Petroleum Exploration and Development >

2021 , Vol. 48 >Issue 1: 243 - 255

DOI: https://doi.org/10.1016/S1876-3804(21)60020-4

Anisotropy of crack initiation strength and damage strength of coal reservoirs

  • Xianjie HAO ,
  • Yingnan WEI ,
  • Ke YANG ,
  • Jian SU ,
  • Yingfeng SUN ,
  • Guangpei ZHU ,
  • Shaohua WANG ,
  • Haibo CHEN ,
  • Zhuowen SUN
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  • 1. State Key Laboratory of Coal Resources and Safe Mining, China University of Mining and Technology (Beijing), Beijing 100083, China
    2. Beijing Key Laboratory for Precise Mining of Intergrown Energy and Resources, China University of Mining and Technology (Beijing), Beijing 100083, China
    3. State Key Laboratory of Water Resource Protection and Utilization in Coal Mining, Beijing 100083, China
    4. Key Laboratory of Safety and High-efficiency Coal Mining, Ministry of Education (Anhui University of Science and Technology), Huainan 232001, China
    5. State Key Laboratory of Mining Response and Disaster Prevention and Control in Deep Coal Mines, Anhui University of Science and Technology, Huainan 232001, China
    6. PetroChina Research Institute of Petroleum Exploration & Development, Beijing 100083, China
    7. College of Engineering, Peking University, Beijing 100083, China
    8. CAS Key Laboratory of Mechanical Behaviour and Design of Materials, University of Science and Technology of China, Hefei 230026, China

Received date: 2020-03-12

  Revised date: 2020-12-21

  Online published: 2021-02-07

Supported by

National Natural Science Foundation of China(51804309);National Natural Science Foundation of China(51861145403);State Key Laboratory of Water Resource Protection and Utilization in Coal Mining, China(SHJT-17-42.10)

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Abstract

The crack volume strain method and acoustic emission (AE) method are used to analyze the anisotropy of the crack initiation strength, damage strength, the failure mode and the AE characteristics of coal reservoir. The results show that coal reservoirs show obvious anisotropic characteristics in compressive strength, cracking initiation strength and damage strength. The compressive strength of coal reservoirs decreases with the increase of bedding angle, but the reservoirs with bedding angles of 45° and 90° differ little in compressive strength. The crack initiation strength and damage strength decrease first and then increase with the increase of bedding angle. The crack initiation strength and damage strength are the highest, at the bedding angle of 0°, moderate at the bedding angle of 90°, and lowest at the bedding angle of 45°. When the bedding angle is 0°, the failure of the coal reservoirs is mainly steady propagation of large-scale fractures. When the bedding angle is 45°, one type of failure is caused by steady propagation of small-scale fractures, and the other type of failure is due to a sudden instability of large-scale fractures. When the bedding angle is 90°, the failure is mainly demonstrated by a sudden-instability of small-scale fractures. Compared with the cumulative count method of the AE, the cumulative energy method is more suitable for determining crack initiation strength and damage strength of coal reservoirs.

Key words： coalbed methane; coal reservoir; crack initiation strength; damage strength; hydraulic fracturing; bedding; crack volume strain; acoustic emission

Cite this article

Xianjie HAO , Yingnan WEI , Ke YANG , Jian SU , Yingfeng SUN , Guangpei ZHU , Shaohua WANG , Haibo CHEN , Zhuowen SUN . Anisotropy of crack initiation strength and damage strength of coal reservoirs[J]. Petroleum Exploration and Development, 2021 , 48(1) : 243 -255 . DOI: 10.1016/S1876-3804(21)60020-4

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