Surge & Swab Pressure Calculator

    Calculate surge and swab pressures while tripping pipe in or out of the hole. Essential for managing wellbore stability, preventing kicks, and avoiding lost circulation.

    Calculation Inputs

    Wellbore or casing inside diameter

    Drill string or casing outer diameter

    Normal circulating flow rate

    Circulating friction gradient in annulus

    Length of pipe string being moved

    Rate of pipe movement (RIH or POOH)

    True vertical depth for ECD calculation

    Static mud weight

    Select flow regime for friction scaling

    What Are Surge and Swab Pressures?

    Surge and swab pressures are dynamic pressure changes at the bottom of the wellbore caused by running or pulling pipe in the hole. Moving pipe into the hole tends to increase bottomhole pressure (surge), while pulling pipe out of the hole tends to reduce bottomhole pressure (swab).

    Bottomhole Pressure and Equivalent Density

    Surge or swab effects are often expressed as a change in equivalent density at the depth of interest. A general relationship between pressure and equivalent density in oilfield units is:

    Density_ppg = P_psi / (0.052 × TVD_ft)

    Where P_psi is the total pressure at that depth (hydrostatic plus any dynamic components such as surge, swab, or friction).

    Conceptual Use in Surge & Swab Analysis

    The surge & swab calculator estimates the additional pressure at bottomhole due to pipe movement, based on:

    • Annular geometry
    • Mud rheology and density
    • Tripping speed and direction
    • Pipe and tool OD

    That additional pressure is then combined with static hydrostatic pressure and expressed as an equivalent density using the same 0.052 × MW × TVD relationship.

    Operational Risks

    • Excessive surge: can push effective bottomhole pressure above fracture pressure and cause lost circulation.
    • Excessive swab: can reduce effective bottomhole pressure below pore pressure and lead to an influx or kick.

    Surge & Swab Best Practices

    • Control tripping speed, especially in narrow pressure windows.
    • Monitor pits and flow closely during trips.
    • Use conservative assumptions for rheology when conditions are uncertain.
    • Plan trip speeds based on modeled surge and swab results.

    Surge & Swab FAQ

    Does well deviation affect surge and swab?

    Yes. Deviated and horizontal wells often have more complex annular geometry and may be more sensitive to surge and swab effects, particularly where cuttings beds and eccentricity are present.

    Can surge and swab be eliminated?

    Surge and swab cannot be eliminated entirely because any pipe movement in fluid causes some displacement. They can be managed by adjusting mud properties, trip speeds, and pipe movement patterns.

    Basic Formula:

    AV = 24.51 × Q / (D_hole² - D_pipe²)
    AV_surge = AV_circ + V_trip
    AV_swab = |AV_circ - V_trip|

    Turbulent Flow:

    ΔP_surge = g_circ × (AV_surge/AV_circ)² × L

    Laminar Flow:

    ΔP_surge = g_circ × (AV_surge/AV_circ) × L

    ECD is calculated from bottomhole pressure: ECD = BHP / (0.052 × TVD)

    Get the App

    Access all calculators on the go with our mobile app

    Disclaimer: All calculators and tools provided on DrillingCalculator.com are for informational and educational purposes only. While every effort has been made to ensure accuracy, results may vary depending on input data, assumptions, and field conditions. DrillingCalculator.com makes no warranties or guarantees, expressed or implied, regarding the completeness, accuracy, or reliability of any calculation or result. Use of this site and its calculators is entirely at your own risk, and DrillingCalculator.com assumes no responsibility or liability for any decisions or outcomes based on their use.