Repurposing a Mature Fluvial Sandstone Reservoir in Colombia for Miscible CO ₂ -EOR and Storage: Scheme Optimization and Efficiency–Retention Trade-Offs

This study evaluates CO2-enhanced oil recovery with associated storage in a mature fluvial sandstone reservoir in Colombia under ongoing waterflood. A compositional sector model was built in tNavigator using a Peng–Robinson equation of state tuned to laboratory data. Minimum miscibility pressure for a flare-gas-derived injectant containing 50.74 mol % CO2 was computed via the multiple-mixing-cell method, confirming miscibility within the operating pressure envelope. Forecasts were used to compare continuous (CGI), alternating (WAG), tapered, and hybrid schemes to improve sweep conformance. Results show that all CO2 strategies increased cumulative oil (Np) and recovery factor (RF) relative to continued waterflood, with incremental RF of 5.6–12.0%. The hybrid CGI-WAG delivered the largest oil uplift, with the preferred variant achieving a CO2 utilization of 72 kg CO2/stb-inc and net storage of 13.3 kt CO2. Tapered WAG maximized storage (23.5 kt CO2) but at higher utilization (268 kg CO2/stb-inc), consistent with a larger water fraction and partial gas placement below the water–oil contact. These outcomes quantify the efficiency–retention trade-off and demonstrate a viable route to repurpose flare gas for recovery and storage. Implementation of CO2-compatible materials, corrosion inhibition, and surveillance is addressed to ensure mechanical integrity.