Effect of bedding planes on wave velocity and AE characteristics of the Longmaxi shale in China
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ORIGINAL PAPER
Effect of bedding planes on wave velocity and AE characteristics of the Longmaxi shale in China Feng Xu 1,2 & Chunhe Yang 1 & Yintong Guo 1 & Lei Wang 1 & Zhenkun Hou 3 & Haoran Li 4 & Xiaoming Hu 1,2 & Tongtao Wang 1
Received: 8 May 2016 / Accepted: 1 March 2017 # Saudi Society for Geosciences 2017
Abstract The experimental work described in this paper was carried out in order to discover more about the effects of bedding planes on wave velocity and acoustic emission (AE) characteristics of shale. Two groups of specimens, which were collected from the Longmaxi shale outcrop in Chongqing, China and cored perpendicular and parallel to the bedding planes, were tested under uniaxial compression, and the wave velocity and AE were monitored. There were obvious differences in the acoustic characteristics of shale with different bedding plane orientations. The experimental results show that (1) the average increasing rates of P- and S-wave velocities were 39.86 and 54.41%, respectively, for the specimen with a load perpendicular to the bedding planes (Y-0). The P-wave velocity and axial strain of specimen show a marked logarithmic relationship. However, the average increasing rates of P- and S-wave velocities were 5.44 and 10.54%, respectively, for the specimen with a load parallel to the bedding planes (Y-90). The good linear relationship between P-wave velocity and axial strain before failure of specimen has been built. Generally, S-wave velocity was more sensitive to axial strain than P-wave velocity. (2) AE characteristics for Y-0 showed that a few signals → quiet period → stable increase * Lei Wang [email protected]
1
State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences, Wuhan 430071, China
2
University of Chinese Academy of Sciences, Beijing 100049, China
3
State Key Laboratory for Coal Mine Disaster Dynamics and Control, Chongqing University, Chongqing 400044, China
4
Structural Health Monitoring and Control Institute, Shijiazhuang Tiedao University, Shijiazhuang 050043, China
→ steep increase; for Y-90: quiet period → stable increase → sudden increase → sharp increase. The AE energy for two groups of specimens was concentrated on low and middle of amplitudes (45-80 dB), but the proportion of amplitudes (80– 100 dB) and the total counts of AE for Y-0 was 1.95, 2.2 times as much as that for Y-90, respectively. The results preliminarily revealed the effect of bedding orientation on the wave velocity and AE properties of shale and may provide guidance for the improvement of acoustic logging and microseismic monitoring in the field. Keywords Longmaxi shale . Bedding planes . Acoustic emission . Wave velocity . Mechanical properties
Introduction Shale containing bedding planes is one of the most complicated rock types in oil-field engineering applications because of the marked intrinsic anisotropy of many of its properties, including strength, permeability, wave velocity, and AE characteristics (Kuila et al. 20
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