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406 KiB

Open AccessArticle

Submarine Slope Failure Primed and Triggered by Bottom Water Warming in Oceanic Hydrate-Bearing Deposits

by Tae-Hyuk Kwon and Gye-Chun Cho

Energies 2012, 5(8), 2849-2873; https://doi.org/10.3390/en5082849 - 6 Aug 2012

Cited by 32 | Viewed by 7851

Abstract

Many submarine slope failures in hydrate-bearing sedimentary deposits might be directly triggered, or at least primed, by gas hydrate dissociation. It has been reported that during the past 55 years (1955–2010) the 0–2000 m layer of oceans worldwide has been warmed by 0.09 [...] Read more.

Many submarine slope failures in hydrate-bearing sedimentary deposits might be directly triggered, or at least primed, by gas hydrate dissociation. It has been reported that during the past 55 years (1955–2010) the 0–2000 m layer of oceans worldwide has been warmed by 0.09 °C because of global warming. This raises the following scientific concern: if warming of the bottom water of deep oceans continues, it would dissociate natural gas hydrates and could eventually trigger massive slope failures. The present study explored the submarine slope instability of oceanic gas hydrate-bearing deposits subjected to bottom water warming. One-dimensional coupled thermal-hydraulic-mechanical (T-H-M) finite difference analyses were performed to capture the underlying physical processes initiated by bottom water warming, which includes thermal conduction through sediments, thermal dissociation of gas hydrates, excess pore pressure generation, pressure diffusion, and hydrate dissociation against depressurization. The temperature rise at the seafloor due to bottom water warming is found to create an excess pore pressure that is sufficiently large to reduce the stability of a slope in some cases. Parametric study results suggest that a slope becomes more susceptible to failure with increases in thermal diffusivity and hydrate saturation and decreases in pressure diffusivity, gas saturation, and water depth. Bottom water warming can be further explored to gain a better understanding of the past methane hydrate destabilization events on Earth, assuming that more reliable geological data is available. Full article

(This article belongs to the Special Issue Natural Gas Hydrate 2011)

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2400 KiB

Open AccessArticle

Methane Hydrate Pellet Transport Using the Self-Preservation Effect: A Techno-Economic Analysis

by Gregor Rehder, Robert Eckl, Markus Elfgen, Andrzej Falenty, Rainer Hamann, Nina Kähler, Werner F. Kuhs, Hans Osterkamp and Christoph Windmeier

Energies 2012, 5(7), 2499-2523; https://doi.org/10.3390/en5072499 - 16 Jul 2012

Cited by 144 | Viewed by 14412

Abstract

Within the German integrated project SUGAR, aiming for the development of new technologies for the exploration and exploitation of submarine gas hydrates, the option of gas transport by gas hydrate pellets has been comprehensively re-investigated. A series of pVT dissociation experiments, combined with [...] Read more.

Within the German integrated project SUGAR, aiming for the development of new technologies for the exploration and exploitation of submarine gas hydrates, the option of gas transport by gas hydrate pellets has been comprehensively re-investigated. A series of pVT dissociation experiments, combined with analytical tools such as x-ray diffraction and cryo-SEM, were used to gather an additional level of understanding on effects controlling ice formation. Based on these new findings and the accessible literature, knowns and unknowns of the self-preservation effect important for the technology are summarized. A conceptual process design for methane hydrate production and pelletisation has been developed. For the major steps identified, comprising (i) hydrate formation; (ii) dewatering; (iii) pelletisation; (iv) pellet cooling; and (v) pressure relief, available technologies have been evaluated, and modifications and amendments included where needed. A hydrate carrier has been designed, featuring amongst other technical solutions a pivoted cargo system with the potential to mitigate sintering, an actively cooled containment and cargo distribution system, and a dual fuel engine allowing the use of the boil-off gas. The design was constrained by the properties of gas hydrate pellets, the expected operation on continental slopes in areas with rough seas, a scenario-defined loading capacity of 20,000 m³ methane hydrate pellets, and safety as well as environmental considerations. A risk analysis for the transport at sea has been carried out in this early stage of development, and the safety level of the new concept was compared to the safety level of other ship types with similar scopes, i.e., LNG carriers and crude oil tankers. Based on the results of the technological part of this study, and with best knowledge available on the alternative technologies, i.e., pipeline, LNG and CNG transportation, an evaluation of the economic competitiveness of the methane hydrate transport technology has been performed. The analysis considers capital investment as well as operational costs and comprises a wide set of scenarios with production rates from 20 to 800 10³ Nm³·h⁻¹ and transport distances from 200 to 10,000 km. In contrast to previous studies, the model calculations in this study reveal no economic benefit of methane hydrate transportation versus competing technologies. Full article

