Abstract: Most previous studies focused on establishing the relationship between pore compression sensitivity and permeability at the macroscopic level. However, the effect of different pore-structures at multi-scales on the evolution of permeability characteristics is still not clear. Also, many mesoscopic studies have showed that the closure degree of pores at multi-scales are significantly different under the action of stress. Thus, the pore compression sensitivity at different scales is crucial to predict the evolution of permeability accurately. In this study, the hydro-mechanical experiments of sandstone were performed using a multi-field coupling NMR experimental system to obtain the variations of permeability and pore-size distribution under different stress conditions. The pore diameter is divided into three categories: large pore (>1 ?m), middle pore (0.1–1 ?m), and small pore (<0.1 ?m). The pore compressibility coefficients at different scales and transforming factors were calculated. A calculation formula for sandstone permeability considering pore compression sensitivity at different scales was also proposed. The results show that the compressibility of pores at different scales of sandstone is significantly different. The larger the pores are, the higher the compression sensitivity is. The proposed permeability formula considering the pore compression sensitivity at different scales are in good agreement with the experimental results.

Key words: hydro-mechanical coupling, pore size distribution, compression sensitivity, sandstone, permeability evolution