The Experts below are selected from a list of 318 Experts worldwide ranked by ideXlab platform
Mingjun Yang - One of the best experts on this subject based on the ideXlab platform.
-
The enhancement effect of water-gas two-phase flow on Depressurization process: Important for gas hydrate production
Applied Energy, 2020Co-Authors: Huiru Sun, Mingjun Yang, Yuechao Zhao, Bingbing Chen, Guojun Zhao, Yongchen SongAbstract:Abstract Depressurization is one of the most efficient methods in the production testing of natural gas hydrates. However, problems such as hydrate reformation, ice generation and insufficient dissociation driving force in the later period of Depressurization adversely affect the gas production. It has been confirmed that controlling the flowrate ratio of a water-gas two-phase flow can help enhance the hydrate dissociation. However, the effect of the water-gas flowrate ratio on the hydrate dissociation behaviors during Depressurization is unclear. In this study, three dissociation modes involving a combination of water-gas flow and Depressurization were examined: mode 1 (concurrent start of Depressurization and water-gas flow), mode 2 (Depressurization is first used to dissociate the hydrate, and the water-gas flow is initiated after 15 min), and mode 3 (Depressurization is first used, and the water-gas flow is initiated after 30 min). The feasibility of water-gas flow to accelerate hydrate dissociation and mitigate ice generation was confirmed during the Depressurization process. In all the modes, the higher water-gas flowrate ratio and lower dissociation pressure significantly increased the energy recovery rate and decreased the energy input. Additionally, the water-gas flow, especially that with a higher flowrate ratio, effectively accelerated the elimination of the dark-zone (mixture of ice and hydrate) by providing continuous heat transfer. Mode 1 corresponded to the highest energy recovery rate, lowest energy input and most rapid disappearance of the dark-zone under the same experimental conditions. Therefore, mode 1 was regarded as the most efficient mode to dissociate hydrate in an actual hydrate production.
-
Visualization study on the promotion of Depressurization and water flow erosion for gas hydrate production
Energy Procedia, 2019Co-Authors: Bingbing Chen, Mingjun Yang, Huiru Sun, Dayong Wang, Lanlan Jiang, Yongchen SongAbstract:Abstract Natural gas hydrates (NGHs) are a potential energy source for the future. The efficient exploitation of NGHs has been a hot topic of worldwide research. At present, the Depressurization is considered as the most effective method for NGHs exploitation. However, the lacking of hydrate decomposition driving force in Depressurization anaphase and the ice generation phenomenon haven’t been solved effectively. The combination method of Depressurization with water flow erosion was carried out in this study. The experimental results indicated that driving force for MH decomposition will be not enough when the exploitation backpressure was higher than 2.4 MPa. The combination of Depressurization with water flow erosion will efficiently solve the lacking of drive force for Depressurization in anaphase and shorten the time of hydrate exploitation. The existence of chemical potential difference accelerated the hydrate decomposition.
-
Experimental investigation of natural gas hydrate production characteristics via novel combination modes of Depressurization with water flow erosion
Fuel, 2019Co-Authors: Bingbing Chen, Huiru Sun, Dayong Wang, Mingjun YangAbstract:Abstract Depressurization is considered the most efficient method for natural gas hydrates (NGHs) exploitation. However, ice formation, hydrate reformation, and insufficient decomposition driving forces in the later stages of Depressurization are the main issues to be solved. In this study, a more effective combination of Depressurization with water flow erosion for the production of NGHs was investigated to promote efficient exploitation of methane hydrate (MH) by using in-situ magnetic resonance imaging. Three different MH decomposition modes were used, and water flow erosion was employed to eliminate the problem of incomplete MH decomposition in the later stages of Depressurization, which is caused by insufficient driving forces and slower heat and mass transfer due to lower decomposition pressure and the protection effect of water films. The promotion of MH decomposition by water flow erosion was experimentally confirmed. Depressurization could decrease water-phase permeability in the sediment core and further optimize the water flow environment. Water flow erosion could greatly accelerate heat and mass transfer and provided extra driving force by increasing the chemical potential difference in the later stages of Depressurization. In addition, the phenomenon of ice formation caused by sudden Depressurization could be relieved by water flow erosion, which improved the ambient heat transfer, further changing the MH decomposition characteristics. The mutual promotion of MH decomposition by water flow erosion and Depressurization was clearly demonstrated in this study.
