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Topic drive string swivel and free rotation capabilities (torque and drag?)
25 June 2019
For those that remember.

Kelly gets racked back in its mousehole. 
We unlock the blocks to let the string, links and elevators below swivel component now rotate freely when POH/RIH. When into cased hole we then generally locked the swivel component.

Extent of hole condition now represented via drag up/down on the weight indicator and the string visibly seen to rotate anti-clockwise as we POH to see the extent of hole spiralling etc. 

We never backreamed as we could not. Majority of wells we simply managed to get out of hole simply by pulling, working string up/down and when excessive drag was noted pumping out in singles etc. Personally never experienced a string left in the ground while drilling tripping with a Kelly rig. (Checking the hole every 30ft drilled to make a connection may with zero upward rotation, have been more beneficial than today realised.)  

As we run in the hole again downward drag and string is seen to rotate clockwise. Often when conditions permitted us to do so, we would trip at 1mins / stand (5500ft/hr).  RIH one would see the swivel links elevators and string rotate a lot of revs in a hole that was heavily spiral due to bit/bha defects despite practices used.  e.g. low rotation / high ROP, poorly designed and optimised bit/BHA stabilisation placement etc often results in a more spiral hole.

Never having really though too much about this before until today ie differences when using a top drive. Is there any raises the following question.

Using a SWOT analysis w.r.t Top drive utilisation.

What are  Top drives and string pros/cons and ability to freely rotate the string pros and cons when RIH/POH?
Weaknesses ?

Thoughts, experiences, evident case studies?


5 answer(s)
Senior Advisor Well Engineering Global Skillpool
Total Posts: 5
Join Date: 25/12/15

Hi Peter,

as a young engineer we still had Kelly rigs and some two or three years into my career we installed a top drive. One of my experienced supervisor saw three major problems with the TDS:

1) thread damage due to stress on the threads when using the TDS for make-up und unscrewing, if the driller does not exactly keep the balance

2) the string not being able to turn freely when pulling out of hole and running in hole - could be an issue with hole spiralling or, which I think more likely, the issue with stabilizers. Anyway, the string could move freely through hole sections when allowed to turn freely, where a TDS rig would see either overpull and/or potential backreaming.

3) the backreaming option makes things quite easier as sections with hole problems could easily be passed through, but - and this is something that Peter aims at - hole quality does not get better with the excessive use of backreaming. This was one of the issues of the "good old times" that before pulling out of hole you made damned sure that the hole is in good condition. 

Drilling and tripping practices consequently changed with the use of TDS's as pumping out or rotating out of hole became the common option. This is still the issue of a good supervisor/experienced driller to adjust the drilling/tripping procedures in a way to arrive at an optimum output!

Kind regards,


Mentor to the youth of our industry
Total Posts: 131
Join Date: 27/02/08
I think that rather than putting the majority of blame on hole spiraling for the turning of the pipe when POH and RIH the stabilizers should shoulder a fair proportion of blame.
Senior Wells Advisor
Redstone Drilling
Total Posts: 39
Join Date: 13/09/07
Is it not a matter of what drilling practices are applied? It is easy to apply kelly drilling practices with a TDS, the opposite would be rather difficult.
Furthermore, with the introduction of rig automation and AI on the modern drilling rigs, a kelly would not be the most efficient drive mechanism to achieve this.

On a final point, if I remember correctly the kelly was racked back in the rathole ....
Drilling Specialist/Well Engineer/Training Consultant
Kingdom Drilling
Total Posts: 471
Join Date: 10/01/05
Thanks Leo for taking the time to respond with your experiential sharing. 

Rest assured I am firmly in your camp where from a Kelly drilling background, we rarely needed to rotate out is the start point. 

We then figured using similar reason/rationale that alleged 'best top drive practices' had to challenged as observed on my first top drive 'MODU Sonat rather' back in the early 90's. (Note. As a SDSV drilling vertical exploration wells on the UKCS.)

We simply asked, Where the evidence to support "as a matter of course or the purpose being served here"

Where from then until today all hydraulics, hole cleaning, drill string mechanics/dynamics and wellbore quality perspectives. 

Will prove and evidently demonstrate that Rotating into the well delivers far greater and superior wellbore and operational benefits where getting this 'right first time' is the absolute priority to prevent vs cure a majority of connection and/or tripping problems that result if engineers, supervisors and drillers are not doing the right things in the first place to meet this mandate.

Keep up the good work, stay operationally safe.
General Manager Drilling and Completions
Greymouth Petroleum
Total Posts: 10
Join Date: 15/03/13
Hi Peter,

the most common way of getting stuck is when we are back-reaming, particularly in deviated wells. What can happen is that cuttings accumulated in washouts are suddenly freed, pushed up and packed off around the BHA when the bit is pulled across the washouts. The pack-off happens very quickly and pressure can reach 3000-4000 psi blowing the PRV and the BHA is then irreversibly stuck.

Coal layers often wash out accumulating lots of cuttings.

How to reduce the risk when POOH:
  1. If possible avoid pumping across washed out hole sections
  2. If pumping is required to POOH, limit back reaming to one pump
  3. Pumping at full rate should only be done without POOH at the same time. Rotation is always OK.
  4. Focus on pump pressure rather than MD, and shut down pump and slump string if there is a pressure spike.

    Regards, Leo

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