(This article belongs to the Special Issue Natural Gas Hydrate 2011)

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8597 KiB

Open AccessArticle

Kinetics of the Formation and Dissociation of Gas Hydrates from CO₂-CH₄ Mixtures

by Kristine Horvat, Prasad Kerkar, Keith Jones and Devinder Mahajan

Energies 2012, 5(7), 2248-2262; https://doi.org/10.3390/en5072248 - 6 Jul 2012

Cited by 30 | Viewed by 8240

Abstract

Sequestration of carbon dioxide (CO₂) in the form of its hydrates in natural methane (CH₄) hydrate reservoirs, via CO₂/CH₄ exchange, is an attractive pathway that also yields valuable CH₄ gas as product. In this paper, [...] Read more.

Sequestration of carbon dioxide (CO₂) in the form of its hydrates in natural methane (CH₄) hydrate reservoirs, via CO₂/CH₄ exchange, is an attractive pathway that also yields valuable CH₄ gas as product. In this paper, we describe a macroscale experiment to form CO₂ and CH₄-CO₂ hydrates, under seafloor-mimic conditions, in a vessel fitted with glass windows that provides visualization of hydrates throughout formation and dissociation processes. Time resolved pressure and temperature data as well as images of hydrates are presented. Quantitative gas conversions with pure CO₂, calculated from gas chromatographic measurements yielded values that range from 23 – 59% that correspond to the extent of formed hydrates. In CH₄-rich CH₄-CO₂ mixed gas systems, CH₄ hydrates were found to form preferentially. Full article

(This article belongs to the Special Issue Natural Gas Hydrate 2011)

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1243 KiB

Open AccessArticle

Methane Production from Gas Hydrate Deposits through Injection of Supercritical CO₂

by Christian Deusner, Nikolaus Bigalke, Elke Kossel and Matthias Haeckel

Energies 2012, 5(7), 2112-2140; https://doi.org/10.3390/en5072112 - 25 Jun 2012

Cited by 108 | Viewed by 12611

Abstract

The recovery of natural gas from CH₄-hydrate deposits in sub-marine and sub-permafrost environments through injection of CO₂ is considered a suitable strategy towards emission-neutral energy production. This study shows that the injection of hot, supercritical CO₂ is particularly promising. [...] Read more.

The recovery of natural gas from CH₄-hydrate deposits in sub-marine and sub-permafrost environments through injection of CO₂ is considered a suitable strategy towards emission-neutral energy production. This study shows that the injection of hot, supercritical CO₂ is particularly promising. The addition of heat triggers the dissociation of CH₄-hydrate while the CO₂, once thermally equilibrated, reacts with the pore water and is retained in the reservoir as immobile CO₂-hydrate. Furthermore, optimal reservoir conditions of pressure and temperature are constrained. Experiments were conducted in a high-pressure flow-through reactor at different sediment temperatures (2 °C, 8 °C, 10 °C) and hydrostatic pressures (8 MPa, 13 MPa). The efficiency of both, CH₄ production and CO₂ retention is best at 8 °C, 13 MPa. Here, both CO₂- and CH₄-hydrate as well as mixed hydrates can form. At 2 °C, the production process was less effective due to congestion of transport pathways through the sediment by rapidly forming CO₂-hydrate. In contrast, at 10 °C CH₄ production suffered from local increases in permeability and fast breakthrough of the injection fluid, thereby confining the accessibility to the CH₄ pool to only the most prominent fluid channels. Mass and volume balancing of the collected gas and fluid stream identified gas mobilization as equally important process parameter in addition to the rates of methane hydrate dissociation and hydrate conversion. Thus, the combination of heat supply and CO₂ injection in one supercritical phase helps to overcome the mass transfer limitations usually observed in experiments with cold liquid or gaseous CO₂. Full article