-
assessment of gas production from natural gas hydrate using Depressurization thermal stimulation and combined methods
RSC Advances, 2016Co-Authors: Yongchen Song, Mingjun Yang, Lunxiang Zhang, Zheng Ling, Jiafei ZhaoAbstract:The largest sources of hydrocarbons worldwide are distributed in the permafrost and submarine sediments in the form of methane hydrates, but exploitation of these hydrocarbons is still years away from being economical, safe, and commercially viable; thus, further research is needed. To analyze the characteristics of methane hydrate (MH) dissociation and evaluate the gas production during the application of different MH decomposition methods, this study firstly compared MH dissociation during Depressurization, thermal stimulation, and combined method (Depressurization + thermal stimulation) treatments using magnetic resonance imaging (MRI) in situ observation. In particular, the influences of back-pressure and temperature on hydrate dissociation, the hydrate saturation, the rate of hydrate dissociation and MRI images from each of the three methods were investigated. The results proved that during application of the Depressurization and combined methods at different back-pressures (2.2–2.6 MPa), the MH dissociation proceeded via radial dissociation rather than axial dissociation; moreover, during the application of the thermal stimulation method at different dissociation temperatures (278.15–288.15 K), the MH dissociated uniformly. Overall, a combination of Depressurization and thermal stimulation at the initial stage of hydrate decomposition was proposed and comparison of the three methods demonstrated that the combined method had obvious advantages for methane treatment. Specifically, the combined method was capable of solving the problems related to low gas production and poor energy efficiency that were encountered when using either the Depressurization or thermal stimulation method alone.
-
In Situ Observation of Methane Hydrate Dissociation under Different Backpressures
Energy & Fuels, 2015Co-Authors: Shenglong Wang, Mingjun Yang, Pengfei Wang, Yuechao Zhao, Yongchen SongAbstract:Depressurization has been considered an economic and practicable method for natural gas hydrate (NGH) exploitation. To obtain the kinetic data of methane hydrate (MH) dissociation under different backpressures, MH dissociation by Depressurization in a porous medium was investigated in situ using magnetic resonance imaging (MRI). MH was dissociated under backpressures that were varied from 2.8 to 2.2 MPa, and the hydrate saturation variation during dissociation was analyzed. One experimental case was carried out with constant backpressure, and four cases of variable backpressure Depressurization experiments were carried out. The radial dissociation pattern during Depressurization was confirmed. During hydrate dissociation, free water was observed to move toward the outlet of the vessel and decreased the water saturation after the hydrate totally dissociated in the field of view (FOV). The MRI data provided excellent information on the spatial distribution of water in the porous media during hydrate dissoci...
Yongchen Song - One of the best experts on this subject based on the ideXlab platform.
-
The enhancement effect of water-gas two-phase flow on Depressurization process: Important for gas hydrate production
Applied Energy, 2020Co-Authors: Huiru Sun, Mingjun Yang, Yuechao Zhao, Bingbing Chen, Guojun Zhao, Yongchen SongAbstract:Abstract Depressurization is one of the most efficient methods in the production testing of natural gas hydrates. However, problems such as hydrate reformation, ice generation and insufficient dissociation driving force in the later period of Depressurization adversely affect the gas production. It has been confirmed that controlling the flowrate ratio of a water-gas two-phase flow can help enhance the hydrate dissociation. However, the effect of the water-gas flowrate ratio on the hydrate dissociation behaviors during Depressurization is unclear. In this study, three dissociation modes involving a combination of water-gas flow and Depressurization were examined: mode 1 (concurrent start of Depressurization and water-gas flow), mode 2 (Depressurization is first used to dissociate the hydrate, and the water-gas flow is initiated after 15 min), and mode 3 (Depressurization is first used, and the water-gas flow is initiated after 30 min). The feasibility of water-gas flow to accelerate hydrate dissociation and mitigate ice generation was confirmed during the Depressurization process. In all the modes, the higher water-gas flowrate ratio and lower dissociation pressure significantly increased the energy recovery rate and decreased the energy input. Additionally, the water-gas flow, especially that with a higher flowrate ratio, effectively accelerated the elimination of the dark-zone (mixture of ice and hydrate) by providing continuous heat transfer. Mode 1 corresponded to the highest energy recovery rate, lowest energy input and most rapid disappearance of the dark-zone under the same experimental conditions. Therefore, mode 1 was regarded as the most efficient mode to dissociate hydrate in an actual hydrate production.
