Our subsea storage unit (SSU) technology increases the value for field developments and reduces the need for topside modifications by storing water on the seabed. This storage system is energy efficient with a low environmental footprint, and it is developed based on experience from existing storage solutions to be a competitive alternative for future field developments requiring temporary storage.
Subsea produced water treatment technology is maturing, and large subsea water tanks are under development as a last separation stage to achieve high water cleanliness and robustness. The Produced Water Treatment Tank (PWTT) system is designed to achieve a buffer volume to both smooth out variation in the outlet water quality and achieve the required water quality of dispersed oil-in-water at 30 ppm or lower. The treated water could either be re-injected into the reservoir or discharged to sea.
The system is designed with high residence time (24 hours) for settling of solid particles and flotation of oil droplets by gravimetric separation to maximize the regularity of operation. Finding the best treatment solution for produced water technology is important, and there is a need to develop a more efficient and suitable system to achieve higher water cleanliness. The technology aims to eliminate surface facilities associated with water treatment to reduce overall development costs.
The PWTT system consists of a sand accumulator and a PWTT unit. The PWTT consists of an SSU structure that employs the concept of a membrane protected by a dome for storage on the seafloor. It can be placed at any water depth and is adjustable in size depending on operator needs during the development and expansion of the field. The seawater outside the dome surrounds the membrane through free-flow seawater openings in the dome, such that the hydrostatic pressure acts directly on the stored fluid. A subsea sand accumulator included in the system is designed to remove sand from the produced water stream before the sand can cause problems with downstream equipment.