Saber Mohammadi, Carl Fredrik Berg, Heiner Schümann
Subsea water separation and treatment (SWST) technologies represent a key advancement in offshore oil and gas operations by enabling the separation, treatment, and reinjection or discharge of produced water on the seabed. This work provides a comprehensive, offshore-oriented assessment of SWST, emphasizing both technical innovations and strategic implications. By eliminating energy-intensive lifting to topside facilities, SWST significantly reduces CO 2 and methane emissions, optimizes flow assurance, and enhances production efficiency. In mature fields, it mitigates the rapid production decline caused by high water-cuts, offering a strategic advantage in late-life reservoir management. Here, a detailed comparative evaluation of major SWST technologies─including gravity-based separators, hydrocyclones, gas flotation units, membrane systems, and compact separators─was presented, incorporating lessons learned from global field deployments (e.g., Troll, Tordis, Pazflor, and Perdido). Case studies show that SWST can achieve up to 38% lifetime energy savings and more than 80% reduction in water volumes requiring topside handling. This work situates SWST within broader industry priorities, including net-zero operations, carbon management, and digital integration. Looking ahead, SWST will increasingly rely on AI-driven control, digital diagnostics, and advanced materials compatible with high-pressure and high-temperature (HPHT) environments. Through compatibility with all-electric subsea systems and alignment with emissions regulations, SWST supports a strategic shift toward low-emission, digitally autonomous, and cost-effective offshore operations.