f Estimating the mean permeability: how many measurements do you need?

The question of the number of permeability measurements that are required to estimate the mean permeability of a reservoir interval is not generally considered during reservoir evaluation. Permeability sampling is traditionally carried out with core plugs (1.0-1.5 inch or 2.5-3.8 cm cylindrical samples) at a spacing of about 1 foot or 0.3 m. This spacing has evolved from considerations of practicality, cost and the need for core conservation, and takes little account of the underlying rock variability.