Joined up separation

Dutch firms Frames and Royal IHC are taking a step into the deep, quite literally, as well as figuratively. Elaine Maslin sets out the detail.

3D model of the SwirlSep with explanation. Photos from Frames.

Frames, which is used to developing specialist process equipment for topsides and onshore, is working with Royal IHC – with its expertise in the subsea business – to develop a subsea separation package. The two firms are also planning to look at produced water treatment equipment for water reinjection. Both are key challenges for the subsea industry as operators look to process more production on the seabed.

But, the firms are not starting from scratch. The work will build on the SwirlSep, a compact controllable inline separator Frames has been developing since it acquired the exclusive license of Twister SwirlSep – a separation technology able to handle changes in flow rate – by combining SwirlValve, a pressure actuated valve technology, and an inline separator.

SwilSep was developed as a compact solution for debottlenecking brownfield facilities where space is at a premium. But, given changing flow regimes on brownfields, the firm decided the technology needed to do more than handle a limited flow regime.

One of the problems with conventional technologies, says Raoul Liew, R&D engineering, SwirlSep, is that they’re not flexible enough to handle changes in flow regime, flow rates as well as oil-water ratios, etc., which often occurs on brownfield sites but also over the long-term.“Most people know how a cyclone works. You inject the mixture and it forms a swirling flow,” he says. “Centrifugal forces are generated and the heavy material swirls to the outside and the lighter material to the inside. That works well if you design the system in such a way it can handle a certain flow range.”

The drawback is that the centrifugal force is generated by the flow, which means if your flow rate drops, you limit the range, or turndown, the separator is able to operate at. You need something that can overcome this, something that can handle turn down and changing gas/liquid ratios, etc.,” he says. “We started looking in to SwirlSep and a two phase separator idea.”

While SwirlSep also uses centrifugal forces, these are maintained by using the SwirlValve, developed by Dutch firm Twister. SwirlValve is ΔP controlled with tangential orientated holes around the SwirlValve’s “swirl trim cage,” maintaining the swirl velocity, reducing pressure drop and so maintaining the centrifugal forces.

This makes SwirlSep unique because it is controllable, Liew says. “This controllability means we can handle fluctuating flow rates to a higher extent – demisting, bulk separation, etc. – and we think that is unique, especially for a small device.” With a viable compact separator on its hands, the step towards offering this technology as a subsea solution was obvious.

Subsea processing is seen as attractive because moving technologies to the seafloor can debottleneck topsides facilities as well as reduce other requirements in the field and increase efficiency – and ultimately recovery rates. “Getting liquids to surface [from subsea wells] comes at a cost,” Liew says. “Because of the water depth, you need to get over the high head to keep producing. If you can lower your equipment to the sea floor, you can separate the flow there and then boost it to the surface. This means you don’t need complex multiphase pumps. Power consumption is much lower. The system is less complex. Umbilicals are less complex.”

3D model of the SwirlSep with flow scheme.

Providing a compact system also has big benefits. “Systems on the market are a development of conventional systems, which are voluminous and taking them subsea makes them very expensive,” says Henk Cornegé, senior business development manager, IHC. “The equipment we are developing will be a fraction of the size and weight of current systems.”

To date, SwirlSep has been designed for a number of applications and depending on the application Frames is at different technology readiness levels (TRLs). The most advanced was a liquids and solids removal system used in 2014 to help clean out gas wells on a NAM-operated field in the Netherlands, taking it to TRL 7-8.

There will be field trials beginning next year on bulk separation together with a Middle East customer, taking a liquid gas separation version to TRL-7. Further experiments are also starting focusing on the behavior of the separator when in liquid degassing mode and the company plans to continue lab work on bulk separation and demisting, to further validate models, Liew says.

The next step will be developing the technologies to withstand subsea conditions. “One of the challenges we see over the life span of the components is the maintenance intervals,” Cornegé says. “Onshore you can access them quite easily. Replacing components subsea is not so easy. We are going to have to guarantee the life span and access by ROV (remotely operated vehicle), which means looking at choice of materials, wear patterns, etc.”

Another key challenge is designing a control system to control the outlet flow rates as well as the pressure drop over the system, similar to what is done on a hydrocyclone. However, as the equipment is compact, it needs a fast control system with fast sensing. It will also require flow meters, which means you are effectively creating a multiphase flow meter, Liew says, which can also be used as a test separator, but also using data from the well itself.

But, before Frames and IHC develop a full subsea system, they will be looking to the operator community for a partner to make sure they’re developing what the industry needs, as well as to eventually take it forward to trials.

They also have their sights set on subsea produced water treatment, which would mean water could be reinjected instead of having to be lifted to the surface, says Jeroen Bergman, product manager, Produced Water Treatment, Frames. The challenge will be what to do with any sand that comes with that water, as reinjecting sand can damage the reservoir. The market might not be quite ready yet for such technologies, but it will come. “In the future we will see heavy oil fields, which contain sand being produced,” Bergman says. “So, we do see a serious challenge to deal with sand content in water,” especially when it comes to limited topsides space.

There’s a lot of work to be done, and it could be 2-3 years, before the technology is ready, but the two firms think they have the right partnership to make it happen.