North Sea platform produced water systems were designed up to 10 years ago utilising plant largely developed for other industries. Generally the systems were designed without adequate knowledge of the produced water itself or the flow-rates. Many fields are now experiencing injection water break-through and consequently far greater flow rates than envisaged. By reference to Britoil's Thistle and Beatrice platforms, this paper describes some of the short-comings of systems, the resultant modifications and extensions, and performance data before and after modifications.
By applying basic process principles proven by both scale model work of fluid flow patterns and also offshore trials, the existing equipment was drastically modified. Together with many 'minor' changes, system performance has been raised by 25% to the required levels. The minor performance has been raised by 25% to the required levels. The minor changes were often of a relatively detailed nature and emerged from experience of corrosion, scale deposits, process transients, and start-up and shut-down phenomena.
The paper addresses the fundamentals of produced water treatment technology and presents operating data from:-
Laboratory model testing and offshore pilot trials of cartridge coalescers.
Modified tilted plate assemblies.
Induced and dissolved gas processes.
System interactions and practical operating problems.
This work will be relevant to some extent to all produced water systems as:-
Improvements in the reliability and understanding of the, clean-up processes are necessary to obtain the plant performance, to satisfy reservoir requirements.
Testing totally new plant and modified equipment is essential to enable improved equipment designs to be brought forward.
Britoil currently operates two producing oil fields in the North Sea, Thistle and Beatrice. The produced waters and their treatment problems are quite different whilst the problems are similar.