Cement mule shoe
10 March 2008
We would like to standardize what we use to set cement plugs for P&A
& Sidetracks, what would the preferred tool be? Have had various
suggestions, namely the length of the shoe, is it best to be open
ended or closed end tapered. Personally I have used a 4ft tube with a
tapered open end with various slots cut in it. Some suggest a longer
one of up to 15ft, some say to have closed end, others say best to
have open ended. Appreciate any input with this. Attached one
suggestion. Thanks Mike
I have read with interest the comments regarding what the end of the cement stinger should look like for laying balance plugs and agree generally with all the options and whatever seems to be working should continue to be used, I personally would opt for a closed rounded nose and numerous holes of a diameter that seem appropriate to the size of the tubing being used, but no smaller than 1/2", and certainly some several feet from the end of the joint to avoid plugging if tagging etc, however what I feel is much more important to the success of placing a balanced cement plug is using a tool that controls the u-tubing and free-fall effects. I have some experience of a tool first used by Enterprise Oil on the Nelson template wells many years ago developed by a company called XLT that contains a convoluted flow path inside a drill pipe sub, that does not restrict the flow area, but creates a back-pressure, to negate the imbalance and controls the free-fall so that the planned displacement pump rate determines the placement rate, not free-fall, plus when the differing densities of fluid, cement, mud, spacer pass through the tool different pressure traces are observed, to be able to track the job rather than zero on the pressure gauge until the cement has turned the corner, so if this tool is placed above the planned top of cement at the end of the job when the last barrel of cement passes through it the pressure changes and you now know the top of the cement inside the drill-pipe above the tubing stinger. This simple but effective tool can add significant reliability to the placement and quality of balanced cement plugs in just about every instance. This no moving parts tool is a simple sub and if anyone wants to know more they can contact firstname.lastname@example.org
I tend to agree with Jorrit, but the whole issue is a real can of worms! I was once on a job where my back-to-back and myself both had our 'own' cement stingers on site, because we'd got mutually fed up with the other modifying the design!
My personal preference was for an open-ended muleshoe, but in fact I've come to change that opinion, especially when setting multiple plugs, which can only be weight-tested. My current preference is for a closed-end design, slotted, and about six foot long, for ease of handling. Constructed by the rig welder from a piece of otherwise scrap tubing.
But I don't think there will ever be a true consensus of opinion on this. Though personally I doubt that a diverter sub is really any better than a home-made piece of kit.
Past laboratory studies by Amoco are detailed in JPT
paper dated Nov. 1984 "improved method of setting
successful cement plugs". This advocates the use of a
blanked off guide shoe with radial outlet ports.
( For details, please consult Technical Paper SPE 11415)
Other techniques, such as expendable fibreglass singers have also
been experimented with..
I cannot think of a one stinger design that would fit all situations
and slurries and situations. If P and A a long horizontal open hole
section with some strange cement recipe and spacers or P and A a
short section out of a casing shoe for a side track.
I use the rule that when running a stinger in open hole, have the
bottom plugged off and a stinger with a series of slots alone the
length of a scrape piece of tubing. The end of the stinger should
have a "pear shaped" piece of plate to aid guiding over ledges, and
since it will be plugged off, no formation can get inside and plug
off the stinger. Higher weight slurry with a lot of solids = more
slots to avoid the solids plugging up your slots, standard light
slurries less slots, to P and A some perforated casing, use just open
ended tubing cut with a mule shoe shape. On my present location I
have at least 3 or 4 stinger designs in the barang box, ready to go.
in 3.1/2" tubing and 2.7/8" tubing for slim hole.
Then there is the scrap tubing abandonment, where we abandon 2500m of
open hole with one plug and a hydraulic release sub with another
stinger above that on the hydraulic release, but that is another
- It is well documented that a diverter sub is preferred vs any home
made mule-shoe. (either closed or open ended, slotted or whatever
will not lend to a better job.)
- In unison pumping and placement is vitally important so that cement
does not channel (is turbulent or laminar flow expected?) etc. This
all depends on mud weight, spacers, wellbore size angle etc and will
affect if plug flips or not.
Note: This can happen even with a viscous pill or retainer on bottom
and a diverter sub in use?