Oil & Gas Geology ›› 2022, Vol. 43 ›› Issue (4): 990-1004.doi: 10.11743/ogg20220419

• Methods and Technologies • Previous Articles     Next Articles

Time scale and quantitative identification of sequence boundaries for the Oligocene Huagang Formation in the Xihu Sag, East China Sea Shelf Basin

Xian Liu1(), Jiawang Ge1,2(), Xiaoming Zhao1,2, Guofeng Yin3, Xuesong Zhou1, Jianwei Wang3, Maolin Dai1, Li Sun3, Tingen Fan4   

  1. 1.School of Earth Science and Technology,Southwest Petroleum University,Chengdu,Sichuan 610500,China
    2.Sichuan Provincial Key Laboratory of Natural Gas Geology,Chengdu,Sichuan 610500,China
    3.Exploration and Development Research Institute,Shanghai Offshore Oil and Gas Company,SINOPEC,Shanghai 210002,China
    4.Research Institute Corporation Ltd. ,CNOOC,Beijing 100028,China
  • Received:2022-04-01 Revised:2022-05-06 Online:2022-07-14 Published:2022-07-14
  • Contact: Jiawang Ge E-mail:3474180093@qq.com;gjwddn@163.com

Abstract:

The Xihu Sag is one of the petroliferous sags in the East China Sea Shelf Basin. Recent exploration has confirmed that the Oligocene Huagang Formation is the major gas pay zone in the sag. However, sequence division of the formation is still in dispute, seriously impeding the isochronous correlation of sand bodies and the fine exploration of oil and gas. Based on the sequence stratigraphy and astronomical cycle theory, the study mathematically analyzes natural gamma curves with wavelet transform and INPEFA(Integrated predication error filter analysis) technology to obtain signal curves, spectrums and INPEFA curves for the establishment of a geologic time scale and high-precision sequence boundary framework for the Huagang Formation. The GR curves are reconstructed through wavelet transformation into different wavelet signal curves and spectrums with the sequence interfaces and cycle information highlighted by abnormal vibration and energy group change trend. At the same time, the maximum entropy spectrum analysis technology is used to integrate the GR curves into the INPEFA curves with sequence boundaries and cycle information highlighted by inflection points as well as positive and negative trends. The Huagang Formation is divided into five third-order sequences (namely SQ1 to SQ5 from top to bottom). Spectral characterization of strata superimposition and cycles within these sequences are combined with their wavelet signal curves to divide the Huaguang Formation into a total of 12 fourth-order sequences (namely H1 to H12 from bottom to top). The multi-window spectrum analysis of GR curves shows 1 to 3 Ma development duration for the five third-order sequences. The multi-scale and multi-method integration of logging technology for the construction of multi-order isochronous stratigraphic frameworks in the areas lacking of cores and paleontological fossils is proved to have certain promotional value for the future oil and gas exploration in the Oligocene Huagang Formation of the Xihu Sag.

Key words: wavelet transform, INPEFA, astronomical cycle, sequence stratigraphy, Huagang Formation, Oligocene, Xihu Sag, East China Sea Shelf Basin

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