This paper presents a full scale subsea separation installation in the seabed, which enables separation of oil, sand and water on the sea floor, water treatment in the sea floor and in-situ injection of low sulfate and low salinity water for IOR (increased oil recovery) in the Bohai Bay oilfield. Contrary to traditional topside approaches, the seabed separation system separates water from oil and sand and cleans water in the seafloor. The system is mainly composed of separator and de-sander vessel, water treatment components, boosting components, multi-phase and water injection pumps, leakage detectors, protection components, and pipeline manifold. Production stream is circulated into the system and then water, sand, and oil are separated. Oil is pumped into the platform through multi-phase pumps. Sand is separated and injected into the dump reservoir. Water is cleaned through the membranes in the water treatment system and rejected directly into the subsea injection wells. Water quality report of the cleaned water in seabed indicates considerable low sulfate level, low chloride level and low salinity water. The membranes in the water treatment systems last a considerable long time without any degradation issues in performance. The system treats water subsea and lowers well head pressure, which increases oil production and oil recovery. The benefits also include reduction of weight and area topside, increased water separation capacity compared with conventional platform space limitations, and elimination of long injection lines and water injectors from platform. The subsea separation installation can handle up to 700 kg sand per month, which greatly boosts and extends the current IOR project. This system separates and treats water in-situ in the seabed in the Bohai Bay oilfield. This technique enables a flexible and cost effective solution for subsea IOR projects.
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