Along Hole Components of Force
Consider a short element of a BHA which has a weight W.
Effective weight in drilling mud = W(BF)
Component of weight acting along borehole = W(BF)cosq
If the BHA is not rotated, the force of friction, FFR acting up the borehole
on the BHA element is given by:
FFR = mN
...where m is the coefficient of friction,
N is the normal reaction force between the BHA element and the borehole
wall. If this normal reaction is due only to the weight of the BHA element
itself, then:
N = W(BF)sinq and hence
FFR = mW(BF)sinq
The net contribution to the WOB from this BHA element is therefore
WBIT = W (BF) (cosq - msinq)
Consider a short element of a BHA which has a weight W.
Effective weight in drilling mud = W(BF)
Component of weight acting along borehole = W(BF)cosq
If the BHA is not rotated, the force of friction, FFR acting up the borehole
on the BHA element is given by:
FFR = mN
...where m is the coefficient of friction,
N is the normal reaction force between the BHA element and the borehole
wall. If this normal reaction is due only to the weight of the BHA element
itself, then:
N = W(BF)sinq and hence
FFR = mW(BF)sinq
The net contribution to the WOB from this BHA element is therefore
WBIT = W (BF) (cosq - msinq)
