Oil & Gas Geology ›› 2005, Vol. 26 ›› Issue (3): 329-336.doi: 10.11743/ogg20050311

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Reconstruction of Early-Middle Triassic basin in North China and hydrocarbon generation in Palaeozoic

Xu Huazheng1, Zhou Xinke1, Gao Jinhui1, Wang Xingwu2   

  1. 1. Exploration & Production Research Institute, SINOPEC, Beijing;
    2. Scientific Research Institute of Exploration and Development of Zhongyuan Oilfield Company, SINOPEC, Puyang, Henan
  • Received:2005-03-19 Online:2005-06-25 Published:2012-01-16

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Abstract:

Middle-Lower Triassic in eastern part of North China is fragmentarily distributed in small areas;however, they have similar lithologies,fades and rhythmic characteristics,indicating a depositional setting of a large basin.It can be observed in a wide area that the grain size of sandstone is fining,shale content is increasing,and sediment is thickening apparently from NW to SE,indicating that sedimentary features in Early-Middle Triassic were similar with that in late Late Permian(Shiqianfeng age).Middle-Lower Triassic has inherited not only the Late Permian palaeogeodynamic setting of“convergence in the north and divergence in the south”,but also the palaeogeographie flamework of high in the northwest and low in the southeast.All these show that Hercynian movement would have lasted till Middle Triassic.Several methods including vitrinite reflectance(Ro),interval transit time and apatite fission track, are used to reconstruct the sedimentary thickness of Middle-Lower Triassic,and to plot the isopach map of the prototype basin.The sedimentary-subsidence center is located in Linqing-Dongpu-Taikang and Huainan-Huaibei areas, where the Middle-Lower Triassic is as thick as 2000～2600m.At the end of Meddle Triassic,the burial depth of the top of Majiagou Formation in Lower Paleozoic would have reached 3080～3690m,the palaeogeotemperature would be 112.4～130.7℃,and the Ro would be 0.85%～1.10%.The Lower Paleozoic source rocks,mainly consisting of marine organic matters,would have passed the peak oil generation stage,with 80% of the organic matters have been converted into oil,thus the hydrocarbon generation potential in later stage would be very low.While the Upper Paleozoic source rocks,mainly consisting of coal formation,were still in the early stage of hydrocarbon generation with relatively good hydrocarbon generating potential,because the peak hydrocarbon generation of humic coal would lag behind the Type Ⅰ-Ⅱ1 kerogens.

Key words: denudation thickness, source rocks, prototype basin, Middle-Lower Triassic, North China basin

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