EVALUATION OF WATER-BEARING STRATA COLLECTIVE PROPERTIES CHANGE AT THE STORAGE OF GASEOUS HYDROCARBONS

The current economic and energy situation in industrial regions of Ukraine, along with need to address the problems of importing and developing its own natural gas deposits, predetermines the need to establish the suitability and search for aquiferous geological structures for accumulation of seasonal reserves of gaseous hydrocarbons. Based on the analysis of geological-structural and hydro-geodynamic conditions, West Donbass was divided into districts and Leventsovskaya geological structure was chosen, in a section of which the Permian-Triassic aquifer is located. Dedicated reservoir is represented by greenish-gray, quartz-feldspar coarse-grained sandstones with interlayers of strongly kaolinized sands and comparatively homogeneous in physico-mechanical properties and granulometric composition. The waters contained in it are characterized by an increased mineralization, high rigidity and are completely unsuitable for domestic and technical purposes. Interpretation of data from the experimental filtration works performed on a site, carried out on a basis of adequate hydrogeological and technological schematization, analytical calculations and graphoanalytical method, showed that the coefficients of filtration and piezoconductivity of an aquifer vary, respectively, from 1.51 to 3.66 m/day and 4.5 to 9.1·106 m2/day. The calculated values of filtration parameters allow considering this reservoir as promising water-bearing gas storage and can be used to determine its capacitive characteristics. To assess the degree of influence of accumulated gas on filtration properties of the dedicated reservoir and the hermeticity of the assumed storage, a series of special laboratory experiments was conducted, based on a reproduction of a long-term contact of gaseous hydrocarbons with samples of water-bearing rocks under pressure and periodic determination of their permeability in a TriSCAN stability meter. The studies have established a significant (15-20%) increase in absolute permeability of an aquifer and underlying rocks when hydrocarbon gases are stored within. It is shown that the destructive changes of a rock matrix caused by aggressive gas impact occur in a near-surface zone with a thickness of several millimeters and will not create a threat of depressurization of the storage during a designed period of operation.