The most common method to increase oil recovery is to inject treated seawater into a reservoir from topsides, but such platform based processing can be expensive.
A cost-effective alternative to this process is a new technology for seabed-based water injection and treatment (SWIT), which moves treatment and injection of raw seawater to the seabed. The system addresses essential requirements for treatment by including techniques for solids reduction, seawater sterilisation and system sterilisation. A pilot treatment plant was installed on the seabed in July 2009. The unit at 60m depth is remotely controlled, and only external electrical supply is needed.
This paper centres on the control system for this pilot treatment plant. It is, to the author"s knowledge, the first subsea system in the world that has implemented control of sterilisation equipment and particle reduction as well as subsea chemical injection.
In addition, the control and power system for the injection pump that will be part of a full subsea system is introduced. Although it is not part of the pilot, such a high power pump is a key to any subsea treatment system. Lastly, the paper discusses the road ahead, and of particular interest is the plan for verifying water quality and system health.
Injection of processed seawater into a reservoir from topsides is the most common technique for increased oil recovery (IOR). However, such platform based processing can be costly.
A new technology for seabed-based water injection and treatment (SWIT) offers a costeffective alternative for injection (Hallset and Pinchin, 2007); it moves treatment and injection of raw seawater to the seabed, as illustrated in Figure 1. The SWIT system has been designed to address the treatment requirements for seawater that shall be injected into oil reservoirs. Thus, the system comprises techniques for solids reduction, seawater sterilisation and system sterilisation. Its only interface with topsides is a single signal/power cable (Figure 1).
It combines new technologies with existing ones to reduce solids content and provide sterile water to prevent biofilms, microbial induced corrosion (MIC) and reservoir souring. The system contains significant levels of innovation in three areas:
Solids removal- removal of all inorganic solids above 30 microns and an average of approximately 8 microns on remaining particles
Seawater sterilisation- sterilisation by electro-chlorination and hydroxyl radical generation to ensure that completely sterile seawater is delivered to its required destination
All-electric operation- usage of a single electrical cable to provide the relatively low power requirements of electrical sterilisation and control signals.
In general the SWIT technology can give reservoir engineers more flexibility in order to maximise oil recovery via water flood, while significantly reducing costs and timescales for installation. It also can be applied at any stage of a field's lifetime and can be added to, changed or modified at any time without affecting platform infrastructure.
Well Processing AS, an affiliate company of Poseidon Group AS, has been responsible for the development of this method of performing water treatment on the seabed