<p>Injection of CO₂ into depleted hydrocarbon reservoirs is an innovative and reliable technique for enhancing oil recovery by restoring formation pressure. It also provides profitable and effective solutions for reducing greenhouse gas emissions by storing CO₂ in geological formations. Tracking and monitoring the injected CO₂ instills confidence in its long-term safety and management. In this research, seismic monitoring of CO₂ injection into depleted hydrocarbon reservoirs was simulated and subsequently validated experimentally using core samples. For this purpose, the rock physics method was employed to model the host rock (a mixture of clay, calcite, and quartz) containing fluids (oil and brine), which are common in conventional hydrocarbon reservoirs. Then, CO₂ was injected into the host rock at in-situ pressure and temperature, initially saturated with oil and gas (depleted reservoir). Next, physical and seismic parameters (e.g., density, P- and S-wave velocities, Lamé parameters) were extracted from various CO₂ flooding scenarios. The results obtained were used as decision diagrams and curves to monitor CO₂ sequestration. The findings indicated that with incremental injection into reservoir rock, the presence of CO₂ can be detected based on elastic parameters using the proposed diagrams with suitable accuracy. Additionally, a workflow was developed to obtain Amplitude Versus Offset and Extended Elastic Impedance responses for monitoring CO₂ sequestration through seismic inversion data. Consequently, the proposed methodology was validated using ultrasonic measurements on a core sample from a real case study. The research findings are summarized in the applicability of elastic parameters for detecting initial fluid type, CO₂ saturation level, and host rock lithology during the CO₂ injection process. Furthermore, a novel chart and diagram were introduced to aid in monitoring CO₂ injection in depleted hydrocarbon reservoirs. The proposed methodology and results may face limitations and uncertainties. To address this, the impact of anisotropy, pore type, and fluid type on seismic monitoring of CO₂ injection was discussed in detail.</p>