What
if we see no pressure increase?
Our results show that a pumped choked drift lands out successfully 98%
of the time so the first thing to note is the chance of this happening
is remote. Nevertheless what do you do if it does happen? You have one
major advantage in that you know before you trip out there is an obstruction
that needs to be removed. Your only option is to manually drift to find
the obstruction after first performing a risk assessment. Once located
the remainder of the pipe can be choke drifted as normal. Still saving
time compared to the derrick method and minimising crew exposure to dropped
objects.
How
quickly will I see a pressure increase? -> 10-15 minutes
The viscosity, well path and mud speed will vary this figure, by the time
the top drive is reconnected for pumping the drift may be much of the
way to the sub. However a good guide is 1000-1500ft per minute. Above
55 degrees the drift will begin to travel slower than the mud. By comparing
this to the time to manually drift (20-30 minutes per 1000ft) we get in
the region of 97% drift time saving.
How
do I select my drift OD?
Check the drift/OD specifications of your chosen liner/screen activation/retrieval
systems and cement plug diameters with your supplier and ensure the drift
is greater of equal to the required diameter. See
our specifications page
How
do I select my catcher location and ID?
Ideally this will locate above the BHA and heavy-weight (unless HW it
is to be used for liner RIH). The ID of the sub will be only fractionally
tighter than the drift so ensure that all ID's above the sub can allow
the drift and that any activation devices required below the sub will
pass through the ID.
How
do I select my choke size?
Refer to the lookup table to chose a
pressure that will be visible ratio up the pressure according to you mud
weight from the data referenced at 10ppg (e.g. 13ppg plus 30%). Select
a pressure change that will be clearly observed at surface then check
your maximum flow rate pressure loss at that size is acceptable if in
the unlikely event you need to pump in open hole.
If in doubt please call and we will happily advise.
Neither device will
show a pressure
increase at surface
when obstructed
