Annular capacity between casing and multiple strings of tubing

Input(s)

$\mathrm{D}_{\mathrm{i}}$: Inner Diameter of Casing (in.)

$\mathrm{T}_{1}$: Diameter of Tubing 1 (in.)

$\mathrm{T}_{2}$: Diameter of Tubing 2 (in.)

Output(s)

$\mathrm{C}_{\mathrm{a}}$: Annular Capacity $(\mathrm{gal} / \mathrm{ft})$

Formula(s)

$$ \mathrm{C}_{\mathrm{a}}=\frac{\mathrm{D}_{\mathrm{i}}^{2}-\left(\mathrm{T}_{1}^{2}+\mathrm{T}_{2}^{2}\right)}{1029.4} $$

Reference(s)

Lyons, W. C., Carter, T., and Lapeyrouse, N. J., 2012, Formulas and Calculations for Drilling, Production and Workover, Third Edition, Gulf Professional Publishing, Page: 15.