Annular capacity is one of basic values that you really need to understand. This post demonstrates you how to calculate annular capacity between casing or hole and drill pipe, tubing, or casing. There are several formulas as shown below to calculate annular capacity depending on unit of annular capacity required.
Note: Dh is bigger ID and Dp is smaller OD. The examples below will show the Dh as hole size and Dp is drill pipe OD
a) Calculate annular capacity in bbl/ft
Annular capacity, bbl/ft = (Dh2 – Dp2) ÷1029.4
Example: Hole size (Dh) = 6-1/8 in.
Drill pipe OD (Dp) = 3.5 in.
Annular capacity, bbl/ft = (6.1252 – 3.5 2) ÷1029.4
Annular capacity = 0.0245 bbl/ft
b) Calculate annular capacity in ft/bbl
Annular capacity, ft/bbl = 1029.4 ÷ (Dh2 – Dp2)
Example: Hole size (Dh) = 6-1/8 in.
Drill pipe OD (Dp) = 3.5 in.
Annular capacity, ft/bbl = 1029.4 ÷ (6.125 2 – 3.5 2)
Annular capacity = 40.743 ft/bbl
c) Calculate annular capacity in gal/ft
Annular capacity, gal/ft = (Dh2 – Dp2) ÷ 24.51
Example: Hole size (Dh) = 6-1/8 in.
Drill pipe OD (Dp) = 3.5 in.
Annular capacity, gal/ft = (6.125 2 – 3.52) ÷24.51
Annular capacity = 1.031 gal/ft
d) Calculate annular capacity in ft/gal
Annular capacity, ft/gal = 24.51 ÷ (Dh2 – Dp2)
Example: Hole size (Dh) = 6-1/8 in.
Drill pipe OD (Dp) = 3.5 in.
Annular capacity, ft/gal = 24.51 ÷ (6.125 2 – 3.5 2)
Annular capacity, ft/gal = 0.97 ft/gal
Please find the Excel sheet for calculating annular capacity.
Ref book: Formulas and Calculations for drill, production and workover by Norton J. Lapeyrouse
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