The thesis is devoted to establishing the regularities the transformation of the closed porosity of the carbonic sandstones of the Donbass, depending on the catagenetic changes of the rocks.
Based on the results of the studies, a new subtype of closed porosity - grain, was first identified, based on which it was proposed to divide closed porosity into cement (isolated pores in the cementing material of the rock) and grain (fluid inclusions in rock-forming rock grains).
Grain closed porosity is formed with numerical inclusions in the fragments of sandstones. Inclusions are mainly gas, less gas-liquid. Most of the gas inclusions were formed directly in the Donetsk Basin, during catagenetic processes. The peculiarity of gas inclusions of quartz grains of Donbas sandstones is their small size. On average, they are 1.5-2 microns.
Electronic and optical microscopy methods were used to study the grain porosity. The most informative method was optical microscopy, at magnification 1200 times with the using of an immersion liquid.
The preparations used were thin section of carbon sandstones of the Donbas, which were made from samples taken in areas of distribution of various coal grades. Due to this it was possible to determine the size of micropores, their number, shape, volume, patterns of changes, depending on the degree of conversion of rocks in conditions of catagenesis. Inclusions and microdeformations were taken into account in quartz grains with a size of at least 0.05 mm, which corresponds to the minimum grain size of the sand fraction.
Using optical studies, it was found that the size of fluid inclusions in quartz grains of sandstones of the Donbass decreases linearly with increasing degree of catagenesis of rocks.
Using the developed technique, the volumes of fluid inclusions in clastic grains of sandstones of the Donbass have been established, the maximum values of which reach 3-4% at the middle stage of rock catagenesis.
It was established that the volumes of grain closed porosity in average 1.5-2 times exceed the indicators of cement closed porosity. If the indicator of closed porosity, which is calculated for the difference between total and open porosity, for sandstones in the Donbas is on average 1-2%, then depending on the grain porosity, it can reach 4% or more.
The obtained results are important for the study of porosity of rocks. It is known that porosity is one of the indicators that are taken into account when forecasting gas-dynamic phenomena and prediction of reservoir properties of rocks. When establishing the absolute porosity index, it is important to take into account the volume of closed pores, which is found in the grains of rocks, in the form of gas inclusions. This will allow getting more accurate data and the probability of the obtained indicators.
The necessity of taking into account the parameters of closed grain porosity when predicting gas-dynamic phenomena in coal mines is substantiated, since its maximum values are established for sandstones of the middle stage of catagenesis, which is characterized by the greatest number of gas-dynamic phenomena.
Key words: fluid inclusions, quartz grains, sandstones, catagenesis, Donbass.
