Maximum Weight on Bit Formula
Maximum Weight on Bit calculates maximum weight on bit for drillstring and rig mechanics workflows in drilling engineering.
How engineers use this formula
Use this formula when the listed inputs (L_d, W_d, BF, alpha, SF) 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, WOB equals 53,500.751626 lbf.
500
147
0.85
10
1.15
Inputs
L_d
ftLength of drill collars
W_d
lbf/ftUnit weight of drill collars
BF
dimensionlessBuoyancy factor
alpha
degreeWellbore inclination
SF
dimensionlessSafety factor
Outputs
WOB
Maximum weight on bit
L_d
Length of drill collars
W_d
Unit weight of drill collars
BF
Buoyancy factor
alpha
Wellbore inclination
SF
Safety factor
Source and review
reviewed501 Solved Problems and Calculations for Drilling Operations, Robello, S.E. (2015)
Samuel, E. Robello. 501 Solved Problems and Calculations for Drilling Operations, Sigma Quadrant, Houston, Texas, 2015, Page 380.
Source