface which, owing to their –OH group oriented towards the liquid phase, significantly influences water orientation near the interface and decreases the value of F4. The net outcome of these opposing effects of CH3OH on hydrate-like ordering of HSW is the observation of a maximum in the value of F4 order parameter at a distance beneath the surface of the liquid and a progressive decrease from this maximum on moving further closer to the surface. The observed features of the value of F4 order parameter profile are explained based on the analysis of the intrinsic structure of the liquid–gas interface. The results indicate that, the presence of CH3OH leads to a region beneath the liquid surface where the extent of hydrate-like organization of HSW becomes maximum. However, CH3OH molecules significantly limits the availability of water molecules around aqueous gas, justifying the action of methanol as an inhibitor for hydrate formation when present at high concentrations. The results indicate that the effect of an amphiphile on GH formation is determined by its interaction with dissolved gas as well as by the influence of surface adsorbed amphiphile on water orientation and gas availability near the interface.

Molecular insight into the dissociation and re-formation of methane hydrate in silica nano-slit

Unveiling the nature of hydrate dissociation and re-formation in sediments is fundamental before the commercial exploitation of methane hydrates. In this work, molecular dynamics simulations were performed to investigate the dissociation process and re-formation mechanism of methane hydrate in silica-slit and bulk water. Our results indicate that methane hydrate dissociates layer-by-layer in a shrinking core manner with the generation of nanobubbles due to the supersaturation of solution. Hydrophilic quartz surface is verified to be conductive to the formation and stable existence of the ordered structures of interfacial water molecules, resulting in the survival of more residual water rings in the silica nanopore than in the bulk phase after hydrate decomposition. In the process of hydrate regeneration, it is found that intact/semi hydrate cages are verified to be beneficial for the hydrate re-formation, while the existence of large nano-bubbles induced by the long-time decomposition will be adverse to triggering the memory effect and prolong the induction time of hydrate regeneration comparing with the homogeneous supersaturated water-methane system. Moreover, the loci of hydrate re-crystallization are dominated by the concentration of dissolved methane gas in the solution and the diffusivity of water molecules. Hydrate cages are preferentially generated in the dense solution which is rich in dissolved methane gas for the unconfined water system, and the entrance of the nano-slit is usually the optimal site of hydrate reformation for the confined system due to the high concentration of dissolved gas and the appropriately restricted diffusion of water molecules. Furthermore, compared with the bulk water, a lower methane concentration is needed to trigger hydrate nucleation in silica nanopore. These findings are beneficial for a better understanding of dissociation and re-formation kinetics of hydrates at the molecular scale and provide guidelines for efficient hydrate exploitation in marine sediments.

Application of in-situ heat generation plugging removal agents in removing gas hydrate: A numerical study

Under the condition of low temperature and high pressure, natural gas will form solid gas hydrates in oil and gas wellbore and pipeline, resulting in blockage, pressure increase, production reduction, and even shutdown. Methods such as heat preservation, heating, and injection of inhibitors are often used in engineering to avoid the formation of hydrates. The latter, injection of inhibitors, is the most widely used means of hydrate prevention and control at present. A special inhibitor, namely an in-situ heat generation plugging removal agent, has the advantages of both heating and chemical plugging removal and is a kind of hydrate inhibitor with great potential. In this study, a new mathematical model is developed based on hydrate phase equilibrium thermodynamics and decomposition kinetics, which is used to solve the heat and mass transfer problems in the plugging removal process of the gas hydrate by using in-situ heat generation plugging removal agents. Numerical simulation is used to solve the mathematical model, and the plugging removal process and parameter variation of pure in-situ heat generation system (high/medium/low temperature), electrolyte in-situ heat generation system (containing Na+/Mg2+), and alcohol in-situ heat generation system (containing MeOH/DEG) are studied respectively. Based on the experimental results, the quantitative relationship between the plugging removal time, the dosage, and the concentration of the plugging removal agent is calculated and analyzed. Our proposed model is verified through experimental study and the calculated values of the mathematical model are in good agreement with the experimental values under different working conditions. It is concluded that the rapid removal of hydrates and the prevention of secondary formation of hydrates can be achieved by configuring the high-temperature in-situ heat generation plugging removal agents, and the efficiency of plugging removal can be enhanced by adding appropriate concentration of electrolyte and alcohol without changing the heating property of the original plugging removal agent. This study can provide theoretical guidance for the safety of oil and gas flow and the efficient development of hydrate.

