Annular Capacity Calculator

    Calculate the volume capacity of annular spaces between two cylindrical objects such as casing and tubing, or wellbore and drill pipe.

    Calculation Inputs

    Casing or wellbore diameter

    Tubing or drill pipe diameter

    Feet or meters

    What Is Annular Capacity?

    Annular capacity is the volume of fluid that can be held in the space between two concentric strings, such as casing and drillpipe, or casing and open hole. It is used to estimate the volume of mud, spacer, or cement required to fill a given annular interval.

    Annular Capacity Formula (Oilfield Units)

    When diameters are in inches and length is in feet, a common field formula for annular capacity in barrels is:

    Cap_bbl_per_ft = (Dh_in² − Do_in²) / 1029.4

    Where:

    • Dh_in = hole or casing inner diameter (inches)
    • Do_in = drillpipe or casing outer diameter (inches)

    For a specific interval length in feet:

    Volume_bbl = Cap_bbl_per_ft × Length_ft

    Example Annular Capacity Calculation

    Suppose:

    • Hole size = 12.25 in
    • Casing OD = 9.625 in
    • Interval length = 1,000 ft

    First compute capacity per foot:

    Cap_bbl_per_ft = (12.25² − 9.625²) / 1029.4Cap_bbl_per_ft ≈ (150.06 − 92.64) / 1029.4 ≈ 0.0559 bbl/ft

    Then compute total volume:

    Volume_bbl = 0.0559 × 1,000 ≈ 55.9 bbl

    Typical Uses of Annular Capacity

    • Estimating required mud or spacer volume for displacement.
    • Planning cement jobs and verifying coverage.
    • Checking volume gains and losses during circulation and displacements.

    Annular Capacity FAQ

    Does annular capacity change with depth?

    The formula assumes constant diameters over the interval. If the hole is washed out, undergauge, or has varying strings, capacity should be calculated in segments.

    Can I calculate annular capacity in metric units?

    Yes. In metric, the same geometric concept applies, but diameters are in millimeters and volumes in liters or cubic meters. The calculator handles the appropriate unit conversions internally.

    Related Calculators

    Hydrostatic PressureAnnular VelocityMud Weight ConverterBuoyancy Factor

    Basic Formula:

    V = (D₁² − D₂²) × L / 1029.4

    Result in barrels when diameters are in inches and length is in feet

    D₁: Outer diameter (inches)
    D₂: Inner diameter (inches)
    L: Length or interval (feet)
    1029.4: Conversion constant for barrels

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