Special Issue "Gas Hydrate: Environmental and Climate Impacts"

A special issue of Geosciences (ISSN 2076-3263).

Deadline for manuscript submissions: closed (31 March 2019).

Special Issue Editors

Dr. Umberta Tinivella
E-Mail Website
Guest Editor
Istituto Nazionale di Oceanografia e di Geofisica Sperimentale - OGS, Geophysical Division, via Treviso 55, 33100 Udine, Italy
Interests: gas hydrate; theoretical modelling; pore fluid; overpressure; seismic processing; amplitude versus offset (AVO); wave equation datuming; synthetic data; geohazards; multidisciplinary analysis
Dr. Michela Giustiniani
E-Mail Website
Guest Editor
Istituto Nazionale di Oceanografia e di Geofisica Sperimentale - OGS, Geophysical Division, Borgo Grotta Gigante 42/C, 34010, Sgonico (TS) , Italy
Interests: gas hydrate; seismic processing; advanced techniques for seismic data analysis; geohazards; multidisciplinary analysis
Dr. Ivan de la Cruz Vargas Cordero
E-Mail Website
Guest Editor
School of Geology, Andrés Bello University, Chile
Interests: geological processes in subduction zones; seismic processing from multichannel seismic data; seismic processing, and imaging of seismic data using modern techniques (migration velocity analysis, Kirchhoff pre-stack depth migration); fluid migration information by using advanced processing (seismic attributes, AVO analysis, velocity modeling, true amplitude analysis)
Dr. Atanas Vasilev
E-Mail Website
Guest Editor
Institute of Oceanology - Bulgarian Academy of Sciences, Bulgaria
Interests: marine geophysics; gas hydrates models; geohazards; greenhouse gases emissions; Black Sea

Special Issue Information

Dear Colleagues,

In the last few decades, gas hydrates have been considered as a possible reservoir of natural gas, even if the actual global estimate is very rough, and also they are related to global changes and geohazards. In fact, the increasing attention regarding gas hydrates is increasing from: (1) the assessment of methane hydrates as a new ‘clean’ energy source, (2) the relationship between gas hydrate and global climate, and (3) the geological hazards related to the gas hydrate. Gas hydrates can be related to environmental risks because their dissociation can affect seafloor stability and release methane (and associated gases) into the water column. In fact, methane is an important greenhouse gas and any release of methane to the atmosphere would have an impact on climate change.

Generally, gas hydrate deposits are investigated using geophysical methods. The seismic technique, which is the most used, allows detecting a clear indicator of the hydrate and free gas accumulations, known as bottom simulating reflector. Moreover, the seismic data provides information about the geometry of the main geological structures, allowing possible explanations of the presence/absence of gas hydrate. In the last few years, the integration of geophysical (mainly seismic and electromagnetic data), geochemical, and heat-flow data allowed detecting and characterising gas hydrate and free gas volumes and distribution in the sediments. Thus, reviews of extensive geophysical surveys and direct measurements combined with geological interpretation and theoretical modelling will increase our understanding on the occurrence, distribution, and concentration of gas hydrate and the underlying free gas beneath the ocean bottom and the permafrost.

This Special Issue on gas hydrate offers the scientific community an opportunity to illustrate their research. Therefore, we invite you to submit original research and review articles on this topic.

Dr. Umberta Tinivella
Dr. Michela Giustiniani
Dr. Ivan de la Cruz Vargas Cordero
Dr. Atanas Vasilev
Guest Editors

Manuscript Submission Information

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Keywords

  • Natural gas hydrate
  • Methane cycle
  • Global change
  • Ecosystem
  • Geohazards
  • Risk assessment
  • Environmental impact
  • Multidisciplinarity
  • Blue growth

Published Papers (11 papers)

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Editorial

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Open AccessEditorial
Gas Hydrate: Environmental and Climate Impacts
Geosciences 2019, 9(10), 443; https://doi.org/10.3390/geosciences9100443 - 18 Oct 2019
Abstract
This Special Issue reports research spanning from the analysis of indirect data, modelling, laboratory and geological data confirming the intrinsic multidisciplinarity of the gas hydrate studies. The study areas are (1) Arctic, (2) Brazil, (3) Chile and (4) the Mediterranean region. The results [...] Read more.
This Special Issue reports research spanning from the analysis of indirect data, modelling, laboratory and geological data confirming the intrinsic multidisciplinarity of the gas hydrate studies. The study areas are (1) Arctic, (2) Brazil, (3) Chile and (4) the Mediterranean region. The results furnished an important tessera of the knowledge about the relationship of a gas hydrate system with other complex natural phenomena such as climate change, slope stability and earthquakes, and human activities. Full article
(This article belongs to the Special Issue Gas Hydrate: Environmental and Climate Impacts)

