Mining Institute, Ural Branch, Russian Academy of Sciences (Perm, Russia)

I. I. Chaikovskiy, Head of Department, Doctor of Geologo-Mineralogical Sciences, Professor, ilya@mi-perm.ru
S. S. Andreyko, Chief Researcher, Doctor of Engineering Sciences, Professor
O. V. Ivanov, Leading Researcher, Candidate of Engineering Sciences
E. A. Nesterov, Senior Researcher, Candidate of Engineering Sciences
O. V. Korotchenkova, Senior Researcher, Candidate of Geologo-Mineralogical Sciences

The study focused on natural gases and the composition of bound gases in rocks of the Tolbachan suite. Slightly transformed primary rocks were examined: rock salt, marl, limestone, dolomite containing anhydrite and dolomite, as well as secondary dolomites and recrystallized limestones. 74 rock samples collected in mine workings were examined using a VEGA 3 LMH scanning electronic microscope with an Oxford Instruments INCA Energy 250/Xmax 20 energy-dispersive X-ray microanalysis system (Tescan, Czech Republic). Observations were conducted in BSE mode with a focal length of 10–20 mm and an accelerating voltage of 20 kV. Determining the gas content of rocks based on bound gases involved measuring the volume of gases released during dry mechanical disintegration of rock samples with constant pressure and temperature monitoring in a vessel isolated from the atmosphere using a PM GrindControl system. Chromatographic analysis of the gas component composition was performed on a Varian Inc. 450-GC gas chromatograph. It was established that the observed marl → limestone or marl → dolomite (+ anhydrite) → halite cyclicity in the Tolbachan suite indicates a change from terrigenous-carbonate sedimentation to carbonate sedimentation, and then sulfate and chloride sedimentation, reflecting a significantly increased degree of salinization of the basin, which was accompanied by brine halocatagenesis or gravitationalbrine catagenesis processes and caused dolomitization (and silicification) of the underlying limestones and leaching of calcium with the formation of voids into which gases are squeezed under high pressure. Quantitative indicators of the gas content of primary and secondary rocks by bound gases were determined. It was observed that secondary rocks – dolomites and recrystallized limestones – are the most gas-bearing. The methane-nitrogen composition of bound gases in the Tolbachan suite rocks has been determined. Textural features (cavernosity) and mineral signatures (dolomitization and silicification) identified during studies of gas content of the Tolbachan suite rocks allows to identify and predict intervals prone to gasdynamic phenomena using core samples from advance and control wells.
The study was carried out with financial support from the Ministry of Science and Higher Education of the Russian Federation under state assignment (R&D Project No. 126012716039–2; 124020500052–9).

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