Subsea Separation made easy! What are the business benefit for subsea separation?
Subsea separation has been in the making for the last 20 years after the initial pilot installations on Petrobras Marlim, Equinor Tordis and Troll Pilot, but not really been a viable option for field developers, before now. These initial subsea pilot installations where attempted marinating topside technologies for subsea application leading to oversized and overcomplicated system installations. The arrival of the Dual Pipe Separation (DPS) system from Seabed Separation AS changes all this and in addition their subsea separation system is retrievable to surface.
Background and introduction
Seabed Separation AS has developed a novel approach to the separation of hydrocarbon liquids, where we ensure excellent qualities of all phases – gas, oil and water. Our full scale high pressure testing with Equinor in Porsgrunn, Norway, with live crude from the Troll field have shown excellent liquid qualities; Oil in water <15 ppm consistently and Water in oil BSW < 0,5 %.
DNVGL have been our independent 3rd party verification partner through the entire system qualification process. We are now at Technology Readiness Level (TRL) 4, and thus ready to go offshore for field installation.
Our application sweet spot is for subsea applications due to the large IOR potential we can generate, but we are also pursuing opportunities to modify the system for topside and land application together with clients.
By removing the water close to the source and thus avoid bringing it up to the surface, we enable IOR and accelerated production through two main contributors;
• Increased Oil Recovery – We remove the water at the seabed and thus reduce the back pressure on the reservoir resulting in improved production
• Accelerated Production – We remove the water from the existing subsea infrastructure and thus we enable faster start-up of new wells and fields that can exploit the new capacity, and production testing without production losses and with increased allocation accuracy
In addition, we will significantly reduce the CO2 footprint of a subsea development, mainly due to reduced need for fabrication of new infrastructure and modification of existing, but also because we save the energy from not having to lift the produced water to the surface.
Our separation solution – how does it work?
Our overall separation system comprises three main sub-systems;
- The Gas Harp – The hydrocarbons arrive at the Gas Harp, where the gas is separated from the liquid stream and potential slugs are managed. The Gas Harp is a guarantee for stable flow of liquids though to the next stage
- Conditioning pipe section – The liquids are forced through a set of conditioning pipes where we have set up a liquid lock and a water lock, and the liquid stream will stabilise into two separate phases going through this sub-system
- The Dual Pipe Separator (DPS) – The DPS is a set of inclined separator pipes where the liquid flow is slowed down through an expanding inner pipe section. The oil is then routed through perforations in the inner pipe and into the oil phase in the DPS, and the water is routed into the water phase in the DPS. The water is the decanted off the bottom of the DPS whilst the oil flows freely into an export pipeline, where the oil can be spiked back with the gas that was removed in the Gas Harp upstream.
Our solution can be integrated together with other subsea processing system to ensure the operators gain the extra performance compared to standard industry solution available today.
Production testing functionality
We have recently patented the test functionality we can provide with our DPS system. This is achieved by designing in a valve arrangement to enable one (or more) of the DPS units to become a separate test system, and at the same time maintain the overall field production. This not only reducing the production losses during production testing, but it also improves the accuracy of the testing since it is done close to the wellhead and under a more representative operational regime.
Our separation system has been technically qualified to TRL4/5 for subsea application by DNVGL, and we are currently conducting a series of development studies for a number of operators on the NCS, with the aim to qualify as a financially viable and thus a real development option for subsea fields (brownfield and greenfield).
The system set-up is such that the design is similar in most applications, and the system is therefore highly scalable, both in design and during operation;
- Capacity – every DPS pipe unit can handle 15 000 BPD of liquids. You just add a number of DPS units to match your required capacity – e.g. 60 000 BPD required 4 DPS pipe units (see below)
- Water depth – the design is based on pipe class rather than vessel, so the unit will scale much better, both on wall thickness, overall weight and cost. Application at extreme water depths and pressure regimes is therefore not an issue for the DPS
- Co-mingling of various well and reservoir streams – this is not an issue in the DPS compared to a gravity based separator.
We are in close collaboration and discussions with several subsea integrators to see how our system can be integrated into their overall subsea offering, and thus improve the overall total cost of ownership for the end customers, the operating companies.
Business Case example
Working with the operators we get a unique opportunity to better understand how they calculate their business cases before taking the opportunities on to the next decision gate process. The typical benefits our DPS System bring to the table is as per the case example below.
The overall benefit for this subsea separation and testing system for a 40 000 bbls/day field would be in the order of 15, 5 % or 102,8 MUSD for the 1st year.