Introduction to Petroleum Casing for Oil Wells
I. What is petroleum casing for oil wells?
Petroleum casing for oil wells is a type of steel pipe used to support the walls of oil and gas wells. It plays a key role in the oil and gas extraction process, ensuring that drilling goes smoothly and that the well operates properly after completion.
II. The need for multi-layer casing
a. Due to the different drilling depths and geological conditions of each well, it is often necessary to use multiple layers of casing. This design can effectively deal with the complex underground environment and prevent the well wall from collapsing.
b. After the casing is lowered into the well, cementing operations are also required to further strengthen the well wall.
III. Characteristics of oil casing for oil wells
Unlike oil pipe and drill pipe, oil well petroleum casing cannot be reused and is a disposable consumable material. Therefore, its consumption in oil and gas wells is very large, accounting for more than 70% of the total consumption of oil tubing.
IV. Speciality of petroleum casing for offshore drilling
In offshore drilling, petroleum casing for offshore drilling needs to have higher strength and corrosion resistance to cope with the complex marine environment and high pressure conditions.
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| Outer Diameter (OD) | Wall Thickness (WT) | Applicable Steel Grade | Notes |
|---|---|---|---|
| 2 7/8" (73.02mm) | 0.154" (3.91mm) | J55, N80 | For shallow and medium-depth wells |
| 3 1/2" (88.9mm) | 0.203" (5.16mm) | J55, N80 | For medium-depth wells |
| 4 1/2" (114.3mm) | 0.250" (6.35mm) | N80, P110 | For deep wells |
| 5 1/2" (139.7mm) | 0.322" (8.18mm) | N80, P110 | For deep wells |
| 7" (177.8mm) | 0.462" (11.73mm) | L80, P110 | For complex geological conditions |
| 9 5/8" (244.5mm) | 0.656" (16.66mm) | L80, P110 | For ultra-deep wells |
| 13 3/8" (339.7mm) | 0.750" (19.05mm) | L80, P110 | For extreme environments |
| 17 1/2" (444.5mm) | 0.910" (23.12mm) | L80, P110 | For ultra-deep wells and high-pressure environments |
| 20" (508mm) | 1.000" (25.4mm) | L80, P110 | For extreme environments and special applications |
Description:
I. Outer diameter (OD): available in both inches and millimetres for easy reference by international users.
II. Wall Thickness (WT): Adjusted according to application scenarios and steel grades to ensure that different well depths and geological conditions are met.
III. Applicable steel grades: Covering a wide range of steel grades from shallow wells to ultra-deep wells to meet different strength and corrosion resistance requirements.
| Steel Grade | Yield Strength (MPa) | Tensile Strength (MPa) | Hardness (HB) | Chemical Composition (Mass Fraction %) |
|---|---|---|---|---|
| J55 | 379-552 | ≥517 | ≤241 | C: 0.20-0.34, Mn: 0.60-1.25 |
| N80 | 552-758 | ≥689 | ≤241 | C: 0.20-0.34, Mn: 0.60-1.45 |
