青藏高原冻土温度与厚度

Assessing the permafrost temperature and thickness conditions favorable for the occurrence of gas hydrate in the Qinghai–Tibet Plateau

Wu Qingbai *,Jiang Guanli,Zhang Peng

State Key Laboratory of Frozen Soil Engineering,Cold and Arid Regions Environmental and Engineering Research Institute,Chinese Academy of Sciences,Lanzhou 730000,China

a r t i c l e i n f o Article history:

Received 28March 2009Accepted 30October 2009

Available online 16December 2009Keywords:

Qinghai–Xizang Plateau Permafrost

Natural gas hydrate Geothermal gradients

a b s t r a c t

Permafrost accounts for about 52%of the total area of the Qinghai–Tibet Plateau,and the permafrost area is about 140Â104km 2.The mean annual ground temperature of permafrost ranges from À0.1to À5°C,and lower than À5°C at extreme high-mountains.Permafrost thickness ranges from 10to 139.4m by borehole data,and more than 200m by geothermal gradients.The permafrost geothermal gradient ranges from 1.1°C/100m to 8.0°C/100m with an average of 2.9°C/100m,and the geothermal gradient of the soil beneath permafrost is about 2.8–8.5°C/100m with an average of 6.0°C/100m in the Qinghai–Tibet Plateau.

For a minimum of permafrost geothermal gradients of 1.1°C/100m,the areas of the potential occur-rence of methane hydrate (sI)is approximately estimated to be about 27.5%of the total area of perma-frost regions in the Qinghai–Tibet Plateau.For an average of permafrost geothermal gradients of 2.9°C/100m,the areas of the potential occurrence of methane hydrate (sI)is approximately estimated about 14%of the total area of permafrost regions in the Qinghai–Tibet Plateau.For the sII hydrate,the areas of the potential occurrence of sII hydrate are more than that of sI methane hydrate.

Ó2009Elsevier Ltd.All rights reserved.

1.Introduction

Gas hydrates are ice-like crystalline solids composed of water and gas in which water molecules trap gas molecules in a cage-like structure known as a clathrate,which can be formed when gas and water mixtures are subjected to high pressure or low temperature conditions [15].Gas hydrates widespread in permafrost regions and beneath the sea in sediments of outer continental margins.Although estimates of its occurrence vary widely,the carbon re-serves of gas hydrate in the world may reach 2Â1016m 3,twice of explored conventional sources of energy [10].Gas hydrates are a new kind of potential and clean energy resource.And gas hy-drates,especially methane hydrate,may easily to dissociate with variations of temperature and pressure.And the dissociation of hy-drates may play a great role in climate change due to their strong greenhouse effect [12–14].

Now,the direct confirmation of gas hydrates was obtained in permafrost regions in northern hemisphere,for example,in the North Slope of Alaska,the Mackenzie Delta–Beaufort Sea area,Can-ada,and the west Siberian basin,Russia [4].All available data show that the methane-hydrate stability zone locates generally 300–600m beneath the permafrost.The sample of intra-perma-frost gas hydrates was obtained in the Mackenzie Delta,Northwest

Territories,Canada [5].Although the sample of the intra-perma-frost gas hydrate cannot be obtained in west Siberian,amounts of evidences collected on gas release indicated that the intra-per-mafrost gas hydrates may exist [20].Gas hydrates in permafrost re-gions are nearly related to permafrost conditions [2,3,6,7].Two primary factors affecting the distribution of the gas hydrates stabil-ity zone:the geothermal gradient and the gas composition deter-mine the temperature and pressure conditions for the gas hydrate formation and its accumulations,and some other factors,such as the pore-fluid salinity and the pore-pressure,have a little effect,too [4].

The potential occurrence of gas hydrates in permafrost regions in the Qinghai–Tibet Plateau has a significant impact to the utilization of new energy resource,the climate change and the environment.Amounts of conductive works were developed to study the potential occurrence of gas hydrates in permafrost regions [1,9,18,19,22,25].It is generally believed that geological conditions are conducive to gas hydrates formation.Gas hydrate,containing H 2S,C 2H 6and C 3H 8and CH 4may exist beneath permafrost in the Qinghai–Xizang Plateau [9,19,22].Chen et al.[1]estimated the amount of gas hydrates in per-mafrost regions of the Qinghai–Tibet Plateau according to the natu-ral gas component in Xingjiang and Caidamu areas and permafrost conditions,ranged from about 1.2Â1011–2.4Â1014m 3.

Permafrost conditions are critical to the potential occurrence of gas hydrates in the Qinghai–Tibet Plateau,especially permafrost thickness and temperature.In this work,permafrost conditions,

0196-8904/$-see front matter Ó2009Elsevier Ltd.All rights reserved.doi:10.1016/j.enconman.2009.10.035

*Corresponding author.

E-mail address:qbwu@ (W.Qingbai).

Energy Conversion and Management 51(2010)

783–787

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