CO2 storage in geological formations represents today one of the main new technological solutions for CO2 emission mitigation. Carbon capture and storage technology (CCS) includes capture of anthropogenic CO2 from various emitters, its transportation and injection in different types of geological formations such as: depleted oil and gas reservoirs, saline formations, unmined coal beds, partially depleted oil reservoirs for enhanced oil recovery (EOR-CO2 method) and others. The analysis of numerous criteria that are determining the success of process implementation from a technical, safety, ecological and economic point of view is necessary for considering the optimal CO2 geological storage option. In this paper, an overview of CO2 geological storage types is presented, with an emphasis on criteria for selection of most adequate CO2 storage option. They include geological, physical, thermodynamic, hydrodynamic, techno economic, social criteria, as well as the regulatory issues that are key factors for CCS technology development and further deployment.

Artificial lift methods have applications in oil wells where oil production is no longer possible due to natural reservoir energy, so this necessary energy is added by introducing lift methods. In order to achieve optimum production, the selection of an artificial lift method is very important. This paper uses fuzzy logic as a mathematical and conceptual model for selection of the optimal artificial lift method. The outcome or IF-THEN rules, as the central part of the model, is based on empirical data from the selected oil fields. Results are presented in two ways: according to the surfaces of irregular geometric bodies, and their gravity with the scattering of results, i.e., on smaller and greater possibilities of interpreting results when there are small differences in outputs. Finally, a sensitivity analysis of the model is presented.

Gas wells, particularly those situated onshore, play a vital role in the global energy sector by supplying a significant portion of natural gas. However, operational challenges, notably gas hydrate formation, pose substantial issues, leading to complications such as flowline blockages and unexpected well shutdowns. Gas hydrates, crystalline structures resembling ice, form under specific conditions of low temperature and high pressure. This paper explores the complex process of hydrate formation in gas wells, emphasizing the challenges it presents and the need for specialized strategies to address these issues. The primary focus is a case study of an onshore gas well experiencing recurrent hydrate-related problems. Leveraging PipeSim software, a well model is developed, followed by a sensitivity analysis under various operational scenarios. The study investigates mitigation strategies, including choke position adjustments and methanol introduction, crucial for the safe production of oil and gas fields. The significance of this study lies in its aim to optimize well performance and mitigate risks associated with hydrate formation. Findings contribute to existing knowledge and offer practical solutions for industry practitioners and researchers dealing with onshore gas wells. The paper's structure includes a review of related work, details on the experimental setup and results, and concluding remarks. The perennial challenge of hydrate formation in gas wells necessitates a case-specific assessment and individualized approaches. Nodal analysis and well modeling software have become indispensable tools for engineers in developing preventative measures. This paper presents a methodological approach using a specific well as an example, evaluating the effectiveness of three methodologies: downhole choke installation, methanol dosing, and well transfer to a high-pressure separator.

In Serbia, there are about 1200 abandoned oil and gas wells, which have significant potential to produce thermal energy. Abandoned wells, depending on their location and thermal potential, can be used to produce thermal energy or electricity, or for the combined production of electricity and thermal energy. Thermal energy that is produced from abandoned wells is obtained using geothermal energy, so the electrical energy and/or thermal energy that would be obtained using such heat sources are balanced as energy obtained from renewable energy sources. The costs of equipping deep wells and applying the technology that would be used to produce thermal energy and/or electricity represent a far smaller part of the costs compared to the costs of making deep wells, so these abandoned wells represent an already existing significant material resource. The production of thermal energy from abandoned wells, which is based on pressing the working medium into the well, heating it and pushing it to the surface, is less energy intensive since the same well is used for the transfer of hot energy - through the appropriate working medium through tubing (narrow pipe) to the surface, and then the used cooled water is returned to the same well through the intermediate space. The paper presents a methodology for calculating the theoretical thermal potential of abandoned oil and gas wells, which was applied to the example of wells K-1, T-1, S-1 and M-1 located in Serbia, with a depth of 2.000 m, 2.250 m, 1.700 m and 2.102 m. It is shown that the theoretical temperature of the working fluid on the surface of the earth is in the range of 77.59 to 94.46°C.

Even in the third decade of the 21st century, large power plants are still responsible for more than half of the electricity production in Europe. They predominantly use fossil fuels in their work, which results in the emission of pollutants into the air. Nevertheless, thanks to EU directives, as well as disturbances on the market, emissions of carbon dioxide from large combustion plants in the EU-27 are intensively decreasing in the last two decades. Although the use of coal, especially in the countries of the European Union, is in constant decline, there is space for additional reduction. Through this paper, the authors wanted to present the completely actual situation of emissions of CO2 from thermal power plants in Europe, that have used coal for electricity production, as well as to compare such plants with those operating in the Republic of Serbia. The CO2 emission was analysed in relation to the installed capacity, as well as compared to the energy produced and supplied to the system. By analysing the obtained values of the ratio of emissions to the number of inhabitants, the area of the territory, production and consumption of electricity, as well as to the GDP, it is noticeable that a much larger amount of CO2 is generated on the territory of the Republic of Serbia to achieve a similar energy, industrial and economic effect compared to the EU-27. By researching location data of coal burning in the production of electricity in the Republic of Serbia revealed the existence of a large difference in the amount of CO2 emissions, which is a consequence of the composition of the coal used and the combustion modes in thermal power plants.

Natural gas consists of a mixture of hydrocarbons with the largest share of methane, and non-hydrocarbon impure components such as N2, CO2 and H2S. In order to fulfill the gas market requirements, it is necessary to separate these unwanted components from the natural gas stream. There are several available technologies for the separation of CO2 from natural gas, such as: polymeric membranes, cryogenic distillation, absorption and adsorption. In this paper is presented the mechanism of CO2 separation using membrane technology, as well as the process of separation CO2 depending on the number of membranes in the system for a typical gas reservoir in Serbia.