Injecting CO₂ for enhanced oil recovery and storage (CCUS-EOR) in offshore reservoirs presents a promising solution to mitigate climate change and reduce carbon emissions. Given the high operational costs associated with offshore projects, water-alternating-gas (WAG) injection emerges as an effective strategy to lower CO₂ usage costs while enhancing oil recovery, albeit at the potential expense of reduced CO₂ storage. This study employs numerical simulations to evaluate the effects of different WAG ratios (0:1, 1:1, 2:1) on oil recovery and CO₂ storage. Additionally, the WAG ratio is analyzed in conjunction with economic factors such as oil price, CO₂ price, and carbon trading market price using the Box-Behnken response surface method (RSM) in Design Expert. The optimal WAG ratio is determined to maximize oil recovery, CO₂ storage, and net present value (NPV). Results indicate that increasing the WAG ratio from 0 to 1 improves oil recovery by 8%, though CO₂ storage decreases significantly. When the WAG ratio increases from 1 to 2, oil recovery declines by 1%, with a negligible reduction in CO₂ storage. Single-factor analysis shows that NPV is most strongly influenced by oil price, followed by WAG ratio, CO₂ price, and carbon market price. At a carbon price of 50 RMB/ton and an oil price of 500 RMB/barrel, the optimal WAG ratio is identified as 0.5, offering valuable guidance for maximizing both oil recovery and CO2 storage in offshore CCUS projects.
 

CCUS, CO2-EOR, WAG ratio optimization, Box-Behnken design, techno-economic analysis