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Use of an activate-able scraper in a drilling or cleanout BHA
02 August 2018
Dear all,

Here's another item that keeps cropping up.

A well re-entry is being planned. The well has was temporarily-suspended with a cement plug inside 11¾" liner and the shoetrack had not been drilled out.  

The re-entry plan requires  a USIT/CBL to be conducted to investigate the bond outside the liner.

Due to drilling out a cement plug, and - possibly part of the shoetrack - the wireline company has requested that we scrape the casing. The team are looking at various options, which include:
  1. Incorporate a 'drilling scraper' in the BHA (ODfjell's DrillRdillo comes to mind): these are run in the 'collapsed' state and after drilling is finished, they are activated (ball) and then the casing can be scraped.
  2. Incorporate a 'non-rotating' scraper in the BHA (MI-Swaco's Razorback comes to mind), and anticpating that the drilling bit/mill will grind the cement up small enough so as not to cause a problem
  3. Don't bother running a scraper at all (after all scrapers are hardly ever run before bond logs)
We'd really value your experience in any of the three (3) options above, plus any other options you can think of.


Note added later: The reason that we need to know about the cement bond is because the contingency plan (if we cannot re-use the old hole below the liner) is to conduct a cased-hole sidetrack.

6 answer(s)
Total Posts: 108
Join Date: 05/03/08
Hi Dave,

A bit late to the party, but my thoughts for what it's worth;

If the hole condition is so unstable that you couldn't get the liner to bottom, is it going to be stable enough to actually be able to get a solid enough base for the cement plug to do it's job?

While Peter's question is valid for a conventional oilfield well, is it valid in this particular case, as I presume the goal is scientific rather than finding hydrocarbons?

Presuming it's a vertical well (thanks for the link, BTW), although Colin makes very valid points, in all honesty I wouldn't make a separate dedicated scraper run for the CBL.

Finally, a question - what is the reason for wanting to avoid running an expandable across the whip face? Is it the potential for a high DLS or something else?

All the best.


Answers (oh the joys of being moderator, to see responses 6-12 hours before they are published):

1.  Agreed that hole is unlikely to be good enough to get a stinger in there to set a plug (at Shell Expro, on UMC, we had to run a tricone with no nozzles to get the stinger down to the required depth!).

2.  Only reason for concersn about running expandable through the window is that they can be worked to bottom (rotated) but the window profile (ramp and/or window edges) may damage the mild-steel wall of the expandable.

Thanks Scott!

Total Posts: 23
Join Date: 16/08/10
Good discussion and enjoyed reading. #3 for me: you just need mechanical integrity as opposed to hydraulic for ease of casing exit. So, while fully respecting Colin's insights, logging companies will always recommend perfect conditions: (covers themselves) but I dont see the need here- just need see good cement ( as Colin asked ), similarly some operator engineers will also recommend maximum knowledge ( cover themselves ).= Ferrari vs Lada kinda thing.
On reentry of OH for a few hundred feet, that will be a mess from trying to picture this history, probable uncontrolled OH sidetrack anyway ( could well be best outcome ! ! ):  
Drilling Specialist/Well Engineer/Training Consultant
Kingdom Drilling
Total Posts: 358
Join Date: 10/01/05

Interesting discussion ( I learned a lot from Colin's knowledgeable response, thanks for sharing this.) and thanks for filling in some of the evident bits needed. (every SPREAD discussion needs to be more Evidence based.)

Based on what I can gather.

Why does 're-entry plan requires  a USIT/CBL to be conducted to investigate the bond outside the liner'. ????? Seems a waste of time and money?

My view would be on drilling out shoe track one needs to
- Conduct a well integrity test? This will give you either the output good or bad needed.

- So drilling the shoe track is the first step?

- If integrity test is poor what difference does the log make as you know you have a problem at the shoe.

- So you get a log what are you going to do with it? 
what does this do? what will change?

- Is there a porous permeable pressurized hydrocarbon zone around the liner annulus (I doubt it)? 
So where is the risk driving this log etc?

- Worst case poor leak off. 
That's why you have your expandable as stated?

- So you do some drilling and set this extra string of pipe to isolate the problem (as per plan) so as not to compromise getting well to final TD required. 

