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Agitator - above or below Jar and why?
30 March 2019
Kind folk of the Community;

When drilling with an Agitator for directional wells - who places the Agitator above the jar, who places the Agitator below the Jar - and in all cases - what are you reasons for your chosen placement?

Just interested to poll peoples opinions....
6 answer(s)
Regis STUDER
General Manager
DrillScan
Total Posts: 17
Join Date: 27/02/16

Hello,

With regards to your question:

  • A further consideration I am thinking about is the reflection / partial absorption of the shock wave from the Jar in case Jarring is required.
  • Surely - both impact and impulse would be affected?

As suggested on my previous post, I’m in favour of placing an oscillation tool rather above the Drilling Jar, if possible*, to benefit from optimized weight transfer for both sliding steering of the directional BHAs AND preventing differential sticking in applications exposed to this stuck-pipe mode risks. But also, to help in effective Jarring in case of differential sticking while sliding, reducing flow-rate to the low range the oscillating tool can still propagate impulses.

Keeping the Drilling Jar in micro axial movement while sliding warrants more effective chances operating it should differential sticking occurs. Quick action from the driller is of essence in such cases.

Placement optimization of an oscillation tool in a string requires modelling of same accounting for the excitation force position, amplitude and frequency. On that basis, wave propagation of oscillations’ impulses up and down the string can be assessed and *best placement in a given string for a given application can be derived. Independent modelling is available today in that domain.

To answer your question: the impact forces of Jarring and associated shock-waves are an order or two of magnitude higher than the impulse forces of an axial oscillation tool. Example for 8’’ tools:

  • 8’’ Axial Oscillation Tool forces in play: ± 2000-3000lbs of excitation force at 15-20hz
  • 8’’ Drilling Jar forces in play: ± 300 000lbs Jar Load and ± 2 000 000lbs Jar Blow

The Jar Blow is a product of the Energy Equation:

E = ½* (W/g)*V²

Where E is the energy available to perform the impact work (adequate BHA design) and accelerates the Jar Weight (W) to the Velocity (V) which is exponential in value.

In my opinion an Axial Oscillation Tool would not degrade Jarring efficiency in any applications.

Regards
Régis




hendo
Mentor to the youth of our industry
OILSERV
Total Posts: 131
Join Date: 27/02/08
Gents.
A further consideration I am thinking about is the reflection / partial absorption of the shock wave from the Jar in case Jarring is required.
Surely - both impact and impulse would be affected?
Regis STUDER
General Manager
DrillScan
Total Posts: 17
Join Date: 27/02/16
Hello

Extending the discussion to all Oscillation Tools, there is added value to position these devices above the Drilling Jar to mitigate the loss of jarring capabilities in case of differential sticking.
Equality in case of borehole packing-off, Jarring Down may be lost due to buckled pipe above Drilling Jar while slacking-off, an Oscillator may help in that case too.
Régis
PatrickLemmers
Technical Mgr - Drilling Tools
Franks International
Total Posts: 5
Join Date: 10/11/16

Hi Chris,

Have run Ag-Itators both up in the string (above the Jars) and below the jars. Used them for different mechanisms and different reasons. Typically when using them for axial string movement to overcome the friction of the string when sliding, NOV has a certain "ideal" calculated placement. This is however also dependent on the MWD company, as the generated pulse could interfere with the MWD signal. Was on a job some years ago where Weatherford preferred the Ag-Itator 300m above their MWD system (worked well, by the way).

As said, also run them below the Jars, even below the MWD: the effect was that it certainly improved drilling performance, as it induces a kind of "jack-hammer" effect. Mind you, this can be quite fierce on the smaller tools, such as 4 3/4" motors, where we once had all ACME connections of the motor belled up by it. When running below the MWD, some systems could also have issues, due to the pressure pulse generated by the Ag-Itator which can spike once in a while.

Good tool though 


IainDD
Lead ERD Advisor
Merlin ERD Limited
Total Posts: 7
Join Date: 04/05/16
Chris,

Is this not more a question of jar placement in a long lateral, as this is the primary environment for running the agitator? Placement of the agitator would tend to put it above the jars if you are running the jars where I would recommend to put them in the BHA, no matter what well design you are drilling.

When I worked for NOV the gurus talked about the agitator having a major influence on the string 600m either side of it and as such the agitator was placed above the jars. They now have a software package to calculate the best placement but I would suspect in all cases it would recommend the placement above the BHA and hence above the jar - as long as you are an advocate for the jars in the BHA on laterals and not back in the cased hole section, kilometers away from were you are likely to be stuck.

Regards, Iain
mhayes
Consultant Driling Engineer / ERD Advisor
Stanfield-Hayes Consulting
Total Posts: 38
Join Date: 25/03/11
I'm afraid to say fro me its not a straight binary answer, it does depend on the situation and need.

Whilst ideally I'd prefer to design without the need there are times when they may be needed to improve weight transfer and it becomes a design point of where they are going to be most effective for the run at hand and may take (significant) design reiteration to get the best position.

Most commonly I've designed stems with the agitator above jars to focus on the points where they can make the biggest impact (or where the biggest weight loss is), in the early days I think I may have designed BHAs where they were run below the jars, but not recently. Though this could be a factor of the challenges being faced.

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Chris Henderson

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