Subsea bulk oil-water separation (Annual Report 2020-2021)

“To Make more efficient subsea bulk oil-water separation by improving separation design, understanding multiphase flow fundamentals and preventing undesired phenomena during separation process.”: 

Green shift impact: Subsea separation of produced water increases the recovery rates for brown field installations. Removing produced water on the seabed increases production rates, removes topside produced water bottlenecks and enables better utilization of existing topside facilities.             

1.     Background

Management of produced water is one of the most important issues in production from mature oil fields. Subsea separation can be used to address this problem and brings additional benefits. It is therefore important to develop cost-effective subsea separator technologies, making the business case for subsea separation more attractive. The benefits of subsea separation can be outlined as three separate aspects: Subsea separation of produced water can reduce the load on topside capacity and facilities, allowing for prolonged, increased production and avoiding bottlenecking. Subsea water separation also reduces the fluid pressure losses from the seabed to the topside, thus enabling more energy-efficient production. Finally, separation close to the well means less mixing and agitation, reducing dispersion formation and allowing for better separation.

This project is a continuation of previous project 2.9, conducted by Håvard Skjefstad. Håvard developed a concept for bulk oil-water separation in pipe, tested it for several operational conditions and studied fundamental phenomena in oil-water separation in pipe.

2.     Research activities and deliverables

During the last year we have worked on how to mimic the separation characteristics of real crudes-water mixtures by adding small amounts of crude to a model oil (Exxsol D60). We had technical meetings with experts from Total and Sintef to get advice and design our experimental procedures. Water-oil separation bottle tests were performed on the crude oil at high temperature and for several spiking concentrations at ambient temperature. Our results indicate that a spiking concentration of 400 ppm has similar separation characteristics than the original crude-water mixture.  

We have also started to run some preliminary tests on the separator prototype.

3.     Final Impact

Results of this research can be readily used by the industry to manufacture a new oil-water separator based on our technology or to improve the design of existing oil-water separators on the market. Ultimately, we hope to contribute to improve and facilitate the management of produced water and optimize oil and gas production.

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