scholarly journals Methane seepage in a Cretaceous greenhouse world recorded by an unusual carbonate deposit from the Tarfaya Basin, Morocco

2017 ◽  
Vol 3 (1) ◽  
pp. 4-37 ◽  
Author(s):  
Daniel Smrzka ◽  
Jennifer Zwicker ◽  
Sadat Kolonic ◽  
Daniel Birgel ◽  
Crispin T.S. Little ◽  
...  
Keyword(s):  
Methane Seepage ◽  
Carbonate Deposit

Calcium carbonate deposit formation under isothermal conditions

1996 ◽  
Vol 74 (6) ◽  
pp. 911-919 ◽  
Author(s):  
N. Andritsos ◽  
M. Kontopoulou ◽  
A. J. Karabelas ◽  
P. G. Koutsoukos
Keyword(s):  
Calcium Carbonate ◽  
Deposit Formation ◽  
Isothermal Conditions ◽  
Carbonate Deposit

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>

scholarly journals Proposed Methodology to Quantify the Amount of Methane Seepage by Understanding the Correlation Between Methane Plumes and Originating Seeps

2021 ◽  
Vol 9 ◽  
Author(s):  
Chiharu Aoyama ◽  
Nidomu Maeda
Keyword(s):  
Environmental Impact ◽  
Target Position ◽  
Energy Resources ◽  
Basic Data ◽  
Methane Seeps ◽  
Remotely Operated Vehicle ◽  
Methane Seepage ◽  
The World ◽  
Backscattering Strength ◽  
The Mean

In recent years, discoveries of methane plumes (also called methane flares) have been reported in various sea areas around the world. Clusters of naturally seeping methane bubbles rising from the seafloor are visualized as methane plumes on the echograms of quantitative echo sounders and multibeam sonars. In order to determine if seeping methane can be used as energy resources and its environmental impact, it is necessary to estimate the amount of naturally seeping methane. From April, 2020, a 3-year project is being conducted in Japan to evaluate the amount of methane seepage from methane plumes. The authors propose the following steps to quantify the amount of methane seepage accurately. First of all, methane plumes in the Exclusive Economic Zone (EEZ) of Japan are mapped out using acoustic devices such as quantitative echo sounders and multibeam sonars. Secondly, methane bubbles of a few millimeters in diameter from methane seeps at seafloor are collected and sampled using a cone-shaped collector with 20 cm in diameter, operated by Remotely Operated Vehicle (ROV). If we can identify the number of seep mouths that form into one single plume, we will be able to quantify the methane seepage from one plume. Based on this result, calibration of the mean backscattering strength and the amount of seeping methane from methane plumes becomes possible and will be applied to the mapped plumes in order to estimate the methane seepage in the EEZ of Japan. Once this calibration is established, it can be applied to the methane plumes observed worldwide, and methane seepage can be quantified simply by acoustic observations of methane plumes. In this study, a method to verify the correlation between methane plumes and methane seeps is introduced, as well as a method to locate methane seeps effectively using the Target Position function of a quantitative echo sounder. The authors intend to use this as the basic data for establishing a method to estimate the amount of methane released from a methane plume by observing the methane plume acoustically.

Seasonal variability of natural methane seepage offshore Western Svalbard

2021 ◽  
Author(s):  
Manuel Moser ◽  
Knut Ola Dølven ◽  
Bénédicte Ferré
Keyword(s):  
Gas Hydrate ◽  
Bottom Water ◽  
Methane Flux ◽  
Mixing Rate ◽  
Bottom Water Temperature ◽  
Acoustic Data ◽  
Methane Seepage ◽  
Continental Shelves ◽  
Water Conditions ◽  
Methane Fluxes

