Characterization and evaluation on the source rock of gas hydrate in Muli permafrost area, Nanqilian Basin

China's first permafrost gas hydrate samples were collected by China Geological Survey in 2008 in Muli permafrost area, Nanqilian Basin. There exist different opinions concerning the genesis or origin of gases from gas hydrate. The organic geochemical indictors were systematically analyzed on the gas source rocks of the Middle Jurassic and the Upper Triassic from recently drilled 3 wells. The results show that the organic matter values are at high levels in source rocks of the Middle Jurassic strata (Jiangcang and Muli Formation) in the study area. 78.9% of TOC values are more than 1.0%, and 72.2% of chloroform bitumen 'A' are more than 0.1%. The main organic matter is of type Ⅱ₂ and Ⅱ₁. The vitrinite reflectances of most samples are between 0.7% to 1.2%. The average value of total hydrocarbon generation potential is 8.8mg/g rock in total 71 samples. So the organic matters in most samples are at mature levels, or at condensate levels, which are good and very good source rocks for the gases of gas hydrates. The organic matter values are also at high levels in source rocks of the Upper Triassic strata (Galedesi Formation). 76.9% of TOC values are more than 1.0%. The chloroform bitumen 'A' is less than 0.05%. The main organic matters are of type Ⅲ and Ⅱ₁. The vitrinite reflectances of most samples are between 1.1% and 1.77%. Hence the organic matters in most samples are at post mature levels, or at dry gas levels, but the average value of total hydrocarbon generation potential is only 0.35 mg/g rock in total 39 samples, suggesting poor source rocks or barren rocks for the gases of gas hydrates.