Cyclic Experimental Studies on Damage Evolution Behaviors of Shale Dependent on Structural Orientations and Confining Pressures

Cheng Cheng and Xiao Li
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Cheng Cheng: Key Laboratory of Shale Gas and Geoengineering, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
Xiao Li: Key Laboratory of Shale Gas and Geoengineering, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China

Energies, 2018, vol. 11, issue 1, 1-20

Abstract: Damage process of shale is of great importance when considering the wellbore stability and reservoir stimulation during the work of shale gas recovery. As shale has typical transversely isotropic structures and may be under different stress states in the reservoir, the damage process should be studied while considering both loading directions and confining pressures. A series of cyclic uniaxial and tri-axial compressive tests have been carried out on the shale samples with different oriented weak planes and confining pressures. The dissipated strain energy and its ratio to the releasable elastic strain energy have been studied comparing with the fracturing patterns of the samples. Based on the strain energy dissipation, damage variable is defined and the damage evolution equation is built to describe the damage process of shale samples dependent on loading directions and confining pressures. The damage equation shows that the damage of the shale samples increases as a power function of the axial stress. Under higher confining pressures, the damage is limited in the early loading stage, while it increases significantly with the formation of macro shear fractures when the peak strength is approaching. The change of increasing rate is weak for the shale samples ( ? = 60°) as the main failure pattern is slip along the weak planes. This study is helpful for understanding the damage process and failure of wellbore, as well as the stimulation effect of the shale gas reservoir.

Keywords: shale; damage process; strain energy dissipation; orientation of weak planes; confining pressure; anisotropic behavior (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2018
References: View references in EconPapers View complete reference list from CitEc
Citations: View citations in EconPapers (2)

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