A type of organic compound of carbon and hydrogen that contains one or more saturated cyclic (ring) structures, or contains such structures as a major portion of the molecule. The general formula is C_nH_2n. Naphthenic compounds are sometimes called naphthenes, cycloparaffins or hydrogenated benzenes. Naphtha is a refined petroleum fraction that contains a high percentage of these types of hydrocarbons. In drilling fluids, particularly oil-base muds, the amounts and types of hydrocarbons in the mud can be an important parameter in the overall performance of the mud.