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Special Issue "Natural Gas Hydrate 2011"

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A special issue of Energies (ISSN 1996-1073).

Deadline for manuscript submissions: closed (31 January 2012)

Special Issue Editor

Guest Editor
Prof. Richard B. Coffin (Website)

Department of Physical and Environmental Sciences, Texas A&M University - Corpus Christi, 6300 Ocean Drive, Corpus Christi, TX 78421, USA
Interests: variation in methane hydrate abundance in world ocean coastal regions; shallow sediment methane cycling; methane flux to the atmosphere; elemental isotope analyses

Special Issue Information

Dear Colleagues,

Gas hydrates, recognized to be distributed through the world coastal oceans, are a significant energy source, have potential to influence coastal ocean platform stability, are an important component in climate change, and may contribute significantly to the overlying water column carbon cycles. Large investments for evaluation of methane hydrates as an energy source are ongoing at the Mackenzie Delta and Prudhoe Bay in the Arctic, the Nankai Trough off Japan, the Bay of Bengal near India, and on the Texas-Louisiana Shelf in the Gulf of Mexico. In addition to these large scale efforts, preliminary investigation of hydrate as a resource has started off on the coasts of New Zealand, Korea, Russia, Norway, Chile and other countries. Methane in hydrates is also being studied in Arctic coastal permafrost as a contribution to climate change. Addressing the development of this resource requires integration of a wide array of chemical, physical, geophysical and biological laboratory and field data. This special issue will combine papers on methods for evaluating deep sediment hydrate quantities, regional resource characterization, the methane contribution to shallow sediment and overlying water column carbon cycling, and predicted contributions to climate change. A primary goal is to share a thorough global overview of the current activity related to methane hydrate research.

Dr. Richard B. Coffin
Guest Editor

Keywords

  • energy
  • methane hydrates
  • climate change
  • carbon cycling
  • biogeochemistry
  • ocean modeling

Published Papers (19 papers)

