Layer Orientation Effect on Fracture Mode and Acoustic Emission Characteristics of Continental Shale

Abstract

Based on the Brazilian tests of continental shale with different layer orientations, combined with AE monitoring, the influence of layer orientation on the anisotropy of mechanical properties, fracture mode, and fracture mechanism of continental shale was analyzed. The results show that the tensile strength and deformation at the peak stress decrease with the increase of layer orientation at a constant deformation loading rate of 0.06mm/min, and the splitting modulus decreases first and then increases. The tensile strength was 90° > 60° > 45° > 30° > 0°, and the maximum and minimum tensile strengths were 5.154 MPa and 0.669 MPa, respectively. Under the action of splitting load, the samples with 30°, 45°, and 60° layer orientations mainly undergo shear failure along the layer orientation, while the samples with 0° and 90° layer orientations undergo tensile failure. In addition, the crack propagation in the 0° and 30° samples penetrated the bedding. These characteristics have important reference significance for the study of the mechanism of hydraulic fracture communication, propagation, and activation of structural planes.

Recognition Algorithm of AE Signal of Rock Fracture Based on Multiscale 1DCNN-BLSTM

“…It can be seen that the brittleness of rock mass has an important infuence on the fracture form of rock mass [4][5][6]. When the content of brittle minerals reaches 50%, the internal cracks of the rock become reticular after fracturing, and the rock has reached the fracturing state [4]. Terefore, four typical AE signals released by rock fracturing with brittle content of 0%, 10%, 30%, and 50% are recognized in this study.…”

“…Figure 8 shows the acoustic emission signals released by the fracturing test of the rock, which are segmented and intercepted. When the brittle mineral content of the rock reaches 50%, the internal cracks of the rock become a network after fracture, and the rock has reached a fractured state [4]. Terefore, the four rock samples with mineral brittleness of 0%, 10%, 30%, and 50% were divided into 3571 data samples for identifcation testing.…”

“…With the increase of brittle mineral content in the rock mass, various fracture modes and multiple fracture planes appear, and fracture behavior and acoustic emission phenomena occur in many areas. It can be seen that the brittleness of rock mass has an important infuence on the fracture form of rock mass [4][5][6]. When the content of brittle minerals reaches 50%, the internal cracks of the rock become reticular after fracturing, and the rock has reached the fracturing state [4].…”

A SVM-based method for identifying fracture modes of rock using WVD spectrogram features of AE signals

“…Ren et al (2019) analyzed the AE signals using an improved time-difference localization algorithm and moment tensor theory to reveal the fine view crack expansion mechanism of tensile fractures, such as crack location, type, and expansion direction in the Brazilian disc test. Wang (2017) analyzed the AE signals of the fracture extensile process in different brittle shale fractures to reveal the extensile laws of tensile-type fracture, sheartype fracture and mixed-type fracture in brittle shale, then and established the AE propagation fluctuation equation and moment tensor discrimination method for crack propagation. The moment tensor analysis can identify rock fracture modes and reveal the crack propagation.…”