(This article belongs to the Special Issue Natural Gas Hydrate 2011)

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1535 KiB

Open AccessArticle

Evidence of Gas Hydrates in Block 26—Offshore Trinidad

by Jill Marcelle-De Silva, Adrian Thomas, Wanda Lee De Landro Clarke and Michelle Allum

Energies 2012, 5(5), 1309-1320; https://doi.org/10.3390/en5051309 - 3 May 2012

Cited by 4 | Viewed by 7894

Abstract

Natural gas hydrates are increasingly viewed as a potential economic resource as energy demands rise. In this study, three-dimensional seismic data for Block 26 in the Atlantic Continental Margin offshore Trinidad were evaluated to determine if there is the potential for oceanic hydrate-bearing [...] Read more.

Natural gas hydrates are increasingly viewed as a potential economic resource as energy demands rise. In this study, three-dimensional seismic data for Block 26 in the Atlantic Continental Margin offshore Trinidad were evaluated to determine if there is the potential for oceanic hydrate-bearing sediments. The seismic dataset covered an area of approximately 1210 km² of the continental slope. A bottom simulating reflector which generally ran parallel to the sea floor and cut the dominant stratigraphy was observed and mapped over approximately 43% of the study area. Full article

(This article belongs to the Special Issue Natural Gas Hydrate 2011)

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7933 KiB

Open AccessArticle

Heat Transfer Analysis of Methane Hydrate Sediment Dissociation in a Closed Reactor by a Thermal Method

by Jiafei Zhao, Chuanxiao Cheng, Yongchen Song, Weiguo Liu, Yu Liu, Kaihua Xue, Zihao Zhu, Zhi Yang, Dayong Wang and Mingjun Yang

Energies 2012, 5(5), 1292-1308; https://doi.org/10.3390/en5051292 - 2 May 2012

Cited by 56 | Viewed by 8684

Abstract

The heat transfer analysis of hydrate-bearing sediment involved phase changes is one of the key requirements of gas hydrate exploitation techniques. In this paper, experiments were conducted to examine the heat transfer performance during hydrate formation and dissociation by a thermal method using [...] Read more.

The heat transfer analysis of hydrate-bearing sediment involved phase changes is one of the key requirements of gas hydrate exploitation techniques. In this paper, experiments were conducted to examine the heat transfer performance during hydrate formation and dissociation by a thermal method using a 5L volume reactor. This study simulated porous media by using glass beads of uniform size. Sixteen platinum resistance thermometers were placed in different position in the reactor to monitor the temperature differences of the hydrate in porous media. The influence of production temperature on the production time was also investigated. Experimental results show that there is a delay when hydrate decomposed in the radial direction and there are three stages in the dissociation period which is influenced by the rate of hydrate dissociation and the heat flow of the reactor. A significant temperature difference along the radial direction of the reactor was obtained when the hydrate dissociates and this phenomenon could be enhanced by raising the production temperature. In addition, hydrate dissociates homogeneously and the temperature difference is much smaller than the other conditions when the production temperature is around the 10 °C. With the increase of the production temperature, the maximum of ΔT_oi grows until the temperature reaches 40 °C. The period of ΔT_oi have a close relation with the total time of hydrate dissociation. Especially, the period of ΔT_oi with production temperature of 10 °C is twice as much as that at other temperatures. Under these experimental conditions, the heat is mainly transferred by conduction from the dissociated zone to the dissociating zone and the production temperature has little effect on the convection of the water in the porous media. Full article

(This article belongs to the Special Issue Natural Gas Hydrate 2011)

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374 KiB

Open AccessArticle

Characteristics of CO₂ Hydrate Formation and Dissociation in Glass Beads and Silica Gel

by Mingjun Yang, Yongchen Song, Xuke Ruan, Yu Liu, Jiafei Zhao and Qingping Li

Energies 2012, 5(4), 925-937; https://doi.org/10.3390/en5040925 - 16 Apr 2012

Cited by 50 | Viewed by 7624

Abstract

CO₂ hydrate formation and dissociation is crucial for hydrate-based CO₂capture and storage. Experimental and calculated phase equilibrium conditions of carbon dioxide (CO₂) hydrate in porous medium were investigated in this study. Glass beads were used to form the [...] Read more.