Spatial-Temporal Evolution of the Gas Hydrate Stability Zone and Accumulation Patterns of Double BSRs Formation in the Shenhu Area

The current study examines the methane gas hydrate stability zone (GHSZ) in the Shenhu area in the northern South China Sea (SCS) as an example to calculate the thickness of the GHSZ and reconstruct its evolution since 8.2 Ma. Two mechanisms for typical double BSRs in the Shenhu area are shown, and the relationship between the evolving thickness of the GHSZ and the dynamic accumulation of NGHs at typical stations in the Shenhu area is clarified. The results show that the thickness of the GHSZ varies over time with overall thickening in the Shenhu area. The current thickness of the GHSZ is between 160.98 and 267.94 m. Two mechanisms of double BSRs in the Shenhu area are summarized: the double BSRs pattern based on changes in formation temperature, pressure and other conditions and the double BSRs pattern based on differences in gas source and composition. The formation process and occurrence characteristics of double BSRs and hydrate at site SH-W07-2016 in the Shenhu area are also closely related to the changes in thickness of the GHSZ. In addition, the age when gas source first enters the GHSZ has a considerable influence on the dynamic accumulation process of hydrate. Since the formation of hydrate above the BSR at site SH-W07-2016, the GHSZ has experienced up to two periods of thickening and two periods of thinning at this site. With the changes in the thickness of the GHSZ, up to two stages of hydrate formation and at most two stages of hydrate decomposition have occurred. This paper is of great value for understanding the formation of multiple bottom-simulating reflectors (BSRs) as well as the migration, accumulation and dissipation of natural gas hydrate (NGH) during the dynamic accumulation process.

Methane Hydrate Formation in Hollow ZIF-8 Nanoparticles for Improved Methane Storage Capacity

Methane hydrate has been extensively studied as a potential medium for natural gas storage and transportation. Due to their high specific surface area, tunable porous structure, and surface chemistry, metal–organic frameworks are ideal materials to exhibit the catalytic effect for the formation process of gas hydrate. In this paper, hollow ZIF-8 nanoparticles are synthesized using the hard template method. The synthesized hollow ZIF-8 nanoparticles are used in the adsorption and methane hydrate formation process. The effect of pre-adsorbed water mass in hollow ZIF-8 nanoparticles on methane storage capacity and the hydrate formation rate is investigated. The storage capacity of methane on wet, hollow ZIF-8 is augmented with an increase in the mass ratio of pre-adsorbed water and dry, hollow ZIF-8 (RW), and the maximum adsorption capacity of methane on hollow ZIF-8 with a RW of 1.2 can reach 20.72 mmol/g at 275 K and 8.57 MPa. With the decrease in RW, the wet, hollow ZIF-8 exhibits a shortened induction time and an accelerated growth rate. The formation of methane hydrate on hollow ZIF-8 is further demonstrated with the enthalpy of the generation reaction. This work provides a promising alternative material for methane storage.

Molecular dynamics of C–S–H production in graphene oxide environment

Abstract The process of calcium silicate hydrate (C–S–H) generation in graphene oxide (GO) nanoslits was investigated via molecular dynamics simulations using the structural polymerization reaction of silica chains in the synthesis of silica gels. The structural evolution of C–S–H, radial distribution functions, chemical components, and distribution of Q n units in the system were analyzed to investigate the influence of GO on the early growth mechanism of C–S–H and compare the structural differences of C–S–H in the presence and absence of GO. The results showed that the proportion of silicon atoms bonded to bridge-site oxygen atoms in the C–S–H structure increased in the presence of oxygen-containing graphene groups. Ion adsorption in the GO surface layer led to an increase in the degree of polymerization of C–S–H. The nucleation and templating effects of GO were confirmed, revealing the intrinsic mechanism for the formation of GO-modified reinforced cementitious materials.

A gas hydrate process for high-salinity water and wastewater purification

This study investigates the effectiveness of a hydrate-based water purification process on high-salinity and wastewater samples. Testing involved a 4-L-scale novel apparatus using HFC134a as a guest molecule during a continuous hydrate formation–pelletization–dissolution process. Each stage of the succeeded in removing 80–85% of individual dissolved contaminants from highly polluted water. This is the first study to meaningfully demonstrate the ability to purify highly polluted water by applying the proposed method to water with very high concentrations of salts or sugars that exceed the range treatable by reverse osmosis. In a single-stage hydrate process with no pre-or and post-treatment, the average removal efficiencies of ionic compounds in seawater, hypersaline brine (total dissolved solid ⁓150,000 mg/L) and contaminants from wastewater (Coca-Cola beverage, chemical oxygen demand ⁓80,000 mg/L) were 89%, 80%, and 81%, respectively. This study illustrates the effective and economic application of the proposed method and apparatus to the purification of high-salinity water and wastewater under various conditions.

