Apply torque in string when jarring down ?
02 October 2014
I am currently updating at Stuck Pipe Manual.
I have noticed that most manuals says: "Apply torque to string when jarring down. Do not apply torque when jarring up.
Anybody can come up with an explanation when to apply torque when jaaring down and not up.
Current surgestions are;
Due to stabilizer will pull BHA down with torque, good when jarring down and bad when jarring up.
Due to it will help (rotate) freeing the string from the wall.
Thanks for opening this can of worms. I am delighted to read Peters Airds' comments (in his first few paragraphs) about the need to act fast.
Whatever the siutation, the driller needs to be empowered to take immediate action once the pipe gets stuck. Things like 'wind in maximum RH torque and jar down with maximum force" need to be clear .. no need to have to call the Toolpusher or the Drilling Supervisor .. by then it's too late!
As I heard it said, and I am probably mis-quoting, "logging-whilst-drilling is a great phrase, how about watching-whilst- sticking?!"
Excellent post where there is not a best suit for all Im afraid, general comments as follows.
Best practice and most common event is to wind 'torque into a string' to the max, is surely when differentially stuck?, where the combined force and if fortune holds i.e. having the ability to jar down, all quickly applied, at the higher end permissible limits, is still as I know considered the best freeing method in this case.
Furthermore everything is designed to go downward and clockwise and as the well likely has the same spiralling tendancy, this combined 'max force applied' rotation, slumping and jarring down, method to get free' simply best fits, for all these reasons.
In a mechanically stuck situation when pulling out, the best practice is to jar down in the opposite direction. Here rotation may help is some specific cases, as they cannot be covered by a rule for all, but each case may have to be applied with thought and caution. e.g. Rotating in this case will as stated shorten string and could pull you in to a lets get-more-well-stuck scenario.
When running in and getting stuck in a tight or underguaged hole, again as stated combined torque, overpull and jarring could cause another component to fail or the string to twist off elsewhere. Since in this case, far greater combined 'von mises' stress will exist. e.g. as illustrated when backreaming for example in high angle wells, where simple rotating and pulling, fact! often places the drillstring string under 70% more combined stress than when the bit was drilling on bottom. So therefore overpulling, and rotating, torquing up string and jarring is not viewed as best practise.
In a pack off situation, where the hole has collapsed due to either failed mechanical and/or hydraulic reasons. My own view and experience is that again rotation and resulting torque, often does not help nor assist and is to be considered very carefully. Where generally only after circulation is established would I personally then initiate slow pipe rotation, carefully monitoring torque, to assure we are doing the right things to get the string free. Once circulating and moving free, then by all means rotate up and work pipe in stages to working rotating speed etc.
In high angle and horizontal wells what often results is that a simple mechanical or pack off situation where jar is working quickly deteriorate into a differential and well-more-stuck situation. e.g. Observed through jar now failing to work.
Final best practise comment is that if it was easy to get stuck it is generally easier to work the pipe free if best practices have been discussed, well understood and immediately acted upon.
So consider rotating and applying torque very carefully on a case by case basis.
However excepting differential sticking, where torque and slumping is well recognised, what I generally review is that too often, too much forces, and/or rotation and torque is too quickly applied resulting in more counter productive than beneficial effect and freeing intent.
As it was simply explained to me many years ago...
When you torque a drill string up, you shorten it, so when jarring down the string will also want to expand up to it's pre-torque normal length. This actually helps you with a downward force.
Jarring up is different in that you stand a chance of parting the pipe as you are pulling against the "normal" DP tension and that unknown value you've artificially put in with the torque
Everyone knows about the legendary gentleness of drillers, especially when it comes to stuck pipe.
In my view, if you just look at the Torque-Tension graph for a given pipe / TJ config, you have your answer.
You will observe that you tension allowance reduces with torque applied on your string.
As you will tend to put the max allowed (uniaxial) while jarring up, you may then break your pipe if torque is applied, even under the max allowed tension.
This has almost no chance to happen while jarring down
Example: A 5"-19.5# G105 can take 436kips tension with no torque, it goes down to about 350kips max with 30klbs*ft torque applied.