Innovative Isotopes Tracking: A Cost-Effective Approach for Monitoring of Injected CO2 Flood Advancement in Oil Reservoirs

Abstract Assessing sweep efficiency and recognizing the point of breakthrough are critical for evaluating an Enhanced Oil Recovery (EOR) effort employing miscible CO2 Gas injection. This study aimed to employ CO2 carbon isotope composition and molar concentration to monitor sweep efficiency and breakthrough in production wells of an ADNOC Onshore field to optimize the project, such as adjusting injector and future production well placements. The integration of CO2 molar concentration data along with carbon and oxygen isotope readings, helped to assess the influence of CO2 Injection EOR. The project relied on the premise that using a distinct isotopic signature for injected CO2-deriving from a steel mill and notably lighter in comparison to CO2 associated with the oil-would aid in determining sweep efficiency and breakthrough levels. CO2 is injected through specific horizontal injectors in the north area of the field. Initial values of oil-associated CO2 carbon and oxygen isotope served as a benchmark to evaluate the progress of sweep efficiency and breakthrough. Frequently, compositions and isotopic values of injected CO2 are recorded. Subsequent periodic analyses of these components’ composition and isotopes in oil and water producing wells indicate the degree of breakthrough. Findings from CO2 molar and isotope measurements in both injector and producer wells demonstrate that injected CO2 tends to breakthrough preferentially in certain regions, signifying a varied reservoir quality across the field with superior reservoir quality, and CO2 injection distribution experiencing faster breakthrough. These compositional and isotopic metrics have proven sensitive enough to detect changes in producer wells. It is intriguing to note that the CO2 δ13C isotope signals a breakthrough sooner than the CO2 molar concentration. Data also indicates that CO2 WAG is a much more efficient EOR process compared with continues CO2 injection.