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An introduction to cyclonic separation together with coiled tubing

Coiled Tubing (CT) is a standard industry practice which is used widely to resolve well intervention issues. More recently, it can be used in drilling operations.

When used in conjunction with a cyclonic desander, CT can be particularly effective as part of a sand management cleanout campaign. This article will give you an introduction to CT, summarise common issues with CT and discuss how cyclonic separation can be applied during CT to overcome these issues.

What is Coiled Tubing (CT)

CT is a well-known practice for well intervention using a flexible metal pipe that is stored on a reel. It can be used for many reasons, such as clean-outs, milling, fracking operations, completion operations and plug and abandonment (P&A). Common reasons why CT is considered by operators:

It is possible to continue with deployment and retrievability while the circulating fluids are in operation
The need to kill the well is removed because there is the potential to work with the surface pressure.
Without the need to kill the well, minimized formation damage results.
Increase health and safety is achieved thanks to the reduced heavy lifting, and associated logistics, relative to a full-sized mobile drill rig.
Common issues with CT?
CT can accumulate fatigue damage and reduce the service life of the tubing string. This can occur because bend-cycling operations can cause plastic deformation in the coiled tubing string.
Limitations around the reel height and weight mean that only a limited length of CT can be spooled onto a service reel at any given time.
It is common to experience high pressure losses when fluids are being pumped through CT. This happens because of the small diameters and long string lengths.
CT and solids management
The biggest questions faced by operators around CT come from a solids management perspective. This usually happens with sand cleanouts.

To undergo a cleanout operation, the process involves pumping a fluid into the well, gathering or sweeping the solids up into the wash fluid and carrying the solids to the surface via the wash fluid. At this point, the wash fluid and solids are held in surface return tanks that allow the solids to ‘settle’ out of the fluid.

However, issues can arise where unmanaged solids enter the separators and subsequently travel down through the production facility. This can occur if a large volume of solids has been produced. In this situation, the solids could flood the surface return tanks and enter the production facility. The accumulation of solids in the production facility can result in solids handling limitations topside, lower efficiency, and cause erosion. In this case, a shutdown would become inevitable.

A shutdown would subsequently result in a pause in production, causing lost revenue and an increased requirement for manual handling and associated risks.

It is important to note that CT is not a long-term solution to solids build up in the well. It can remove a build-up which has developed, but it cannot then mitigate further build up once the operation has taken place. As a result, a clean out will inevitably be required to happen again. Therefore, to prevent the requirement for clean outs to take place, a proactive long-term solids management solution is required.
Applying cyclonic desander technology during CT
To establish a proactive, long-term solids management solution, a cyclonic desander can be included in the CT process. The desander actively manages the solids returning to the surface and ensures continuous solids-free fluid, before it enters the rig process facility. Typically, this approach would utilise a cyclonic desander, such as the DualFlow 5K desander.

The DualFlow 5K consists of two single liners that provide a lot more flexibility on the flow regime compared to other multiple liners with a restricted flow window. This unique design approach provides optimum efficiency for managing high volumes of solids within a short time frame, as can be the case for many CT operations.
Including a cyclonic desander in the CT process
To start, CT equipment is rigged on to the well. With the pump tied on to one end of the coil, the other end is prepared to be inserted into the well with the assistance of an injector.
The DualFlow and choke are rigged on to the flow tee assembly, for handling CT returns. Together this package will create a closed loop system. The closed loop system is important, as this means the DualFlow 5K can be operated on a live well with no costly well killing operation.
The coil is then moved down to target depth, and the pump is started to clean out the solids.
Returning fluid then travels along the outside of the coil towards the surface.
When the fluid is at surface, it goes through the DualFlow 5K and choke assembly. The choke maintains the required wellhead pressure.
With two vessels in one unit, normally in serial, the design ensures double fluid cleaning. When in flushing mode, one vessel can be isolated and flushed while the return fluid continues through the other.
The fluid pumped in the hole actively returns out of the hole via the DualFlow 5K and into the separator on the rig facility.
The value case

By deploying a cyclonic desander in the CT process, the risks associated with typical CT operations are overcome. Wider risk reduction and QHSE benefits can also be realised:
It is possible to completely avoid any solids entering the process facility and remove the risk of solids filling up the separator.
In turn this avoids the risk of lower efficiency, and ultimately having to pause production for the clean-out to take place.
By removing the risk of solids entering the process facility, the DualFlow 5K also reduces the damage to valves and instrumentation, which can be costly and similarly impact production.
The risk of manual handling to remove the solids from the production facility are completely removed, improving HSE risk.
Solids free production is guaranteed with the DualFlow 5K proven efficiency rate of 99.8%. Real-time data and solids weighing, when running in hole is achieved via the 560 inbuilt sensors. This allows enhanced monitoring and control which enable a better understanding of the volume of solids taken out from each bite and reduces downtime.
With a 2×2 metre footprint, the DualFlow 5K is the smallest dual cyclonic desander on the market. Therefore, it is possible to integrate it onto a crowded rig floor alongside a CT stack. The choke is stackable and can be located under the DualFlow, this means that the footprint is the same when the DualFlow is used together with a choke. FourPhase can also conduct full 3D modelling pre-installation to plan installations in advance.
No additional personnel are needed offshore. As the first automated solids management system with remote operation capabilities available on the market, it’s possible to reduce POB and operate the DualFlow 5K remotely if required.
It has a positive impact on ESG reports. This is due to the reduced separator jetting operations caused by solids.
All these points relate to the integration of CT and a desander. However, if contact with the reservoir can be achieved, the cleanout operation can be carried out without the need for the coil. This means that only the DualFlow 5K is required to get the well producing again, delivering even more benefits…more on that soon.