China Petroleum Exploration ›› 2020, Vol. 25 ›› Issue (3): 56-65.DOI: 10.3969/j.issn.1672-7703.2020.03.006

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New understandings of the distribution characteristics of the Sinian Dengying Formation in the southwestern Sichuan Basin and its significance for oil and gas geological exploration

Wen Long1, Wang Wenzhi1, Li Linjuan2, Hong Haitao1, Luo Bing1,Zhang Xihua1, Peng Hanlin1, Li Kunyu1, Jia Min1, Tian Xingwang1   

  1. 1 Research Institute of Exploration and Development, PetroChina Southwest Oil & Gasfield Company; 2 PetroChina Southwest Oil & Gasfield Company
  • Online:2020-05-15 Published:2020-05-15
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Abstract: The Dengying Formation of the Sinian system in the Sichuan Basin has significant consequences for exploration and great potential. Analysis of the petrological and geochemical characteristics of outcrops and cores in the southwestern Sichuan Basin was carried out in combination with seismic data. Comprehensive study shows that the Sinian Dengying Formation in Well Hanshen 1, which is located in the Hanwangchang structure in southwestern Sichuan, is characterized by poor algae content, rich silicon content, relatively low Ca and Mg contents, high Si content, and low δ13C and δ18O contents. This is basically consistent with the 4th member of Dengying Formation (hereinafter Deng-4 member) in terms of lithologic characteristics, major elements and isotopic content, and it is therefore considered that the penetrated stratum is the Deng-4 member of Dengying Formation. According to the prediction of well-seismic combination, the Deng-4 member in the southwestern Sichuan Basin is mainly distributed in the west of the Chengdu-Qianwei area, with a thickness of 200?300 m and a distribution area of 1.5×104 km2 in the basin, extending southward to the Xichang and Yunnan areas. The Deng-4 member gradually thins towards the Deyang-Anyue rift, which is characterized by gentle slope type platform margin. The reservoirs in the Deng-4 member are well developed in the southwestern Sichuan area, which is close to Cambrian high-quality source rocks in the rift. In the oil generation stage, the reservoirs were located at the high position of the paleo-uplift, so that paleo oil reservoirs were formed. In the later stage, after several tectonic movements, oil cracking gas was re-adjusted and re-accumulated. This provided the geological conditions to form gas reservoirs of structural type, structural-lithologic type and structural-stratigraphic type. The areas of Qionglai-Daxingchang-Meishan are favorable zones for petroleum exploration.

 

Key words: Sichuan Basin, Dengying Formation, stratigraphic distribution, isotope, hydrocarbon accumulation conditions, gentle slope type platform margin

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