| Qiangtang basin, as the second marine sedimentary basins in China, has a great of prospects in oil and gas resources. It is located in the eastern Tethyan tectonic domain, which has enriched oil gas of the world. Qiangtang Basin has experienced various events of marine transgressions and regressions during the late Paleozoic. It has generated a set of mudstone and carbonate source rocks. And there are most potential layers for source rocks, such as the Upper Triassic Tumengela Formation, the Quse Formation of the Lower Jurassic and the Sewa Formation of the Middle Jurassic. In this study, the Anduo Formation of the Middle Jurassic is acted as a new hydrocarbon source rock, which is shale. Based on results of previous fruits, combined the study of the field geological survey and the relative analysis data, we have proceeded a comprehensive study on organic abundance, kerogen maceral, vitrinite reflectance, pyrolysis peak temperature and other indicators of the Tumengela Formation, the Quse Formation and the Sewa Formation. Furthermore, in order to provide a basis for a fully understanding of the oil and gas resource potential of Qiangtang Basin, a comprehensive study has been analysed and evaluated. It shows that there are acquaintances been summarized as follows:1. The abundance of organic matter in the Quse-Sewa Formation is lacked, while the hydrocarbon types are dominated by ?1 kerogen, and only few samples are in favor of the criterion of poor oil source rock, and the organic matters of source rocks of the Upper Triassic mainly be a high and over-mature stage, which reflecting poorly producing oil capacity. Nearly eighty percent of source rocks' abundance of the Upper Triassic belong to poor-medium source class. They belong to ? organic type, and partially contained ? ones and high mature signature. The organic matters' maturity of source rock of the Anduo Formation is mainly in mature stage with a high abundance. So it is indicated that it is the most potential source rock in the south Qiangtang depression, Tibet.2. The hydrocarbon source rock of Upper Triassic and the lower to the Medium Jurassic possibly have five areas, which is high-quality source rock generation in south Qiangtang depression. They distributed as a direction of the E-W and the NW-SE. There are two generation areas, which are respectively located in Shuanghu Duopuleinai-Chalangla area and Amdo Dazhuoma-Tumen area, while Angdaercuo area, Zhaqu area and Damaer area belong to Quse-Sewa?s black shales. The source rock of the Anduo Formation also has a superior source rock locally in No. 114 road maintenance squad.3. Depositional environments, sea level changes and the paleotectonic topography of Qiangtang basin, all of those have played a significantly role in the development of superior source rocks. There are three different sedimentary facies patterns of muddy source rocks in south Qiangtang depression, including the delta genetic pattern, the shelf genetic pattern and the trench genetic pattern. The second pattern of source rocks is the worst possessing high maturity and low organic carbon abundance, while the first model is better. The abundance of organic matter formed in the trench genetic model with good organic matter type is relatively high, and has highly oil and gas capacity. Therefore, the trench genetic source rock should be the preferred target for oil and gas exploring in the southern Qiangtang depression, Tibet. |
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