-
the effects of compressibility of natural gas hydrate bearing sediments on gas production using Depressurization
Energy, 2019Co-Authors: Xiang Sun, Yu Liu, Yongchen SongAbstract:Abstract Natural gas hydrate is a new alternative energy that has attracted global attention in recent years. Depressurization is considered a fundamental method of producing natural gas from gas hydrate-bearing sediments (GHBSs). However, soil compaction during Depressurization is a significant problem for production efficiency and safety. The compressibility of soil affects the hydrate dissociation in the coupled process of heat transfer, fluid flow, and soil compaction. In this study, a fully coupled Thermo-hydro-chemo-mechanical (THCM) model is applied to simulate Masuda's core-scale gas production experiments. The effects of compressibility on the changes in gas production rate, pore pressure, temperature, hydrate saturation, permeability, and heat conductivity are investigated by varying the parameters governing compressibility including the bulk modulus of host sediments and hydrate-enhanced bulk modulus. The results show that the higher compressibility corresponds to a larger reduction in porosity further impacting the variation in effective permeability, heat conductivity, and heat convection during Depressurization. In Masuda's test, the pressure changes indicate that the soil compaction might occurs during Depressurization. Because the real field production is implemented under confining condition, Masuda's test should be developed to consider the compressibility of GHBSs.
-
Visualization study on the promotion of Depressurization and water flow erosion for gas hydrate production
Energy Procedia, 2019Co-Authors: Bingbing Chen, Mingjun Yang, Huiru Sun, Dayong Wang, Lanlan Jiang, Yongchen SongAbstract:Abstract Natural gas hydrates (NGHs) are a potential energy source for the future. The efficient exploitation of NGHs has been a hot topic of worldwide research. At present, the Depressurization is considered as the most effective method for NGHs exploitation. However, the lacking of hydrate decomposition driving force in Depressurization anaphase and the ice generation phenomenon haven’t been solved effectively. The combination method of Depressurization with water flow erosion was carried out in this study. The experimental results indicated that driving force for MH decomposition will be not enough when the exploitation backpressure was higher than 2.4 MPa. The combination of Depressurization with water flow erosion will efficiently solve the lacking of drive force for Depressurization in anaphase and shorten the time of hydrate exploitation. The existence of chemical potential difference accelerated the hydrate decomposition.
-
analysis of Depressurization mode on gas recovery from methane hydrate deposits and the concomitant ice generation
Applied Energy, 2017Co-Authors: Bin Wang, Pengfei Wang, Jiafei Zhao, Zhen Fan, Yu Liu, Yongchen SongAbstract:Abstract Natural gas hydrates have garnered worldwide attention as an important potential non-conventional fossil fuel resource. When extracting natural gas from gas hydrate deposits via Depressurization, problematic ice generation and hydrate reformation can occur under conditions of fast depressurizing and low production pressures, due to insufficient heat transfer in the surrounding sediments. In this work we conduct in situ magnetic resonance imaging (MRI) visualization and analysis of hydrate decomposition behavior for different Depressurization modes; we visually determine the volumetric and spatial characteristics of the hydrate decomposition during Depressurization induced gas production operation. Our results indicate that fast Depressurization rate can result in a fast hydrate decomposition rate, therefore, a rapid gas production rate. In addition, the radial extension behavior of the decomposition front confirms that ambient heat transfer is a critical factor driving hydrate decomposition into free gas and liquid water. Obvious hydrate reformation and ice generation phenomenon, seen in some of the sudden Depressurization experiments, can be effectively avoided using piecewise and continuous Depressurization methods. The findings of this study clearly demonstrate how production pressures affect the gas production behavior from hydrate deposits and provide further insight for establishing optimal production techniques for utilizing hydrate resources in the field.
