Private Forums
Jars and accelerators
09 January 2009
I am interested to know peoples feelings and preferences on
accelerator placement.
My feelings are they are good in top hole to act as a kind of shock
absorber to protect the contractors equipment, but wonder about the
effectiveness of these tools in deeper environments, and would like
to poll different views on placement strategies.
4 answer(s)
Consultant [retired Shell staff]
Total Posts: 228
Join Date: 02/09/05

You may like to read the conclusions/recommendations of publication:

IADC/SPE 14746 Computerised Drilling Jar placement, Anadrill. (1994)

Dansk Geotermi
Total Posts: 9
Join Date: 20/04/11
Chris, this is late, but I just saw your posting,

Accelerators or Energizers are useful in all holesections, regardless of pipe stretch for the simple reason of friction.  When you are pulling on stuck pipe, the overpull is translated into pipe stretch.  When the jar fires, it is the contraction of the drillpipe that determines the acceleration and terminal velocity of the hammer hitting the anvil inside the jar.  The contraction of the drillpipe is dependent of the friction factor for the entire string from the jar to the surface.   If you have an energizer/accelerator in the string above the jar, it is only the pipe/DC´s from the jar to the energizer that is subjected to friction.  The energizer has mechanically de-coupled the rest of the string.  So, apart from storing energy in the Belleville springs, is if also foremost a ”œfriction remover” that provides a higher terminal velocity.

Best regards
Total Posts: 5
Join Date: 28/05/08
I recommend to position the jar above the DC if your going to use
accelerators (to be under tension)to avoid putting the jar or the
accelerator in neutral. On the other hand if the jar will be used
without accelerator i recommend to be positioned near the expected
the stuck point (to be under compression). using jars placement
software also helps when drilling a deviated and horizontal wells.

Borai ElSamari
bp, Egypt
Drilling Specialist/Well Engineer/Training Consultant
Total Posts: 339
Join Date: 10/01/05

Happy new year to ya.

Fundamental but often forgotten on this subject?
Ref. Page one of the old Bowen fishing catalogue:
'Jar and accelerators to be applied in shallow and deep, deviated
wells'. If only it was that easy, lol!

A fundamental but never to be forgotten yet often abused statement.
Where I have had many heated discussions on over the years.

As an example on one particular occasion, offshore Norway, we got
stuck drilling shallow riserless wellbore at about 2,000ft in 17-
1/2" hole, with a jar only, strongly against my wishes!.

Bits then started falling off the top drive in about the first
1/2hr! So accelerator is the engineered and preferred solution if
you want to jar shallow, i.e. to protect the surface kit!

After 4hrs, debris on the drill floor, the Jars never got us free
but we did evolve and adopt what ius now a best practices solution
to get free with no jar required, in about 5minutes after being
stuck for 4hrs! So here like many cases its horses for course and
why everyone has perhaps such different opinions w.r.t jar only, jar
and accelerator, two jars, two jars and accelerators etc etc.??

However in some shallow environments e.g. deepwater, notably where
you have unconsolidated silt/sands for me, based on evidence I have
seen and observed, you won't generally jar free. Hence little point
in running a jar anyway. Best practice being the PLF technique
i.e. assess if you are deep enough, pump at max rate, frac the
formation inject the sands into somewhere, to get the sand moving
and you can suck yourself out and free in minutes! i.e. Been there
and got the tee shirt! Other issues in deepwater is cold
temperatures and time for jar/accelerator to cock and fire etc, i.e.
it may take a while??

Once you have enough stretch in the drillstring, you can run jars
only, if data, amount of pull/torque you have on rig available,
states they are needed. e.g. In some areas where hundereds of wells
have been drilled, they have been equated as non value adding and
are not used at all.

Once you go into high day rates, high angle and horizontal wells
etc. First assess what are the typical stuck pipe problems you would
expect and nbe needed to jar?. e.g. Do you need impact e.g. for
ledges etc, or impulse for tight hole, differential sticking or
both? Then weigh up all pro's cons accordingly.

For me I ALWAYS would get a 3rd party jar company and a good service
hand to run a jar/accelerator placement program so I can assess
benefits of jar, jar/accelerator etc or not for the typical problems
I expect. Plus what hammer anvil requirements are needed?
e.g. Here how many times do you see a drilling program change the
jar/accelerator postion when in the build section vs. drilling

Most recent case where it did pay dividends is we were drilling a
quite fractured and variable chalk section horizontally. Jar and
accelerator in BHA. Took some overpull during POH, on a known
transition, fractured zone, got stuck, i.e. couldn't move pipe at
all. After discussion made it clear to everyone we were going to
only jar away from the problem ONLY. However Lost jar action after
1/2hr. Now convinced we were differentially stuck. So took our mud
weight to balance, immediately regained jar/accelerator action and
in two licks we were free, having jarred away from problem. Note: I
sincerely believe we wouldn't have got free if we did not have a
jar/accelerator in this case.

Another key industry lesson learned in this subject is the fact that
98% of all jars/accelerators stated as failed in the field, work in
the shop when they get them back onshore. So the problem isn't
often the Jar, its the people?

Knowing hazards, risk, downhole problems expected, well type,
local area, data-set knowledge then getting drilling Supts,
engineers onshore, and drillers, toolpushers to DD's and company men
trained, educated and developed in best practices of how
jars/accelerators are to be worked, is the key.

No easy answers I am afraid just a mixed set of variables to weigh
up and assess all options to then deliver best solution(s) to

Final word for top drive drillers? It is fact for me that the most
common stuck pipe scenario I have seen in a ratio of perhaps seven
to one, is coming off bottom rotating and getting stuck. Because?
the time the driller reacts to the overpull, due to combined
rotation that exists, they have additionally pulled and torqued into
the problem, big time. Therefore not a good thing in my book to do
in first place?. Invariably then often pulling more and jarring up
as the immediate action then recommended? I'll let the mud logs of
incidents I have support me in this statement?

Solution for me has always been not to rotate off bottom or please
just at a minimal RPM. Allowing ability to react to overpull not to
get stuck in first place. When stuck, then slack off all bar kitchen
sink and hope you have a jar/accelerator (if at high angle) in the
sting above jar point so you can jar down to get free. Note: Another
reason why the old fashioned 'kelly-way' way of picking up off
bottom with no rotation is always for me the first, foremost and
fundamental way to come off bottom in my book.

Have a jar-stuck free year everyone.



Jump to top of the page