Complete subsea separation

Short summary of the project

Water treatment is an essential part of emission reduction, de-bottlenecking, and exploiting marginal fields.

Previous work on SUBPRO has investigated various separation concepts, but so far typically in isolation (e.g., a hydrocylone or a novel bulk separator), but not the larger value chain.

This project will expand the scope to investigate a complete subsea separation system, with a focus on produced water. The ultimate goal is to be able to remove all produced water subsea, with compact devices, and have the produced water be sufficiently clean to inject or dispose to sea, subsea.

Objectives

• Perform a feasibility study of merging existing separation laboratory facilities at NTNU
• Choose components to be used in a complete subsea separation system, including o Bulk separation o Gas handling o Water treatment o Injection/disposal solution
• Combine existing laboratory facilities at NTNU
• Develop methods to optimize and control the combined water treatment facility
• Test the methods in the lab

Detailed project 

Water treatment and subsea separation are crucial components of the future of oil and gas extraction. An enormous amount of water is produced from typical wells, and the removal and treatment of it is both a major expense and a major source of emissions.

SFI SUBPRO has dedicated significant research into investigating this problem, both on the bulk separation side and the water treatment side. This project aims to develop a complete subsea separation concept, building upon and expanding this previous knowledge. The end goal is a complete subsea separation system concept, where the water stream is pure enough to discharge or re-inject for disposal or pressure support.

This work will expand upon SUBPRO projects Automatic control of subsea separation, Compact separation concepts, and Subsea bulk oil-water separation. The former investigated hydrocyclones for water treatment, and the latter a novel pipe separator concept (the Multiple Parallel Pipe Separator, MPPS) for bulk oil/water separation. Two separate laboratory facilities were constructed and used for this purpose. The work resulted in multiple PhD theses and publications.

Results from previous SUBPRO projects show that significant performance gains can be made relatively simple control structures (e.g., a supervisory layer on top of traditional PDR control for hydrocyclones [1] and PI control based on DP measurements for the MPPS [2]). The work also indicates that further significant performance increases can be realized by a combined, overall, and optimal control structure that views the system holistically rather than discretely.

A chief aim of this project is to merge the two laboratories and create a complete laboratory setup. A pre-study is being conducted, and a possible P&ID is shown in Figure 1. Most of the existing equipment can be re-used or re-purposed, and the costs of the rebuilding can be covered by previously allocated funding.

With the new facility, and existing models and simulation tools, it will be possible to study the behavior of a complete subsea separation facility concept. In this project, we will study the behavior of this system, and design an optimal control strategy. This will allow for optimal behavior of the entire system, with the controllers working in tandem rather than at cross purposes to ensure that the maximum amount of water is extracted from the fluid stream while maintaining sufficient purity of the water output for re-injection or discharge to sea.

This project and proposed Project 1.1 Decision-support methods for holistic water management (water value chain) complement each other, and significant collaboration should be expected. It may also be possible to test results developed in SUPRO for micro-scale behavior of oil in water on macro scale in the new, expanded laboratory, allowing for cross-collaboration with proposed Project 2.3 Improving detection of partitioning of production chemicals and crude oil components into produced water. In the future, it may also be possible to add a floatation system in addition to or in replacement to the hydrocyclones in the laboratory, also allowing for a collaboration with proposed Project 2.4 Gas Flotation for Subsea Produced Water Treatment II. Another future expansion possibility is to add gas handling to the facility.

Innovation potential

If successful, this project will help improve subsea separation, reduce emissions associated with produced water, increase production through water injection, and lower costs associated with transporting produced water topside.