Documentation / Tubing Capacity

Tubing Capacity

Calculate fluid volumes inside tubing, annular space between tubing and casing, and void capacity above fluid level. Includes 338 pre-calculated tubing/casing combinations using API dimensional standards.

Tubing Volume Calculation

Tubing capacity is calculated from the internal diameter, which varies by tubing size, weight (wall thickness), and coupling type (EUE upset vs. non-upset).

Capacity (bbl/ft) = ID² × 0.000971
Capacity (gal/ft) = ID² × 0.0408

Where:

ID = Internal diameter (inches)

0.000971 = Conversion factor for barrels per foot

0.0408 = Conversion factor for gallons per foot

Derivation

These factors come from the volume of a cylinder converted to oilfield units:

Volume = π × r² × length
bbl/ft = π × (ID/2)² × (1 ft) × (1 bbl / 9702 in³)
bbl/ft = π × ID² / 4 × 12 in / 9702 in³/bbl
bbl/ft = ID² × 0.0009714...

Tubing Dimensional Data

Internal diameters vary significantly by weight class. Heavier tubing (thicker walls) has smaller ID and lower capacity per foot.

OD (in) Weight (lb/ft) ID (in) bbl/ft Coupling
2-3/8" 4.70 1.995 0.00387 EUE
2-3/8" 5.95 1.867 0.00339 EUE
2-7/8" 6.50 2.441 0.00579 EUE
2-7/8" 8.70 2.259 0.00496 EUE
3-1/2" 9.30 2.992 0.00870 EUE
3-1/2" 12.95 2.750 0.00735 EUE

Note: The calculator includes additional weight classes and both upset (EUE) and non-upset coupling configurations. Non-upset tubing has slightly smaller coupling ID, which can matter for wireline or coiled tubing operations but is typically neglected for fluid volume calculations.

Annular Capacity

The annular volume between tubing OD and casing ID. Critical for calculating displacement volumes, circulating times, and fluid volumes during workover operations.

Annular (bbl/ft) = (IDcasing² - ODtubing²) × 0.000971

Where:

IDcasing = Casing internal diameter (inches)

ODtubing = Tubing outer diameter (inches)

Common Casing Sizes

Casing ID varies by weight (wall thickness). Heavier casing has smaller ID.

Casing OD Weight (lb/ft) ID (in) Common Application
4-1/2" 11.60 4.000 Slim-hole production
5-1/2" 17.00 4.892 Standard unconventional
5-1/2" 20.00 4.778 Standard unconventional
5-1/2" 23.00 4.670 High-pressure zones
7" 26.00 6.276 Large-bore production
7" 32.00 6.094 High-pressure/deep

Pre-Calculated Combinations

ESP Calc includes 338 pre-calculated tubing/casing combinations covering:

Select your tubing and casing from the dropdowns to get the annular capacity without manual calculation.

Void Capacity

The void volume is the portion of tubing above the fluid level. Relevant for estimating gas volume in the tubing string or calculating fluid required to fill.

Void Length = Tubing Length - Fluid Level Above Pump
Tubing Void Capacity = Void Length × Capacity (bbl/ft)
Casing Void Capacity = Void Length × Annular Capacity (bbl/ft)

When Void Matters

Field Application: When pulling an ESP, the void capacity tells you how much fluid will flow back when the pump unseats from the seating nipple. For wells with a check valve above the pump, subtract the void capacity from total displacement.

Calculation Example

Consider a well with:

Step 1: Tubing Capacity

ID = 2.441 in (from table)
Capacity = 2.441² × 0.000971 = 0.00579 bbl/ft
Total Volume = 0.00579 × 8,500 = 49.2 bbl

Step 2: Void Capacity

Void Length = 8,500 - 800 = 7,700 ft
Void Capacity = 0.00579 × 7,700 = 44.6 bbl

Step 3: Annular Capacity

Casing ID = 4.778 in (20 lb/ft)
Tubing OD = 2.875 in
Annular = (4.778² - 2.875²) × 0.000971 = 0.0142 bbl/ft
Total Annular = 0.0142 × 8,500 = 120.7 bbl

Data Sources

Tubing and casing dimensions are based on:

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