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Mitigating Residual Cement Sheath In Liners Following Seawater Displacement
13 April 2017

We recently performed a seawater displacement during a 4 ½” liner cement job on a long reach platform well. The 1,500ft liner was hung off on a hanger loaded with a single cement wiper plug, with the dart pumped down through a 4” x 5” DP tapered drillstring (S Shaped Well Profile) to ~19,000ft, to latch the plug in the hanger. The cement job went as planned and we recorded a positive plug bump at the expected strokes, however following the displacement we drifted the well on wireline to confirm access for the guns and held up around 200’ above the landing collar, leading to the requirement to perform a clean out run.


This was our 3rd seawater displacement which has saved considerable time/cost by negating the need to perform a clean-up and so far we have not experienced any issues. It is thought that the length of this well and the drill string transition has caused the dart to “flower” leading to possible fluid bypass. There are also other theories about incorrect line up’s and residual cement in surface lines possibly contributing to this.


The next well in our sequence calls for a 4,400ft horizontal 5 ½” liner which we intend to cement to the hanger and again displacement with seawater, we then need to run a 3 3/8” TCP gun string to depth and perforate. In order to mitigate any potential cement sheath which could potentially cause the guns to hold up, it has been suggested that we displace  the cement with a viscous pill in the liner, dosed with cement retarder (Sugar, citric or similar) to prevent any cement which may remain in the liner from setting up. The desire is to avoid the requirement to perform a tractor conveyed drift run due to the associated time and cost of this operation (which would erode the benefit of performing a seawater displacement).


Does anyone have any similar experience of these issues or the mitigations we are considering?



Neil Deeney

5 answer(s)
Total Posts: 112
Join Date: 10/04/08

Neil, I had some further thoughts on your liner job. The liner wiper plug is likely to have a lock down latch in feature with seal so if bumped gives you an extra back-pressure device. You could have pre-use tested your float equipment before load out but as its already offshore you could check it a little more thoroughly at the rig floor by running it in a little deeper empty to ensure it does not fill, if you do this, best to fill a joint or two and pick up to make sure it empties first, then when drained and empty again run in empty to let the mud hydrostatic act on the float, then when you stop place cling film over the box to see if mud is pushing air out to check the floats are holding. I'd take at least 5 minutes to do this check. Most people don't.
Senior Drilling Engineer / Supervisor
CNR International
Total Posts: 5
Join Date: 19/03/17


Paul - Thank you for your comments on this matter, there are some very useful ideas here that I will explore further.


In terms of cleaning the drill string the intention is to drop a drift, but I will explore the feasibility of performing a calibration run as this is something which has come up before when we perform cemented completions. As the cementing and float equipment is already mobilised I may have limited options here on this well.


I am confident on the wiper plug deign for this well as it will be 5” DP all the way this time which will be less torturous that the previous tapered string, but the previous plugs were designed accordingly with variable sized fins. Another of the DE’s here suggested chasing the dart with a foam ball which could offer a simple low cost solution to assist the displacement if it is mechanically possible and wont impact on the hanger system.


The point about control of actual ID is definitely something which can be overlooked and its impact underestimated.


Agusto -  We are using 2 x single floats ( 1 x in the shoe and 1 x  in the FC) and we are using fairly standard specification float equipment.


Scott – We are on to a single 5” DP for this well so there is less concern over the fin sizing. The dart was only loaded just prior to the job, but I am aware of the issues with leaving darts loaded and for this reason we have a maximum of 8 days in the system before we require it to be replaced.


Additionally we will review the surface system line up and pumping sequence to ensure best practise here, is we acknowledge that this is an area of the operation which could compromise the job if not properly managed.


Thanks to all who contributed on this and contacted me by email.


Neil Deeney

SPREAD Associates
Total Posts: 149
Join Date: 05/03/08
Hi Neil,

I agree with Paul's comment about doing a dummy run.

