1.Chengdu Center,China Geological Survey;2.School of Geoscience and Technology, Southwest Petroleum University;3.The sixth Geological Brigade of Sichuan
[Objective] Dark shales in Lower Carboniferous upper are widely distributed in the Yadu-Ziyun-Luodian aulacogen, the upper Yangtze Platform, and its thickness varies greatly. In particular, the development characteristics and hydrocarbon generation center distribution of the dark shale of the Jiusi Fr in the northwest section of the rift aulacogen are not clear. [Methods] The strata, sedimentary facies, dark shale distribution and organic geochemical characteristics of Jiusi dark shale in well GWD-2 are studied in detail by the logging, core observation, rock thin-section identification, kerogen type microscopic identification, TOC, vitrinite reflectance measurement and other experimental test data. And the following research results were obtained. [Results] First, the drilling thickness of Jiusi Fr in the well GWD-2 is 1148.67m, according to the characteristics of rock combinations, the Lower Carboniferous Jiusi Fr can be divided into two members and five sub members, Second, the dark shales are mainly distributed in the first member of Jiusi Fr, which are mainly composed of tidal flat by delta and shallow shelf facies deposits, the cumulative thickness of shale is 525m, the cumulative thickness of shale with TOC value greater than 1% is 425m. Third, The TOC value of Jiusi shale of the well is concentrated in the range of 1% ~ 2%, the type of organic matter is mainly type II2 kerogen and III kerogen, the organic matters are in the early stage of over maturity. The last, it is predicted that the subsidence center of Jiusi Fr is distributed in a long strip with NW-SE direction, and the distribution of hydrocarbon generation center is consistent with the subsidence center. The thickness of argillaceous source rock with TOC value greater than 1% can reach more than 300m. The hydrocarbon generation center has the hydrocarbon generation conditions of argillaceous source rock with huge thickness, good organic matter type and high degree of thermal evolution. [Conclusions] It is concluded that the shale of Lower Carboniferous Jiusi Fr in the hydrocarbon generation center of the northwest section of Yadu-Ziyun-Luodian aulacogen has considerable hydrocarbon generation intensity and total hydrocarbon generation, and has good natural gas exploration potential.