Low-Purity CO₂ utilization for sustainable enhanced oil recovery: A comparative assessment of CO₂-WAG and Carbonated Water Injection Techniques

The sustainable exploitation of offshore hydrocarbon reserves requires innovative integration of carbon utilization technologies with enhanced oil recovery (EOR) processes. This study evaluates and compares the technical, economic, and environmental viability of two CO₂-based EOR techniques—Carbonated Water Injection (CWI) and Immiscible CO₂ Water Alternating Gas (WAG) injection—using low-purity CO₂ streams (20%, 50%, and 70%) sourced from flue gas on offshore Floating Production Storage and Offloading (FPSO) units. Leveraging Aspen HYSYS for surface facility modeling and CMG for reservoir and core-scale simulations, the Norne field E-Segment was used as a representative offshore case study. Simulation results demonstrate that oil recovery efficiency increases with higher CO₂ purity and injection rates for both EOR methods. CO₂-WAG achieved the highest recovery (58.2% of Original Oil in Place) under 70% CO₂ purity and optimal injection parameters, while CWI yielded the best economic outcome with a net present value (NPV) of $830 million under 50% CO₂ purity. Additionally, a novel hybrid method—Carbonated Water Alternating Gas (CWAG)—was introduced, outperforming both CWI and CO₂-WAG in preliminary trials with a recovery factor exceeding 70% OOIP. Environmental benefits were assessed using the Time-Adjusted Value of Carbon Sequestration (TVCS) framework, which revealed significant CO₂ sequestration potential across all scenarios. The CO₂-WAG scenario with highest recovery sequestered over 0.3 million tons of CO₂, providing measurable emissions reductions. This work offers a scalable framework for integrating carbon capture and reuse into offshore operations, advancing both energy efficiency and environmental responsibility. The findings position low-purity CO₂-based EOR not only as a viable recovery method but also as a transitional technology supporting decarbonized offshore oil production in alignment with global sustainability goals.