scholarly journals Gas hydrate pingoes: Deep seafloor evidence of focused fluid flow on continental margins

Geology ◽  
2012 ◽  
Vol 40 (3) ◽  
pp. 207-210 ◽  
Author(s):  
Christophe Serié ◽  
Mads Huuse ◽  
Niels H. Schødt
Keyword(s):  
Fluid Flow ◽  
Gas Hydrate ◽  
Continental Margins

Susceptibility assessment of gas hydrate dissociation occurrence along European continental margins and adjacent areas. GARAH project (GeoERA)

2021 ◽  
Author(s):  
Ricardo León ◽  
Christopher Rochelle ◽  
André Burnol ◽  
Carmen Julia Giménez- Moreno ◽  
Tove Nielsen ◽  
...  
Keyword(s):  
Fluid Flow ◽  
Gas Hydrate ◽  
Control Factor ◽  
Continental Margins ◽  
Baseline Scenario ◽  
Submarine Landslides ◽  
Susceptibility Assessment ◽  
Map Algebra ◽  
Hydrate Dissociation ◽  
Density Map

<p>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.</p><p>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.</p><p> </p><p><strong>Acknowledgment</strong></p><p>GARAH project. GeoERA - GeoE.171.002</p>

Time Constraints on Seepage Through Fractured Regions on the Vestnesa Ridge off the W-Svalbard Coast

2021 ◽  
Author(s):  
Hariharan Ramachandran ◽  
Andreia Plaza-Faverola ◽  
Hugh Daigle ◽  
Stefan Buenz
Keyword(s):  
Fluid Flow ◽  
Effective Stress ◽  
Gas Hydrate ◽  
Fluid Pressure ◽  
Fracture Network ◽  
The Arctic ◽  
Stability Zone ◽  
Methane Seepage ◽  
Carbonate Formation ◽  
Hydrate Stability

<p>Evidences of subsurface fluid flow-driven fractures (from seismic interpretation) are quite common at Vestnesa Ridge (around 79ºN in the Arctic Ocean), W-Svalbard margin. Ultimately, the fractured systems have led to the formation of pockmarks on the seafloor. At present day, the eastern segment of the ridge has active pockmarks with continuous methane seep observations in sonar data. The pockmarks in the western segment are considered inactive or to seep at a rate that is harder to identify. The ridge is at ~1200m water depth with the base of the gas hydrate stability zone (GHSZ) at ~200m below the seafloor. Considerable free gas zone is present below the hydrates. Besides the obvious concern of amount and rates of historic methane seeping into the ocean biosphere and its associated effects, significant gaps exist in the ability to model the processes of flow of methane through this faulted and fractured region. Our aim is to highlight the interactions between physical flow, geomechanics and geological control processes that govern the rates and timing of methane seepage.</p><p>For this purpose, we performed numerical fluid flow simulations. We integrate fundamental mass and component conservation equations with a phase equilibrium approach accounting for hydrate phase boundary effects to simulate the transport of gas from the base of the GHSZ through rock matrix and interconnected fractures until the seafloor. The relation between effective stress and fluid pressure is considered and fractures are activated once the effective stress exceeds the tensile limit. We use field data (seismic, oedometer tests on calypso cores, pore fluid pressure and temperature) to constrain the range of validity of various flow and geomechanical parameters in the simulation (such as vertical stress, porosity, permeability, saturations).</p><p>Preliminary results indicate fluid overpressure greater than 1.5 MPa is required to initiate fractures at the base of the gas hydrate stability zone for the investigated system. Focused fluid flow occurs through the narrow fracture networks and the gas reaches the seafloor within 1 day. The surrounding regions near the fracture network exhibit slower seepage towards the seafloor, but over a wider area. Advective flux through the less fractured surrounding regions, reaches the seafloor within 15 years and a diffusive flux reaches within 1200 years. These times are controlled by the permeability of the sediments and are retarded further due to considerable hydrate/carbonate formation during vertical migration. Next course of action includes constraining the methane availability at the base of the GHSZ and estimating its impact on seepage behavior.</p>

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

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

<p>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 δ<sup>13</sup>C and heavy δ<sup>18</sup>O 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 3<sup>rd</sup> 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.</p><p> </p>

Controls on gas hydrate system evolution in a region of active fluid flow in the SW Barents Sea

2015 ◽  
Vol 66 ◽  
pp. 861-872 ◽  
Author(s):  
Sunil Vadakkepuliyambatta ◽  
Matthew J. Hornbach ◽  
Stefan Bünz ◽  
Benjamin J. Phrampus
Keyword(s):  
Fluid Flow ◽  
Gas Hydrate ◽  
Barents Sea ◽  
System Evolution ◽  
Active Fluid

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

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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