Investigation of the formation characteristics of methane hydrate in frozen porous media

The replacement technique of CO2–CH4 hydrate in naturally occurring gas hydrates is a promising method for achieving CO2 storage and CH4 recovery in permafrost regions. Revealing the formation characteristics of CH4 hydrate becomes an urgent need in porous medium below the freezing point. For this purpose, the formation experiment was carried out under different conditions and the formation characteristics were systematically investigated. The result indicated that the initial pressure was the key factor affecting the formation process of CH4 hydrate. And the final pressure drop was greater at higher initial pressure conditions. The final pressure drop reached to 0.92 MPa when the initial pressure was 9 MPa under the same temperature conditions. The results also illustrated that, the formation rate of hydrate was the fastest when the temperatures were closely to the freezing point. The average formation rate of CH4 hydrate reached to 0.646 mmol/h when the temperature was 273.15 K. Moreover, the smaller the particle size was, the higher the final conversion rate of ice. The final conversion rate reached to 56.5% when the initial pressure was 9 MPa. The results are of significance for exploiting natural gas hydrate in the permafrost regions. Highlights The formation characteristics of methane were studied in porous media below the freezing point. The higher initial pressure could enhance the final conversion rates of ice. The formation rate of methane was the fastest when the temperature was closely to the freezing point. The pressure disturbance could improve the formed amount of methane hydrate in porous media.

Hybrid hydrate processes for CO2/H2 mixture purification: A techno-economic analysis

In this work, hydrate based separation technique was combined with membrane separation and amine-absorption separation technologies to design hybrid processes for separation of CO 2 /H 2 mixture. Hybrid processes are designed in the presence of different types of hydrate promoters. The conceptual processes have been developed using Aspen HYSYS. Proposed processes were simulated at different flow rates for the feed stream. A comprehensive cost model was developed for economic analysis of novel processes proposed in this study. Based on the results from process simulation and equipment sizing, the amount of total energy consumption, fixed cost, variable cost, and total cost were calculated per unit weight of captured CO 2 for various flow rates of feed stream and in the presence of different hydrate promoters. Results showed that combination of hydrate formation separation technique with membrane separation technology results in a CO 2 capture process with lowest energy consumption and total cost per unit weight of captured CO 2 . As split fraction and heat of hydrate formation increases, the share of hydrate formation section in total energy consumption increases. When TBAB is applied as hydrate promoter, due to its higher hydrate separation efficiency, more amount of CO 2 is captured in hydrate formation section and consequently the total cost for process decreases considerably. Hybrid hydrate-membrane process in the presence of TBAB as hydrate promoter with 29.47 US$/ton CO 2 total cost is the best scheme for hybrid hydrate CO 2 capture process. Total cost for this process is lower than total cost for single MDEA-based absorption process as the mature technology for CO 2 capture. • Hydrate-based separation was combined with membrane and chemical absorption technologies to purify CO 2 /H 2 mixture. • The processes were designed and simulated in the presence of different hydrate promoters. • Techno-economic study was performed to estimate energy consumption, operating cost, and fixed cost of proposed processes. • Hybrid hydrate-membrane process in the presence of TBAB has the lowest total cost as 29.47 US$/ton CO 2 .

Advances in Characterizing Gas Hydrate Formation in Sediments with NMR Transverse Relaxation Time

The formation process, structure, and distribution of gas hydrate in sediments have become focal points in exploring and exploiting natural gas hydrate. To better understand the dynamic behavior of gas hydrate formation in sediments, transverse relaxation time (T2) of nuclear magnetic resonance (NMR) is widely used to quantitatively characterize the formation process of gas hydrate and the change in pore characteristics of sediments. NMR T2 has been considered as a rapid and non-destructive method to distinguish the phase states of water, gas, and gas hydrate, estimate the saturations of water and gas hydrate, and analyze the kinetics of gas hydrate formation in sediments. NMR T2 is also widely employed to specify the pore structure in sediments in terms of pore size distribution, porosity, and permeability. For the recognition of the advantages and shortage of NMR T2 method, comparisons with other methods as X-ray CT, cryo-SEM, etc., are made regarding the application characteristics including resolution, phase recognition, and scanning time. As a future perspective, combining NMR T2 with other techniques can more effectively characterize the dynamic behavior of gas hydrate formation and pore structure in sediments.

