Permeability differences based on three-dimensional geometrical information of void spaces

In this study, the permeabilities of Berea and Otway sandstones were measured under different confining pressures, and porosity was investigated through mercury intrusion porosimetry (MIP). The total porosities of the Berea and Otway sandstones were approximately 17.4% and 25%, respectively. Pore size distributions of each sandstone were almost the same, but the pores in the Otway sandstone were slightly narrower. However, the permeability of the Otway sandstone was smaller than that of the Berea sandstone by one order of magnitude. Three-dimensional (3D) void geometry and geometrical properties of the void spaces relevant to flow were compared to obtain the relation between the permeability differences and porosities of the two sandstones. The 3D geometrical analysis using microfocus X-ray computed tomography (CT) was performed, and the pore geometries of both sandstones were compared using the 3D medial axis (3DMA) method. Pore and throat radii, pore coordination number, tortuosity, number of connecting paths, connecting path volume, and other factors were determined using 3DMA. The Otway sandstone was characterized by a small effective throat/pore radius ratio. Based on the fluid flow mechanism, the lower effective throat/pore radius ratio results in a lower permeability induced by the fluid energy loss, which means that the 3D geometrical shape of void spaces affects the permeability value.