-
assessment of gas production from natural gas hydrate using Depressurization thermal stimulation and combined methods
RSC Advances, 2016Co-Authors: Yongchen Song, Mingjun Yang, Lunxiang Zhang, Zheng Ling, Jiafei ZhaoAbstract:The largest sources of hydrocarbons worldwide are distributed in the permafrost and submarine sediments in the form of methane hydrates, but exploitation of these hydrocarbons is still years away from being economical, safe, and commercially viable; thus, further research is needed. To analyze the characteristics of methane hydrate (MH) dissociation and evaluate the gas production during the application of different MH decomposition methods, this study firstly compared MH dissociation during Depressurization, thermal stimulation, and combined method (Depressurization + thermal stimulation) treatments using magnetic resonance imaging (MRI) in situ observation. In particular, the influences of back-pressure and temperature on hydrate dissociation, the hydrate saturation, the rate of hydrate dissociation and MRI images from each of the three methods were investigated. The results proved that during application of the Depressurization and combined methods at different back-pressures (2.2–2.6 MPa), the MH dissociation proceeded via radial dissociation rather than axial dissociation; moreover, during the application of the thermal stimulation method at different dissociation temperatures (278.15–288.15 K), the MH dissociated uniformly. Overall, a combination of Depressurization and thermal stimulation at the initial stage of hydrate decomposition was proposed and comparison of the three methods demonstrated that the combined method had obvious advantages for methane treatment. Specifically, the combined method was capable of solving the problems related to low gas production and poor energy efficiency that were encountered when using either the Depressurization or thermal stimulation method alone.
Bingbing Chen - One of the best experts on this subject based on the ideXlab platform.
-
The enhancement effect of water-gas two-phase flow on Depressurization process: Important for gas hydrate production
Applied Energy, 2020Co-Authors: Huiru Sun, Mingjun Yang, Yuechao Zhao, Bingbing Chen, Guojun Zhao, Yongchen SongAbstract:Abstract Depressurization is one of the most efficient methods in the production testing of natural gas hydrates. However, problems such as hydrate reformation, ice generation and insufficient dissociation driving force in the later period of Depressurization adversely affect the gas production. It has been confirmed that controlling the flowrate ratio of a water-gas two-phase flow can help enhance the hydrate dissociation. However, the effect of the water-gas flowrate ratio on the hydrate dissociation behaviors during Depressurization is unclear. In this study, three dissociation modes involving a combination of water-gas flow and Depressurization were examined: mode 1 (concurrent start of Depressurization and water-gas flow), mode 2 (Depressurization is first used to dissociate the hydrate, and the water-gas flow is initiated after 15 min), and mode 3 (Depressurization is first used, and the water-gas flow is initiated after 30 min). The feasibility of water-gas flow to accelerate hydrate dissociation and mitigate ice generation was confirmed during the Depressurization process. In all the modes, the higher water-gas flowrate ratio and lower dissociation pressure significantly increased the energy recovery rate and decreased the energy input. Additionally, the water-gas flow, especially that with a higher flowrate ratio, effectively accelerated the elimination of the dark-zone (mixture of ice and hydrate) by providing continuous heat transfer. Mode 1 corresponded to the highest energy recovery rate, lowest energy input and most rapid disappearance of the dark-zone under the same experimental conditions. Therefore, mode 1 was regarded as the most efficient mode to dissociate hydrate in an actual hydrate production.
-
Visualization study on the promotion of Depressurization and water flow erosion for gas hydrate production
Energy Procedia, 2019Co-Authors: Bingbing Chen, Mingjun Yang, Huiru Sun, Dayong Wang, Lanlan Jiang, Yongchen SongAbstract:Abstract Natural gas hydrates (NGHs) are a potential energy source for the future. The efficient exploitation of NGHs has been a hot topic of worldwide research. At present, the Depressurization is considered as the most effective method for NGHs exploitation. However, the lacking of hydrate decomposition driving force in Depressurization anaphase and the ice generation phenomenon haven’t been solved effectively. The combination method of Depressurization with water flow erosion was carried out in this study. The experimental results indicated that driving force for MH decomposition will be not enough when the exploitation backpressure was higher than 2.4 MPa. The combination of Depressurization with water flow erosion will efficiently solve the lacking of drive force for Depressurization in anaphase and shorten the time of hydrate exploitation. The existence of chemical potential difference accelerated the hydrate decomposition.
