A Preliminary Study On The Thermoluminescence Characteristics Of Sediment And Drill Core From The Scientific Drilling Project Of Gas Hydrate In Qilian Mountain Permafrost

Gas hydrate is ice-like solid, under specific conditions of relative high pressure and low temperature. It has become the focus of international interest over the past few years because of its abundance and its potential importance as an energy resource. Gas hydrates were found at the 133-400m intervals of Middle Jurassic Jiangcang formation lying under the permafrost zone from the Scientific Drilling hole of DK-2 and DK-3 in 2009 summer. This is the first discovery of gas hydrate in China's permafrost and in the low-middle latitude permafrost of the world.Based on the theory of hydrocarbon exploration by thermoluminescence (TL), it was considered that the natural TL in sediment has stored accumulated irradiated dose since the sediment deposited and the formation of radioactivity abnormal areas was related to hydrocarbon migration. Consequently TL determination on sediment, this kind of abnormal areas with weak radioactivity can be effectively discovered, and the corresponding underground gas hydrate reservoir can then be found.In order to explore the relationship between the sediment and gas hydrate which lying under the permafrost, collecting 54 superficial deposit samples and 311 drill core samples respectively, and the TL measurement and analysis was implemented.According to the compositive geological data, the down-hole layer carried out stratigrahic division and correlation. Based on the well logging information, the TL distribution and feature in the gas hydrate layer was analyzed; suggested the TL response mode in the study area.There are closed minimum of TL with pinch-and-swell form over the gas hydrate reservoir. The data show that the radioactivity anomalies are continuous from the deep layer to the surface. The radioactive anomaly may reduce as the stratigraphic younging. The TL signals generated form hydrocarbon was enhanced on the top of diffusion layer. All of these exhibit the direct evidence for the vertical migration of radioactive materials in the ground.Gas hydrate and its related anomalous phenomena mainly occur in fissures and pore space and are evidently controlled by fissures. When hydrocarbon gases are generated by organic matter, they are driven by all grades of fractures to migrate upwards; when they arrived in the stability zone, they are coupled by cryogenic permafrost, leading to their preferable occurrence in fissures. Further research founding that TL anomalous is good at distinguish fissures. Results confirm that the application of TL information of sediment to find out subsurface gas hydrate reservoir is feasible.