Study On Hydrocarbon Source Rocks Of Adula And Xiali Formations In Tumen Qiangtang Basin

Qiangtang Basin is a Mesozoic hydrocarbon-bearing marine basin in China. It has the most developed hydrocarbon source rocks strata in Qinghai-Tibet Plateau with relict sediments which thickness up to 12000 m. And Tumen region has the best potential gas source rock condition of gas hydrate accumulation in this area. In order to detect the reserves of potential hydrocarbon resource in Qiangtang Basin, and provide guidance for subsequent exploration and development, key segments and typical regions in this basin were taken as research objects in this paper. Focusing on key hydrocarbon source rock sections of Triassic Adula formation and Jurassic Xiali formation in Tumen area, combined with the results of previous studies, characteristics of tectonic setting、petrology、sedimentology、organic geochemistry and pyrolytic simulation experiment pyrolytic simulation were discussed in this paper. All the works showed that Tumen area has great potential hydrocarbon resource. The main basis and results are summarized as follows:(1) Lithologic and paleotological features of Xiali and Adula sections proved that they are swamp facies or tidal flat facies with developed organic matter.We identify that the sedimentary phase of Adula group is shore swamp phase in terrigenous clastic depositional system and Xiali group belongs to lagoon or lagoon tidal phase.(2) The main lithology assemblage of Adula and Xiali formations are dark marl and shale with rich organic matter. Adula group is a set of coal clastic rock, with shale, mudstone and multi-seam coal clamp or marl, micritic dolomite. Xiali group is a set of assemblage of mud-shale, shale, marl.(3) According to the abundance of organic matter, Xiali and Adula formations reached the range of effective hydrocarbon source rocks. For example, the organic carbon content(TOC)> 0.4%, pyrolysis organic carbon content(S1 + S2)> 0.3mg / g, chloroform bitumen( "A")> 0.05 ‰.(4) According to the types of organic matter, Adula group source rocks is Ⅱ1 type,which contains sapropel group mainly and vitrinite group and inertinite group. The type of source rocks in the Xiali group is Ⅱ2 type containing sapropel group, humic group, liptinite group and inertinite group.(5) According to the maturity of organic matter, mid-Jurassic Xiali group’s organic matter is basically in a high mature stage of evolution, and typeⅡkerogen in the rock is in oil generation stage; And organic matter in Adula group is basically in mature- past mature stage of evolution, and the source rock is in the peak gas generation stage.According to the study of hydrocarbon source rocks of Jurassic and Triassic Adula group, we affirmed that organic matter in Xiali and Adula group is effective oil- gas source rock.