-
Experimental investigation of natural gas hydrate production characteristics via novel combination modes of Depressurization with water flow erosion
Fuel, 2019Co-Authors: Bingbing Chen, Huiru Sun, Dayong Wang, Mingjun YangAbstract:Abstract Depressurization is considered the most efficient method for natural gas hydrates (NGHs) exploitation. However, ice formation, hydrate reformation, and insufficient decomposition driving forces in the later stages of Depressurization are the main issues to be solved. In this study, a more effective combination of Depressurization with water flow erosion for the production of NGHs was investigated to promote efficient exploitation of methane hydrate (MH) by using in-situ magnetic resonance imaging. Three different MH decomposition modes were used, and water flow erosion was employed to eliminate the problem of incomplete MH decomposition in the later stages of Depressurization, which is caused by insufficient driving forces and slower heat and mass transfer due to lower decomposition pressure and the protection effect of water films. The promotion of MH decomposition by water flow erosion was experimentally confirmed. Depressurization could decrease water-phase permeability in the sediment core and further optimize the water flow environment. Water flow erosion could greatly accelerate heat and mass transfer and provided extra driving force by increasing the chemical potential difference in the later stages of Depressurization. In addition, the phenomenon of ice formation caused by sudden Depressurization could be relieved by water flow erosion, which improved the ambient heat transfer, further changing the MH decomposition characteristics. The mutual promotion of MH decomposition by water flow erosion and Depressurization was clearly demonstrated in this study.
Yi Wang - One of the best experts on this subject based on the ideXlab platform.
-
Combined styles of Depressurization and electrical heating for methane hydrate production
Applied Energy, 2021Co-Authors: Zhao-yang Chen, Yi Wang, Yu Zhang, Zhi-ming Xia, Changyu YouAbstract:Abstract The combined styles of Depressurization and electrical heating have an important influence on hydrate recovery and energy use in hydrate exploitation. However, the efficient combined styles of Depressurization and electrical heating have not been achieved at present. In this work, six combined styles of Depressurization and electrical heating were designed. In order to determine efficient combined styles, a depressurized vertical wellbore and a heated horizontal wellbore were used to model these combined styles and further to dissociate hydrate-bearing samples prepared by the excess-water method. The results showed that electrical heating should be started before Depressurization. Specifically, considering hydrate saturation increase of 0.327–2.47% in the hydrate stability region, electrical heating was proposed to start at the onset of fresh hydrate formation. Subsequently, the soaking through electrical heating was performed at a pressure below the equilibrium pressure at the ambient temperature, which increased the averaged hydrate dissociation rate by 7.72%. A lower shut-in pressure for the soaking could enlarge the effective heating radius in samples to improve hydrate dissociation. During Depressurization, no electrical heating reduced the averaged water production rate by 80.99% and increased energy efficiency by 18.06%. So electrical heating was proposed to stop in the temperature recovering stage, but whether it was used or not in the temperature reducing stage should depend on exploiting conditions, due to secondary hydrate formation and ice formation at a lower back pressure. This work may offer some reference on the arrangement of Depressurization and electrical heating in future field tests for hydrate exploitation.
-
Sediment deformation and strain evaluation during methane hydrate dissociation in a novel experimental apparatus
Applied Energy, 2020Co-Authors: Yi Wang, Jingchun Feng, Xuan Kou, Yu ZhangAbstract:Abstract Natural gas hydrate is an efficient alternative future energy source because huge reserves of methane gas are caged in hydrate-bearing sediments. The research on the deformation of sediments during hydrate dissociation is important for safe hydrate production. In this work, a novel experimental apparatus was designed and built to investigate sediment deformation and strain evaluation during methane hydrate dissociation by Depressurization. Experimental results are compared for methane hydrate dissociation for various hydrate saturations, porosities, and particle sizes of sediments. Experimental results illustrate that gas hydrate dissociation by Depressurization experienced three main stages. The phenomenon secondary hydrate formation was found during hydrate dissociation by Depressurization, which leads to the decrease of sediment permeability. The strain of the sediment is proportional to the volume of methane gas production. Higher hydrate saturation leads to larger sediment deformation by hydrate decomposition. Higher sediment porosity leads to looser sediment particles and larger sediment deformation during hydrate dissociation by Depressurization. Larger sediment particle sizes lead to smaller interface areas between hydrate and sediment particles, and larger sediment deformation during hydrate dissociation by Depressurization.
