What
is passive in-hole drifting?
Dropping a standard drift in-hole can appear an attractive and economical
option. The plan being to allow the drift to settle to the bottom of the
string as it is POOH. Unfortunately there is no immediate indication that
the drift was good so it is only certain that the pipe has drifted if
the drift is later found in the upper BHA area.
In most cases this will not cause too much delay or inconvenience. However if not located where expected, there will be a rack full of pipe that needs checking on RIH with the liner (see manual drifting RIH method) this cannot happen with the Drift Catcher.
A more serious issue stems from a potential incomplete hand-over at crew change. Note manual and positive drifting are instantaneous whereas passive drifting is initiated and completed on separate shifts normally. It has happened on many occasions that the retrieving crew forget to locate and remove the drift and ran it back into hole above the liner. In 2008 a GOM operator estimated a loss of $30M dollars when it attempted set liner below a forgotten drift.
How can a mistake like this happen?
"It wasn't my fault! I couldn't find the drift so I presumed they never dropped it, last time I woke them up to ask a question they went mad!"
"It wasn't my fault! We had issues with ......... so I went to help out and thought the guys would remember to locate the drift"
So yes passive drifting is a low cost alternative and it is definitely safer than the derrick method but it comes with operational risks because there is no inbuilt confirming communication system and is therefore susceptible to human error. It can be a free lunch most days but on occasions it can be very expensive!!
"It wasn't my fault! This was my first hour on this rig nobody told
me to look for the drift, I usually drift in the derrick"
