Key words: polymer drilling muds, core, porosity, permeability, specific electric resistance.
On the example of a field in Orenburg region the authors researched an issue of adequate data obtained when analyzing the core taken using the polymer-clay drilling mud. It was shown that the drilling muds based on the polymers of polysaccharide class do not exert any significant distorting impact on the defined-by-the-core basic parameters (porosity, permeability, and electrical resistance at 100 % water saturation). In the meantime, when researching the rock samples of cavernous and porous type we should take into account the occurrence of transformation phenomenon of the porous space geometry as a result of separation of the particles of the rock matrix by the action of the water that is filtering through it, which may cause an artificial understatement of permeability after the water wash of the core.
