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The paper presents results of the experimental study of geochemical processes in the “formation water – CO – rock” system at reservoir conditions for waterand oil-saturated intervals of several typical terrigenous and carbonate formations of Urals-Volga region. Compositions of formation water and dissolved gas are analyzed at each stage of the experiments, as well as mineral composition of core samples before and after the interaction. Based on the experimental results, a summarizing analysis is presented of possible physical and chemical processes occurring in the “formation water – CO2– rock” system during carbon dioxide injection into waterand oil-bearing formations. The results of the experiments allow us to highlight the significant effects of dissolution and resuspension of carbonates and halite during exposure of carbonized formation water with core material of different lithology and saturation character. In a number of experiments, significant changes in the iron and sulfate anions content were recorded, indicating the interaction of the solution with pyrite and gypsum. There were no significant qualitative and quantitative differences in the results of experiments with core material from water-saturated and oilsaturated intervals of the same lithology.

The paper presents the results of experimental evaluation of oil displacement efficiency by flue gas of a thermal power plant, compared to water, for a carbonate reservoir in the Ural-Volga region. The experiments were performed under two different injection schemes using an original laboratory complex for coreflood studies, with recombined reservoir oil, model of formation water, reservoir core material, and under reservoir thermobaric conditions. It has been confirmed that due to the prevailing nitrogen content and low values of reservoir pressure and temperature, flue gas is ineffective as an independent displacement agent either for injection from the beginning of reservoir development or as a tertiary method after waterflooding. Taking into account the relevance of synergy between increasing oil recovery and sequestration of industrial emissions, evaluation of flue gas injection as part of water-gas mixtures (SWAG) is recommended.

Application of hydrogeochemical modeling using PHREEQC software to study interaction of formation water, carbon dioxide and reservoir rock minerals during CO2 injection for enhanced oil recovery or underground storage is discussed. Hydrogeochemical modeling is a powerful tool to evaluate the physicochemical processes occurring in the “gas phase – aqueous solution – solid phases” system depending on initial parameters such as temperature, pressure and reactant concentrations. The use of hydrogeochemical simulators provides a wide range of opportunities to analyze the processes of dissolution and precipitation of minerals, changes in the ionic composition and pH of the solution, which can affect the efficiency of CO2 injection, fluid flow, well and equipment operation. A step-by-step method for modeling interactions in the “formation water – CO2 – rock” system using the PHREEQC hydrogeochemical simulator provides good reproducing accuracy for the results of laboratory experiments and analysis of their correspondence to the processes occurring under different conditions. The obtained results are useful for optimization of oil and gas production processes involving carbon dioxide, planning and stability assessment of underground carbon dioxide storage facilities and other geological applications.