Abstract
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 CO2 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.