Depending upon the plug design, the nose of the dart may not be held clear of the inside of the DP during displacement, and over a long displacement may become worn so it doesn't seal properly when latching into the LW Plug.

In addition, make sure the DP dart can actually latch properly into the LW plug at high inclination. Just because it went at the correct time doesn't mean it latched in - it may just have stood up on the LW Plug and pressure on the fins sent the LW Plug on it's way.

I don't know how the fins are designed on the DP wiper plug, but for a taped DP string, I strongly prefer a DP fin design that has two separate sets of fins for each DP ID, rather than a 'one size cleans all' design.

As an aside, probably done this already, but just check that the ID of the 4" x 5" DP X/O is tapered and not square shouldered.

Also, how long had the DP and Liner Wiper plugs been loaded prior to the job?

In the past, I've investigated two liner cement job failures where fin deformation was thought to be the root cause of failure.

On these jobs, as normal, the DP wiper dart was loaded into the plug launching head prior to the job and laid back down.

In both cases, hole problems meant that it was several days before the actual job was performed. Because the plugs were stored in a horizontal position, the fins had deformed and allowed cement to bypass.

At least one of the Liner Hanger vendors (WFD) did some tests which confirmed this is a problem. They changed their running procedures as a result, but this was over 10 years ago so this may have been omitted in a revision / update.

Best Regards

Scott McNeil
Consultant [retired Shell staff]
SPREAD Associates
Total Posts: 273
Join Date: 02/09/05
I would like to know the design of the float equipment, the very important internal BOP.
There are designs which are approved by design/test others that survive on the wrong grand father clause.
Unfortunately, the acceptable liner hanger designs do not have an equivalent float equipment to go with it.
If you are using a single float there is no redundancy; moreover, if a floating ball is used, check the geometry. The designs which I was aware of only work below 45 degrees inclination. Above, the ball does not  close the entry hole.
Another weakness is the cement that holds the floating system. It is very fragile and it may break while transporting on the surface or running in the hole.
I need more technical details to elaborate further.

Total Posts: 112
Join Date: 10/04/08

I am not sure that trying to stop cement that gets above the plug or above the dart and ends up above the landing collar from setting with chemicals is the answer as getting down past unset cement may be equally difficult or risks getting a tool string stuck.

I would suggest looking at the areas to ensure the plugs or darts don't by-pass or leak. I'd do some work to ensure the drill string is clean and when at TD do a dummy dart run and pump a dart down on the trip out of the hole so you can calibrate the string and inspect the dart up retrieval. Use the same dart design you plan to use on the liner and land it on a ported ball seat type sub or below a rupture disc sub so you can pull dry. You might get an accurate displacement figure this way too.

I'd do some work in the area of releasing the dart from the cement head to ensure it has not been in the head too long before release and rig up lines so you can flush with displacement fluid to the cement head before releasing and ensure that any u-tubing is not letting air in the string.

I'd look carefully at the liner wiper plug design and ensure the fins and the back-up rings behind the fins are suitable for the weight of liner pipe you have. Getting a good handle on the actual ID of the liner and its true displacement volume may assist to arrive at your likely true total displacement value.

Lastly, and I have not tried this myself, but last week one of the expandable companies told me they release their drill pipe darts and immediately or at the same time release a foam wiper ball behind the dart so that the dart and the foam wiper ball travel down the string together. They said this is something that they and their client had found helped ensure cement did not get above the wiper dart during the displacement.

This idea sounds plausible to me and may be worth investigating if a dart can be loaded in the cement head with a foam wiper ball on top of it and both released at the same time. 

Good luck with the next job regardless.

I am attaching a flyer on a new cement head I just released that is designed to allow darts and balls to be released without the need for pre-loading and prevents by-passing and u-tubing whilst releasing that you may find of interested.


Note from moderator: Paul has been good enough to provide a comprehensive answer to this question and so we have no issues with him promoting a product that may help.
Posted by

Neil Deeney

Senior Drilling Engineer / Supervisor

CNR International

Total Posts: 5
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