Abstract: Offshore hydrocarbon (e.g. oil) production units that produce considerable contaminated water (produced water), are able to repeatedly dispose of the produced water so each production unit requires only a moderate-sized tank to hold the produced water, and most of the tank storage capacity of the production unit can store hydrocarbons. A mobile water-treatment plant is provided on a converted tanker that sails from one production unit to another one, transferring produced water from the oil production units and separating out contaminants as by settling, to leave clean water that can be dumped into the sea and contaminants that cannot be dumped into the sea. The mobile plant occasionally sails to an on-shore facility where it is allowed to dump contaminants.

Abstract: Offshore hydrocarbon (e.g. oil) production units that produce considerable contaminated water (produced water), are able to repeatedly dispose of the produced water so each production unit requires only a moderate-sized tank to hold the produced water, and most of the tank storage capacity of the production unit can store hydrocarbons. A mobile water-treatment plant is provided on a converted tanker that sails from one production unit to another one, transferring produced water from the oil production units and separating out contaminants as by settling, to leave clean water that can be dumped into the sea and contaminants that cannot be dumped into the sea. The mobile plant occasionally sails to an on-shore facility where it is allowed to dump contaminants.