Annular capacity, abbreviated as AC, also called annular volume, is used to determining the volume of drilling fluids that can be held in the annular space between the drillstring (casing) and the wellbore.
Annular Capacity Formula |
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\( AC \;=\; \dfrac{ D_h^2 - D_{pod}^2 }{ 1029.4 } \) (\(bbl\;/\;ft\)) \( AC \;=\; \dfrac{ D_h^2 - D_{pod}^2 }{ 24.51 } \) (\(gal\;/\;ft\)) \( AC \;=\; \dfrac{ D_h^2 - D_{pod}^2 }{ 1,273,240 } \) (\(m^3\;/\;m\)) \( AC \;=\; \dfrac{ D_h^2 - D_{pod}^2 }{ 1,273.24 } \) (\(l\;/\;m\)) |
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| Symbol | English | Metric |
| \( AC \) = Annular Capacity | - | - |
| \( D_h \) = Drill Hole Size | \(in\) | - |
| \( D_{pod} \) = Casing / Drill Pipe OD | \(in\) | - |
