THE POROSITY DISTRIBUTION MESOSCOPIC SIMULATION ANALYSIS OF THE PERMEABILITY EVOLUTION PROPERTY OF SANDSTONE

In this paper, triaxial tests were carried out to study the changes of the permeability of sandstones under different confining pressures. The DEM numerical model of sandstone was built based on the laboratory testing results. The volumetric strain, porosity distribution and contact fracture characteristics of sandstone under compression was obtained by DEM simulation. The results reveal the influence of the dynamic porosity distribution on the permeability from mesoscopic mechanism. The research shows that under low confining pressure, the connected shear bands of sandstone and fissures develop easily, which has significant effect on the seepage. A higher the confining pressure would bring greater numbers and scope of fracture contacts, as well as more fissures. The seepage is inhibited because the fissures and pores are more compressible. The permeability of sandstones increases quickly with the increasing number of connected opening fissures, but slowly with the tortuous and intermittent opening fissures. The completely isolated opening fissures wrapped around closed fissures and compacted pores contribute little to the permeability.