Oil & Gas Geology ›› 2014, Vol. 35 ›› Issue (2): 199-206.

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Diagenesis and diagenetic facies of the Chang 4+5 tight sandstone reservoirs in Longdong area, Ordos Basin

Wang Feng1, Chen Rong2, Tian Jingchun1, Li Mingrui3, Zhang Huiruo3, Liu Xin4   

  1. 1. Institute of Sedimentary Geology, Chengdu University of Technology, Chengdu, Sichuan 610059, China;
    2. Museum of Chengdu University of Technology, Chengdu, Sichuan 610059, China;
    3. The Exploration Department of Changqing Oilfield Company, PetroChina, Xi'an, Shaanxi 710021, China;
    4. Research Institute of Exploration and Development, Changqing Oilfield Company, PetroChina, Xi'an, Shaanxi 710021, China
  • Received:2013-11-30 Online:2014-04-08 Published:2014-05-21

Abstract: Based on thin sections,SEM,X-ray diffraction,mercury injection,this paper analyzed the diagenesis and its impact on Chang4+5(the 4th and 5th Member of the Yanchang Fm)oil layers in Longdong area,Ordos Basin.Based on the analysis results,we studied the characteristics of diagenetic facies and the distribution of favorable facies.The Chang4+5 oil layers is at the mid-diagenetic A-B stage,and the early compaction and carbonate cementation resulted in loss of great numbers of primary pores,resulting in poor reservoir quality.However,the early chlorite thin film was favorable for the protection of primary pores and dissolution improved reservoir quality.According to the impact of the diagenesis on reservoir quality,five types of diagenetic facies were identified,namely chlorite thin film-residual intergranular pore facies,kaolinite cementation-feldspar dissolution facies,illite cementation-feldspar dissolution facies,carbonate cementation facies and siliceous-illite cementation facies.High quality reservoirs are closely related to the diagenetic facies,and the chlorite thin film-residual intergranular pore diagenetic facies is the best in reservoir physical property and petroliferous property,thus is the most favorable diagenetic facies for oil enrichment in this area.

Key words: diagenetic facies, diagenesis, tight sandstone, Longdong area, Ordos Basin

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