Fluid treatment tank and a well fluid processing system comprising such a tank

A well fluid processing system, comprising:

• at least one separator vessel for gravitational separation of oil and water contents of well fluid,
• a water treatment unit for de-oiling water withdrawn from the separator vessel,
• a fluid treatment tank comprising at least three compartments, including an oil treatment compartment for receiving oil from a separator vessel of the well fluid processing system so as to allow stabilization and/or final separation and treatment of the oil, a reject treatment compartment for receiving reject fluid from one or more water treatment units of the well fluid processing system so as to allow gravitational separation of heavier and lighter components of the reject fluid, and a water treatment compartment for receiving de-oiled water from one or more water treatment units of the well fluid processing system so as to allow degassing and/or final separation of the water, wherein the oil treatment compartment of the fluid treatment tank is connected to the separator vessel so as to receive oil withdrawn from the separator vessel, the reject treatment compartment of the fluid treatment tank is connected to the water treatment unit so as to receive reject fluid withdrawn from the water treatment unit, and the water treatment compartment of the fluid treatment tank is connected to the water treatment unit so as to receive water de-oiled by the water treatment unit.