Fig 1.
Experimental procedure flow.
Fig 2.
Mineral fractions of rock samples.
Fig 3.
T2 spectra distribution of samples.
Fig 4.
Schematic diagram of test stress unloading path.
Fig 5.
Images of SEM after unloading disturbance.
Note: (a) The unloading amplitude is 10MPa; (b) The unloading amplitude is 20MPa; (c) The unloading amplitude is 30MPa; (d) The unloading amplitude is 40MPa; (e) The unloading amplitude is 50MPa; (f) The unloading amplitude is 60MPa.
Fig 6.
Images of SEM after binary processing.
Fig 7.
Note: (a) Continuous image that has been projected onto the sensor array; (b) Results of image sampling and quantization.
Table 1.
Porosity and void ratio of each binary image.
Table 2.
Microcosmic pores parameters calculation results.
Table 3.
Percentage of different dmax/dmin.
Table 4.
Statistical parameters of T2 energy spectrum under different unloading amplitudes.
Fig 8.
Image details.
Fig 9.
Statistics of pore structure parameters in selected areas.
Fig 10.
Aperture parameters.
Fig 11.
Number percentage of pores with different dmax/dmin ratios.
Fig 12.
Area percentage of pores with different dmax/dmin ratios.
Fig 13.
Shale T2 energy spectrum with different unloading amplitudes.
Fig 14.
T2 energy spectrum area growth rate after pores after different unloading amplitudes.
Fig 15.
Proportion of various unloading amplitudes.
Fig 16.
Percent stacking chart of micropore, mesopore, and macropore spectrum area.
Fig 17.
T2 spectrum distribution in the saturated state and after centrifugation.
Table 5.
Pore change of rock samples with unloading amplitudes.
Fig 18.
Variation of shale void ratio and expansion rate after unloading disturbance.
Fig 19.
Shale triaxial compression test after unloading disturbance.
Fig 20.
Variation of shear strength and elastic modulus with different unloading amplitudes.
Table 6.
Porosity and expansion rate under unloading disturbance after returning to formation stress.
Fig 21.
Changing law of rock expansion rate with different unloading amplitude.
Table 7.
Rock shear strength limit value and damage variable after unloading disturbance.
Table 8.
Model parameters.
Fig 22.
Variation law of damage variables after unloading disturbance.