-
large scale experimental investigation of influence of heat conduction and heat convection on hydrate dissociation by Depressurization in sandy sediment
Energy Procedia, 2019Co-Authors: Yi Wang, Jingchun FengAbstract:Abstract Natural gas hydrate can be regarded as alternative energy source in future due to huge reserves of methane gas trapped in hydrate bearing formations. According to the laboratory studies and field programs, Depressurization method has been considered as the most cost-effective and practical way to dissociate gas hydrates. Rates of hydrate dissociation by Depressurization mainly depend on heat transfer rate. The heat transfer during hydrate dissociation mainly includes heat conduction and heat convection. In this work, the Pilot-Scale Hydrate Simulator (PHS), with an inner volume of 117.8 L, was applied to investigate the influence of heat conduction and heat convection on hydrate dissociation. Different thermal boundary conditions and different flow directions during gas recovery from hydrate reservoir by Depressurization were performed in the PHS. The experimental results indicate that hydrate dissociation rate with isothermal boundary is fast than that with semi-adiabatic boundary. However, the influence of heat convection direction on heat dissociation in the CP stage may not be obviously. The heat transfer rate in the CP stage of the Depressurization mainly depends on the heat conduction rate.
-
pilot scale experimental evaluation of gas recovery from methane hydrate using cycling Depressurization scheme
Energy, 2018Co-Authors: Yi Wang, Jingchun Feng, Lei ZhanAbstract:Abstract Methane hydrate is considered as a potential source of methane for energy supply. Therefore, developing approaches for enhancing gas recovery from hydrate reservoir is attracting extensive attention. The Pilot-Scale Hydrate Simulator (PHS), with an inner volume of 117.8 L, was applied to investigate gas recovery approach from hydrate reservoir. A novel cycling Depressurization was carried out to improve the production efficiency of Depressurization method. Three different schemes for gas recovery from hydrate reservoir were performed in the PHS, which were the Regular Depressurization (RD), the Semi-Cycling Depressurization (Semi-CD), and the Cycling Depressurization (CD), respectively. The production behaviors and heat transfer characteristics during hydrate dissociation in sandy sediments by different methods were compared and investigated. The advantages of the novel cycling Depressurization were analyzed. The experimental results indicate that the effective average gas production rate in the experiments by CD is 17 times larger than that by RD. The energy cost per volume of gas production by the CD scheme can be significantly reduced by comparing with the RD scheme. Therefore, the production efficiency can be strongly enhanced by using cycling Depressurization method. If the hydrate is dissociated by RD, the heat transfer is strongly coupled with the hydrate dissociation. However, if the hydrate is dissociated by Semi-CD or CD, the coupling of heat transfer and hydrate dissociation may be changed. During the well closing stage in the Semi-CD or CD scheme, the lower fluids flow rate in pores leads to a lower heat transfer rate, which leads to a lower hydrate dissociation rate in well closing stage.
-
large scale experimental investigation on influences of reservoir temperature and production pressure on gas production from methane hydrate in sandy sediment
Energy & Fuels, 2016Co-Authors: Yi Wang, Yu Zhang, Jingchun Feng, Zhao-yang ChenAbstract:The Pilot-Scale Hydrate Simulator (PHS), a three-dimensional 117.8 L pressure vessel, was applied to study the methane hydrate dissociation with different reservoir temperatures and different production pressures in the sandy sediment. The volume of the vessel is big enough to simulate the field-scale gas production from hydrate reservoir. The Depressurization method and the Depressurization assisted with heat stimulation method were performed as the hydrate dissociation methods. Three different temperatures, which are 4.7 °C, 8.8 °C, and 13.0 °C, were selected as the reservoir temperatures. The range of temperature in this work is the most common temperatures of hydrate reservoir in the ocean sediment. The experimental results indicate that, for the Depressurization method, the temperature drop in the reservoir during hydrate dissociation is the key factor for the amount of hydrate dissociation in the Depressurization (DP) stage and the rates of hydrate dissociation in the constant-pressure (CP) stage, w...
Huiru Sun - One of the best experts on this subject based on the ideXlab platform.
