Wellbore Stability Calculator

Calculate safe mud weight window from pore pressure, fracture gradient, and collapse pressure

True vertical depth of the point of interest, not measured depth. Used to convert between pressure (psi) and equivalent mud weight (ppg).
ft
Formation pore pressure as equivalent mud weight. Normal = 8.5-9.0 ppg. Overpressured formations can reach 14+ ppg.
ppg
Maximum pressure the formation can withstand before fracturing, expressed as EMW. From LOT/FIT data or Eaton/Daines method.
ppg
Minimum mud weight to prevent borehole collapse. Depends on rock strength (UCS), in-situ stresses, and wellbore orientation.
ppg
Safety margin above pore pressure for swab effects during tripping. Industry standard: 0.3-0.5 ppg.
ppg

Results

Min MW (Collapse)-ppg
Min MW (Pore Press + Trip Margin)-ppg
Recommended Minimum MW-ppg
Maximum MW (Fracture Gradient)-ppg
Safe Operating Window-ppg
References & Formulas:
Min MW = max(Collapse Gradient, Pore Pressure + Trip Margin)
Max MW = Fracture Gradient
Safe Window = Max MW − Min MW
Pressure (psi) = 0.052 × MW (ppg) × TVD (ft)

Aadnoy & Looyeh: Petroleum Rock Mechanics. Zoback: Reservoir Geomechanics.