Research

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Open AccessArticle
Role of Warming in Destabilization of Intrapermafrost Gas Hydrates in the Arctic Shelf: Experimental Modeling
Geosciences 2019, 9(10), 407; https://doi.org/10.3390/geosciences9100407 - 20 Sep 2019
Cited by 1
Abstract
Destabilization of intrapermafrost gas hydrates is one of the possible mechanisms responsible for methane emission in the Arctic shelf. Intrapermafrost gas hydrates may be coeval to permafrost: they originated during regression and subsequent cooling and freezing of sediments, which created favorable conditions for [...] Read more.
Destabilization of intrapermafrost gas hydrates is one of the possible mechanisms responsible for methane emission in the Arctic shelf. Intrapermafrost gas hydrates may be coeval to permafrost: they originated during regression and subsequent cooling and freezing of sediments, which created favorable conditions for hydrate stability. Local pressure increase in freezing gas-saturated sediments maintained gas hydrate stability from depths of 200–250 m or shallower. The gas hydrates that formed within shallow permafrost have survived till present in the metastable (relict) state. The metastable gas hydrates located above the present stability zone may dissociate in the case of permafrost degradation as it becomes warmer and more saline. The effect of temperature increase on frozen sand and silt containing metastable pore methane hydrate is studied experimentally to reconstruct the conditions for intrapermafrost gas hydrate dissociation. The experiments show that the dissociation process in hydrate-bearing frozen sediments exposed to warming begins and ends before the onset of pore ice melting. The critical temperature sufficient for gas hydrate dissociation varies from −3.0 °C to −0.3 °C and depends on lithology (particle size) and salinity of the host frozen sediments. Taking into account an almost gradientless temperature distribution during degradation of subsea permafrost, even minor temperature increases can be expected to trigger large-scale dissociation of intrapermafrost hydrates. The ensuing active methane emission from the Arctic shelf sediments poses risks of geohazard and negative environmental impacts. Full article
(This article belongs to the Special Issue Gas Hydrate: Environmental and Climate Impacts)
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Open AccessArticle
A Quick-Look Method for Initial Evaluation of Gas Hydrate Stability below Subaqueous Permafrost
Geosciences 2019, 9(8), 329; https://doi.org/10.3390/geosciences9080329 - 26 Jul 2019
Cited by 1
Abstract
Many studies demonstrated the coexistence of subaqueous permafrost and gas hydrate. Subaqueous permafrost could be a factor affecting the formation/dissociation of gas hydrate. Here, we propose a simple empirical approach that allows estimating the steady-state conditions for gas hydrate stability in the presence [...] Read more.
Many studies demonstrated the coexistence of subaqueous permafrost and gas hydrate. Subaqueous permafrost could be a factor affecting the formation/dissociation of gas hydrate. Here, we propose a simple empirical approach that allows estimating the steady-state conditions for gas hydrate stability in the presence of subaqueous permafrost. This approach was derived for pressure, temperature, and salinity conditions typical of subaqueous permafrost in marine (brine) and lacustrine (freshwater) environments. Full article
(This article belongs to the Special Issue Gas Hydrate: Environmental and Climate Impacts)
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Open AccessArticle
Methane Hydrate Stability and Potential Resource in the Levant Basin, Southeastern Mediterranean Sea
Geosciences 2019, 9(7), 306; https://doi.org/10.3390/geosciences9070306 - 11 Jul 2019
Cited by 2
Abstract
To estimate the potential inventory of natural gas hydrates (NGH) in the Levant Basin, southeastern Mediterranean Sea, we correlated the gas hydrate stability zone (GHSZ), modeled with local thermodynamic parameters, with seismic indicators of gas. A compilation of the oceanographic measurements defines the [...] Read more.
To estimate the potential inventory of natural gas hydrates (NGH) in the Levant Basin, southeastern Mediterranean Sea, we correlated the gas hydrate stability zone (GHSZ), modeled with local thermodynamic parameters, with seismic indicators of gas. A compilation of the oceanographic measurements defines the >1 km deep water temperature and salinity to 13.8 °C and 38.8‰ respectively, predicting the top GHSZ at a water depth of ~1250 m. Assuming sub-seafloor hydrostatic pore-pressure, water-body salinity, and geothermal gradients ranging between 20 to 28.5 °C/km, yields a useful first-order GHSZ approximation. Our model predicts that the entire northwestern half of the Levant seafloor lies within the GHSZ, with a median sub-seafloor thickness of ~150 m. High amplitude seismic reflectivity (HASR), correlates with the active seafloor gas seepage and is distributed across the deep-sea fan of the Nile within the Levant Basin. Trends observed in the distribution of the HASR are suggested to represent: (1) Shallow gas and possibly hydrates within buried channel-lobe systems 25 to 100 mbsf; and (2) a regionally discontinuous bottom simulating reflection (BSR) broadly matching the modeled base of GHSZ. We therefore estimate the potential methane hydrates resources within the Levant Basin at ~100 trillion cubic feet (Tcf) and its carbon content at ~1.5 gigatonnes. Full article
(This article belongs to the Special Issue Gas Hydrate: Environmental and Climate Impacts)
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Open AccessArticle
Geotectonic Controls on CO2 Formation and Distribution Processes in the Brazilian Pre-Salt Basins
Geosciences 2019, 9(6), 252; https://doi.org/10.3390/geosciences9060252 - 05 Jun 2019
Cited by 1
Abstract
