Recently, Enhanced Oil Recovery (EOR) application in offshore oil fields is receiving significant attention. The size of targeted offshore oil fields is generally large, because their Original-Oil-In-Place (OOIP) should be sufficiently large to overcome the high cost of offshore oil field development. Therefore, the amount of recoverable oil using EOR may be enormous. The risks of applying EOR are lower than the exploration for deep-water oil, because EOR except for thermal EOR is usually applied to the already producing oil fields. Because of the above reasons, offshore EOR application has been considered as a highly acceptable option. However, application conditions for offshore oil fields are more complex than onshore oil fields due to the unique parameters present in offshore fields. Therefore, successful EOR application in an offshore oil field requires screening criteria that are different from the conventional onshore screening criteria. A comprehensive database for onshore applications of EOR processes, together with a limited offshore EOR application database, are analyzed in this paper; and the important parameters for successful offshore application are incorporated into the new EOR screening criteria.
In this paper, screening criteria for highly acceptable EOR processes in offshore fields including hydrocarbon (HC) gas miscible, CO2 miscible and polymer are presented. Gas EOR using produced hydrocarbon gas has high potential for light oil recovery in offshore fields because of high availability of injectant and its reduced handling cost. For medium oil and even heavier oil recovery, polymer process is highly acceptable because it is a well proven technology by the earlier onshore and even offshore applications. CO2 miscible process has been proven as a successful technology worldwide, mainly in onshore fields. In many cases, minimum miscibility pressure of CO2 is lower than hydrocarbon gas; hence, the CO2 miscible process has a wider range of field candidates. In view of the current active interests in seeking synergy between CO2 storage and the high efficiency of the CO2-based oil recovery, this process has high potential for offshore EOR application if CO2 can be available economically.
Suggested screening criteria for these EOR processes comprise quantitative boundary and qualitative considerations. Quantitative screening criteria are mostly based on quantifiable data including oil and reservoir properties. Most screening criteria suggested in this paper are generally similar to those previously suggested. Due to the recent significant polymer development efforts and their active applications, however, the difference for oil viscosity criteria in the polymer process is relatively large. There is a high potential for further criteria extension in the polymer process. Qualitative screening considerations mainly focuses on operational issues present in offshore including limited space on the platform, limited disposal option, injectant availability and flow assurance matters (mainly hydrate formation and difficulty in emulsion separation). These considerations are very hard to be quantified and highly depend on operational limitation of each EOR process in specific fields. However, it is found that economical availability of injectant is most critical parameter in early stage of EOR screening.