From the previous post, you learn how to calculate annular capacity and this article shows you how to use the same principle to calculate internal capacity factor of open hole & inside cylindrical objects such as tubular, drill pipe, drill collars, tubing, casing, etc.

There are several formulas to calculate inner capacity depending on unit of inner capacity required. The formula are listed below;

## Oilfield Unit

## Calculate Internal Capacity Factor in bbl/ft

Inner Capacity in bbl/ft = (ID)^{2}÷1029.4Where;

Internal Diameter (ID) in inch

**Example:**

Determine Internal Capacity Factor in bbl/ft of a 6-1/8 in. hole:

Internal Capacity Factor in bbl/ft = 6.125^{2}÷1029.4

Internal Capacity Factor in bbl/ft = 0. 0364 bbl/ft

## Calculate Internal Capacity Factor in gal/ft

Inner Capacity in gal/ft = (ID in.)^{2}÷24.51

Where;

Internal Diameter (ID) in inch

**Example:**

Determine Inner Capacity Factor in gal/ft of 6-1/8 in. hole:

Internal Capacity Factor in gal/ft = 6.125^{2}÷ 24.51

Internal Capacity Factor in gal/ft = 1.53 gal/ft

## Metric Unit

## Calculate Internal Capacity Factor in cu-meter/meter (m^{3}/m)

Annular capacity inm^{3}/m= (ID^{2}) ÷1,273,240Where;

Internal Diameter (ID) in mm

**Example:**

Hole size (ID) = 155.56 mm.

Internal Capacity Factor in m^{3}/m = (155.56^{2} ) ÷1,273,240

Internal Capacity Factor in m^{3}/m = 0.0190 m^{3}/m

## Calculate Internal Capacity Factor in liter/meter (l/m)

Annular capacity inm^{3}/m= (ID^{2}) ÷1,273.24Where;

Internal Diameter (ID) in mm

**Example:**

Hole size (ID) = 155.56 mm.

Internal Capacity Factor in l/m = (155.56^{2} ) ÷1,273.24

Internal Capacity Factor in l/m = 19.0 l/m

**Volume can be determined by this following formula;**

## Oilfield Unit

Volume = Internal Capacity Factor x LengthWhere;

Volume in bbl

Internal Capacity Factor in bbl/ft

Length in ft

Example:

Internal Capacity Factor = 0. 0364 bbl/ft

Hole Length = 3,000 ft

Volume = 0. 0364 x 3,000 = 109.2 bbl.

## Metric Unit

Volume = Internal Capacity Factor x LengthWhere;

Volume in cu.meter

Internal Capacity Factor in cu.meter/meter

Length in meter

Example:

Internal Capacity Factor in m^{3}/m = 0.0190 m^{3}/m

Hole Length = 3,000 m

Volume = 0. 0190 x 3,000 = 57 m^{3}

**Download Free Excel Spread Sheet**

Please find the excel sheet on how to calculate internal capacity factor.

**Ref books: **

Lapeyrouse, N.J., 2002. Formulas and calculations for drilling, production and workover, Boston: Gulf Professional publishing.

Bourgoyne, A.J.T., Chenevert , M.E. & Millheim, K.K., 1986. SPE Textbook Series, Volume 2: Applied Drilling Engineering, Society of Petroleum Engineers.

Mitchell, R.F., Miska, S. & Aadny, B.S., 2011. Fundamentals of drilling engineering, Richardson, TX: Society of Petroleum Engineers.