Abstract:Salt rock,as a medium with extremely low permeability,has been widely used for oil and gas underground storages and high-level radioactive waste disposals in many countries. Twenty standard salt rock samples with dimensions of 25 mm in diameter and 50 mm in height,taken from the Yunying salt mine in Hubei Province,are tested by the automated core measurement system and the X-ray industrial CT to obtain their permeability characteristics and meso-scale structures. The test results indicate that the porosity of salt rock samples is less than 0.25% and the permeability is as low as 10-16–10-18 m2,and all decrease gradually with the increase of confining pressure in general. The mechanism of very low permeability subjected to meso-structure of salt rock is revealed by the X-ray industrial CT tests. It is shown that the salt rock is very compact at the meso-scale,and there are very few micropores and microfissures in pure salt rocks;and interlayer in salt rock is even more compact than that of pure salt rock,resulting in a shielding effect on permeability of bedded salt rock. Moreover,the effects of confining pressure and seepage lead to an obvious decrease in permeability. And the decrease of permeability agrees well with the decrease of porosity along with confining pressure.