CO₂ hydrate formation and dissociation is crucial for hydrate-based CO₂capture and storage. Experimental and calculated phase equilibrium conditions of carbon dioxide (CO₂) hydrate in porous medium were investigated in this study. Glass beads were used to form the porous medium. The experimental data were generated using a graphical method. The results indicated the decrease of pore size resulted in the increase of the equilibrium pressure of CO₂ hydrate. Magnetic resonance imaging (MRI) was used to investigate the priority formation site of CO₂ hydrate in different porous media, and the results showed that the hydrate form firstly in BZ-02 glass beads under the same pressure and temperature. An improved model was used to predict CO₂ hydrate equilibrium conditions, and the predictions showed good agreement with experimental measurements. Full article

(This article belongs to the Special Issue Natural Gas Hydrate 2011)

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775 KiB

Open AccessArticle

Direct Observation of THF Hydrate Formation in Porous Microstructure Using Magnetic Resonance Imaging

by Kaihua Xue, Jiafei Zhao, Yongchen Song, Weiguo Liu, Weihaur Lam, Yiming Zhu, Yu Liu, Chuanxiao Cheng and Di Liu

Energies 2012, 5(4), 898-910; https://doi.org/10.3390/en5040898 - 5 Apr 2012

Cited by 37 | Viewed by 7129

Abstract

The porous microstructure of hydrates governs the mechanical strength of the hydrate-bearing sediment. To investigate the growth law and microstructure of hydrates in porous media, the growth process of tetrahydrofuran (THF) hydrate under different concentration of THF solution is directly observed using Magnetic [...] Read more.

The porous microstructure of hydrates governs the mechanical strength of the hydrate-bearing sediment. To investigate the growth law and microstructure of hydrates in porous media, the growth process of tetrahydrofuran (THF) hydrate under different concentration of THF solution is directly observed using Magnetic Resonance Imaging (MRI). The images show that the THF hydrate grows as different models under different concentration of THF solution (19%, 11.4% and 5.7% by weight) at 1 °C. When the concentration is 19% (stoichiometric molar ratio of THF/H₂O = 1:17), the THF hydrate grows as cementing model. However, with the decreasing concentration of THF, the growth model transfers from cementing model to floating model. The results show that the growth of the THF hydrate was influenced by the dissolved quantity of THF in the water. The extension of the observed behavior to methane hydrate could have implications in understanding their role in seafloor and permafrost stability. Full article

(This article belongs to the Special Issue Natural Gas Hydrate 2011)

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268 KiB

Open AccessCommunication

Using Submarine Heat Pumps for Efficient Gas Production from Seabed Hydrate Reservoirs

by Yasuhiko H. Mori, Jun-ichi Ochiai and Ryo Ohmura

Energies 2012, 5(3), 599-604; https://doi.org/10.3390/en5030599 - 2 Mar 2012

Cited by 5 | Viewed by 5519

Abstract

This article reports our novel idea about the thermal stimulation of seabed hydrate reservoirs for the purpose of natural gas production. Our idea is to use submarine heat pumps, which are to be placed near the hydrate reservoir and work to recover thermal [...] Read more.