-
The enhancement effect of water-gas two-phase flow on Depressurization process: Important for gas hydrate production
Applied Energy, 2020Co-Authors: Huiru Sun, Mingjun Yang, Yuechao Zhao, Bingbing Chen, Guojun Zhao, Yongchen SongAbstract:Abstract Depressurization is one of the most efficient methods in the production testing of natural gas hydrates. However, problems such as hydrate reformation, ice generation and insufficient dissociation driving force in the later period of Depressurization adversely affect the gas production. It has been confirmed that controlling the flowrate ratio of a water-gas two-phase flow can help enhance the hydrate dissociation. However, the effect of the water-gas flowrate ratio on the hydrate dissociation behaviors during Depressurization is unclear. In this study, three dissociation modes involving a combination of water-gas flow and Depressurization were examined: mode 1 (concurrent start of Depressurization and water-gas flow), mode 2 (Depressurization is first used to dissociate the hydrate, and the water-gas flow is initiated after 15 min), and mode 3 (Depressurization is first used, and the water-gas flow is initiated after 30 min). The feasibility of water-gas flow to accelerate hydrate dissociation and mitigate ice generation was confirmed during the Depressurization process. In all the modes, the higher water-gas flowrate ratio and lower dissociation pressure significantly increased the energy recovery rate and decreased the energy input. Additionally, the water-gas flow, especially that with a higher flowrate ratio, effectively accelerated the elimination of the dark-zone (mixture of ice and hydrate) by providing continuous heat transfer. Mode 1 corresponded to the highest energy recovery rate, lowest energy input and most rapid disappearance of the dark-zone under the same experimental conditions. Therefore, mode 1 was regarded as the most efficient mode to dissociate hydrate in an actual hydrate production.
-
Visualization study on the promotion of Depressurization and water flow erosion for gas hydrate production
Energy Procedia, 2019Co-Authors: Bingbing Chen, Mingjun Yang, Huiru Sun, Dayong Wang, Lanlan Jiang, Yongchen SongAbstract:Abstract Natural gas hydrates (NGHs) are a potential energy source for the future. The efficient exploitation of NGHs has been a hot topic of worldwide research. At present, the Depressurization is considered as the most effective method for NGHs exploitation. However, the lacking of hydrate decomposition driving force in Depressurization anaphase and the ice generation phenomenon haven’t been solved effectively. The combination method of Depressurization with water flow erosion was carried out in this study. The experimental results indicated that driving force for MH decomposition will be not enough when the exploitation backpressure was higher than 2.4 MPa. The combination of Depressurization with water flow erosion will efficiently solve the lacking of drive force for Depressurization in anaphase and shorten the time of hydrate exploitation. The existence of chemical potential difference accelerated the hydrate decomposition.
-
Experimental investigation of natural gas hydrate production characteristics via novel combination modes of Depressurization with water flow erosion
Fuel, 2019Co-Authors: Bingbing Chen, Huiru Sun, Dayong Wang, Mingjun YangAbstract:Abstract Depressurization is considered the most efficient method for natural gas hydrates (NGHs) exploitation. However, ice formation, hydrate reformation, and insufficient decomposition driving forces in the later stages of Depressurization are the main issues to be solved. In this study, a more effective combination of Depressurization with water flow erosion for the production of NGHs was investigated to promote efficient exploitation of methane hydrate (MH) by using in-situ magnetic resonance imaging. Three different MH decomposition modes were used, and water flow erosion was employed to eliminate the problem of incomplete MH decomposition in the later stages of Depressurization, which is caused by insufficient driving forces and slower heat and mass transfer due to lower decomposition pressure and the protection effect of water films. The promotion of MH decomposition by water flow erosion was experimentally confirmed. Depressurization could decrease water-phase permeability in the sediment core and further optimize the water flow environment. Water flow erosion could greatly accelerate heat and mass transfer and provided extra driving force by increasing the chemical potential difference in the later stages of Depressurization. In addition, the phenomenon of ice formation caused by sudden Depressurization could be relieved by water flow erosion, which improved the ambient heat transfer, further changing the MH decomposition characteristics. The mutual promotion of MH decomposition by water flow erosion and Depressurization was clearly demonstrated in this study.