Negative WOB!!!!1

[suresh.upes11]

While drilling many times i have seen WOB value in negative.Is it really sending some operational information or calibration errors of sensors.Need advice on this.

[willbe]

Hi suresh.upes11,

Multiple things can happen.
1) Assuming you reset WOB to 0 before tagging bottom at the beginning of a stand. When the block goes further down while drilling, more drilling line will have moved from the draworks and will be hanging in the derrick. This will mean the sensor on the dead line anker will measure more hookload. For you looking at the weight indicator it might appear the WOB goes down and even becomes negative. Suggest picking of bottom and reset your WOB.

2) What formation are you drilling when it happens...maybe it is a particular formation which has some packing off tendencies. If the pump pressure goes up, the pressure is trapped around the BHA and will force / push your string up.. Don't underestimate these forces....they easily become thens of thousend of pounds with a couple of hundred psi... (easy calculation - 1/4 x PI x bitdiameter squared x delpa Pressure in psi's). Also nice way to get stuck if not proper reacted upon. Is the BHA balled up arouns stabs or bit after POOH?? Or maybe you are drilling unstable coal formation etc..

3) Sometimes when bearings in the crown or traveling block are not really in good shape anymore you can get weird results..... for example up weight lower than down weight etcetera...

4) Also when using hydraulic pancake style weight sensor, temperature can be of influence. If the day start and temparature rises and maybe sun start heating up the sensor, measurements will be influenced especialy when working in arctic or desert conditions. Normally you don't notice this if you drill a stand at a normal / fast speed. If you drill slowly though it might have some influence

Hard to say what is happening with the info you provided...