Abstract
The microstructure of rock plays a vital role in the deformation and fracturing process when subjected to external loading. Conglomerate, being a pivotal part of unconventional reservoir, is characterized by a distinct composition structure and high degree of heterogeneity. Thus, a proper understanding of the impact of microstructure on the mechanical properties of conglomerate is crucial. We conduct uniaxial and triaxial compression tests on conglomerate samples, accompanied by monitoring acoustic emission events and ultrasonic wave velocity. Experimental results show that: (1) conglomerate fails in tension under uniaxial compression, but in shear fracture or cataclastic flow with volume expanding under triaxial compression; (2) the deformation transforms from brittle to ductile with increasing confining pressure. Two failure modes may exist in the brittle–ductile transition regime, namely, shear fracture and cataclastic flow; (3) the relationship between the mechanical characteristics and average gravel size is consistent with the “Hall–Petch” empirical relationship. The confining pressure required for brittle–ductile transformation reduces with larger average gravel size. Microscopic observation demonstrates that two gravels contacting with each other may fail in Hertzian fractures. Shear slip and rotation of gravel occurs under triaxial compression. We propose a conceptual model to describe the deformation of conglomerate under different confining conditions and compare the deformation properties of conglomerate with sandstone.
Highlights
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The effects of microstructural and micromechanical properties on the deformation of conglomerate deformation are studied.
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Both the peak strength and the brittle–ductile transition pressure reduce with higher average gravel size.
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Discrepancy between gravel and matrix deformation dominates the cracks initiation, while the location of gravel affects the propagation.
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Acknowledgements
The corresponding author appreciates the financial support from the project ZR2020YQ44 supported by Shandong Provincial Natural Science Foundation, and the Natural Science Foundation Project of China (No.: 51909138). The data for conglomerate in triaxial compression condition are available from https://doi.org/10.6084/m9.figshare.19930406 or by contacting the corresponding author.
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Li, J., Duan, K., Meng, H. et al. On the Mechanical Properties and Failure Mechanism of Conglomerate Specimens Subjected to Triaxial Compression Tests. Rock Mech Rock Eng 56, 973–995 (2023). https://doi.org/10.1007/s00603-022-03110-4
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DOI: https://doi.org/10.1007/s00603-022-03110-4