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Loss of Grease Seal
17 February 2019

Hi All!

Recently we had a big problem with 7 days NPT - loss of grease seal during PLT.
We rigged up WL PCE (cable cutter, triple BOP, lubricator, grease injection system and stuffing box) rated for 15K. The problem began as we start to run, the weight of the tool was not heavy enough to overcome the wellhead pressure, so we closed the downhole valve, released the pressure and ran the tool. At the halfway, we pressure up the tubing to equalize at the downhole valve (DV) and open it. Later we noticed the loss of grease from the return line and gas coming from the top of PCE. Stopped the run, closed the stiffing box but could not managed to regain the grease seal - gas was coming from the return. Pulled the tool above the DV and closed the well at the DV. 
Then we checked all flow tubes, changed the grease, tested the grease injection pump but the next two runs were also unsuccessful - always the loss the grease seal... The service company at this moment cannot explain why we are losing the seal. Taking the grease as the main source of problem.

Now we planning to run the tools on slickline as the temporary decision.

Has anybody had a such problems and what was the solutions? 


5 answer(s)
Askhat
Well Test Engineer
ALMEX PLUS
Total Posts: 22
Join Date: 24/12/14
Dear All,

The full investigation is ongoing and one of the directions is to check compatability of the grease and glycol. Preliminary the ingibitors in the grease react with glycol and it increases the grease's viscocity.
Askhat
Well Test Engineer
ALMEX PLUS
Total Posts: 22
Join Date: 24/12/14
Doug,
We checked to have the cable so-called seasoned, with a new cable definitely we've had the problem you described.
Now we are investigating the problem, as soon as we have the results - I let you know.
Now our team are working on possibilities to perform PLT job on:
1) Coiled tubing
2) Slickline
3) Digital slickline
4) StreamLINE Polymer-Encapsulated Wireline Cable by Schlumberger.

Regards,
Askhat
DougP
Retired
Marathon Oil
Total Posts: 19
Join Date: 18/08/05
Many years ago we had a similar problem when making multiple perforation runs on new HP Gas Wells on a production platform with multiple wells.  We tried everything and eventually solved the issue by changing out the wire being used (we had a new Wireline Unit on a new platform with new wire).  The problem disappeared immediately and we had no further problems.  We concluded that it took time for grease to fully penetrate all the spaces in the wire before we could establish a good gas seal with the high pressures involved. 
Askhat
Well Test Engineer
ALMEX PLUS
Total Posts: 22
Join Date: 24/12/14
Collin,

1) We exprected that the weight is not enogh, we are limited with rig's height.
2) The sizes of flow tubes and the cable are OK, number of tubes is 10.
3) We used all possible grease:
768 vis 12  (-23°C to +7°C) - used originaly, then change for:

765D (-23°C to -1°C)
765G (-15°C to 15°C)
765A (-51°C to -23°C) - was not used, too thick.

ColinCGB
Operations Petrophysicist
Gaia Earth Sciences Ltd
Total Posts: 16
Join Date: 21/12/11
Askhat, any response posted here will obviously be based on your description rather than a complete job and equipment analysis.  But here are my thoughts:
1. Job design from the service contractor is critical. One of those considerations is whether or not the toolstring is heavy enough to overcome the WHP.  It is not clear if it was expected that the tool would not be heavy enough to overcome the pressure. If it was unexpected or not considered,  then I would wonder about the thoroughness of the job design.
(sometimes you have no choice but to accept this situation,  adding tool weight can increase length, increasing frictional forces and increase the required lubricator height).
2. Job design also includes choice of flow-tubes (grease tubes),  the optimum ID vs the cable size,  and the number of flow-tubes to be used.e.g.  you will need more tubes for a gas well than an oil well (generally speaking).
This step is a CRITICAL consideration affecting ability to retain seal and minimise grease-loss or grease consumption during a job.
If this step is not correct, you can have a situation that you can do nothing about.
The larger the annulus between the cable and the flow-tube inner wall, the more grease you will use and the more difficult it might be to maintain seal.
3. The next area I would look at is the grease-type used.  It is a few years since I ran a WL PCE job,  but back in the day we had some very effective (and expensive) grease types for hi-pressure/hi-rate gas wells.
So, were they using the best grease recommended, or even  the grease that they have used on similar wells without problem?
4. It is not clear from your post - but I wonder did they close the grease return while trying to regain seal?
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