Bottomhole Assembly Length for Desired Weight on Bit Formula
Bottomhole Assembly Length for Desired Weight on Bit calculates required bottomhole assembly length for drillstring and rig mechanics workflows in drilling engineering.
How engineers use this formula
Use this formula when the listed inputs (W_b, f, W_d, BF) are known and the assumptions behind the cited drillstring and rig mechanics relationship match the engineering case being checked.
Assumptions
- Input values are representative for the well, reservoir, fluid, or equipment case being evaluated.
- The declared units match the field-unit constants used in the formula.
- The cited formula applies to the selected petroleum engineering workflow.
Limitations
- The calculation does not replace a full engineering model or operating procedure.
- Accuracy depends on the source correlation, assumptions, input quality, and unit consistency.
Common mistakes
- Mixing unit systems without converting the inputs.
- Using default example values as field recommendations.
- Applying the formula outside the source assumptions.
Default example
Using the default inputs, L equals 276.110444 ft.
30000
1.15
147
0.85
Inputs
W_b
lbDesired Weight on Bit
f
dimensionlessSafety Factor
W_d
lb/ftDrill Collar Unit Weight
BF
dimensionlessBuoyancy Factor
Outputs
L
Required Bottomhole Assembly Length
W_b
Desired Weight on Bit
f
Safety Factor
W_d
Drill Collar Unit Weight
BF
Buoyancy Factor
Source and review
reviewedFormulas and Calculations for Drilling, Production and Workover, Lapeyrouse, N.J. (2002)
Lapeyrouse, N.J. 2002. Formulas and Calculations for Drilling, Production and Workover, 2nd Edition, Gulf Professional Publishing, Page 42.
Source