Oil & Gas Geology ›› 2022, Vol. 43 ›› Issue (2): 341-352.doi: 10.11743/ogg20220208

• Petroleum Geology • Previous Articles     Next Articles

Reinterpretation of gas sources in the Middle Triassic Leikoupo Formation in Western Sichuan gas field, Sichuan Basin

Chengpeng Su1,2(), Ying He1,2(), Xiaobo Song2, Bo Dong1, Xiaoqi Wu3   

  1. 1.Development Project Department of Pengzhou Gas Field (Marine Facies),Southwest Oil and Gas Branch of SINOPEC,Pengzhou,Sichuan 611930,China
    2.Research Institute of Exploration and Development,Southwest Branch of SINOPEC,Chengdu,Sichuan 610041,China
    3.Research Institute of Petroleum Exploration and Production,SINOPEC,Chengdu,Sichuan 610041,China
  • Received:2020-12-14 Revised:2022-01-22 Online:2022-04-01 Published:2022-03-11
  • Contact: Ying He E-mail:suchengpeng90@163.com;heywz@126.com

Abstract:

The Western Sichuan gas field with proven geologic reserves of over 1 000 × 108 m3 of natural gas ranks third in scale in the Sichuan Basin following Puguang and Yuanba gas fields. Recently, there have been some controversies regarding to the sources of gas in the Leikoupo reservoir, rendering the necessity to make further analysis. The natural gas in the upper and lower pay zones in the 3rd submember of the 4th member of Leikoupo Formation (hereinafter referred to as Lei 43) in different structures is analyzed for natural gas components and alkane isotopic compositions, which indicate that the lower and upper gas reservoirs in the Lei 43 shale the same gas source. While the gas sources vary with structural belts. Natural gas from Shiyang and Yazihe structural belts, is characterized by high content of H2S and CO2, low δ13C2 (mean: -32.5 ‰), and carbon isotope reversal of alkane, typical of oil-derived gas. However, in the Jinma Structure, the natural gas features relatively low content of H2S and CO2, high δ13C2 (mean: -27.5 ‰), and normal carbon isotope sequence pattern, showing the characteristics of mixed gas. In addition, based on the analysis of gas-migration conditions and previous studies, we consider that the natural gas in the Shiyangchang and Yazihe structural belts is mainly derived from the Leikoupo source rocks, and that in the Jinma structural belt mainly derived from the source rocks of Leikoupo and the Permian Longtan Formations, though without excluding minor contributions by the Ma'antang-Xiaotangzi source rocks.

Key words: natural gas composition, alkane isotope, migration condition, structural difference, gas reservoir, Leikoupo Formation, Western Sichuan Depression, Sichuan Basin

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