Statistical determination of representative elementary volume for petrophysical properties of vesicular basalts

The determination of the representative elementary volume (REV) is crucial for predicting the large-scale fluid flow behaviour in rocks. Previous studies have explored REV analysis for sandstones and carbonate rocks, where pervasive pore network structures exist between, and through, mineral grains. This paper investigates the REV of vesicular basalt samples from Port Fairy, Australia. These samples are characterised by a wide range of pore sizes with a substantial proportion of pores having volumes significantly larger than those characteristic of sandstones and carbonates. We explore the REV for these samples by using two properties, porosity and permeability using three different statistical approaches. A statistical REV approach was applied to processed and segmented 3D micro-CT images of the basalt samples from the study area. The distributions of the properties of interest were used to systematically converge towards the property-specific REV values. The results indicated that the REV sized sub-volumes for studying basaltic rock are over 1000 times larger than those typically needed for previously investigated sandstone and carbonate samples. Furthermore, the results indicated that the REV depends on the sample orientation due to anisotropy in pore connectivity. This highlights the critical role of considering directional effects when studying such heterogeneous rocks.