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Mud Weight Calculator

Work out mud weight instantly with clear inputs, formula shown and shareable results.

About Mud Weight Calculator

Mud weight must exceed the pore pressure gradient to keep formation fluids in place, with a trip margin of 0.2-0.5 ppg to cover swabbing when pulling pipe. It must stay below the fracture gradient or the formation breaks down and circulation is lost. The gap between the two is the drilling window.

Formulas

Pore pressure gradient

Gradient (ppg) = pore pressure (psi) / (0.052 x TVD (ft))

Mud weight

Mud weight = pore gradient + trip margin; must remain below fracture gradient

Worked example

With the default values below, Mud Weight Calculator returns Required Mud Weight of 9.391. Change any input above and every figure here is recalculated in your browser.

Inputs used

Pore Pressureminimum 0 psi
5,200 psi
True Vertical Depthminimum 0.01 ft
11,000 ft
Trip Marginminimum 0 ppg
0.3 ppg
Fracture Gradientminimum 0.01 ppg equivalent
16.5 ppg equivalent

Results

Required Mud Weight
9.391
Pore Pressure Gradient
9.091
Remaining Drilling Window
7.109
Bottom Hole Pressure
5,371.6

Step by step

  1. 1Values used
  2. 2Pore pressure gradient
  3. 3Mud weight
  4. 4Required Mud Weight= 9.391
  5. 5Pore Pressure Gradient= 9.091
  6. 6Remaining Drilling Window= 7.109
  7. 7Bottom Hole Pressure= 5,371.6

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
  • Mud weight selection is a well control safety decision. It must be made by qualified personnel against a verified pore pressure and fracture gradient prognosis, with a tested barrier envelope in place.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Mud weight selection is a well control safety decision. It must be made by qualified personnel against a verified pore pressure and fracture gradient prognosis, with a tested barrier envelope in place.

Frequently Asked Questions

What happens if the drilling window closes?

Neither overbalance nor circulation can be maintained, and casing must be set. In narrow-margin wells, managed pressure drilling or dual-gradient techniques extend the window.

Why 0.052?

It converts pounds per gallon and feet to psi: 1 ppg over 1 foot exerts 0.05195 psi. It is the fundamental constant of well control arithmetic.

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