Permeability evolution of sandstone under short-term and long-term triaxial compression

• Conduct short-term and creep tests for sandstone under triaxial compression.
• Analyze permeability evolution behavior of sandstone under short-term compression.
• Investigate permeability evolution behavior of sandstone under creep compression.
• Discuss the creep failure mechanism of sandstone with different pore fluids.

Permeability of sandstone under increasing deviatoric stress both in short-term and creep compression condition are measured with pulse transient technique. Based on the experimental results of short-term triaxial compression coupled with gas permeation, the influence of confining stress on the strength and failure mode of sandstone specimen are analyzed. The results show that the variation patterns of permeability under different confining stresses are similar, and the pressure differential has little influence on the mechanical behavior of sandstone. The crack volumetric strain is also calculated, and a linear relationship between the crack volumetric strain and permeability of sandstone specimen can be concluded. According to the creep test results with various loading procedures and different permeation fluids, the permeability evolution of sandstone is characterized as having four stages according with the typical deformation stages in a monotonic loading creep test. The failure strength of sandstone specimen under cyclic loading creep is lower and the system of cracks is more complicated than that under multi-stage loading creep with the same confining stress and permeation pressure.