Note: The comments apply for semi/drillship operations only where
Platform and land based conductors may have different reasons to run
a stab in stinger!
The time and safety issues to run an inner string then pull and lay
it down equates to a bunch of risks, time and money. On a 500K semi I
wouldn't even give any thought to running a stinger or stab in as
for me it actually can result in a less effective final displacement
and cement job. Read on!
Safety issues are handling stands of pipe with a C-plate, elevators
on top of the conductor joint. We would rather therefore pick up the
running tool, with cement sub, and hose all pre-made in the stand
with anything from a 5-15ft pup joint below, i.e. straight to
conductor jt for ease of make up and minimal handling.
With some operators, we have indeed made up running tool assembly and
pup jt below from the derrick and to a 2 x 20ft x 5" (40ft) 'pre-
made on deck' fibre glass stinger, placed then in the mouse hole.
Pick the fibre glass tail-pipe out of the mouse hole and RIH the
running tool stand and assembly complete to top conductor joint with
little handling or safety issues involved.
With an 80-100ft of stinger this covers about 1/2 - 3/4 of the
However there are genuine risks of cementing in a tailpipe or an even
extended stinger (e.g. it has happened twice that I know of). Here if
one cannot release the running tool at end of job, e.g. due to
current, hydraulic lock down, can't get ROV in too release and view
etc. due to visibility. By the time this is achieved the cement has
set and real fun and expensive downtime results sorting this mess
out. Why operators most likely moved away from the stab in an steel-
pipe stingers and evolved to fibre glass stingers or none at all
back in the late 80's
Bear in mind the reality of a conductor cement job and what you are
trying to achieve?. E.g. We normally pump 200-300% excess hole
volume or more and/or keep pumping until cement can be seen at
surface (to avoid topping up?). At this point as the conductor is
then full of cement below what ever you have?. Here I would
challenge what are 'best cement practices' where for me the real
benefit is having a conductor full of cement vs. a small volume in a
stab in stinger?. i.e. one can crank the muds pumps up i.e. 2 x 100
to really get good displacement, to rally benefit final stages of
cement. Again personally a shorter stinger allows far more latitude
to do this?
In displacing it is always important that strokes are properly
measured and displacement! Here a bit short and more cement is Ok as
long as it is well below stinger and inside smaller ID pipe if you
have a swedge? This method from experience has never proved to be a
problem with good cement always tagged where expected whether a 5ft
or 100ft stinger below the conductor housing joint was run or not.
If running swedge, again a 30" x 20" x 13.3/8" swedge down is
preferred with at least 20ft of 20" for displacement reasons as
stated and so that the 12-1/4" bit will drill this cement cylinder
with less cement block issues, i.e. that can be a problem if you
have to drill 30" conductor ID and cement out. Also running a 17-
1/2" x 26" x 26" bit/hole opener combination, properly nozzled and
spaced out to accommodate pipe and avoid big cement blocks falling
down from annulus as you are drilling out also seems to work best.