During in situ thermal injection in oil shale mining, the shear properties of oil shale at real-time high temperatures considerably affect the stability of injection and production wellbore as well as oil and gas production. The results of this study show that the shear strength and modulus of oil shale decrease with an increase in the shear angle at real-time high temperatures. With increasing temperature, the shear strength and modulus first decrease and then increase, reaching their lowest values at 400 °C. Thereafter, at temperatures above 400 °C, the energy accumulated in the elasticity and crack propagation stages is released and a large amount of energy is liberated during the instability failure. Finally, with rising temperature, the failure stage of oil shale changes from brittle to ductile, secondary fractures gradually increase and the failure characteristics step-by-step turn from through to nonthrough cracking characteristics.
1. Razvigorova, M., Budinova, T., Petrova, B., Tsyntsarski, B., Ekinci, E., Ferhat, M. F. Steam pyrolysis of Bulgarian oil shale kerogen. Oil Shale, 2008, 25(1), 27‒36.
https://doi.org/10.3176/oil.2008.1.04
2. Wang, L., Zhao, Y. S., Yang, D., Kang, Z., Zhao, J. Effect of pyrolysis on oil shale using superheated steam: A case study on the Fushun oil shale, China. Fuel, 2019, 253, 1490‒1498.
https://doi.org/10.1016/j.fuel.2019.05.134
3. Wang, L., Yang, D., Kang, Z. Q., Zhao, J., Meng, Q. R. Experimental study on the effects of steam temperature on the pore-fracture evolution of oil shale exposed to the convection heating. J. Anal. Appl. Pyrol., 2022, 164, 105533.
https://doi.org/10.1016/j.jaap.2022.105533
4. Al-Ayed, O. S., Hajarat, R. A. Shale oil: Its present role in the world energy mix. Glob. J. Energ. Technol. Res. Updat., 2018, 5, 11‒18.
https://doi.org/10.15377/2409-5818.2018.05.2
5. Avşar, E. An experimental investigation of shear strength behavior of a welded bimrock by meso-scale direct shear tests. Eng. Geol., 2021, 294, 106321.
https://doi.org/10.1016/j.enggeo.2021.106321
6. Serrano, A., Olalla, C., Galindo, R. A. Micromechanical basis for shear strength of rock discontinuities. Int. J. Rock Mech. Min. Sci., 2014, 70, 33‒46.
https://doi.org/10.1016/j.ijrmms.2014.02.021
7. Liang, W. G., Xu, S. G., Zhao, Y. S. Experimental study of temperature effects on physical and mechanical characteristics of salt rock. Rock Mech. Rock Eng., 2006, 39(5), 469‒482.
https://doi.org/10.1007/s00603-005-0067-2
8. Zhao, J., Kang, Z. Q. Permeability of oil shale under in situ conditions: Fushun oil shale (China) experimental case study. Nat. Resour. Res., 2021, 30(1), 753‒763.
https://doi.org/10.1007/s11053-020-09717-0
9. Zhao, G. J., Chen, C., Yan, H., Hao, Y. L. Study on the damage characteristics and damage model of organic rock oil shale under the temperature effect. Arab. J. Geosci., 2021, 14(8), 1‒12.
https://doi.org/10.1007/s12517-021-07046-x
10. Yang, D., Wang, G. Y., Kang, Z. Q., Zhao, J., Lv, Y. Q. Experimental investigation of anisotropic thermal deformation of oil shale under high temperature and triaxial stress based on mineral and micro-fracture characteristics. Nat. Resour. Res., 2020, 29(6), 3987‒4002.
https://doi.org/10.1007/s11053-020-09663-x
11. Yang, S. Q., Yang, D., Kang, Z. Q. Experimental investigation of the anisotropic evolution of tensile strength of oil shale under real-time high-temperature conditions. Nat. Resour. Res., 2021, 30(3), 2513‒2528.
https://doi.org/10.1007/s11053-021-09848-y
12. Li, M., Wang, D., Shao, Z. Experimental study on changes of pore structure and mechanical properties of sandstone after high-temperature treatment using nuclear magnetic resonance. Eng. Geol., 2020, 275, 105739.
https://doi.org/10.1016/j.enggeo.2020.105739
13. Tang, Z. C., Zhang, Q. Z., Peng, J., Jiao, Y. Y. Experimental study on the water-weakening shear behaviors of sandstone joints collected from the middle region of Yunnan province, P.R. China. Eng. Geol., 2019, 258, 105161.
https://doi.org/10.1016/j.enggeo.2019.105161
14. Geng, Z., Chen, M., Jin, Y., Yang, S., Yi, Z., Fang, X., Du, X. Experimental study of brittleness anisotropy of shale in triaxial compression. J. Nat. Gas Sci. Eng., 2016, 36, Part A, 510‒518.
https://doi.org/10.1016/j.jngse.2016.10.059
15. Du, K., Li, X., Wang, S., Tao, M., Li, G., Wang, S. Compression-shear failure properties and acoustic emission (AE) characteristics of rocks in variable angle shear and direct shear tests. Measurement, 2021, 183, 109814.
https://doi.org/10.1016/j.measurement.2021.109814
