Kill Mud Weight Calculator

    Calculate the mud weight required to balance formation pressure during well control operations. Essential for managing drilling kicks and maintaining wellbore stability.

    Calculation Inputs

    Original drilling fluid density

    SIDPP reading at surface

    Vertical distance to formation

    What Is Kill Mud Weight?

    Kill mud weight (KMW) is the mud density required to balance formation pressure after a kick has been taken. It is calculated from shut-in drillpipe pressure (SIDPP), existing mud weight, and true vertical depth. Using the correct KMW is critical for safe well control operations.

    Kill Mud Weight Formula

    A common field formula for kill mud weight in ppg is:

    KMW_ppg = MW_initial_ppg + ( SIDPP_psi / (0.052 × TVD_ft) )

    Where:

    • KMW_ppg = required kill mud weight (ppg)
    • MW_initial_ppg = current mud weight (ppg)
    • SIDPP_psi = shut-in drillpipe pressure (psi)
    • TVD_ft = true vertical depth of the well (ft)

    Example Kill Mud Weight Calculation

    Suppose you have:

    • Current mud weight = 12.0 ppg
    • SIDPP = 800 psi
    • TVD = 10,000 ft

    First, calculate the added mud weight needed to balance the kick:

    ΔMW_ppg = SIDPP / (0.052 × TVD)ΔMW_ppg = 800 / (0.052 × 10,000) ≈ 1.54 ppg

    Then, add it to the original mud weight:

    KMW_ppg = 12.0 + 1.54 ≈ 13.54 ppg

    Understanding SIDPP and TVD

    SIDPP represents the underbalanced portion of the well when the well is shut in with the drillpipe full of original mud. TVD is used in the calculation because hydrostatic pressure depends on vertical depth, not measured depth.

    Kill Mud Weight Best Practices

    • Always use accurate SIDPP readings taken after pressures have stabilized.
    • Verify TVD from the well plan or survey data before calculating KMW.
    • Apply the kill mud weight using an approved, step-by-step well control procedure.
    • Document all readings and calculations in the well control report.

    Kill Mud Weight FAQ

    Can I calculate kill mud weight using metric units?

    Yes. The same principles apply when using metric units such as bar, kPa, and kg/m³. The calculator handles unit conversions internally so you can work in your preferred system.

    Why is kill mud weight higher than the original mud weight?

    The original mud weight was not enough to balance the formation pressure, which is why the well took a kick. The kill mud weight adds enough extra density to offset the measured SIDPP and bring the well back into balance.

    Is kill mud weight the same as final circulating density?

    Kill mud weight is the target static mud weight. During circulation, the effective bottomhole pressure will also include dynamic effects such as annular friction, which should be considered in the well control procedure.

    Basic Formula:

    KMW = MW + (SIDPP / (0.052 × TVD))

    Mud weight required to balance formation pressure

    KMW: Kill Mud Weight (ppg)
    MW: Current Mud Weight (ppg)
    SIDPP: Shut-In Drill Pipe Pressure (psi)
    TVD: True Vertical Depth (ft)
    0.052: Hydrostatic pressure gradient constant

    Formation Pressure:

    FP = (0.052 × MW × TVD) + SIDPP

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