Abstract
This research investigated the miscible gas injection for Enhanced Oil Recovery (EOR) in a carbonate reservoir in Kazakhstan. Five mixtures, each containing varying percentages of methane, ethane, propane, carbon dioxide, and nitrogen, were studied to determine their Minimum Miscibility Pressure (MMP) values through PVTi and slim tube tests. Among them, mixtures #2 (CH4 and C3H8) and #4 (pure CO2) exhibited the best performance, with mixture #2 achieving the lowest MMP value, while CO2 showed the best miscibility at lower pressures and the option of potential carbon sequestration. Most of the results were supported by slim tube experiments, compositional simulations (Eclipse), and phase behavior analysis using Gibbs triangles and ternary diagrams. The study contributed to the EOR research by incorporating multi-component gas evaluation and advanced phase visualization, thereby filling the gaps by previous works focused on single gases. The key findings emphasized the need to balance the technical efficiency, environmental sustainability, and operational viability in gas selection, providing critical insights for optimizing the EOR strategies in similar reservoirs.