Oil & Gas Geology ›› 2023, Vol. 44 ›› Issue (4): 993-1008.doi: 10.11743/ogg20230415

• Petroleum Geology • Previous Articles     Next Articles

Distribution characteristics of Gufeng Member of the Middle Permian Maokou Formation, eastern Sichuan Basin and its petrogeological significance

Sheng LIU1,2(), Cunhui FAN1,2(), Benjian ZHANG3, Ya ZHANG3, Bing LUO3, Xiaoliang BAI4   

  1. 1.School of Geoscience and Technology,Southwest Petroleum University,Chengdu,Sichuan 610500,China
    2.National Key Laboratory of Oil and Gas Reservoir Geology and Exploitation,Southwest Petroleum University,Chengdu,Sichuan 610500,China
    3.Research Institute of Exploration and Development,Southwest Oil & Gas field Company,PetroChina,Chengdu,Sichuan 610051,China
    4.Chongqing Gas Field of Southwest Oil & Gas field Company,PetroChina,Chongqing 401120,China
  • Received:2023-03-08 Revised:2023-05-26 Online:2023-08-01 Published:2023-08-09
  • Contact: Cunhui FAN E-mail:lsengswpu@126.com;fanchswpi@163.com

Abstract:

The distribution characteristics, sedimentary setting and reservoir formation conditions of the Gufeng Member of the Middle Permian Maokou Formation in the eastern Sichuan Basin were studied by means of macroscopic and microscopic observation, as well as the measurement of major and minor elements and rare earth elements (REEs), total organic carbon (TOC) content and vitrine reflectance, while considering the lithologic and electrical properties and outcrop characteristics, combined with regional depositional-tectonic framework. The results are as follows. First, the existence of Gufeng Member of the Maokou Formation in eastern Sichuan Basin confirms that a trough and platform pattern existed in the middle and late depositional stages of the Maokou Formation under the tectonic-sedimentary differentiation. During the deposition of the B sub-member of the second member of the Maokou Formation (i.e., the deposition of Mao 2B sub-member), the Gufeng Member mainly occurred in the northeast corner of the eastern Sichuan Basin. During the deposition of Mao 2A sub-member, the Gufeng Member extended southward to Quxian, Dazhu, and Liangping counties in a NW-SE-striking strip pattern with a thickness of 0.8 to 26.6 m. The Gufeng Member corresponds to the Mao 3 and 4 members in northwest and north Sichuan Basin. Second, the siliceous shale in Gufeng Member is rich in siliceous radiolaria and has high organic matter content, which is typical of deep-water trough facies deposition. The geochemical test data show that the siliceous shale is developed in a deep-water anoxic reducing environment with high salinity, with biogenic silica as the main siliceous source. Third, the source rocks in the Gufeng Member are of high quality and rich in organic matter, with the total organic carbon (TOC) content being relatively high as a whole but in a wide variety, ranging from 1.69 % to 38.27 %, with an average value of 11.51 %, and in the mature to over-mature stage. Fourth, the high-quality source rocks of the Gufeng Member can communicate with the reef-shoal reservoir of Kaijiang-Liangping trough through faults, forming an “upper source rock-lower reservoir” assemblage; and it can also form a juxtaposed “source rock- reservoir” association with the favorable beach reservoir of Maokou Formation. The Gufeng Member in eastern Sichuan is expected to be a successor target for high-quality source rock exploration in the region, which is of great significance to future oil/gas exploration and development in the study area.

Key words: “upper source rock-lower reservoir” assemblage, “juxtaposed source rock-reservoir” assemblage, siliceous shale, deep-water deposition, Gufeng Member, Maokou Formation, eastern Sichuan Basin

CLC Number: