A Quick Guide to;
the Stim Tube™ Tool
the Stim Gun™ Assembly
and the Well Stimulation Tool
These are Halliburton’s three
propellant stimulation tools.
OK, so you are still wondering exactly what are these tools, what do they do and how do
they do it! How about a quick introduction, a few explanations, then some pointers and
we will try to cover the most important do’s and don’ts. At the end we’ll even throw in
some e-mail addresses and phone numbers so you can always get an answer to your
questions.
Why To overcome perforating, drilling and cementing damage in the near wellbore,
initiate fractures and release turturosity in the formation. Propellant has also been used to
overcome scale, asphaltine and wax problems, it can be run in all types of well fluid
including Acid, Brine, Methanol, crude oil and Frac oils.
Propellant- A mixture of potassium perclorate particles bound together with a plastic
resin epoxy. The end product appears to be an industrial plastic, it can be cast in variety
of shapes and colors.
Stim Gun- An assembly that is constructed by adding a sleeve made of propellant to an
expendable hollow steel perforating gun. The sleeve is slid over the gun and secured in
place by two rings. The assembly is then run in the well in the same manner as a
conventional perforating job, the subs on the gun are usually equipped with fins that are
of a larger diameter than the sleeve in order to protect the sleeve. For reasons to be
covered later the sleeve usually covers only 50% of the perforating interval.
Stim Tube- A cylinder of propellant that has a steel pipe cast in the center of it. The ends
of the pipe are threaded to allow for easy assembly. In the center of the steel pipe is a
stainless steel tube that facilitates the running of detonating cord through the center of the
tool.
Well Stimulation Tool This tool looks like exactly like a Stim Tube from the outside, it
is cast in a different color to avoid confusion. Instead of the steel pipe running completely
through the tool there are only short pipe nipples cast in either end of the propellant. This
propellant is run inside steel carriers (3 1/8 or 4 inch OD) with a large number of big
diameter holes to facilitate the movement of gas. This tool is often used in long tubing
conveyed assemblies.
How it works Both the Stim Tube™ Tool and the Well Stimulation Tool use detonating
cord and a blasting cap for ignition. The detonating cord is run through a stainless steel
tube that is cast in the center of the propellant, because everything is exposed to the well
bore (wet system) a non-fluid sensitive blasting cap must be used and the bottom of the
cord must be covered and sealed. When the cap is fired the cord detonates and a shock
wave starts radiating outward from the center of the tool. The tool defelgrates (chemical
burn) a large amount of energy and gas is released, pressure builds up rapidly pushing
through the perforation damage and causing fractures in the near wellbore.
The Stim Gun™ Assembly works on the same basic principles. The major difference is
that the propellant sleeve is ignited by the perforating charges going through it.
How do we Know it works? By using a high-speed recorder that can record data on two
channels at over 100,000 samples per second while with standing shock loads up to
50,000 g’s. We have pressure records and acceleration records, using this data we have
been able to change the burn characteristics of the tool to best suit our needs. We also can
perform computer modeling of a job and compare data to the actual pressure recorder
record.
And now for our Top Ten List
Top Ten Recommendations Associated with the Propellant Technology
1. Complete a computer model and /or technical review for all jobs. Turn down poor applications.
Inform the customer of all possible risks, preferably in writing ahead of time.
2. Historically – most field problems have been caused by running too much propellant. Consider limiting the
amount of propellant coverage to 50% or less of the perforated interval. (Per gun for Stim Gun and per
Run for Stim Tube and the WST tool.)
1. For wire line – 10 feet or 3 meters of sleeve / run maximum of 15 feet or 4.5 meters of WST or Stim Tube™
Tool / run. Rehead rope socket for maximum strength before each run.
(IMPORTANT! These numbers are based on the strength of 5/16” diameter wireline, reduce these
numbers if you are running on a smaller line)
4. Candidate wells must be perforated with a minimum of 4 shots per foot or 13 shots / meter and at least 120
deg. phasing; perforation entry hole diameter is also very important. The OD of the propellant assembly
must also have reasonable clearance inside the casing – ask about these issues as part of the technical
job review.
5. A minimum of 700 psi of hydrostaic pressure is required, this is to produce an optimum burn. Use a
formation compatible fluid -do not over balance a gas well with a damaging fluid.
6. A minimum of 100 feet of air gap from the top of the fluid to the BOPs is required.
7. Stay away from bridge plugs unless they are covered with 20 feet or 6 meters of cement until energy
absorption strategies are resolved. Do not shoot within 12 feet or 4 meters of PBTD or 60 feet or 20 meters
of a packer
8. Remember – casing damage is typically a result of inadequate casing strength and / or cement bond
anywhere within 100 feet or 30 meters of the stimulation the interval.
1. Only 40 grain detonation cord is approved for use with all StimTube™ Tool and WST tools.
10. Run at least N-80 pup joints and tubing in the lower assembly (above firing head) on all tubing conveyed
runs.
If you have any questions or concerns, call anyone listed at the end of this guide.
Now that I’ve given you the top ten guide I could list certain exceptions and special conditions
but I won’t. Follow this list and if anything does not meet these rules ASK !
You’ll have a lot more success that way.
The best advice I can give from experience?
Never forget about rule number 6 above, it is the one that will be most likely to cause damage
and injury.
When you shoot a propellant tool make sure that the area around the wellhead and the area
between the wellhead and the truck is clear of people and loose equipment. It is not normal but
there have been cases where the line has dropped to the ground (tool moving up-hole) and then
jumps violently around (tool moving down hole).
Stay Away From The Line!
When every thing has stabilized check sheeves, slings and line, then first try to move down
hole, hopefully the tool will still be free. Then pull up slowly for 100 to 150 meters, if
everything is free come out of the hole, use caution when you get near surface you should
expect damaged line. Use extra care when laying the tool down your cable head has received a
severe shock load and may part without warning! Record and report, take extra care to note
well conditions, perforations and tool position.
Treat these tools like explosives! They have a blasting cap and detonating cord, even if the
tool won’t burn on surface the cap and cord will (picture hundreds of little pieces of plastic
shrapnel spraying outward).
Change the screws in the firing head after every run and the chance of one shearing off drops.
Those grooves cut in the firing head are so you can use string to tie down your detonator and
any loose wires that you might have. Take a couple of extra seconds and tie it down in two or
three places.
Stay away from the top and bottom edge of a perforated interval, the effect of the tool is
general so being a few feet away from the edge does not stop the energy from reaching it. If
you are sitting with the top of the tool at the top of the interval you run the risk of building up
excessive pressure above the tool (it can not bleed off into the formation). If this pressure
becomes high enough it will push the tool off of the line.
When this effect happens at the bottom edge of a perforated interval, the pressure build up is
under the tool and the tool is shot upwards resulting in cable damage, being stuck in the hole
with cable wrapped around the tool or lost tools.
You don’t have any RDX 40 round detonating cord? You can use RDX40 Flat if you have the
half round inserts for capping but never use a cord above 50 grains per foot or you will have
equipment failure due to excessive pressure and load ratings. That means it will blow things
apart such as tools and possibly casing.
Fill out the job data sheets. Keep good records and share information, both the good and the
bad, we will all benefit from it.
