Porosity is measured from rock plugs in a porosimeter. The method involves the extraction of air from the pores in the rock by a vacuum, and measurement of the bulk volume of the rock. The porosity is calculated by the expression: % porosity = (volume of gas extracted/bulk volume of the rock sample) × 100. Permeability is measured in a permeameter, by determining the pressure drop (P₁ – P₂) from a fluid of known viscosity (μ‎) and flow rate (Q), across a rock sample of known cross-section (A) and length (L). Permeability (K) is then determined by Darcy’s law: K = Qμ‎L/(P₁ – P₂)A.