Exploratory work for hydrocarbons along the southeastern Brazilian Margin discovered high concentrations of CO2 in several fields, setting scientific challenges to understand these accumulations. Despite significant progress in understanding the consequences of high CO2 in these reservoirs, the role of several [...] Read more.
Exploratory work for hydrocarbons along the southeastern Brazilian Margin discovered high concentrations of CO2 in several fields, setting scientific challenges to understand these accumulations. Despite significant progress in understanding the consequences of high CO2 in these reservoirs, the role of several variables that may control such accumulations of CO2 is still unclear. For example, significant differences in the percentages of CO2 have been found in reservoirs of otherwise similar prospects lying close to each other. In this paper, we present a hypothesis on how the rifting geodynamics are related to these CO2-rich accumulations. CO2-rich mantle material may be intruded into the upper crustal levels through hyper-stretched continental crust during rifting. Gravimetric and magnetic potential methods were used to identify major intrusive bodies, crustal thinning and other geotectonic elements of the southeastern Brazilian Margin. Modeling based on magnetic, gravity, and seismic data suggests a major intrusive magmatic body just below the reservoir where a high CO2 accumulation was found. Small faults connecting this magmatic body with the sedimentary section could be the fairway for the magmatic sourced gas rise to reservoirs. Mapping and understanding the crustal structure of sedimentary basins are shown to be important steps for “de-risking” the exploration process. Full article
(This article belongs to the Special Issue Gas Hydrate: Environmental and Climate Impacts)
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Open AccessArticle
Potential Instability of Gas Hydrates along the Chilean Margin Due to Ocean Warming
Geosciences 2019, 9(5), 234; https://doi.org/10.3390/geosciences9050234 - 21 May 2019
Cited by 1
Abstract
In the last few years, interest in the offshore Chilean margin has increased rapidly due to the presence of gas hydrates. We have modelled the gas hydrate stability zone off Chilean shores (from 33° S to 46° S) using a steady state approach [...] Read more.
In the last few years, interest in the offshore Chilean margin has increased rapidly due to the presence of gas hydrates. We have modelled the gas hydrate stability zone off Chilean shores (from 33° S to 46° S) using a steady state approach to evaluate the effects of climate change on gas hydrate stability. Present day conditions were modelled using published literature and compared with available measurements. Then, we simulated the effects of climate change on gas hydrate stability in 50 and 100 years on the basis of Intergovernmental Panel on Climate Change and National Aeronautics and Space Administration forecasts. An increase in temperature might cause the dissociation of gas hydrate that could strongly affect gas hydrate stability. Moreover, we found that the high seismicity of this area could have a strong effect on gas hydrate stability. Clearly, the Chilean margin should be considered as a natural laboratory for understanding the relationship between gas hydrate systems and complex natural phenomena, such as climate change, slope stability and earthquakes. Full article
(This article belongs to the Special Issue Gas Hydrate: Environmental and Climate Impacts)
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Open AccessArticle
Role of Salt Migration in Destabilization of Intra Permafrost Hydrates in the Arctic Shelf: Experimental Modeling
Geosciences 2019, 9(4), 188; https://doi.org/10.3390/geosciences9040188 - 23 Apr 2019
Cited by 2
Abstract
Destabilization of intrapermafrost gas hydrate is one possible reason for methane emission on the Arctic shelf. The formation of these intrapermafrost gas hydrates could occur almost simultaneously with the permafrost sediments due to the occurrence of a hydrate stability zone after sea regression [...] Read more.
Destabilization of intrapermafrost gas hydrate is one possible reason for methane emission on the Arctic shelf. The formation of these intrapermafrost gas hydrates could occur almost simultaneously with the permafrost sediments due to the occurrence of a hydrate stability zone after sea regression and the subsequent deep cooling and freezing of sediments. The top of the gas hydrate stability zone could exist not only at depths of 200–250 m, but also higher due to local pressure increase in gas-saturated horizons during freezing. Formed at a shallow depth, intrapermafrost gas hydrates could later be preserved and transform into a metastable (relict) state. Under the conditions of submarine permafrost degradation, exactly relict hydrates located above the modern gas hydrate stability zone will, first of all, be involved in the decomposition process caused by negative temperature rising, permafrost thawing, and sediment salinity increasing. That’s why special experiments were conducted on the interaction of frozen sandy sediments containing relict methane hydrates with salt solutions of different concentrations at negative temperatures to assess the conditions of intrapermafrost gas hydrates dissociation. Experiments showed that the migration of salts into frozen hydrate-containing sediments activates the decomposition of pore gas hydrates and increase the methane emission. These results allowed for an understanding of the mechanism of massive methane release from bottom sediments of the East Siberian Arctic shelf. Full article
(This article belongs to the Special Issue Gas Hydrate: Environmental and Climate Impacts)
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Open AccessArticle
Evidences for Paleo-Gas Hydrate Occurrence: What We Can Infer for the Miocene of the Northern Apennines (Italy)
