Permeability and Three Dimensional Void Space Information in Sandstone Specimens with Different Porosity

Abstract

To investigate differences on permeability and three dimensional void geometry in two sandstones, permeability evolution by increasing confining pressure was measured and its relationship to three dimensional geometrical information was analyzed with micro focus X-Ray CT. In this research, Berea sandstone and Otway sandstone were used as a specimen, and their total porosity measured by Mercury Intrusion Porosimetry were 18% and 25%, respectively. Pore size distribution of both sandstones was an unimodal manner, but that of Otway sandstone showed slightly narrower peak around 5～7μm. Permeability in both sandstones decreased with increasing effective confining pressure, but its absolute value of Otway sandstone was lower by one order of magnitude than that of Berea sandstone. Three dimensional medial axis method was adopted to compare pore geometry in two sandstones. Several geometrical information was obtained such as pore and throat radius, pore coordination number, tortuosity, number of connecting path, connecting path volume and so on. Otway sandstone was characterized as a large frequency in effective throat/pore radius ratio. In fluid flow mechanism, the larger number of effective throat/pore radius ratio exists in sandstone specimen, the more fluid pressure potential consume. There is some possibility that the magnitude of the radius ratio with adjacent voids governs permeability of sandstone.