DISCUSSION ON GAS HYDRATE ACCUMULATION CONDITIONS IN WULI PERMAFROST ZONE, QINGHAI-TIBETAN PLATEAU

The first trial drilling hole of ZK1 in the Wuli area did not succeed in finding gas hydrate in the permafrost zone, the Qinghai-Tibetan Plateau. In order to find out the reasons of the failure, comparative study was made between the cores of hole ZK1 and the outcrops around the hole. It is found that the source rocks in the area is featured with the type Ⅲ of kerogen and over-maturity, and favors the generation of biogenetic gases. However, the testing results of headspace samples from the hole of ZK1 show that inorganic carbon dioxide (¹³C-CO₂,-4‰~-6‰) accounts for 96% of gas composition. According to regional geology and temperature and pressure conditions, it is concluded that the gas source is mainly composed of carbon dioxide with few biogenetic gases. Furthermore, the strong tectonic movements up to the present and deep faults in the Wuli permafrost zone are not favorable for the preservation of organic and inorganic gases as well as their gas hydrates. The second reason is maybe related to the special sublimation of carbon dioxide and incomplete sampling technology.