Geosciences 2019, 9(3), 134; https://doi.org/10.3390/geosciences9030134 - 20 Mar 2019
Cited by 1
Abstract
The occurrence of seep-carbonates associated with shallow gas hydrates is increasingly documented in modern continental margins but in fossil sediments the recognition of gas hydrates is still challenging for the lack of unequivocal proxies. Here, we combined multiple field and geochemical indicators for [...] Read more.
The occurrence of seep-carbonates associated with shallow gas hydrates is increasingly documented in modern continental margins but in fossil sediments the recognition of gas hydrates is still challenging for the lack of unequivocal proxies. Here, we combined multiple field and geochemical indicators for paleo-gas hydrate occurrence based on present-day analogues to investigate fossil seeps located in the northern Apennines. We recognized clathrite-like structures such as thin-layered, spongy and vuggy textures and microbreccias. Non-gravitational cementation fabrics and pinch-out terminations in cavities within the seep-carbonate deposits are ascribed to irregularly oriented dissociation of gas hydrates. Additional evidences for paleo-gas hydrates are provided by the large dimensions of seep-carbonate masses and by the association with sedimentary instability in the host sediments. We report heavy oxygen isotopic values in the examined seep-carbonates up to +6‰ that are indicative of a contribution of isotopically heavier fluids released by gas hydrate decomposition. The calculation of the stability field of methane hydrates for the northern Apennine wedge-foredeep system during the Miocene indicated the potential occurrence of shallow gas hydrates in the upper few tens of meters of sedimentary column. Full article
(This article belongs to the Special Issue Gas Hydrate: Environmental and Climate Impacts)
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Open AccessArticle
Molecular and Isotopic Composition of Hydrate-Bound, Dissolved and Free Gases in the Amazon Deep-Sea Fan and Slope Sediments, Brazil
Geosciences 2019, 9(2), 73; https://doi.org/10.3390/geosciences9020073 - 31 Jan 2019
Cited by 2
Abstract
In this work, we investigated the molecular stable isotope compositions of hydrate-bound and dissolved gases in sediments of the Amazon deep-sea fan and adjacent continental slope, Foz do Amazonas Basin, Brazil. Some cores were obtained in places with active gas venting on the [...] Read more.
In this work, we investigated the molecular stable isotope compositions of hydrate-bound and dissolved gases in sediments of the Amazon deep-sea fan and adjacent continental slope, Foz do Amazonas Basin, Brazil. Some cores were obtained in places with active gas venting on the seafloor and, in one of the locations, the venting gas is probably associated with the dissociation of hydrates near the edge of their stability zone. Results of the methane stable isotopes (δ13C and δD) of hydrate-bound and dissolved gases in sediments for the Amazon fan indicated the dominant microbial origin of methane via carbon dioxide reduction, in which 13C and deuterium isotopes were highly depleted (δ13C and δD of −102.2% to −74.2% V-PDB and −190 to −150% V-SMOW, respectively). The combination of C1/(C2+C3) versus δ13C plot also suggested a biogenic origin for methane in all analysed samples (commonly >1000). However, a mixture of thermogenic and microbial gases was suggested for the hydrate-bound and dissolved gases in the continental slope adjacent to the Amazon fan, in which the combination of chemical and isotopic gas compositions in the C1/(C2+C3) versus δ13C plot were <100 in one of the recovered cores. Moreover, the δ13C-ethane of −30.0% indicates a thermogenic origin. Full article
(This article belongs to the Special Issue Gas Hydrate: Environmental and Climate Impacts)
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Open AccessArticle
Gas Hydrate Estimate in an Area of Deformation and High Heat Flow at the Chile Triple Junction
Geosciences 2019, 9(1), 28; https://doi.org/10.3390/geosciences9010028 - 08 Jan 2019
Cited by 1
Abstract
Large amounts of gas hydrate are present in marine sediments offshore Taitao Peninsula, near the Chile Triple Junction. Here, marine sediments on the forearc contain carbon that is converted to methane in a regime of very high heat flow and intense rock deformation [...] Read more.
Large amounts of gas hydrate are present in marine sediments offshore Taitao Peninsula, near the Chile Triple Junction. Here, marine sediments on the forearc contain carbon that is converted to methane in a regime of very high heat flow and intense rock deformation above the downgoing oceanic spreading ridge separating the Nazca and Antarctic plates. This regime enables vigorous fluid migration. Here, we present an analysis of the spatial distribution, concentration, estimate of gas-phases (gas hydrate and free gas) and geothermal gradients in the accretionary prism, and forearc sediments offshore Taitao (45.5°–47° S). Velocity analysis of Seismic Profile RC2901-751 indicates gas hydrate concentration values <10% of the total rock volume and extremely high geothermal gradients (<190 °C·km−1). Gas hydrates are located in shallow sediments (90–280 m below the seafloor). The large amount of hydrate and free gas estimated (7.21 × 1011 m3 and 4.1 × 1010 m3; respectively), the high seismicity, the mechanically unstable nature of the sediments, and the anomalous conditions of the geothermal gradient set the stage for potentially massive releases of methane to the ocean, mainly through hydrate dissociation and/or migration directly to the seabed through faults. We conclude that the Chile Triple Junction is an important methane seepage area and should be the focus of novel geological, oceanographic, and ecological research. Full article
(This article belongs to the Special Issue Gas Hydrate: Environmental and Climate Impacts)
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Review

