Study on the damage characteristics of gas-bearing shale under different unloading stress paths


Autoři: Yintong Guo aff001;  Lei Wang aff001;  Xin Chang aff001
Působiště autorů: State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences, Wuhan, China aff001
Vyšlo v časopise: PLoS ONE 14(11)
Kategorie: Research Article
doi: 10.1371/journal.pone.0224654

Souhrn

In order to understand the influence of unloading on the mechanical properties of shale rock, triaxial unloading tests under different stress paths were conducted. In this paper, three types of tests are completed, including: 1) Conventional triaxial compression test;2) Pre-peak constant maximum principal stress-unloading confining pressure test with different initial confining pressures and rates;3) Increasing axial stress-unloading confining pressure test. The deformation and rupture modes characteristics of shale sample under different unloading stress paths were obtained. Research results show that: 1) The confining pressure effect is obvious and the peak strength increases with the increase of initial confining pressure, under conventional triaxial compression test, the samples show obvious elastic-plastic characteristics; Under unloading confining pressure test, it shows obvious elastic brittleness characteristics.2) Compared with conventional triaxial compression test, unloading confining pressure is more prone to deformation and rupture, and the damage is more serious. Under same initial stress level, the brittle characteristics in unloading confining pressure are more obvious and the expansion is more intense. 3) Under same unloading stress path, the higher the initial confining pressure is, the more severe the sample failure is. With the increase of unloading rate, the rupture degree of the sample becomes more complex.4) The brittle rupture characteristic increases with the increase of unloading rate and initial confining pressure. Increasing axial stress-unloading confining pressure, various types of tensile and shear fractures with different mechanisms are well developed. These conclusions reveal loading and unloading mechanical properties of gas-bearing shale under different stress paths; it provides theoretical basis for horizontal drilling, fracturing design and long-term fracturing effect analysis of shale gas reservoirs.

Klíčová slova:

Compression – Deformation – High pressure – Hydrostatic pressure – Mechanical properties – Mechanical stress – Permeability – Shale


Zdroje

1. Wang JG, Ju Y, Gao F, Peng Y, Gao Y. Effect of CO2 anisotropic sorption and swelling on caprock sealing efficiency. Journal of Cleaner Production.2015; 103:685–695.

2. Liu J, Wang JG, Gao F, Ju Y, Zhang XX, Zhang LC. Flow consistency between non-Darcy flow in fracture network and nonlinear diffusion in matrix to gas production rate in fractured shale gas reservoirs. Transport in Porous Media.2016; 111:97–121.

3. Wang JG, Wang HM. Sealing efficiency analysis for shallow-layer caprocks in CO2 geological storage. Environmental Earth Sciences.2018; 77:738.

4. Swanson SR, Brown WS. An observation of loading path independence of fracture rock. International Journal of Rock Mechanics and Mining Sciences and Geomechanics Abstracts.1971;8(3), 277–281.

5. Wu G, Zhang L. Studying unloading failure characteristics of a rock mass using disturbed state concept. International Journal of Rock Mechanics and Mining Sciences.2004;41:181–187.

6. Mario C, Torres S, Adolfo AG, Rafael BD. Effects of loading-unloading and wetting-drying cycles on geomechanical behaviors of mudrocks in the Colombian Andes. Journal of Rock Mechanics and Geotechnical Engineering.2014;6:257–268.

7. Meng Q, Zhang M, Han L, Pu H, Nie T. Effects of acoustic emission and energy evolution of rock specimens under the uniaxial cyclic loading and unloading compression. Rock Mech. Rock. Eng. 2016;49:3873–3886.

8. Li XB, Cao WZ, Zhou ZL, Zou Y. Influence of stress path on excavation unloading response. Tunnelling and Underground Space Technology.2014; 42:237–246.

9. Wang DK, Lv RH, Wei JP, Zhang P, Yu C, Yao BH. An experimental study of the anisotropic permeability rule of coal containing gas. Journal of Natural Gas Science and Engineering.2018;53(5): 67–73.

10. Wang DK, Lv RH, Wei JP, Fu QC, Wang YT, Zhang P, et al. An experimental study of seepage properties of gas-saturated coal under different loading conditions. Energy Science & Engineering.2019; 7(3):799–808.

11. Huang D, Li YR. Conversion of strain energy in triaxial unloading tests on marble. International Journal of Rock Mechanics & Mining Sciences.2014;66:160–168.

12. Sukplum W, Wannakao L. Influence of confining pressure on the mechanical behavior of Phu Kradung sandstone. International Journal of Rock Mechanics & Mining Sciences.2016;86: 48–54.

13. Xue Y, Ranjith PG, Gao F, Zhang DC, Cheng HM, Chong ZH, et al. Mechanical behaviour and permeability evolution of gas-containing coal from unloading confining pressure tests. Journal of Natural Gas Science and Engineering.2017;40:336–346.

14. Pan RK, Fu D, Yu MG, Chen L. Directivity effect of unloading bedding coal induced fracture evolution and its application. International Journal of Mining Science and Technology.2017;27:825–829.

15. Li XP, Xiao TL, Wang B, Xu PC. Experimental study of Jinping Hydropower station marble under loading and unloading stress paths. Chinese Journal of Rock Mechanics and Engineering.2012;31(5): 882–889.

16. Li DY, Sun Z, Xie T, Li XB, Rangith PG. Energy evolution characteristics of hard rock during triaxial failure with different loading and unloading paths. Engineering Geology. 2017;228:270–281.

17. Hua AZ, You MQ. Rock failure due to energy release during unloading and application to underground rock burst control. Tunnelling Undergr Space Technol. 2001;16: 241–246.

18. Li XP, Xiao TL, Wang B, Xu PC. Experimental study of Jinping II hydropower station marble under loading and unloading stress paths. Chinese Journal of Rock Mechanics and Engineering.2012;31(5):882–889.

19. Su CD, Li HZ, Zhang S, Guo PF. Experimental investigation on effect of strain rate on mechanical characteristics of Marble. Chinese Journal of Rock Mechanics and Engineering.2013;32(5):943–950.

20. Olsson WA. The compressive strength of tuff as a function of strain rate from 10−6 to 10−3/s. International Journal of Rock Mechanics and Mining Sciences and Geomechanics Abstracts.1991;28(1):115–118.

21. Ju QH, Wu MB. Experimental studies of dynamic characteristic of rocks under triaxial compression. Chinese Journal of Geotechnical Engineering.1993;15(3):73–80.

22. Ma D, Wang JJ, Cai X, Ma XT, Zhang JX, Zhou ZL, et al. Effects of height/diameter ratio on failure and damage properties of granite under coupled bending and splitting deformation. Engineering Fracture Mechanics. 2019; 220:106640.

23. Ma D, Duan HY, Li XB, Li ZH, Zhou ZL, Li TB. Effects of seepage-induced erosion on nonlinear hydraulic properties of broken red sandstones, Tunnelling and Underground Space Technology.2019; 91: 102993.


Článek vyšel v časopise

PLOS One


2019 Číslo 11