Formation Condition and Distribution Prediction of Gas Hydrate in Qinghai-Tibet Plateau Permafrost

Abstract

Permafrost is one of major geological environments for gas hydrate occurrences. Mean altitude is over 4000m and the permafrost area is about 1.4 x 10(6)km(2) in Qinghai-Tibet Plateau. Based on the thickness of frozen layer and thermal gradient in Qinghai-Tibet Plateau permafrost, the occurrence and distribution of gas hydrate in the low-middle latitude and high altitude permafrost is predicted by using the thermodynamic method of natural gas hydrate stable temperature and pressure. The thermodynamic phase equilibrium of thermogenic and biogenic gas hydrate imply that gas hydrate is buried in depth from similar to 27 to similar to 2070m, and the resource potential of natural gases caged in hydrates are estimated as about 1.2 x 10(11) to 2.4 x 10(14)m(3) in Qinghai-Tibet Plateau permafrost. Gas hydrate is propitious to occur where the frozen layer is thicker and thermal gradient is lower in the permafrost. Seasonal change of air temperature in Qinghai-Tibet Plateau affects only the uppermost sediments 10m and does not affect gas hydrate that is buried below 30m. Under the global warming, gas hydrate will be unstable and degrade in the permafrost. Its distribution area will be gradually reduced and finally disappear in Qinghai-Tibet Plateau permafrost.