Oil & Gas Geology ›› 2020, Vol. 41 ›› Issue (2): 407-415.doi: 10.11743/ogg20200216

• Petroleum Geology • Previous Articles     Next Articles

Characteristic analysis of seismic response of micro-fractures in organic-rich shale: A case study of Well Ning201 in the Changning demonstration zone

Bole Gao1,2(), Renfang Pan1,2,*(), Jineng Jin1,2, Jian Zhang3, Shengxian Zhao3, Jie Yan3   

  1. 1. Key Laboratory of Oil and Gas Resources and Exploration Technology(Yangtze University), Ministry of Education, Wuhan, Hubei 430100, China
    2. School of Geosciences, Yangtze University, Wuhan, Hubei 430100, China
    3. Southwest Oil&Gas Field Branch Company, PetroChina, Chengdu, Sichuan 610000, China
  • Received:2018-12-12 Online:2020-04-01 Published:2020-04-03
  • Contact: Renfang Pan E-mail:gaobole@foxmail.com;rfpan@qq.com

Abstract:

In order to make it clear how the density and strike of structural micro-fractures affect the seismic response features of organic-rich shale in Longmaxi-Wufeng Formations distributed in Changning demonstration zone, Sichuan Basin, we carried out the AVAZ forward modelling based on the geologic model built by the coring data obtained from the dril-ling of organic-rich shale in Well Ning201 and the reflection coefficients calculated by HTI anisotropy media.Meanwhile, the seismic response characteristics of the micro-fractures in organic-rich shales from the well were analyzed combined with the contrast and verification of seismic exploration data in the research area.The results show that:on the one hand, the seismic identification of micro-fractures in organic-rich shale is controlled by incident angle, azimuth and dominant frequency of the seismic data.The incident angles determine the amplitude difference caused by micro-fracture densities, the azimuth affects the identification of micro-fracture strikes, while the dominant frequency ensures that the tuning effect of seismic waves makes no difference to amplitude.On the other hand, the amplitude decreases as the included angle between propagation direction of the seismic wave and the normal direction of the fracture surface increases, and reaches the minimum when the included angle is 90°.The amplitude of azimuth parallel to the micro-fracture strike shall not be affected by the variation of micro-fracture density, while the amplitude of azimuth perpendicular to the fracture surface increases with the increase of micro-fracture density.Overall, the research results may serve as a basis for seismic interpretation later of micro-fractures in the organic-rich shale of Changning demonstration area.

Key words: seismic response characteristics, anisotropy, micro-fracture, organic-rich shale, Longmaxi Formation, Chang-ning demonstration zone, Sichuan Basin

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