Optimization of EOR-CCS core flooding experiments using Taguchi DOE and regression analysis

Enhanced Oil Recovery (EOR), when aligned with Carbon Capture and Storage (CCS) objectives, increases oil production while addressing climate concerns through geological CO₂ storage. Water Alternating-Gas (WAG) is considered an effective enhanced oil recovery (EOR) technique in oil mobilizing and CO 2 storage. The study focuses on identifying variable settings for the optimum trade-off between recovery and storage in the case of immiscible WAG-EOR. The Taguchi-based coreflooding experimental design was conducted to investigate the impact of variable operating parameters on both oil recovery and CO₂ storage efficiency, facilitating a structured analysis of key variables with fewer experimental runs. The experimental design included four control variables: the injector rate, pressure, WAG ratio, and brine salinity, each tested at three levels: 0.15–0.50 mL/min, 650–850 psi, 1:1–2:1, and 20,000–30,000 ppm, respectively. The regression analysis, Signal-to-Noise (S/N) ratios, and an Overall Performance Index (OPI) were employed to evaluate oil recovery and CO₂ storage, both as separate responses and in combination. The findings outlined a clear trade-off between the two objectives: higher injection rates increased oil recovery, whereas lower rates favored CO₂ storage. The WAG ratio had a limited effect on oil recovery but consistently enhanced CO₂ storage, particularly at a 1:2 ratio. Salinity demonstrated a secondary yet positive influence, improving the overall performance, while pressure showed the least noticeable impact. Statistical ranking identified the injection rate as the most influential parameter, followed by salinity, WAG ratio, and pressure. Both the injection rate and WAG ratio were found to have a strong impact on responses. According to the OPI-based optimization results, the most favorable operating conditions were an injection rate of 0.15 mL/min, pressure of 850 psi, salinity of 30,000 ppm, and a WAG ratio of 1:2. In addition, predictive regression models forecasted oil recovery and CO₂ storage across different operating conditions, offering valuable guidance for future experiments and field applications. Overall, the findings highlight the significance of injection rate and WAG ratio in determining immiscible WAG performance, offering practical insights for enhancing EOR-CCS optimization.