Geophysical Indications of Gas Hydrate Occurrence on the Greenland Continental Margins

The Pan-European gas-hydrate relate GIS database of GARAH project has allowed assessing the susceptibility of seafloor areas affected by hydrate dissociation. This study has been applied as a first step for the hydrate related risk assessment along the European continental margins. Several factors and variables have been taken into account. They have been defined by their relationship with the presence of hydrates below seafloor and weighted depending on the confidence of finding hydrates in this site. The maximum weight (or confidence) has been given to the recovered samples of gas hydrates or hydrate-dissociation evidences such as degassing or liquation structures observed in gravity cores. Seismic indicators of the presence of gas hydrate or hydrocarbon seabed fluid flow such as BSR, blanking acoustic, amplitude anomalies or the presence of geological structures of seabed fluid flow in the neighbouring of the GHSZ have been weighted with a lower value. The theoretical gas hydrate stability zone (GHSZ) for a standard composition for biogenic gas has been taken into account as another control factor and constrain feature. Seafloor areas out of the theoretical GSHZ have been excluded as potential likelihood to be affected by hydrate dissociation processes. The base of GHSZ has been classified as a critical area for these dissociation processes.The proposed methodology analyses the geological hazard by means of the susceptibility assessment, defined by the likelihood of occurrence of hydrate dissociation, collapses, crater-like depressions or submarine landslides over seafloor. The baseline scenario is that gas hydrate occurrence is only possible in seafloor areas where pressure (bathymetry) and seafloor temperature conditions are inside the theoretical GHSZ. Inside GHSZ, the occurrence of gas hydrate is directly related to the presence of its evidences (direct samples of hydrates) or indicators (eg. pore water and velocity anomalies, BSR, gas chimneys, among others), as well as the occurrence of hydrocarbon fluid flow structures inside GHSZ. Finally, the likelihood of the seafloor to be affect gas hydrate dissociation processes will be major at the base of the GHSZ and in the neighbouring of the gas hydrate evidences and indicators. In order to proof this initial hypothesis, a susceptibility assessment has been carried out throughout map algebra in a GIS environment from a density map of evidences and indicators and the Pan-European map of the GHSZ over seafloor. Specifically, it has been conceived as a segmentation in three levels by quantiles resulting of the addition of the density map of evidences and indicators and the weighted map of the GHSZ over seafloor.&#160;AcknowledgmentGARAH project. GeoERA - GeoE.171.002

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Gas hydrate destabilization and sea-level changes: insights from Miocene seep carbonate deposits of the northern Apennines (Italy)

10.5194/egusphere-egu21-8529 ◽

2021 ◽

Author(s):

Daniela Fontana ◽

Stefano Conti ◽

Chiara Fioroni ◽

Claudio Argentino

Keyword(s):

Sea Level ◽

Gas Hydrate ◽

Leading Edge ◽

Accretionary Prism ◽

Northern Apennines ◽

Hydraulic Pressure ◽

Continental Margins ◽

Sea Level Changes ◽

Level Lowering ◽

Hydrate Stability

The effects of global warming on marine gas hydrate stability along continental margins is still unclear and discussed within the scientific community. Long-term datasets can be obtained from the geological record and might help us better understand how gas-hydrate reservoirs responds to climate changes. Present-day gas hydrates are frequently associated or interlayered with authigenic carbonates, called clathrites, which have been sampled from many continental margins worldwide. These carbonates show peculiar structures, such as vacuolar or vuggy-like fabrics, and are marked by light &#948;13C and heavy &#948;18O isotopic values. Evidences of paleo-gas hydrate occurrence are recorded in paleo-clathrites hosted in Miocene deposits of the Apennine chain, Italy, and formed in different positions of the paleo foreland system: in wedge-top basins, along the outer slope of the accretionary prism, and at the leading edge of the deformational front. The accurate nannofossil biostratigraphy of sediment hosting paleo-clathrites in the northern Apennines allowed us to ascribe them to different Miocene nannofossil zones, concentrated in three main intervals: in the Langhian (MNN5a), in the upper Serravallian-lower Tortonian (MNN6b-MNN7) and the upper Tortonian-lowermost Messinian (MNN10-MNN11). By comparing paleo-clathrite distributions with 3rd order eustatic curves, they seem to match phases of sea-level lowering associated with cold periods. Therefore, we suggest that the drop in the hydraulic pressure on the plumbing system during sea-level lowering shifted the bottom of the gas hydrate stability zone to shallower depths, inducing paleo gas-hydrate destabilization. The uplift of the different sectors of the wedge-top foredeep system during tectonic migration might have amplified the effect of the concomitant eustatic sea-level drop, reducing the hydrostatic load on the seafloor and triggering gas-hydrate decomposition. We suggest that Miocene climate-induced sea-level changes played a role in controlling gas hydrate stability and methane emissions along the northern Apennine paleo-wedge, with hydrate destabilization roughly matching with sea-level drops and cooling events.&#160;

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Gas hydrate stability and the assessment of heat flow through continental margins

Geophysical Journal International ◽

10.1046/j.0956-540x.2001.01404.x ◽

2001 ◽

Vol 145 (3) ◽

pp. 647-660 ◽

Cited By ~ 76

Author(s):

Ingo Grevemeyer ◽

Heinrich Villinger

Keyword(s):

