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Experimental Study on Mechanical Properties, Permeability and Acoustic Emission Characteristics of Gypsum Rock Under THM Coupling

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Abstract

The mechanical properties and permeability of gypsum caprock have a significant influence on the tightness and stability of salt cavern gas storage, a series of tests were carried out to investigate the mechanical properties, permeability and AE characteristics of gypsum under THM coupling in this work. The peak strength of gypsum increases with the increase of confining pressure and the decrease of temperature, the failure and dilatation failure criteria are obtained by utilizing Mogi failure criterion. The permeability decreases with the increase of temperature in the compaction and linear elastic deformation stage, and the final permeability decreases with the increase of temperature under the confining pressure of 5 MPa and 15 MPa, while increase with the increase of temperature under the confining pressure of 25 MPa and 35 MPa. And the permeability decreases with the increase of confining pressure in the whole test process because of the constrain of confining pressure on the formation of microcracks and pores. The best fitting formulas of the relationship between permeability and confining pressure is given by fitting at 25 °C and 110 °C, which can be expressed by two exponential functions. The AE characteristics also confirmed that the increase of confining pressure and temperature inhibited the formation of microcracks and pores, and the AE peaks have the same hysteresis effect as the stress peaks. It is noted that the peaks of AE ring count increase with the increase of temperature under the confining pressure of 35 MPa.

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Abbreviations

K:

Permeability under THM coupling

μ:

Dynamic viscosity coefficient of nitrogen

β:

Compression coefficient of nitrogen

V:

Volume of nitrogen in cylinders

Δt:

Test time of permeability measurement

A:

Cross-sectional area of the sample

L:

Height of the sample

P0:

Osmotic pressure difference at the initial moment

Pt:

Osmotic pressure difference at the final moment

τoct:

Octahedral shear stress of the stress space of the Mogi failure criterion

σm,2:

Effective Mogi mean stress of the stress space of the Mogi failure criterion

σ1:

First principal stresses under the triaxial test

σ2:

Second principal stresses under the triaxial test

σ3:

Third principal stresses under the triaxial test

\(\tau_{{{\text{oct}}}}^{p}\),\(\sigma_{m,2}^{p}\) :

Octahedral peak shear stress and corresponding effective principal stress

\(\tau_{{{\text{oct}}}}^{d}\),\(\sigma_{m,2}^{d}\) :

Octahedral dilatation shear stress and corresponding effective principal stress

\(k_{p}^{{T = 25^\circ {\text{C}}}}\) :

Final permeability at T = 25 °C

\(k_{p}^{{T = 110^\circ {\text{C}}}}\) :

Final permeability at T = 110 °C

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Acknowledgements

This research was financially supported by the National Natural Science Foundation of China (Grant No. U20A20266, 51874202) and Major Talent Projects, and the Ten Thousands Plan Youth Top Project proposed by the Organization Department of the Central Committee of the CPC.

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Correspondence to Jianfeng Liu.

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The authors declare that the work described has not been published before; that it is not under consideration for publication anywhere else; that its publication has been approved by all co-authors; that there is no conflict of interest regarding the publication of this article.

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Lyu, C., Liu, J., Wu, Z. et al. Experimental Study on Mechanical Properties, Permeability and Acoustic Emission Characteristics of Gypsum Rock Under THM Coupling. Rock Mech Rock Eng 54, 5761–5779 (2021). https://doi.org/10.1007/s00603-021-02586-w

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  • DOI: https://doi.org/10.1007/s00603-021-02586-w

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