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Insights: leveraging data to enhance coiled tubing clean out
As digitalisation improves efficiency, advancements in the capabilities and performance of well-known offshore activities are now possible.

In the field of solids management, desander equipment is an area that is undergoing change. In our last insights article, we examined how cyclonic separation can be used together with coiled tubing (CT). In this piece, we extend that topic by discussing how data can be used to optimise Coiled Tubing Clean-Out (CTCO) and align sand management with the growing shift towards digitalisation in the sector.

There are many benefits that can be derived from using data in CTCO. This article will analyse the issues that arise with the current approach, discuss the benefits of the data and outline how it works in practice.

What is the traditional approach to CTCO?

When solids accumulate in the wellbore, intervention activity is required. A common approach for this is CTCO.

Traditionally, when a CTCO operation is planned, the solids build up in the well is estimated. These estimates are based off several determining factors, such as the size of the tubing or a percentage calculation of the volume of the tube that has been filled with solids.

The coil consists of coiled tubing with a jet nozzle or a motor and mill at the front. The CTCO process usually takes place in stages, often referred to as bites. To start, the coil is Run In Hole (RIH) to the top of the accumulated sand and the fluid pump starts to clean out the first bite. This continues until a pre-determined distance is reached, e.g. 50 meters. The pumping rate at this stage may be too low to lift the solids all the way out of the well.

To ensure all of the solids from that particular bite are out of the wellbore, the fluid pump liquid rate is increased. The tool then begins to clean backwards at a much higher flowrate. At the same time the coil will start Pull Out Of Hole (POOH) back to a given depth. An anticipated volume of solids will now be displaced, and the backward pumping will continue until that expected volume is received at surface as a return. At this point it is assumed that the well has been cleaned out from the nozzle to the top of the well.

Without accurate solids data topside, the coil operator assumes that the well is clean. The process then moves onto the next bite and repeats the same procedure. Problems will arise if the solids are not being lifted out of the well between each bite, as this allows for the potential of several tons of solids to remain in the wellbore. In this scenario, the solids may settle out around the coil in the wellbore. Not only does this leave unwanted solids downhole, but it also creates difficulties for ongoing operations.
What are the benefits of knowing

Interpretation of the solids data alongside the estimated solids calculations provides operators with valuable data to boost the efficiency and quality of CT operations.

Real-time decision making: As the CT operation runs, the solids are tagged and the clean-out starts. If an expected weight of solids is known, the operation plan can be changed instantly should the volume of solids that has been removed not match expected results. This could mean steps are taken, such as increasing the pumping rate or the decision to pull further out of the hole.

Preventing issues associated with a CT getting stuck: A CT getting stuck in the well will mean several scenarios could occur. This includes loss of costly operation time, the tool being released in the well where it will need to be fished out, or in the worst case the well might be shut-in.

Confidence to operate at optimal speeds: Operators will always want to run CT as fast as possible. If the data shows that the solids are coming up, then operators can have the confidence to proceed at the optimal rate. Using live data in correlation with estimated data can quality assure and optimise the CTCO. Decisions can be made on the go as one observes the live data. As soon as the data and trends show a clean wellbore, coil can efficiently move to the next step/bite. This can be done with the knowledge that all of the solids behind the coil tool string are cleaned all of the way out of the well.

Ensure a proper cleanout: By analysing the data in real time, it is possible to know that the solids are being cleaned out in a scheduled, consistent manner. This means that the sand management system topside can handle the solids in an optimum and efficient manner. Compact solids plugs can affect separation efficiency. If this happens, all the accumulated sand will be moved out as one compact huge sand plug. This will put pressure on the sand management system and the efficiency of the system may be reduced. This could lead to some sand that has been transported out of the well reaching the process facility.