Investigation of the anisotropy of black shale in dynamic tensile strength

  • Xiaoshan Shi
  • Da’an Liu
  • Wei Yao
  • Yirui Shi
  • Tiewu Tang
  • Bonan Wang
  • Weige Han
Original Paper
  • 130 Downloads

Abstract

Shale usually exhibits strong anisotropy due to depositional environment and pre-existed microcracks caused by geological loading for a long time. Characterizing mechanical anisotropy properties of shale, especially the tensile strength anisotropy, plays an important role in the successful exploitation of shale gas. In this work, static and dynamic tests with semi-circular bending (SCB) specimen are conducted using hydraulic servo-control machine and modified split Hopkinson pressure bar (SHPB) system, respectively. To survey the tensile strength anisotropy of shale induced by stratification, samples are cored and cut into half by diametrical cutting along different angles relative to the stratification (0°, 30°, 45°, 60°, 90°, C0°). For dynamic tests, the utilization of pulse shaping technique ensures that the samples obtain dynamic equilibrium. The tensile strength values exhibit clear anisotropy under both static and dynamic loading conditions and show typical loading rate dependence at a given angle. An anisotropic index named αk is defined to describe the tensile strength anisotropy at a certain loading rate. The outcomes illustrate that the anisotropic index decreases as the loading rate increases. In addition, failure pattern owns different characteristic under different loading angles with respect to the stratification. These phenomena may be explained by the pre-existing microcracks, and cracks interaction during dynamic loading conditions.

Keywords

Black shale Tensile strength anisotropy SHPB Semi-circular bending test (SCB) Loading angles Anisotropy index 

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Copyright information

© Saudi Society for Geosciences 2018

Authors and Affiliations

  • Xiaoshan Shi
    • 1
    • 2
    • 3
  • Da’an Liu
    • 1
  • Wei Yao
    • 3
  • Yirui Shi
    • 3
  • Tiewu Tang
    • 1
    • 2
  • Bonan Wang
    • 4
  • Weige Han
    • 1
    • 2
  1. 1.Key Laboratory of Shale Gas and Geoengineering, Institute of Geology and GeophysicsChinese Academy of SciencesBeijingChina
  2. 2.University of Chinese Academy of SciencesBeijingChina
  3. 3.Department of Civil EngineeringUniversity of TorontoTorontoCanada
  4. 4.School of Mechanics and Civil EngineeringChina University of Mining and TechnologyBeijingChina

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