Water injection remains the most widely applied method for maintaining reservoir pressure and improving oil recovery offshore. However, conventional topside water-treatment systems face performance limitations because of space, weight, reliability, chemical-handling, and operational issues. Recent advancements in subsea seawater treatment have enabled the development of fully integrated subsea sulfate-removal systems for disinfection, ultrafiltration (UF) technology for solids removal, and nanomembrane (NM) technology for sulfate removal. This paper discusses waterflooding and field-development implications of subsea seawater treatment for improved oil recovery.
Introduction
Experience from large deepwater carbonate fields shows realized water-injection (WI) rates fluctuating between 40 and 80% of planned volumes during early and middle field life, primarily for the following reasons:
- Limited topside space and weight margin for debottlenecking or expansion
- Filtration- and membrane-system fouling and frequent backwash disruptions
- Reliability issues in high-pressure pumps and drive systems
- Chemical handling and health, safety, and environment constraints for oxygen scavengers and other chemicals
- Operational conflicts between production and injection priorities
- Shutdown requirements for maintenance and modification campaigns
Subsea seawater treatment addresses these challenges by moving the injection-water-preparation process from the platform to the seabed.