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Research

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Open AccessArticle Submarine Slope Failure Primed and Triggered by Bottom Water Warming in Oceanic Hydrate-Bearing Deposits
Energies 2012, 5(8), 2849-2873; doi:10.3390/en5082849
Received: 14 May 2012 / Revised: 13 July 2012 / Accepted: 25 July 2012 / Published: 6 August 2012
Cited by 7 | PDF Full-text (406 KB) | HTML Full-text | XML Full-text
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 [...] 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)
Open AccessArticle Methane Hydrate Pellet Transport Using the Self-Preservation Effect: A Techno-Economic Analysis
Energies 2012, 5(7), 2499-2523; doi:10.3390/en5072499
Received: 2 February 2012 / Revised: 9 May 2012 / Accepted: 28 June 2012 / Published: 16 July 2012
Cited by 32 | PDF Full-text (2400 KB) | HTML Full-text | XML Full-text
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 [...] 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)
Open AccessArticle Kinetics of the Formation and Dissociation of Gas Hydrates from CO2-CH4 Mixtures
Energies 2012, 5(7), 2248-2262; doi:10.3390/en5072248
Received: 6 February 2012 / Revised: 3 May 2012 / Accepted: 25 May 2012 / Published: 6 July 2012
Cited by 7 | PDF Full-text (8597 KB) | HTML Full-text | XML Full-text
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 [...] 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)
Open AccessArticle Methane Production from Gas Hydrate Deposits through Injection of Supercritical CO2
Energies 2012, 5(7), 2112-2140; doi:10.3390/en5072112
Received: 5 April 2012 / Revised: 5 May 2012 / Accepted: 7 June 2012 / Published: 25 June 2012
Cited by 19 | PDF Full-text (1243 KB)
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 [...] 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)
Open AccessArticle Evidence of Gas Hydrates in Block 26—Offshore Trinidad
Energies 2012, 5(5), 1309-1320; doi:10.3390/en5051309
Received: 15 March 2012 / Revised: 26 March 2012 / Accepted: 22 April 2012 / Published: 3 May 2012
Cited by 3 | PDF Full-text (1535 KB) | HTML Full-text | XML Full-text
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 [...] 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)
Open AccessArticle Heat Transfer Analysis of Methane Hydrate Sediment Dissociation in a Closed Reactor by a Thermal Method
Energies 2012, 5(5), 1292-1308; doi:10.3390/en5051292
Received: 15 March 2012 / Revised: 13 April 2012 / Accepted: 18 April 2012 / Published: 2 May 2012
Cited by 22 | PDF Full-text (7933 KB) | HTML Full-text | XML Full-text
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 [...] 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 ΔToi grows until the temperature reaches 40 °C. The period of ΔToi have a close relation with the total time of hydrate dissociation. Especially, the period of ΔToi 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)
Open AccessArticle Characteristics of CO2 Hydrate Formation and Dissociation in Glass Beads and Silica Gel
Energies 2012, 5(4), 925-937; doi:10.3390/en5040925
Received: 9 February 2012 / Revised: 21 March 2012 / Accepted: 6 April 2012 / Published: 16 April 2012
Cited by 4 | PDF Full-text (374 KB) | HTML Full-text | XML Full-text
Abstract
CO2 hydrate formation and dissociation is crucial for hydrate-based CO2 capture 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 [...] Read more.
CO2 hydrate formation and dissociation is crucial for hydrate-based CO2 capture 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)
Open AccessArticle Direct Observation of THF Hydrate Formation in Porous Microstructure Using Magnetic Resonance Imaging
Energies 2012, 5(4), 898-910; doi:10.3390/en5040898
Received: 27 December 2011 / Revised: 20 March 2012 / Accepted: 23 March 2012 / Published: 5 April 2012
Cited by 9 | PDF Full-text (775 KB) | HTML Full-text | XML Full-text
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 [...] 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)
Open AccessCommunication Using Submarine Heat Pumps for Efficient Gas Production from Seabed Hydrate Reservoirs
Energies 2012, 5(3), 599-604; doi:10.3390/en5030599
Received: 21 January 2012 / Revised: 20 February 2012 / Accepted: 24 February 2012 / Published: 2 March 2012
Cited by 2 | PDF Full-text (268 KB) | HTML Full-text | XML Full-text
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 [...] 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)
Open AccessArticle The Driving Forces of Guest Substitution in Gas Hydrates—A Laser Raman Study on CH4-CO2 Exchange in the Presence of Impurities
Energies 2012, 5(2), 420-437; doi:10.3390/en5020420
Received: 15 December 2011 / Revised: 2 February 2012 / Accepted: 14 February 2012 / Published: 22 February 2012
Cited by 11 | PDF Full-text (2139 KB) | HTML Full-text | XML Full-text
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 [...] 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 NOx 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)
Open AccessArticle Numerical Simulation of Methane Production from Hydrates Induced by Different Depressurizing Approaches
Energies 2012, 5(2), 438-458; doi:10.3390/en5020438
Received: 23 December 2011 / Revised: 13 February 2012 / Accepted: 17 February 2012 / Published: 22 February 2012
Cited by 12 | PDF Full-text (1730 KB) | HTML Full-text | XML Full-text
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 [...] 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)
Open AccessArticle Thermodynamic Stability of Structure H Hydrates Based on the Molecular Properties of Large Guest Molecules
Energies 2012, 5(2), 459-465; doi:10.3390/en5020459
Received: 31 December 2011 / Revised: 11 February 2012 / Accepted: 14 February 2012 / Published: 22 February 2012
Cited by 8 | PDF Full-text (2289 KB) | HTML Full-text | XML Full-text
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 [...] 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)
Open AccessArticle Experimental Study on Methane Hydrate Dissociation by Depressurization in Porous Sediments
Energies 2012, 5(2), 518-530; doi:10.3390/en5020518
Received: 23 December 2011 / Revised: 6 February 2012 / Accepted: 7 February 2012 / Published: 22 February 2012
Cited by 15 | PDF Full-text (495 KB) | HTML Full-text | XML Full-text
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 [...] 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)
Open AccessArticle Experimental Research on the Mechanical Properties of Methane Hydrate-Ice Mixtures
Energies 2012, 5(2), 181-192; doi:10.3390/en5020181
Received: 8 December 2011 / Revised: 11 January 2012 / Accepted: 17 January 2012 / Published: 30 January 2012
Cited by 13 | PDF Full-text (531 KB) | HTML Full-text | XML Full-text
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 [...] 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)
Open AccessArticle Correlation of the Growth Rate of the Hydrate Layer at a Guest/Liquid-Water Interface to Mass Transfer Resistance
Energies 2012, 5(1), 92-100; doi:10.3390/en5010092
Received: 14 December 2011 / Revised: 10 January 2012 / Accepted: 11 January 2012 / Published: 18 January 2012
Cited by 6 | PDF Full-text (620 KB) | HTML Full-text | XML Full-text
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 [...] 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 TeqTex, where Teq is the equilibrium dissociation temperature of the hydrate and Tex 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)
Figures

Open AccessArticle Water Transfer Characteristics during Methane Hydrate Formation Processes in Layered Media
Energies 2011, 4(8), 1129-1137; doi:10.3390/en4081129
Received: 7 June 2011 / Revised: 26 July 2011 / Accepted: 27 July 2011 / Published: 2 August 2011
Cited by 3 | PDF Full-text (328 KB) | HTML Full-text | XML Full-text
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 [...] 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)

Review

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Open AccessReview The Global Inventory of Methane Hydrate in Marine Sediments: A Theoretical Approach
Energies 2012, 5(7), 2449-2498; doi:10.3390/en5072449
Received: 1 February 2012 / Revised: 29 June 2012 / Accepted: 2 July 2012 / Published: 16 July 2012
Cited by 46 | PDF Full-text (11226 KB) | XML Full-text
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 [...] 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)
Open AccessReview A Review on Research on Replacement of CH4 in Natural Gas Hydrates by Use of CO2
Energies 2012, 5(2), 399-419; doi:10.3390/en5020399
Received: 28 December 2011 / Revised: 6 February 2012 / Accepted: 8 February 2012 / Published: 22 February 2012
Cited by 30 | PDF Full-text (862 KB) | HTML Full-text | XML Full-text
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 [...] 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 CH4 in hydrated with different forms of CO2 is suggested. Full article
(This article belongs to the Special Issue Natural Gas Hydrate 2011)
Open AccessReview Experimental Simulation of the Exploitation of Natural Gas Hydrate
Energies 2012, 5(2), 466-493; doi:10.3390/en5020466
Received: 20 January 2012 / Revised: 7 February 2012 / Accepted: 8 February 2012 / Published: 22 February 2012
Cited by 8 | PDF Full-text (1271 KB) | HTML Full-text | XML Full-text
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 [...] 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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