scholarly journals Effect of permafrost properties on gas hydrate petroleum system in the Qilian Mountains, Qinghai, Northwest China

2014 ◽  
Vol 16 (12) ◽  
pp. 2711-2720 ◽  
Author(s):  
Pingkang Wang ◽  
Xuhui Zhang ◽  
Youhai Zhu ◽  
Bing Li ◽  
Xia Huang ◽  
...  
Keyword(s):  
Late Pleistocene ◽  
Gas Hydrate ◽  
Northwest China ◽  
Qilian Mountains ◽  
Petroleum System ◽  
Stability Zone ◽  
The Qilian Mountains ◽  
Hydrate Stability

Evolution of gas hydrate petroleum system in the Qilian Mountains permafrost: (A) end of Late Pleistocene and (B) modern day. GHSZ indicates gas hydrate stability zone.

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 Actual evapotranspiration of subalpine meadows in the Qilian Mountains, Northwest China

2019 ◽  
Vol 11 (3) ◽  
pp. 371-384
Author(s):  
Yunfei Gao ◽  
Chuanyan Zhao ◽  
Muhammad W. Ashiq ◽  
Qingtao Wang ◽  
Zhanlei Rong ◽  
...  
Keyword(s):  
Northwest China ◽  
Qilian Mountains ◽  
Actual Evapotranspiration ◽  
Subalpine Meadows ◽  
The Qilian Mountains

scholarly journals Role of Salt Migration in Destabilization of Intra Permafrost Hydrates in the Arctic Shelf: Experimental Modeling

Geosciences ◽  
2019 ◽  
Vol 9 (4) ◽  
pp. 188 ◽  
Author(s):  
Evgeny Chuvilin ◽  
Valentina Ekimova ◽  
Boris Bukhanov ◽  
Sergey Grebenkin ◽  
Natalia Shakhova ◽  
...  
Keyword(s):  
Gas Hydrates ◽  
Methane Emission ◽  
Gas Hydrate ◽  
Negative Temperature ◽  
Arctic Shelf ◽  
The Arctic ◽  
Permafrost Degradation ◽  
Stability Zone ◽  
Local Pressure ◽  
Hydrate Stability

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.

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