Rocks have different porosity and permeability characteristics, which means that water does not move around the same way in all rocks below ground.
Permeability greater than 250 mD are considered very good, while permeability less than 1 mD are considered poor.
Low porosity normally results in low permeability, but high porosity does not necessarily imply high permeability. It is possible to have a highly porous rock with little or no interconnections between pores.
