In the oil and gas industry, tubing and casing sizes are standardized by the API (American Petroleum Institute), specifically under Spec 5CT.
The size of these pipes is always referred to by their Outside Diameter (OD). However, because different wall thicknesses are needed for different depths and pressures, the Inside Diameter (ID) varies.
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Casing Sizes
Casing is the large-diameter pipe lowered into a clear borehole and cemented in place. It protects the well from collapsing and prevents fluids from leaking into groundwater.
Common Casing OD Sizes:
Conductor Pipe: 16", 20", 24", or 30" (The first string used).
Surface Casing: 10-¾", 13-⅜" (Protects freshwater zones).
Intermediate Casing: 7-⅝", 8-⅝", 9-⅝" (Used in deeper wells to transition to high-pressure zones).
Production Casing: 4-½", 5", 5-½", 7" (The final string that runs to the reservoir).
Key Metric: Casing is described by OD and Weight per Foot (e.g., 5-½" 17# casing). The weight determines the wall thickness.
Casing sizes specification
| Category | Common OD (Inches) | OD (mm) | Primary Application |
| Conductor | 16", 20", 24", 30" | 406 - 762 | Outermost string; prevents topsoil collapse. |
| Surface Casing | 10-¾", 13-⅜" | 273 - 340 | Protects freshwater zones; supports the BOP stack. |
| Intermediate Casing | 7-⅝", 8-⅝", 9-⅝" | 194 - 244 | Used for complex sections (high pressure or loss zones). |
| Production Casing | 4-½", 5", 5-½", 7" | 114 - 178 | The final string set through or above the reservoir. |
| Liner | Various | - | A string that does not extend to the surface; hangs from the previous casing. |
Tubing Sizes
Tubing is the pipe placed inside the casing. It is the conduit through which the oil or gas actually flows to the surface. Unlike casing, tubing is designed to be pulled and replaced if it corrodes or plugs up.
Common Tubing OD Sizes:
Small (Macaroni) Tubing: 1.050", 1.315", 1.660" (Used for chemical injection or very small wells).
Standard Production Tubing:
2-⅜" (Very common in older or lower-volume wells).
2-⅞" (The industry standard for most onshore oil and gas wells).
3-½" (Used for high-volume wells).
Large Bore Tubing: 4", 4-½" (Used in high-production offshore or subsea wells).
Tubing Sizes specification
| Category | Common OD (Inches) | OD (mm) | Primary Application |
| Macaroni Tubing | 1.050", 1.315", 1.660" | 26.7 - 42.2 | Chemical injection or slim-hole workover operations. |
| Standard Tubing | 2-⅜" | 60.3 | Common in lower-volume or older onshore wells. |
| Standard Tubing | 2-⅞" (Most Common) | 73.0 | The industry standard for most onshore oil/gas wells. |
| Large Bore Tubing | 3-½", 4", 4-½" | 88.9 - 114.3 | High-production wells, offshore, or water injection wells. |
Length Classifications (Ranges)
API defines three "Ranges" for the length of each individual joint of pipe:
| Range | Casing Length (ft / m) | Tubing Length (ft / m) | Remarks |
| Range 1 (R1) | 16 – 25 ft (4.8 - 7.6m) | 20 – 24 ft (6.1 - 7.3m) | Rarely used. |
| Range 2 (R2) | 25 – 34 ft (7.6 - 10.4m) | 28 – 32 ft (8.5 - 9.8m) | Most common industry standard. |
| Range 3 (R3) | > 34 ft (> 10.4m) | 38 – 42 ft (11.6 - 12.8m) | Used for deep wells to reduce connections. |
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FAQ
What is the length of a casing?
Oil/Gas Well Casings: Have standardized API length ranges (R-1: 4.88-7.62m, R-2: 7.62-10.36m, R-3: >10.36m), commonly manufactured between 6-13m.
Flexible Waterproof Casings: Length is custom-calculated per installation as Wall Thickness + Extension Length (typically 40-100mm total).
What is the length of range 2 tubing?
Range 2 tubing has a standard length range of 25 to 34 feet. This specific length is standardized to optimize handling, transportation efficiency, and space utilization on drilling rigs and transport vehicles in industries like oil and gas.
