Surge and Swab Pressure Calculator

Annular Area: A = 0.7854 × (Hole² − Pipe OD²)

Velocity: V = Trip Speed ÷ 60

Friction Pressure: ΔP = f × ρ × V² × L ÷ (2 × Dh × 144)

Yield Pressure: ΔPyp = YP × L ÷ [300 × (Hole − Pipe OD)]

Total Pressure: ΔPtotal = Friction Pressure + Yield Pressure

ECD Change: ΔMW = ΔPtotal ÷ (0.052 × TVD)

Surge adds pressure. Swab subtracts pressure from the effective mud weight.

Enter the mud weight, hole size, pipe size, trip speed, length, viscosity, yield point, and friction factor.

Select surge when running pipe into the well. Select swab when pulling pipe from the well.

Press the calculate button. The result appears above the form and below the header.

Use the CSV button for spreadsheet records. Use the PDF button for reports.

What Surge Pressure Means

Surge pressure happens when pipe moves downward in a well. The pipe displaces drilling fluid. This action pushes fluid against the formation. The wellbore pressure rises during this movement. High surge pressure can fracture weak formations. It can also cause lost circulation. The risk becomes higher in tight annular spaces.

What Swab Pressure Means

Swab pressure happens when pipe moves upward. The moving pipe pulls fluid behind it. This action lowers pressure near the bottom of the well. If the pressure falls too much, formation fluid may enter the wellbore. This can create kick risk. Controlled trip speed helps reduce this danger.

Important Input Factors

Mud weight is a key factor. Heavier mud creates higher hydrostatic pressure. Pipe size and hole size control annular clearance. Smaller clearance increases flow resistance. Trip speed also matters. Faster pipe movement increases pressure change. Mud viscosity and yield point affect fluid drag. These values should come from current mud checks.

Using the Result

The calculator estimates pressure change from movement and fluid resistance. It also converts that change into equivalent mud weight. Surge increases the effective mud weight. Swab decreases the effective mud weight. Compare the final value with pore pressure and fracture pressure limits. Keep enough safety margin before tripping. Use conservative values when the well is narrow, deep, or unstable.

Practical Note

This tool gives planning guidance. Real wells may need more detailed hydraulics. Tool joints, cuttings, eccentric pipe, gel strength, and temperature can change results. Always follow approved drilling procedures and engineering review.

1. What is surge pressure?

Surge pressure is extra wellbore pressure created when pipe moves downward. It can raise bottomhole pressure and may fracture weak formations.

2. What is swab pressure?

Swab pressure is pressure reduction caused by pulling pipe upward. It can reduce bottomhole pressure and may allow formation fluids to enter.

3. Why does trip speed matter?

Higher trip speed moves fluid faster through the annulus. This usually increases pressure losses and raises surge or swab effects.

4. What does effective mud weight mean?

Effective mud weight is the apparent mud density after adding or subtracting dynamic pressure effects from pipe movement.

5. Can this calculator replace drilling software?

No. It is a planning and learning tool. Complex wells need verified hydraulics, field data, and engineering review.

6. Why is annular clearance important?

Narrow clearance increases flow resistance around the pipe. This can increase both surge and swab pressure changes.

7. What friction factor should I use?

A value near 0.02 is a common starting estimate. Use field-calibrated values when available for better accuracy.

8. Does surge increase or decrease pressure?

Surge increases effective pressure while running pipe in. Swab decreases effective pressure while pulling pipe out.