This study investigates the implications of Hydrogen Sulphide (H2S) impurities on Carbon Capture, Utilization, and Storage (CCUS) operations in carbonate reservoirs, with a specific focus on Field X in offshore Malaysia. The research examines the interaction between Carbon Dioxide (CO2) and H2S under reservoir conditions, aiming to better understand their impact on reservoir formation and geochemical interactions. The goal is to gain insights into storage design and predictive capabilities when dealing with impurities. Advanced analytical techniques, including ICP, RCA, XRD, and SEM-EDX, were used to analyze the mineral composition and physical characteristics of core samples from Field X. Experimental tests involved exposing these samples to CO2 with H2S dissolved in brine and aging them under reservoir conditions. The research findings indicate that the presence of H2S in CO2-dissolved brine leads to a reduced rate of dissolution of carbonate rock samples, potentially offering benefits for CCUS storage. These insights into CO2-H2S interactions in carbonate reservoirs can be valuable for optimizing CCUS storage strategies, ensuring long-term stability and security, particularly in offshore Malaysia. Copyright © 2024, International Petroleum Technology Conference.