<p>Natural methane seepage from the seafloor to the water column occurs worldwide in marine environments, from continental shelves to deep-sea basins. Depending on water depth, methane fluxes, and mixing rate of the seawater, methane may partially reach the atmosphere, where it could contribute to the global greenhouse effect. Estimates of annual marine methane fluxes are commonly calculated from hydro-acoustic data collected during single research surveys. These snapshot estimates neglect short (i.e., tide) and long (seasonal) variations.</p><p>Here we compare the seepage activity along the upper limit of the gas hydrate stability zone offshore Western Svalbard in August 2017 (bottom water temperature (BT) ~3.46°C), June 2020 (BT ~1.75°C), and November 2020 (BT ~3.96°C) using high-resolution vessel-based multibeam data. Our results complete annual methane flux estimates by Ferré et al. (2020) and confirm a significantly reduced seepage activity during the cold bottom-water conditions. We investigate short-term variation by comparing a 7.5 km long multibeam section at three phases of the lunar semidiurnal (M2) tide. We will discuss how these processes affect annual methane fluxes estimates offshore Svalbard and further Arctic methane fluxes estimates.</p><p>The research is part of the Centre for Arctic Gas Hydrate, Environment and Climate (CAGE) and is supported by the Research Council of Norway through its Centres of Excellence funding scheme grant No. 223259 and UiT.</p><p> </p><p>Ferré, B., Jansson, P. G., Moser, M., Serov, P., Portnov, A., Graves, C. A., et al. (2020). Reduced methane seepage from Arctic sediments during cold bottom-water conditions. Nat. Geosci. 13, 144–148. DOI: 10.1038/s41561-019-0515-3</p>

Methane seepage and its relation to slumping and gas hydrate at the Hikurangi margin, New Zealand

2006 ◽  
Vol 49 (4) ◽  
pp. 503-516 ◽  
Author(s):  
Kevin Faure ◽  
Jens Greinert ◽  
Ingo A. Pecher ◽  
Ian J. Graham ◽  
Gary J. Massoth ◽  
...  
Keyword(s):  
New Zealand ◽  
Gas Hydrate ◽  
Methane Seepage

scholarly journals Geochemistry, faunal composition and trophic structure in reducing sediments on the southwest South Georgia margin

2016 ◽  
Vol 3 (9) ◽  
pp. 160284 ◽  
Author(s):  
James B. Bell ◽  
Alfred Aquilina ◽  
Clare Woulds ◽  
Adrian G. Glover ◽  
Crispin T. S. Little ◽  
...  
Keyword(s):  
Trophic Structure ◽  
Cold Seep ◽  
Biological Communities ◽  
Isotopic Signatures ◽  
South Georgia ◽  
Methane Seepage ◽  
Bottom Waters ◽  
Report Data ◽  
High Dominance

Despite a number of studies in areas of focused methane seepage, the extent of transitional sediments of more diffuse methane seepage, and their influence upon biological communities is poorly understood. We investigated an area of reducing sediments with elevated levels of methane on the South Georgia margin around 250 m depth and report data from a series of geochemical and biological analyses. Here, the geochemical signatures were consistent with weak methane seepage and the role of sub-surface methane consumption was clearly very important, preventing gas emissions into bottom waters. As a result, the contribution of methane-derived carbon to the microbial and metazoan food webs was very limited, although sulfur isotopic signatures indicated a wider range of dietary contributions than was apparent from carbon isotope ratios. Macrofaunal assemblages had high dominance and were indicative of reducing sediments, with many taxa common to other similar environments and no seep-endemic fauna, indicating transitional assemblages. Also similar to other cold seep areas, there were samples of authigenic carbonate, but rather than occurring as pavements or sedimentary concretions, these carbonates were restricted to patches on the shells of Axinulus antarcticus (Bivalvia, Thyasiridae), which is suggestive of microbe–metazoan interactions.

scholarly journals Community structure and feeding preference of nematodes associated with methane seepage at the Darwin mud volcano (Gulf of Cádiz)

2011 ◽  
Vol 438 ◽  
pp. 71-83 ◽  
Author(s):  
E Pape ◽  
T Nara Bezerra ◽  
H Vanneste ◽  
K Heeschen ◽  
L Moodley ◽  
...  
Keyword(s):  
Community Structure ◽  
Feeding Preference ◽  
Mud Volcano ◽  
Gulf Of Cadiz ◽  
Methane Seepage ◽  
Gulf Of Cádiz
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