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

Permafrost accounts for about 52% of the total area of the Qinghai–Tibet Plateau, and the permafrost area is about 140 × 104 km2. The mean annual ground temperature of permafrost ranges from −0.1 to −5 °C, and lower than −5 °C at extreme high-mountains. Permafrost thickness ranges from 10 to 139.4 m by borehole data, and more than 200 m by geothermal gradients. The permafrost geothermal gradient ranges from 1.1 °C/100 m to 8.0 °C/100 m with an average of 2.9 °C/100 m, and the geothermal gradient of the soil beneath permafrost is about 2.8–8.5 °C/100 m with an average of 6.0 °C/100 m in the Qinghai–Tibet Plateau.For a minimum of permafrost geothermal gradients of 1.1 °C/100 m, the areas of the potential occurrence of methane hydrate (sI) is approximately estimated to be about 27.5% of the total area of permafrost regions in the Qinghai–Tibet Plateau. For an average of permafrost geothermal gradients of 2.9 °C/100 m, 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.