Oil & Gas Geology ›› 2019, Vol. 40 ›› Issue (6): 1168-1184.doi: 10.11743/ogg20190602

• Petroleum Geology • Previous Articles     Next Articles

Mechanism for generation and accumulation of continental tight oil in China

Zhu Rukai1,2,3, Zou Caineng1,2, Wu Songtao1,2,3, Yang Zhi1, Mao Zhiguo1,2,3, Yang Haibo4, Fan Chunyi4, Hui Xiao5, Cui Jingwei1,2,3, Su Ling1,2,3, Wang Huandi6   

  1. 1. Research Institute of Petroleum Exploration and Development, PetroChina, Beijing 100083, China;
    2. National Energy Tight Oil and Gas R & D Center, Beijing 100083, China;
    3. Key Laboratory of Oil and Gas Reservoir, CNPC, Beijing 100083, China;
    4. Xinjiang Oilfield Company Ltd., PetroChina, Karamay, Xinjiang 834000, China;
    5. Changqing Oilfield Company Ltd., PetroChina, Xi'an, Shaanxi 710016;
    6. Petroleum Industry Press, Beijing 100011, China
  • Received:2019-07-22 Revised:2019-09-02 Online:2019-12-28 Published:2019-10-15

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Abstract: Chinese tight oil is mainly distributed in continental petroliferous basins of the Mesozoic to Cenozoic,where tight sandstone oil or tight carbonate oil reservoirs are distributed in large areas and are interlayered with or in contact with lacustrine petroleum source rocks.Recently,great progress has been made in continental tight oil exploration and development.By the end of 2018,an annual production capacity of 3.155 million tons was built for Chinese continental tight oil,and its production rate reached 1.05 million tons in 2018.Lacustrine organic-rich shale in China serves as the main hydrocarbon source rocks of the Chinese continental tight oil.Most of the shale was deposited in fresh,brackish-to-saline water environments with a thickness of tens of to several hundred meters,having a total organic carbon (TOC) content of 0.4% to 16% and a vitrinite reflectance (Ro) of 0.5% to 1.3%. Appropriate volcanism,low sedimentation rate,anoxic and reducing environment,transgression,and stratification of water body are dominant factors controlling the quality of organic-rich shales.Chinese continental tight oil reservoirs include tight sandstone,tight carbonate rock,tight peperite,and tight tuffite,featuring strong heterogeneity and poor physical properties.Their overlying matrix permeability tends to be less than or equal to 0.1×10-3 μm2.Nano-scale pore thoats,complex in structure and with a diameter ranging between 40 nm and 900 nm,are dominant in the reservoir space.Their pressure coefficient varies from 0.7 to 1.8,indicating the coexistence of overpressure and pressure deficiency.Their acquifer energy and oil property vary greatly,with an oil density of 0.75 g/cm3 to 0.92 g/cm3.The continental tight oil in place and technically recoverable resources in China are 178.20×108 t and 17.65×108 t respectively,mainly distributed in the Ordos Basin,Bohai Bay Basin,Songliao Basin,Junggar Basin and Qaidam Basin.In conclusion,we put forward the concept of "sweet spot zone (section)",which tends to develop in local,low amplitude structures in a wide,gentle structure setting.A sweet spot zone refers to a tight oil-rich area with commercial productivity within the distribution area of mature high-quality source rocks; while a sweet spot section refers to a high productivity interval of tight oil with commercial value through artificial stimulation,located in the black shale section intercalated by tight reservoir layers.The source rock quality and the type of source-reservoir configuration serve to control the lateral distribution of the sweet spot zones.Sweet spot zone (section) evaluation methods,including resource assessment technique,logging identification of the "six properties",high-resolution 3D seismic imaging,horizontal well production from well pads,and artificial reservoir alternation,may facilitate the efficient development of tight oil.

Key words: fine-grained sediment, sweet spot zone, tight reservoir, continental tight oil, terrestrial petroliferous basin of the Mesozoic to Cenozoic

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