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

Evgeny Chuvilin,Natalia Shakhova,Boris Bukhanov,Sergey Grebenkin,Valentina Ekimova,Igor Semiletov

doi:10.3390/geosciences9040188

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 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.

Highlights

The Arctic shelf is the most promising hydrocarbon production area
The gas hydrate dissociation in in frozen sediments porous media as a result of salt transfer. They may be important for frozen sediments porous media as a result of salt transfer
New experimental results integrated with the observational data confirm a hypothesis about the primary role of submarine permafrost and hydrate destabilization in a massive methane release in the sediment-water-atmosphere system [11,12,31,49]

Summary

Introduction

The Arctic shelf is the most promising hydrocarbon production area. its development is associated with the solution of a number of problems that are associated with the conditions of relict permafrost and the presence of gas hydrates [1,2,3,4]. Dissociation of gas hydrate formations in bottom sediments makes the largest contribution to methane emissions on the Arctic shelf [5,6,7,8,9,10,11,12]. An important characteristic of gas hydrates is a huge accumulation of gas in the clathrate structure-up to 160 volumes of gas in one volume of hydrate. As it is well known, methane is one of the most active greenhouse gases. The dissociation of Arctic gas hydrates, accompanied by the active emission of methane into the atmosphere, can have a significant greenhouse effect and cause climate change [15,16]

Methods

Results

Discussion

Conclusion