This article reports our novel idea about the thermal stimulation of seabed hydrate reservoirs for the purpose of natural gas production. Our idea is to use submarine heat pumps, which are to be placed near the hydrate reservoir and work to recover thermal energy from the surrounding seawater and supply it into the reservoir. Although the heat pumps need an electricity supply from the sea surface level, they can provide thermal energy which is several times that of the consumed electricity in quantity. As a consequence, the use of submarine heat pumps has a distinct thermodynamic advantage over other thermal stimulation techniques already proposed in the literature. Full article

(This article belongs to the Special Issue Natural Gas Hydrate 2011)

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495 KiB

Open AccessArticle

Experimental Study on Methane Hydrate Dissociation by Depressurization in Porous Sediments

by Lijun Xiong, Xiaosen Li, Yi Wang and Chungang Xu

Energies 2012, 5(2), 518-530; https://doi.org/10.3390/en5020518 - 22 Feb 2012

Cited by 47 | Viewed by 7392

Abstract

Based on currently available data from site measurements in the Shenhu Area of the South China Sea, methane hydrate dissociation behavior by depressurization is studied in a one-dimensional experimental apparatus. According to time variation of temperature, resistance and gas production, the hydrate dissociation [...] Read more.

Based on currently available data from site measurements in the Shenhu Area of the South China Sea, methane hydrate dissociation behavior by depressurization is studied in a one-dimensional experimental apparatus. According to time variation of temperature, resistance and gas production, the hydrate dissociation process is divided into three stages: free gas release, rapid dissociation and gradual dissociation. The experimental results show that as the hydrate saturation increases the proportion of hydrate decomposed decreases in the rapid dissociation stage. The hydrate dissociation rate and the dissociation heat increase as the dissociation pressure decreases. Furthermore, the decrease of the dissociation pressure works against the secondary formation of the hydrate. Full article

(This article belongs to the Special Issue Natural Gas Hydrate 2011)

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2289 KiB

Open AccessArticle

Thermodynamic Stability of Structure H Hydrates Based on the Molecular Properties of Large Guest Molecules

by Kyoichi Tezuka, Tatsuhiko Taguchi, Saman Alavi, Amadeu K. Sum and Ryo Ohmura

Energies 2012, 5(2), 459-465; https://doi.org/10.3390/en5020459 - 22 Feb 2012

Cited by 18 | Viewed by 6807

Abstract

This paper report analyses of thermodynamic stability of structure-H clathrate hydrates formed with methane and large guest molecules in terms of their gas phase molecular sizes and molar masses for the selection of a large guest molecule providing better hydrate stability. We investigated [...] Read more.

This paper report analyses of thermodynamic stability of structure-H clathrate hydrates formed with methane and large guest molecules in terms of their gas phase molecular sizes and molar masses for the selection of a large guest molecule providing better hydrate stability. We investigated the correlation among the gas phase molecular sizes, the molar masses of large molecule guest substances, and the equilibrium pressures. The results suggest that there exists a molecular-size value for the best stability. Also, at a given molecule size, better stability may be available when the large molecule guest substance has a larger molar mass. Full article

(This article belongs to the Special Issue Natural Gas Hydrate 2011)

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1730 KiB

Open AccessArticle

Numerical Simulation of Methane Production from Hydrates Induced by Different Depressurizing Approaches

by Xuke Ruan, Yongchen Song, Jiafei Zhao, Haifeng Liang, Mingjun Yang and Yanghui Li

Energies 2012, 5(2), 438-458; https://doi.org/10.3390/en5020438 - 22 Feb 2012

Cited by 51 | Viewed by 7135

Abstract

Several studies have demonstrated that methane production from hydrate-bearing porous media by means of depressurization-induced dissociation can be a promising technique. In this study, a 2D axisymmetric model for simulating the gas production from hydrates by depressurization is developed to investigate the gas [...] Read more.

Several studies have demonstrated that methane production from hydrate-bearing porous media by means of depressurization-induced dissociation can be a promising technique. In this study, a 2D axisymmetric model for simulating the gas production from hydrates by depressurization is developed to investigate the gas production behavior with different depressurizing approaches. The simulation results showed that the depressurization process with depressurizing range has significant influence on the final gas production. On the contrary, the depressurizing rate only affects the production lifetime. More amount of cumulative gas can be produced with a larger depressurization range or lowering the depressurizing rate for a certain depressurizing range. Through the comparison of the combined depressurization modes, the Class 2 (all the hydrate dissociation simulations are performed by reducing the initial system pressure with the same depressurizing range initially, then to continue the depressurization process conducted by different depressurizing rates and complete when the system pressure decreases to the atmospheric pressure) is much superior to the Class 1 (different depressurizing ranges are adopted in the initial period of the gas production process, when the pressure is reduced to the corresponding value of depressurization process at the different depressurizing range, the simulations are conducted at a certain depressurizing rate until the pressure reaches the atmospheric pressure) for a long and stable gas production process. The parameter analysis indicated that the gas production performance decreases and the period of stable production increases with the initial pressure for the case of depressurizing range. Additionally, for the case of depressurizing range, the better gas production performance is associated with higher ambient temperature for production process, and the effect of thermal conductivity on gas production performance can be negligible. However, for the case of depressurizing rate, the ambient temperature or thermal conductivity is dominant in different period of gas production process. Full article

