Produced-Water-Treating Systems: Comparison of North Sea and Deepwater Gulf of Mexico

In general, water-treatment systems in the North Sea differ from those in the deepwater Gulf of Mexico (GOM). The two most apparent differences are the extensive use of hydrocyclones in the North Sea, and the use of large, multistage horizontal flotation units in the deepwater GOM. Deepwater-GOM platforms use hydrocyclones, but not nearly to the extent that they are used in typical North Sea platforms. Typically in the North Sea, if flotation is used at all, it is a vertical compact unit. The objective of this paper is to provide an understanding of the reasons for these differences. In this paper, field data and modeling results are presented to explain these differences. The models accurately correlate the measured drop size and oil-in-water concentration observed in the two regions. In addition, the modeling tools are used to answer hypothetical “what if” questions. This allows isolation of individual variables such as fluid temperature, shear, separator residence time, and fluid density. Thus, the modeling provides a detailed understanding of the relative importance of these variables. It also provides a direct comparison of the performance of North Sea vs. GOM process configurations. While the qualitative conclusions are well-known (i.e., deepwater separation systems are designed to minimize weight and space), the detailed understanding provided here provides insight into the design of water-treatment systems in general. It also emphasizes, in a quantitative way, the importance of carrying out effective water treatment early in the process and the necessary use of large end-of-pipe equipment when this is not possible.