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Open AccessReview
Gas Seeps at the Edge of the Gas Hydrate Stability Zone on Brazil’s Continental Margin
Geosciences 2019, 9(5), 193; https://doi.org/10.3390/geosciences9050193 - 28 Apr 2019
Cited by 3
Abstract
Gas hydrate provinces occur in two sedimentary basins along Brazil’s continental margin: (1) The Rio Grande Cone in the southeast, and (2) the Amazon deep-sea fan in the equatorial region. The occurrence of gas hydrates in these depocenters was first detected geophysically and [...] Read more.
Gas hydrate provinces occur in two sedimentary basins along Brazil’s continental margin: (1) The Rio Grande Cone in the southeast, and (2) the Amazon deep-sea fan in the equatorial region. The occurrence of gas hydrates in these depocenters was first detected geophysically and has recently been proven by seafloor sampling of gas vents, detected as water column acoustic anomalies rising from seafloor depressions (pockmarks) and/or mounds, many associated with seafloor faults formed by the gravitational collapse of both depocenters. The gas vents include typical features of cold seep systems, including shallow sulphate reduction depths (<4 m), authigenic carbonate pavements, and chemosynthetic ecosystems. In both areas, gas sampled in hydrate and in sediments is dominantly formed by biogenic methane. Calculation of the methane hydrate stability zone for water temperatures in the two areas shows that gas vents occur along its feather edge (water depths between 510 and 760 m in the Rio Grande Cone and between 500 and 670 m in the Amazon deep-sea fan), but also in deeper waters within the stability zone. Gas venting along the feather edge of the stability zone could reflect gas hydrate dissociation and release to the oceans, as inferred on other continental margins, or upward fluid flow through the stability zone facilitated by tectonic structures recording the gravitational collapse of both depocenters. The potential quantity of venting gas on the Brazilian margin under different scenarios of natural or anthropogenic change requires further investigation. The studied areas provide natural laboratories where these critical processes can be analyzed and quantified. Full article
(This article belongs to the Special Issue Gas Hydrate: Environmental and Climate Impacts)
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