(This article belongs to the Special Issue Natural Gas Hydrate 2011)

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2139 KiB

Open AccessArticle

The Driving Forces of Guest Substitution in Gas Hydrates—A Laser Raman Study on CH₄-CO₂ Exchange in the Presence of Impurities

by Bettina Beeskow-Strauch and Judith Maria Schicks

Energies 2012, 5(2), 420-437; https://doi.org/10.3390/en5020420 - 22 Feb 2012

Cited by 31 | Viewed by 6878

Abstract

The recovery of CH₄ gas from natural hydrate formations by injection of industrially emitted CO₂ is considered to be a promising solution to simultaneously access an unconventional fossil fuel reserve and counteract atmospheric CO₂ increase. CO₂ obtained from industrial [...] Read more.

The recovery of CH₄ gas from natural hydrate formations by injection of industrially emitted CO₂ is considered to be a promising solution to simultaneously access an unconventional fossil fuel reserve and counteract atmospheric CO₂ increase. CO₂ obtained from industrial processes may contain traces of impurities such as SO₂ or NO_x and natural gas hydrates may contain higher hydrocarbons such as C₂H₆ and C₃H₈. These additions have an influence on the properties of the resulting hydrate phase and the conversion process of CH₄-rich hydrates to CO₂-rich hydrates. Here we show results of a microscopic and laser Raman in situ study investigating the effects of SO₂-polluted CO₂ and mixed CH₄-C₂H₆ hydrate on the exchange process. Our study shows that the key driving force of the exchange processes is the establishment of the chemical equilibrium between hydrate phase and the surrounding phases. The exchange rate is also influenced by the guest-to-cavity ratio as well as the thermodynamic stability in terms of p-T conditions of the original and resulting hydrate phase. The most effective molecule exchange is related to structural changes (sI-sII) which indicates that hydrate decomposition and reformation processes are the occurring processes. Full article

(This article belongs to the Special Issue Natural Gas Hydrate 2011)

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531 KiB

Open AccessArticle

Experimental Research on the Mechanical Properties of Methane Hydrate-Ice Mixtures

by Yanghui Li, Yongchen Song, Weiguo Liu and Feng Yu

Energies 2012, 5(2), 181-192; https://doi.org/10.3390/en5020181 - 30 Jan 2012

Cited by 55 | Viewed by 7863

Abstract

The mechanical properties of methane hydrate are important to the stability of borehole and methane extraction from a methane hydrate reservoir. In this study, a series of triaxial compression tests were carried out on laboratory-formed methane hydrate-ice mixtures with various methane hydrate contents. [...] Read more.

The mechanical properties of methane hydrate are important to the stability of borehole and methane extraction from a methane hydrate reservoir. In this study, a series of triaxial compression tests were carried out on laboratory-formed methane hydrate-ice mixtures with various methane hydrate contents. Axial loading was conducted at an axial strain rate of 1.33%/min and a constant temperature of −10 °C. The results indicate that: (1) the deformation behavior is strongly affected by confining pressure and methane hydrate content; (2) the failure strength significantly increases with confining pressure when confining pressure is less than 10 MPa, and decreases with methane hydrate content; (3) the cohesion decreases with methane hydrate content, while the internal friction angle increases with methane hydrate content; (4) the strength of ice specimens are higher than that of methane hydrate-ice mixture specimens; Based on the experimental data, the relationship among failure strength, confining pressure and methane hydrate content was obtained, and a modified Mohr-Coulomb criterion considering the influence of methane hydrate content on shear strength was proposed. Full article

