Drilling EngineeringWell Control
Maximum Allowable Annular Surface Pressure from Shoe EMW Formula
Maximum allowable annular surface pressure estimates the casing-shoe pressure limit by comparing shoe equivalent mud weight with current mud hydrostatic pressure.
How engineers use this formula
Use it for well-control margin checks and pressure-limit awareness while circulating or shutting in a well.
Assumptions
- Shoe strength is represented by equivalent mud weight at shoe depth.
- Current mud weight is uniform to the shoe.
- The calculation uses US field units.
Limitations
- Does not replace leak-off, formation integrity, or well-control program limits.
- Does not include weak zones above or below the shoe.
Common mistakes
- Using bit depth instead of shoe depth.
- Confusing MAASP with allowable casing pressure at another depth.
- Ignoring safety factors required by the well program.
Default example
Using the default inputs, MAASP equals 1,619.8 psi.
MW_maxppg
13.95
MWppg
9.5
TVD_shoeft
7000
Inputs
MW_max
ppgMaximum Allowable Equivalent Mud Weight at Shoe
MW
ppgCurrent Mud Weight
TVD_shoe
ftCasing Shoe True Vertical Depth
Outputs
MAASP
psi
Maximum Allowable Annular Surface Pressure
MW_max
ppg
Maximum Allowable Equivalent Mud Weight at Shoe
MW
ppg
Current Mud Weight
TVD_shoe
ft
Casing Shoe True Vertical Depth
Source and review
reviewedDrilling Manual. MAASP In Drilling Definition, Calculations.
Source