Specific materials are available for all types of water - and oil-base mud systems and are evaluated in static filtration tests or in various dynamic filtration tests.

Since the purpose is to minimize alteration, a fresh core has often been drilled with a bland mud, either water - or oil-base, but with a minimum of chemical additives and weighting material.

The measurement results showed that the invasion of the filtrates of oil-base mud and water-base mud has a considerable effect on oil phase permeability.