(This article belongs to the Special Issue Natural Gas Hydrate 2011)

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620 KiB

Open AccessArticle

Correlation of the Growth Rate of the Hydrate Layer at a Guest/Liquid-Water Interface to Mass Transfer Resistance

by Masatoshi Kishimoto and Ryo Ohmura

Energies 2012, 5(1), 92-100; https://doi.org/10.3390/en5010092 - 18 Jan 2012

Cited by 23 | Viewed by 6825

Abstract

Growth rate of a hydrate layer at the guest/liquid-water interface is analyzed considering the conjugate process of the mass-transfer and hydrate crystal growth. Hydrate-layer growth rate data in the literature are often compiled according to the system subcooling (∆T ≡ T_eq [...] Read more.

Growth rate of a hydrate layer at the guest/liquid-water interface is analyzed considering the conjugate process of the mass-transfer and hydrate crystal growth. Hydrate-layer growth rate data in the literature are often compiled according to the system subcooling (∆T ≡ T_eq − T_ex, where T_eq is the equilibrium dissociation temperature of the hydrate and T_ex is the system temperature), suggesting predominant heat transfer limitations. In this paper, we investigate how the existing data on hydrate-layer growth is better correlated to mass transfer of the guest species in liquid water in three-phase equilibrium with bulk guest fluid and hydrate. We have analyzed the conjugate processes of mass-transfer/hydrate-layer-growth following our previous study on the hydrate crystal growth into liquid water saturated with a guest substance. A dimensionless parameter representing the hydrate-layer growth rate is derived from the analysis. This analysis is based on the idea that the growth rate is controlled by the mass transfer of the hydrate-guest substance, dissolved in the bulk of liquid water, to the front of the growing hydrate-layer along the guest/water interface. The variations in the hydrate-layer growth rate observed in the previous studies are related to the dimensionless parameter. Full article

(This article belongs to the Special Issue Natural Gas Hydrate 2011)

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Graphical abstract

328 KiB

Open AccessArticle

Water Transfer Characteristics during Methane Hydrate Formation Processes in Layered Media

by Peng Zhang, Qingbai Wu, Yibin Pu and Yousheng Deng

Energies 2011, 4(8), 1129-1137; https://doi.org/10.3390/en4081129 - 2 Aug 2011

Cited by 5 | Viewed by 6412

Abstract

Gas hydrate formation processes in porous media are always accompanied by water transfer. To study the transfer characteristics comprehensively, two kinds of layered media consisting of coarse sand and loess were used to form methane hydrate in them. An apparatus with three PF-meter [...] Read more.

Gas hydrate formation processes in porous media are always accompanied by water transfer. To study the transfer characteristics comprehensively, two kinds of layered media consisting of coarse sand and loess were used to form methane hydrate in them. An apparatus with three PF-meter sensors detecting water content and temperature changes in media during the formation processes was applied to study the water transfer characteristics. It was experimentally observed that the hydrate formation configurations in different layered media were similar; however, the water transfer characteristics and water conversion ratios were different. Full article

(This article belongs to the Special Issue Natural Gas Hydrate 2011)

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Review

Jump to: Research

11226 KiB

Open AccessReview

The Global Inventory of Methane Hydrate in Marine Sediments: A Theoretical Approach

by Klaus Wallmann, Elena Pinero, Ewa Burwicz, Matthias Haeckel, Christian Hensen, Andrew Dale and Lars Ruepke

Energies 2012, 5(7), 2449-2498; https://doi.org/10.3390/en5072449 - 16 Jul 2012

Cited by 234 | Viewed by 14783

Abstract

The accumulation of methane hydrate in marine sediments is controlled by a number of physical and biogeochemical parameters including the thickness of the gas hydrate stability zone (GHSZ), the solubility of methane in pore fluids, the accumulation of particulate organic carbon at the [...] Read more.

