The permeability for two types of sandstone, Berea sandstone and sandstone from Otway Paaratte formation, under different confining pressure are measured and porosity is investigated 3D micro-focus X-ray CT and 3D medial axis analysis. The permeability is determined using flow pump test and the porosity is determined by mercury intrusion porosimetry. The total porosity of Berea sandstone and Otway sandstone are around 17.4% and 25.0%, respectively. The permeability of both sandstones with 18 MPa of an effective confining pressure were approximately 70% of that with 10 MPa effective confining pressure. However, the permeability of Berea sandstone is higher than that of Otway sandstone by one order. In order to investigate this curious result, we performed 3D medial axis analysis and conclude that the larger porosity does not mean the higher permeability and the lower of throat/pore ratio has lower permeability.
Important factors in the long-term and stable CO2 geological storage are injection capacity, storage capacity and seal capacity etc. Therefore the porosity and permeability of the target formation for geological storage of CO2 should be measured and considered important. In general the higher porosity, the higher permeability, but it is not always. In other words, the permeability of a rock is related to the porosity, but also to the shapes of the pores in the rocks and their level of connectedness etc.
Porosity is a measure of the void spaces in a rock, and it can be defined as a fraction of the volume of voids over the total volume. Voids can be obtained by its geometry information and spatial information. Permeability is a measure of the ability of a porous rock or fractured rock to allow fluids to pass through it. Therefore the permeability of the rocks reflects physical quantity of fluid or ease of fluid flow passing through voids or fractures. That can be expressed in units of cm/sec and m2. The former is known as permeability or hydraulic conductivity and the latter is intrinsic permeability, which is the property of rocks that is an indication of the ability of fluids to flow through rocks.