State-of-the-Art for treatment and disposal of offshore production wastes was established through a review of the regulations, practices and experience in the Gulf of Mexico, the California offshore, Cook Inlet (Alaska) and the North Sea.
Performance and cost of treatment and disposal methods for produced water, ballast and displacement water, and drilling wastes will be reviewed.
In the past 30 years the offshore production industry has developed the technology to solve problems that were once of concern- the discharge of insoluble oil and drilling wastes. Nevertheless, there appears to be continuing concern regarding soluble oil (in particular aromatics) and drill cuttings (when using oil base drilling fluids).
In establishing "State-of-the-Art" we were concerned about establishing which processes were "Proven" and which were "Traditional". In our use of the terminology "Proven Process" means a process that has been used at least once and has operated successfully for at least one or two years. A "Traditional Process" is a proven process that is widely used in the industry. When selecting a waste control technology the risk of failure is controlled by ensuring that the process selected is either a proven process; or a traditional process where the knowledge of how to design a unit is widely available and the process has been successfully used on widely varying waste stream compositions and rates.
This study was based on information drawn from industry and government reports, scientific literature, equipment manufacturers and personal interviews with senior staff from the oil industry and regulatory agencies.
The following treatment processes can be used to separate insoluble oil from water (Brown & Root 1974):
Skim piles: large diameter pipes containing baffled sections and an outlet at the bottom. They are intermittent flow devices. During the period of no flw, oilwill rise to the quiescent areas below the underside of the inclined baffle plates where it coalesces (see Figure 1). Due to the difference in specific gravity, oil is forced upward through oil risers from baffle to baffle. Oil is collected above the flowing stream and removed by either a submerged blowcase or pump. These devices operate intermittently and will move the separated liquid to a skimming vessel for further treatment (Engineering Specialties Inc. 1981) Factors that affect the operation of most gravity separation devices would also affect operation of the skim pile.
Earthen Pits: used for oil/water separation only when the produced fluid is taken to shore for treatment. They are used when high retention time can be provided and thus when space is not limited (see Figure 2).
Tanks: used primarily to provide surge volume and primary separation of oil and water before treatment in a higher performance system such as the processes described below (see Figure 3).
Flotation units: gas under pressure is dissolved in the water/oil mixture which is subsequently de-pressured resulting in the release of minute gas bubbles. The gas bubbles float oil to the surface where it is separated by being skimmed off the surface.
