LABORATORY STUDIES ON THE EFFECTS OF HYDROGEN EXPOSURE ON POROSITY, PERMEABILITY, AND CHEMICAL COMPOSITION OF TERRIGENOUS RESERVOIR ROCKS: A CASE STUDY OF THE BOBRIKOVSKII FORMATIONS IN THE NORTHEAST VOLGA-URAL OIL AND GAS PROVINCE

Аннотация

This article outlines the methodology for conducting laboratory investigations into the effects of hydrogen on reservoir rocks. It details the stages of sample analysis and the instruments employed during the experiments. A comparative evaluation of the porosity and permeability of core samples was undertaken, revealing a 4.6% decrease in porosity and a 7.9% reduction in permeability following hydrogen exposure. Correlation analysis indicated a typical shift in the relationship between these characteristics: post- exposure, the variability of values increased while the correlation coefficient decreased, suggesting alterations in the void structure. The findings suggest that the observed reductions in porosity and permeability are attributed to slight compaction due to effective stresses. Chemical analyses indicated no significant changes in the composition of primary oxides before and Keywords: hydrogen; subsurface gas storage; reservoir rock; properties of porosity and permeability; chemical makeup of rocks; fundamental oxides. Introduction. Recently, there has been a growing focus on eco-friendly production technologies and the reduction of carbon dioxide emissions, including the exploration of alternative energy sources to replace hydrocarbons. In publication [1], the authors highlight the importance of addressing global warming and discuss technologies for capturing and disposing of carbon dioxide. They emphasize that Russia should adopt these technologies through government programs, drawing on international experiences. Hydrogen is anticipated to serve as one of the alternative fuels, raising challenges related to its production and transportation. Articles [2-4] outline various production methods for hydrogen, each with differing levels of energy efficiency and environmental impact. The authors advocate for technologies that do not produce carbon dioxide emissions. Additionally, publications [5-7] indicate that transporting hydrogen necessitates densification (liquefaction) and enhanced safety for tanks and transport systems. A critical consideration in hydrogen energy is the selection of storage facilities. Scientific articles [8-10] indicate that 24 ACADEMIC RESEARCH IN MODERN SCIENCE International scientific-online conference salt caverns may be suitable for storing hydrogen-methane mixtures, but they have both advantages and disadvantages. While salt caverns offer excellent sealing properties, they require significant labor to create, incur high costs, and have limited storage capacity due to structural collapse under external pressures. Some researchers propose utilizing existing underground gas storage facilities (UGS) traditionally used for natural gas [11, 12]. For larger volumes, depleted gas fields, aquifers, or currently operational methane storage facilities are recommended. A significant challenge in hydrogen storage is the embrittlement of steel well strings and downhole equipment. Articles [13-15] provide evidence that exposure to hydrogen can lead to physicochemical changes in commonly used steel grades, resulting in cracking and deterioration of mechanical properties. Such effects can lead to unexpected emergencies in wells and equipment. The metabolic activity of hydrogen-consuming bacteria can also pose issues. Experts [16-18] have noted that certain bacterial species in reservoirs can convert hydrogen into hydrogen sulfide, an aggressive gas that can damage well structures and equipment. When hydrogen is stored in reservoir beds, it can chemically react with the minerals in the rock matrix and the cap rock above. Authors of articles [19- 21] present data showing that hydrogen can interact with pyrite and aluminum- containing minerals, as well as with dissolved carbon dioxide and sulfates, leading to the formation of methane and hydrogen sulfide. These reactions can alter the porosity and permeability of the formation. Publications [22-24] indicate that hydrogen can cause a twofold change in the porosity of core samples, with these effects being dependent on the lithological characteristics of the rocks. Thus, it is recommended to store gas primarily in terrigenous reservoirs free of clay and carbonate impurities. Similar to traditional underground gas storage for methane, storing hydrogen can create a complex geodynamic situation at the operational sites. As shown in articles [25-27], fluctuations in formation pressures during gas injection and withdrawal can cause surface deformations. Therefore, it is essential to establish geodynamic monitoring systems in these UGS. An analysis of the literature reveals that the effects of hydrogen on the porosity and permeability of reservoir rocks, as well as on the chemical composition of the rock matrix, have not been sufficiently studied. This highlights the importance of examining the impact of hydrogen on reservoir properties and the chemical changes in the rocks of the investigated formation. The study focuses on the terrigenous deposit