Hydrostatic Pressure and Mud Weight
Every drilling well control decision starts from one product: mud density times vertical depth gives the pressure holding back the formation.
The equation
P = 0.052 × MW × TVD
- P is hydrostatic pressure in psi
- MW is mud weight in pounds per gallon
- TVD is true vertical depth in feet, never measured depth
Worked example
A 12 pound per gallon mud at 10,000 feet true vertical depth exerts 0.052 × 12 × 10,000 = 6,240 psi. If the formation pore pressure is 5,700 psi the well is overbalanced by 540 psi, a comfortable margin against a kick.
When to use it
The constant 0.052 converts the units: one ppg equals 0.052 psi per foot. In deviated wells the pressure depends only on vertical depth, a fact that has saved and confused many a night shift.
Related Calculators and Reference
- Mud Weight and Pressure Gradient Calculator: convert between ppg, SG, and psi per foot.
- Probabilistic STOIIP Calculator: volumes with uncertainty ranges.
- Pipe Pressure Drop Calculator: add friction loss to the static head before you pick a pump or check a tap.
- PetroWiki by SPE: the industry reference for petroleum engineering.