Heat Flow ◽

Gas Hydrate ◽

Continental Margins ◽

Flow Through ◽

Hydrate Stability

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The Double (or Multiple) BSRs Observations and their Tentative Interpretations

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.734-737.467 ◽

2013 ◽

Vol 734-737 ◽

pp. 467-475

Author(s):

Yi Luo ◽

Xin Su

Keyword(s):

Climate Change ◽

Marine Environment ◽

Gas Hydrate ◽

Seismic Reflection ◽

Continental Margins ◽

Tectonic Movement ◽

Stability Zone ◽

Bottom Simulating Reflector ◽

Seismic Reflection Profiles ◽

Hydrate Stability

Gas hydrate is a solid ice-like compound and is stable at low temperature and high pressure conditions found beneath permafrost and in marine sediments on continental margins offshore. In the marine environment, the bottom-simulating reflector (BSR) in seismic reflection profiles is interpreted to indicate the base of the gas hydrate stability zone (GHSZ).In many locations two or more sub-parallel BSRs have been reported. We not only compared the BSRs characteristics from reported areas but also discussed the mechanism of GHSZ shifts by climate change, sedimentation process and tectonic movement. We also considered the mix gases composition hydrate stability in certain marine environment and gave a simple model for the BSR differences on water depth.

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Estimation of the global inventory of methane hydrates in marine sediments using transfer functions

Biogeosciences ◽

10.5194/bg-10-959-2013 ◽

2013 ◽

Vol 10 (2) ◽

pp. 959-975 ◽

Cited By ~ 95

Author(s):

E. Piñero ◽

M. Marquardt ◽

C. Hensen ◽

M. Haeckel ◽

K. Wallmann

Keyword(s):

Transfer Function ◽

Marine Sediments ◽

Gas Hydrates ◽

Gas Hydrate ◽

Large Scale ◽

Transfer Functions ◽

Methane Hydrates ◽

Continental Margins ◽

Transport Reaction ◽

Methane Generation

Abstract. The accumulation of gas hydrates in marine sediments is essentially controlled by the accumulation of particulate organic carbon (POC) which is microbially converted into methane, the thickness of the gas hydrate stability zone (GHSZ) where methane can be trapped, the sedimentation rate (SR) that controls the time that POC and the generated methane stays within the GHSZ, and the delivery of methane from deep-seated sediments by ascending pore fluids and gas into the GHSZ. Recently, Wallmann et al. (2012) presented transfer functions to predict the gas hydrate inventory in diffusion-controlled geological systems based on SR, POC and GHSZ thickness for two different scenarios: normal and full compacting sediments. We apply these functions to global data sets of bathymetry, heat flow, seafloor temperature, POC input and SR, estimating a global mass of carbon stored in marine methane hydrates from 3 to 455 Gt of carbon (GtC) depending on the sedimentation and compaction conditions. The global sediment volume of the GHSZ in continental margins is estimated to be 60–67 × 1015 m3, with a total of 7 × 1015 m3 of pore volume (available for GH accumulation). However, seepage of methane-rich fluids is known to have a pronounced effect on gas hydrate accumulation. Therefore, we carried out a set of systematic model runs with the transport-reaction code in order to derive an extended transfer function explicitly considering upward fluid advection. Using averaged fluid velocities for active margins, which were derived from mass balance considerations, this extended transfer function predicts the enhanced gas hydrate accumulation along the continental margins worldwide. Different scenarios were investigated resulting in a global mass of sub-seafloor gas hydrates of ~ 550 GtC. Overall, our systematic approach allows to clearly and quantitatively distinguish between the effect of biogenic methane generation from POC and fluid advection on the accumulation of gas hydrate, and hence, provides a simple prognostic tool for the estimation of large-scale and global gas hydrate inventories in marine sediments.

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Gas Hydrate on Continental Margins

Journal of Geological Research ◽

10.1155/2012/781429 ◽

2012 ◽

Vol 2012 ◽

pp. 1-2 ◽

Cited By ~ 1

Author(s):

Umberta Tinivella ◽

Michela Giustiniani ◽

Xuewei Liu ◽

Ingo Pecher

Keyword(s):

Gas Hydrate ◽

Continental Margins

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Pore-water anomalies in gas hydrate-bearing sediments of the deeper continental margins: Facts and problems

Journal of Inclusion Phenomena and Macrocyclic Chemistry ◽

10.1007/bf01131292 ◽

1990 ◽

Vol 8 (1-2) ◽

pp. 117-138 ◽

Cited By ~ 10

Author(s):

Reinhard Hesse

Keyword(s):

Pore Water ◽

Gas Hydrate ◽

Continental Margins ◽

Hydrate Bearing Sediments

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Evidences for Paleo-Gas Hydrate Occurrence: What We Can Infer for the Miocene of the Northern Apennines (Italy)

Geosciences ◽

10.3390/geosciences9030134 ◽

2019 ◽

Vol 9 (3) ◽

pp. 134 ◽

Cited By ~ 2

Author(s):

Claudio Argentino ◽

Stefano Conti ◽

Chiara Fioroni ◽

Daniela Fontana

Keyword(s):

Gas Hydrates ◽

Gas Hydrate ◽

Northern Apennines ◽

Stability Field ◽

Continental Margins ◽

Shallow Gas ◽

Hydrate Decomposition ◽

Oxygen Isotopic ◽

The Stability ◽

Seep Carbonate

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.

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