- If well integrity test is good (this would not be the first time we gat a surprise) you get on with the work as planned and still have the expandable as the fall back?  
MSc Drilling and Well Engineering Student & SME owner
Robert Gordon University
Total Posts: 10
Join Date: 17/04/09
Hi Dave,

I no longer work for MI or Odfjell, and was the inventor of the DrillRdillo.  So here are my two cents:

The DrillRdillo would be my preferred option however I dont see any reason why you could not use either, although I know that the Razorback technical manuals state not to run the Razorback though drilled out float equipment and to place the tool 1 stand above the bit when drilling cement and not to use when drilling in open hole. 

This means you would not be able to scrape the shoe track, I always thought that was a tad over-cautious having run hundreds of Razorback jobs over the years, the tool is robust enough, especially in 11-3/4" and Heavy Duty form.  So you may need to sign a waiver releasing MI from liability for damage...... or risk DBR charge.  I know this is not the forum for sales, but you are no doubt aware of a vendor which sells similar tools which you can do as you wish with.......

The DrillRdillo removes all these restrictions, so can be run directly above a bit + string mill and can be run into open hole should you choose to drill some rat hole as well.  The only downside I might think of is whether it is available in those sizes.  When I left Odfjell last year we had 9-5/8" and 7" models, with 13-3/8" planned next.  Suggest you contact Stephen Mair [email protected] for an update.

All the best
Managing Director (
Relentless Pursuit Of Perfection Ltd.
Total Posts: 403
Join Date: 10/01/05
Hi Colin

All good points, thanks.  The purpose of running the bond log is to determine a suitable place for setting a cased-hole whipstock.

It's a l-o-n-g story, but this is a well re-entry, with the 11¾" liner set quite a distance off bottom; severe hole problems caused this. The cement job was also compromised.  Before suspending the well, two shoe squeezes were performed with inconclusive results.

The re-entry will probe the rat-hole for the purposes of setting a kick-off plug and an attempt will be made to kick-off below the existing liner shoe; an open-hole (OH) sidetrack.

The contingency is a cased-hole sidetrack as deep down the liner as possible. One of the reasons for prefering an OH sidetrack is that the next casing string is an expandable liner and it's prefered to avoid the whip-face if possible.

I hope that gives a bit more insight, and thanks - Colin - for taking the time to reply.

Best wishes


(in Japan)
Operations Petrophysicist
Gaia Earth Sciences Ltd
Total Posts: 15
Join Date: 21/12/11

I would disagree with the sweeping statement that a scraper is hardly ever run before cement evaluation logging. Some clients will run a scraper before any cement evaluation log, and regard it as a best practice.

For some operators a scraper is always run before cement evaluation logging, unless there is a strong reason why it cannot be accommodated.

Generally speaking, the scraper run is recommended to ensure "clean casing" with no cement sheath, or patches of cement.

There are two main considerations:

1. the response of a cement evaluation tool can be adversely affected by any cement left on the inner surface of the casing

(Ultrasonic measurements are more likely to be affected, or likely to be affected to a greater degree, than a traditional CBL tool, but in my experience all the major logging providers recommend a scraper run regardless of the specific tool technology to be run). 

 If you are planning to run an ultrasonic tool such as USIT or CAST, they are very likely give better data and more accurate results in a casing that is free from cement coating, deposits, scale or corrosion.

I have never seen a complete log affected ie over the entire logged interval, but I have seen effects ranging from clear degradation of data (to the point of introducing uncertainty in the interpretation) right through to completely unusable or completely uninterpretable data over key sections.

2. Cement evaluation tools generally require strong and effective centralisation - mechanically you do not want cement-debris on the inside of the casing
Additionally a tool with a rotating sub can become fouled by cement left on the inside of the casing and then dislodged during the logging tool rih and log-up by the centralisers.
In many cases after a recent cement job, of course a scraper-run can be accommodated in the time that you might wish to "wait on cement" before logging anyway, as long as you remember to rent/mobilise a scraper.

Now, people HAVE run cement evaluation logs without a scraper run and not encountered a problem, but I would always recommend a scraper run as a best-practice. If it has been decided that a cement evaluation log is required, and if people are spending thousands of dollars for the logging crew and the log-data and perhaps several hundred thousand for the rig time, I assume that it is because they want a good quality log and the most best evaluation/interpretation possible.


3. There is probably a third consideration that has come to mind as I write this. Why are you planning to run the cement evaluation logs and what decisions will the results drive? Eg do you actually need a detailed cement evaluation and estimate of isolation or just a top-of-cement?

There may be other issues (eg a particular well's history), and I am sure there may be different viewpoints - but these are mine based on 38 years in the industry working with cement evaluation logs and data, from running logs , to designing programmes and interpreting the data (or being unable to interpret poor data) for end-users.

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