Fuel and power complex of the country is in need for alternative energy sources, where methane being found in coal deposits can be considered as one in the range. The Donets Basin is a perspective area for extracting coalbed methane in the terms of energy resources concomitant. In order to evaluate the possibility of developing the Donbass as a coal gas deposit with complex exploitation it is needed extra research of reservoir rock properties. Previously established regularities of transforming open porosity and volume density of sandstones are of great practical importance, and are the basis for further studies of reservoir rock properties. In this paper, particular attention was paid to the study of transformations of sandstones closed porosity. To observe the transformation process of rocks closed porosity caused by changing conditions was used microscopic method is one of the applied ones giving the possibility to observe gas inclusions in clastic mineral grains at high magnification (from 100 to 1200 power with the use of immersion liquid). Presumably, these gas inclusions are a part of closed porosity so it is suggested to divide the closed porosity into the cement-closed porosity and mineralogical closed porosity. Mineralogical closed porosity can serve as an indicator of rocks transformation grade and the study of gas inclusion transformation taken place in sandstone quartz grains provides the partial answer to the issue of changing gas component in the rocks pore space with increasing rocks catagenesis stage.

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