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, 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.
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.