Subsea Separation: The Way to Go for Increasing Water Production and NPV Optimization
Authors: Capela Moraes Carlos Alberto , Shaiek Sadia 
Published: April 2019

There are still few subsea water removal systems, but looking at deeper offshore scenario the conventional topside water removal and treatment configuration is not acceptable, either from the economic or technical point of view. Increasing water cuts penalizes field revenue outcome along its productive life. The paper will demonstrate on several business cases that the best way to reduce these penalties is to get rid of water as soon as possible with subsea solutions.

We start discussing the economics of a subsea primary separation station. In this focus, some examples based on hypothetical production curves show the gains in terms of increased total volume of recoverable oil that can be obtained with the approach of using a subsea water removal system, compared to conventional topside produced water management system. Some sensitivity on the influence of the parameter hypothetical values used in the analysis is also presented and they show that this trend is indisputable. It can also be concluded that these advantages increase with increasing water depth.

The main conclusion of the paper is that the traditional all topside water management system, although being one business case for a field development, it is not the best configuration and it leads to lower net present value (NPV) for the whole project, since some oil is left behind due to increasing water cuts, and subsea water removal improves NPV of the project. Then it is discussed the question on why, being this the case, not much Operators consider this alternative configuration for production development. On this focus, the paper also discusses the main concerns regarding a subsea processing installation, from the point of view of operation, maintenance and reliability – justifiable concerns that have to be addressed by subsea system suppliers. Finally, it is presented the optimized concept of configuration for subsea water removal, treatment and re-injection system, whose first version was already object of an OTC presentation in 2015 (OTC-25934-MS), and since then it has been further developed and optimized through Joint Industry Projects with Operators. It is shown that this system is conceptually designed in order to increase robustness regarding a wide diversity of field conditions and production issues, requiring low maintenance. This analysis is made comparing SpoolSep concept with the alternative solutions already installed worldwide.

No direct discussion on the losses implied by adopting a conservative "all topside approach" for green field development project (or even a revamp for a brown field) is easily found on literature. This paper addresses these losses and highlights the benefits of taking subsea water removal into account when studying a production development project either during green fields development planning or brown fields revamping planning. Of course, these benefits should be balanced against any sound concerns on subsea processing. Subsea Equipment and System Suppliers, on the other hand, have to focus on simplicity and robustness, aiming to offer to the Operators cost effective subsea processing solutions.