Effect of the Temperature and Tetrahydrofuran (THF) Concentration on THF Hydrate Formation in Aqueous Solution

The knowledge of the mechanism of clathrate hydrate formation is crucial for studying the formation of a natural gas hydrate and developing hydrate-based technologies. In this study, low-field nuclear magnetic resonance (NMR) is applied to observe the processes of tetrahydrofuran (THF) hydrate formation from the solutions with different THF concentrations, and from the analysis of the NMR transverse relaxation time (T2) of hydrates and solutions, the formation mechanism of THF hydrate is discussed. A quantitative relationship between the NMR T2 spectral area and the mass of THF hydrate is established, and it is applied to estimate the hydrate amount in the formation process of THF hydrate. The results obtained show that T2 of THF solution is controlled by the temperature and THF concentration: longer at a higher temperature and shorter at a higher THF concentration. Moreover, the initial THF concentration does not affect the final concentration of the remaining solution after hydrate crystallization, and the formation of THF hydrate from solution follows the thermodynamics of solution reaction, with the THF concentration of the solution ending at the phase line after hydrate crystallization. The kinetics of THF hydrate formation is affected by the temperature and THF concentration: a higher formation rate in the solution with stoichiometric composition (19.06 wt % THF) of THF hydrate than either THF-rich or water-rich solution and a lower formation rate at a higher temperature.

Nuclear magnetic resonance study of the formation and dissociation process of nature gas hydrate in sandstone

In this work, the authors monitored the formation and dissociation process of methane hydrate in four different rock core samples through nuclear magnetic resonance (NMR) relaxation time (T2) and 2D imaging measurement. The result shows that the intensity of T2 spectra and magnetic resonance imaging (MRI) signals gradually decreases in the hydrate formation process, and at the same time, the T2 spectra move toward the left domain as the growth of hydrate in the pores of the sample accelerates the decay rate. The hydrate grows and dissociates preferentially in the purer sandstone samples with larger pore size and higher porosity. Significantly, for the sample with lower porosity and higher argillaceous content, the intensity of the T2 spectra also shows a trend of a great decrease in the hydrate formation process, which means that high-saturation gas hydrate can also be formed in the sample with higher argillaceous content. The changes in MRI of the sample in the process show that the formation and dissociation of methane hydrate can reshape the distribution of water in the pores.©2022 China Geology Editorial Office.

Integrated Investigation on the Nucleation and Growing Process of Hydrate in W/O Emulsion Containing Asphaltene

Integrated Investigation on the Nucleation and Growing Process of Hydrate in W/O Emulsion Containing Asphaltene

Progress in research on dispersants in gas hydrate control technology

Since their discovery, hydrates have become an important part of the oil and gas industry. The formation and dissociation of hydrates affect their production efficiency. Dispersants can be used to control hydrate formation and are irreplaceable in industrial applications, such as pipeline fluid transportation, gas hydration, and environmental treatment. However, research on the control of hydrate formation/decomposition with dispersants remains inadequate, and industrial applications of the hydrate control technology are still in the initial stage. To understand how dispersants influence natural gas hydrates, this paper summarizes the current experimental research results; describes the formation/dissociation mechanism of dispersants in the reaction process of natural gas hydrate, including kinetics, thermodynamics, and rheology; introduces the promotion–inhibition mechanism of the dispersant; and focuses on analyses of traditional chemical surfactants, solid particles, and new component powders. Based on the research trend of dispersants in the hydration reaction, a review of the existing experimental research and the identified blind spots highlights that there have been numerous studies on traditional chemical dispersants. Thus, it is necessary to promote research on the control of the hydrate reaction with other types of dispersants and on the synergistic effect of dispersants and the environment.

Morphology observation on formation and dissociation cycles of methane hydrate in stacked quartz sandy sediments

In this paper, multi-formation and multi-dissociation experiments of methane hydrate in quartz sands (6.5–355 μm) were carried out in a high-pressure visible reactor. The results showed that the cumulative amount, saturation and initial formation rate of hydrate increased with the size of sand particles decreasing, and also increased with the cycles of hydrate formation under the equal experimental time. When the sand particles ranged from 6.5 to 48 μm, the hydrate saturation reached the maximum of 59.5%. Performing experiments with sands of 109–120 μm, the hydrate saturation at the three repetitive formations were 26.2%, 39.3% and 41.7%, respectively. Besides, the hydrate dissociation process was affected by the initial hydrate saturation and the way of its occurrence, which suggested that a higher hydrate saturation would lead to a longer dissociation. The morphology observations indicated that the hydrate formation in the quartz sand mainly existed in the form of pore-filling, and the formation process was actually a dynamic process accompanied with dissociation. Furthermore, in the experiment of layered accumulations, the hydrate firstly formed in the layer of large particle sand, and the forming process of fracture-type hydrate was observed in the layer of 6.5–48 μm particle sand. The results of this work may provide a new insight on the formation and dissociation laws of hydrate and some useful information for the natural hydrate exploration.