FAQs

FLI probes are made using aluminium housings. After extensive customer engagement and experimentation, we have selected 2011/T2 series (UNS A92011) aluminium alloys as our standard housing material. Aluminium is strong, lightweight and, through its widespread use, has predictable properties.

In the vast majority of jobs we plan to leave the FLI probe at the bottom of the well, out of the way. FLI probes are short – typically less than 2 m in length – so they take up very little space in the rathole.

What happens if a FLI probe doesn’t get to its intended depth?
First of all, this is unlikely to happen. We plan FLI jobs carefully, working closely with you, to make sure we understand what you want to achieve. We take into account the anticipated well conditions – eg, fluid types, restrictions, deviations and likelihood of debris. If we don’t think that FLI is the right solution for your particular application, we’ll tell you.

Nevertheless we recognise that, especially in old wells, there may be unforeseen issues. All FLI probes have a standard size of external fishing neck, designed to be latched by an SB-type pulling tool, which allows the FLI probe to be recovered on slickline. We have done a number of jobs where the FLI probe was planned to be fished from the well, and we have never had a FLI probe that has not been fished successfully.

Alternatively, the FLI probe housing is made from a short, thin aluminium tube, which can be easily drilled or dissolved by spotting acid.

We have carried out many intermediate-hole FLI surveys, including cement-cure evaluations and vertical seismic profiles. At the end of the job, the FLI probe is simply left at the bottom of the hole to be destroyed when drilling the next section.

How easy is it to drill out a FLI probe?
It’s very easy! In every case to date the FLI probe has been drilled without issue and without modification to the drilling programme. In fact, given that the main housing of a FLI probe is a short, thin aluminium tube, you are unlikely to even notice it.

We try to make sure that the fibre life is long enough for your intended purpose, and no more. Typically that means you will need the fibre to survive from a few hours to a few days, depending upon the application.

For most surveys we use a “standard grade” optical fibre, which is coated with an acrylate material, to minimise the cost of the FLI probe. Once the job has finished, and the data has been recovered, the fibre serves no further purpose as a sensor and is simply disposed of in the well.

Sometimes you might need FLI to work in extreme environments, or in contact with corrosive fluids, or for extended time periods. In such cases we pick the specification of the fibre to suit, usually by changing the fibre coating. However, so-called specialty fibres can be expensive, and we strongly recommend working with you to see if a specialty fibre is really required.

FLI can provide you with highly reliable depths. We have demonstrated repeatedly that FLI can identify the position of leaks with great precision.

We are able to provide precise depth control through a combination of the following factors:

• The FLI fibre is fixed at the wellhead
• The unspooled fibre closely follows the path of the well
• Optical fibre does not stretch
• The design of the FLI probe itself greatly improves optical range-finding.

If you’d like to find out more about depth control with FLI, or about how we’ve used that in real-world applications, please get in touch.

Typical FLI descent speeds are around 8–15 m/s when falling in gas and 1–2 m/s in liquid.

Of course, there are a wide variety of variables that can affect the tool speeds. This is why we plan each job carefully, using a proprietary FLI tool drag simulator. Our simulator has been calibrated against many real-world jobs, and has been shown to predict reliable descent times, as well as helping to identify potential problems and mitigations.

For more information about our approach to job planning, please contact us.

In free-fall operations, which make up the vast majority of FLI jobs, we have deviation limits similar to those for conventional wireline surveys – ie, around 60°–70°. However, the distribution of forces affecting FLI jobs is very different to wireline jobs: the FLI tool itself has little weight, being made from aluminium, but there is no cable drag. Consequently, we try to minimise the friction of the FLI tool against the pipe wall in order to keep the FLI tool moving.

Using FLI in horizontal wells
We have successfully pumped FLI tools into horizontal wells, with the longest job to date being a horizontal section of more than 1500 m. FLI tools are lightweight and can be easily pumped out to the rathole through the toe sleeve. We have had multiple tools pumped in this way, with no problems or impact on subsequent operations.