Treating Produced Water on Deepwater Platforms: Developing Effective Practices Based Upon Lessons Learned

Abstract

Deepwater platforms in the Gulf of Mexico and elsewhere are transitioning from dry oil or low water cut production to higher water cut production. These platforms face unique challenges resulting from water and crude incompatibilities, high salinity, no advance characterization of the water treatment issues, and a lack of space for water treatment equipment. The lessons learned by deepwater operators can provide an experience base upon which future operators can draw to assist them with projects to debottleneck and/or improve produced water treatment on their deepwater platforms and FPSOs. Equipment and practices which have worked well and not worked well for treating produced water on floating platforms are described and the issues pertinent to the deepwater operation of this equipment are identified. The impact of the deepwater operating environment on produced water treatment systems is discussed. Platform motion, high shear across control valves or pumps, production from multiple reservoirs, process recycle streams, and the use of hydrate inhibitors or other chemicals all impact the design of a water treatment process and the operation of water treating equipment. The experiences detailed in this paper are intended to help engineers avoid the process design and equipment selection issues which were problematic for earlier deepwater operations.

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

“…As shown in Fig. 2, and as discussed in Walsh and Frankiewicz (2010), typical deepwater GOM oil/water systems consist of one or two stages of two-phase separation (gas/liquid), followed by a three-phase free-water knockout. Depending on the hydrate-prevention strategy, the fluids may be cooled somewhat by the long…”

“…The effluent (product) from the hydrocyclones is typically routed to a degassing vessel. As discussed in Walsh and Frankiewicz (2010), the degassing vessel in this configuration acts as a dissolved-gas flotation unit in the sense that gas will break out and help separate oil from water in this vessel. The final stage is a compact flotation unit.…”

“…In this section, modeling tools are applied, together with field data, which demonstrate the differences in a quantitative manner. The models have been developed through the use of fundamental principles (Bothamley 2004;Walsh and Frankiewicz 2010;Walsh and Georgie 2012) and have been validated and adjusted to reproduce field data (Khatib 1996;Bothamley 2004;Walsh and Frankiewicz 2010).…”

“…The differences in water-treatment systems between the two regions have been discussed qualitatively both in the companion paper and in the literature (Bothamley 2004;Walsh and Frankiewicz 2010;Walsh and Georgie 2012). As discussed by Bothamley (2004), there are several differences between facilities in the North Sea and those in the deepwater GOM.…”