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Abstract: We have evaluated the hydrocarbon-bearing potential of Middle Jurassic marine source rocks in the Qiangtang Basin, Tibet, through a comprehensive study of samples from a large number of surface outcrops in different structural units, and from the Qiang-D2 Well in the southern Qiangtang Depression. Data that were acquired, including the depositional environment, thickness of sedimentary units, and organic geochemistry, are used to identify the principal controlling factors and predict the location of favorable hydrocarbon kitchens. The source rocks are mainly platform limestone of the Middle Jurassic Buqu Formation. This formation comprises a suite of intra-platform sag marls, micrites, and black shales that were deposited in a deep-water and restricted depositional environment. The marls form hydrocarbon-rich source rocks with organic matter that is mainly type II and in the mature to highly mature stage. In the Dongco–Hulu Lake and Tupoco–Baitan Lake deep sags, limestone also forms a medium-level source rock. In the Qiangtang Basin, limestone is the favorable source rock kitchen and is more significant in this regard than mudstone. The results provide important constraints on evaluating the hydrocarbon potential of Jurassic marine source rocks and for locating petroleum resources in the Qiangtang Basin. [Copyright &y& Elsevier]

Taking marine source rocks of lower Paleozoic in the Tarim Basin and Paleozoic ones in the Sichuan Basin as examples, their sedimentation process could be classified into four styles: continuous subsidence with deep sedimentation in early stage, continuous subsidence with deep sedimentation in later stage, that deeply buried-uplift-shallowly buried, and that shallowly buried-uplift-deeply buried. Unlike that in East China, the marine source rocks evolvement patterns did not accord with sedimentation styles one by one in superimposed basins in west China. Taking local geothermal field into account, four types of source rock evolvement patterns were built: that evolved fast in early stage, evolved fast in middle stage, evolved continuously and evolved in multistage. Among them, the 1st pattern contributed little to the present industrial oil pools directly, but paleo-oil reservoirs and gases cracked from crude oils were main exploration targets. Although some gases were found in the 2nd pattern, the scale was not big enough. For the 3rd and 4th patterns, the hydrocarbon potential depended on organic matters maturity in early stage. For relatively low mature rocks, it was possible to generate some oils in later stage; otherwise the main products were gases. Paleo-oil reservoirs remained fairly well in the Sichuan Basin, and most source rocks underwent kerogen-oil-gas processes, which was useful reference to gas exploration in the Tarim Basin. [ABSTRACT FROM AUTHOR]