The accumulation of methane hydrate in marine sediments is controlled by a number of physical and biogeochemical parameters including the thickness of the gas hydrate stability zone (GHSZ), the solubility of methane in pore fluids, the accumulation of particulate organic carbon at the seafloor, the kinetics of microbial organic matter degradation and methane generation in marine sediments, sediment compaction and the ascent of deep-seated pore fluids and methane gas into the GHSZ. Our present knowledge on these controlling factors is discussed and new estimates of global sediment and methane fluxes are provided applying a transport-reaction model at global scale. The modeling and the data evaluation yield improved and better constrained estimates of the global pore volume within the modern GHSZ ( ≥ 44 × 10¹⁵ m³), the Holocene POC accumulation rate at the seabed (~1.4 × 10¹⁴ g yr⁻¹), the global rate of microbial methane production in the deep biosphere (4−25 × 10¹² g C yr⁻¹) and the inventory of methane hydrates in marine sediments ( ≥ 455 Gt of methane-bound carbon). Full article

(This article belongs to the Special Issue Natural Gas Hydrate 2011)

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1271 KiB

Open AccessReview

Experimental Simulation of the Exploitation of Natural Gas Hydrate

by Bei Liu, Qing Yuan, Ke-Hua Su, Xin Yang, Ben-Cheng Wu, Chang-Yu Sun and Guang-Jin Chen

Energies 2012, 5(2), 466-493; https://doi.org/10.3390/en5020466 - 22 Feb 2012

Cited by 30 | Viewed by 9026

Abstract

Natural gas hydrates are cage-like crystalline compounds in which a large amount of methane is trapped within a crystal structure of water, forming solids at low temperature and high pressure. Natural gas hydrates are widely distributed in permafrost regions and offshore. It is [...] Read more.

Natural gas hydrates are cage-like crystalline compounds in which a large amount of methane is trapped within a crystal structure of water, forming solids at low temperature and high pressure. Natural gas hydrates are widely distributed in permafrost regions and offshore. It is estimated that the worldwide amounts of methane bound in gas hydrates are total twice the amount of carbon to be found in all known fossil fuels on earth. A proper understanding of the relevant exploitation technologies is then important for natural gas production applications. In this paper, the recent advances on the experimental simulation of natural gas hydrate exploitation using the major hydrate production technologies are summarized. In addition, the current situation of the industrial exploitation of natural gas hydrate is introduced, which are expected to be useful for establishing more safe and efficient gas production technologies. Full article

(This article belongs to the Special Issue Natural Gas Hydrate 2011)

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862 KiB

Open AccessReview

A Review on Research on Replacement of CH₄ in Natural Gas Hydrates by Use of CO₂

by Jiafei Zhao, Kun Xu, Yongchen Song, Weiguo Liu, Weihaur Lam, Yu Liu, Kaihua Xue, Yiming Zhu, Xichong Yu and Qingping Li

Energies 2012, 5(2), 399-419; https://doi.org/10.3390/en5020399 - 22 Feb 2012

Cited by 119 | Viewed by 10536

Abstract

This paper introduces the research advances on replacement of CH₄ in Natural Gas Hydrates (NGHs) by use of CO₂ and discusses the advantages and disadvantages of the method on the natural gas production from such hydrates. Firstly, the feasibility of replacement [...] Read more.

This paper introduces the research advances on replacement of CH₄ in Natural Gas Hydrates (NGHs) by use of CO₂ and discusses the advantages and disadvantages of the method on the natural gas production from such hydrates. Firstly, the feasibility of replacement is proven from the points of view of kinetics and thermodynamics, and confirmed by experiments. Then, the latest progress in CH₄ replacement experiments with gaseous CO₂, liquid CO₂ and CO₂ emulsion are presented Moreover, the superiority of CO₂ emulsion for replacement of CH₄ is emphasized. The latest experiment progress on preparation of CO₂ emulsions are introduced. Finally, the advancements in simulation research on replacement is introduced, and the deficiencies of the simulations are pointed. The factors influencing on the replacement with different forms of CO₂ are analyzed and the optimum conditions for the replacement of CH₄in hydrated with different forms of CO₂ is suggested. Full article

(This article belongs to the Special Issue Natural Gas Hydrate 2011)

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