| L80 (13Cr) | 552-655 | ≥655 | ≤241 | C: 0.15-0.25, Cr: 12.0-14.0 |
| P110 | 758-965 | ≥862 | ≤241 | C: 0.26-0.35, Mo: 0.70-1.10 |
| Outer Diameter | Theoretical Weight | Wall Thickness | Inner Diameter | Clearance | Collar OD | Thread Type | Steel Grade | Length |
|---|---|---|---|---|---|---|---|---|
| 139.7 (5-1/2) | 20.85 (0.244) 23.09 (15.50) 25.32 (17.00) 29.79 (20.00) 34.26 (23.00) |
6.20 (0.244) 6.98 (0.275) 7.72 (0.304) 9.17 (0.361) 10.54 (0.415) |
127.3 (5.012) 125.7 (4.950) 124.3 (4.892) 121.4 (4.778) 118.6 (4.670) |
124.1 (4.887) 122.6 (4.825) 121.1 (4.767) 118.2 (4.653) 115.4 (4.545) |
153.7 (6.050) | Round Thread Pin Thread |
J55 N80 P110 |
8m-12m (26.2-39.4) |
| 177.8 (7) | 25.52 29.79 (20.00) 34.26 (23.00) 38.73 (26.00) 43.20 (29.00) 47.66 (32.00) 52.13 (35.00) 56.60 (38.00) |
5.87 (0.231) 6.91 (0.272) 8.05 (0.317) 9.19 (0.362) 10.36 (0.408) 11.51 (0.453) 12.65 (0.498) 13.72 (0.540) |
166.1 (6.538) 164.2 (6.456) 161.7 (6.366) 159.4 (6.276) 157.1 (6.180) 154.8 (6.090) 152.5 (6.004) 150.4 (5.930) |
162.9 (6.413) 160.8 (6.331) 158.5 (6.224) 156.2 (6.151) 153.9 (6.059) 151.6 (5.969) 149.3 (5.879) 147.2 (5.795) |
194.5 (7.656) | Round Thread Pin Thread |
J55 N80 P110 |
8m-12m (26.2-39.4) |
| 219.1 (8-5/8) | 35.75 (24.00) 41.71 (28.00) 47.66 (32.00) 53.62 (36.00) 59.58 (40.00) |
6.71 (0.264) 7.72 (0.304) 8.94 (0.352) 10.16 (0.400) 11.43 (0.450) |
205.7 (8.093) 203.7 (8.020) 201.2 (7.927) 198.8 (7.827) 196.2 (7.724) |
202.5 (7.972) 200.5 (7.894) 198.0 (7.795) 195.6 (7.701) 193.0 (7.598) |
244.5 (9.625) | Round Thread Pin Thread |
J55 N80 P110 |
8m-12m (26.2-39.4) |
| 244.5 (9-5/8) | 48.11 (32.30) 53.62 (36.00) 59.58 (40.00) 64.79 (43.50) 70.01 (47.00) 71.69 (53.50) |
7.92 (0.312) 8.94 (0.352) 10.03 (0.395) 11.05 (0.435) 11.99 (0.472) 13.84 (0.545) |
228.7 (9.001) 226.6 (8.921) 224.4 (8.835) 222.4 (8.755) 220.5 (8.681) 216.8 (8.535) |
244.7 (8.845) 222.6 (8.765) 220.4 (8.679) 218.4 (8.599) 216.5 (8.525) 212.8 (8.379) |
269.6 (10.625) | Round Thread Pin Thread |
J55 N80 P110 |
8m-12m (26.2-39.4) |
| 273.0 (10-3/4) | 48.78 (32.75) 60.32 (40.50) 67.77 (45.50) 75.96 (51.00) 82.67 (55.50) |
7.09 (0.279) 8.89 (0.350) 10.26 (0.400) 11.43 (0.450) 12.57 (0.495) |
258.9 (10.192) 255.3 (10.050) 252.7 (9.950) 250.2 (9.850) 247.9 (9.760) |
254.9 (10.035) 251.3 (9.894) 248.8 (9.794) 246.2 (9.694) 243.9 (9.604) |
298.5 (11.752) | Round Thread Pin Thread |
J55 N80 P110 |
8m-12m (26.2-39.4) |
| 339.7 (13-3/8) | 71.50 (48.00) 81.18 (54.50) 90.86 (61.00) 101.69 (68.00) |
8.38 (0.330) 9.65 (0.380) 10.92 (0.430) 12.19 (0.480) |
322.9 (12.715) 320.4 (12.615) 317.9 (12.515) 315.3 (12.415) |
319.0 (12.559) 316.5 (12.459) 313.9 (12.359) 311.4 (12.259) |
365.1 (14.374) | Round Thread Pin Thread |
J55 N80 P110 |
8m-12m (26.2-39.4) |
| 73.0 (2-7/8) | 9.53 (6.40) 11.62 (7.90) 12.81 (8.60) |
5.51 (0.217) 7.01 (0.276) 7.82 (0.308) |
62.00 (2.441) 59.00 (2.323) 57.40 (2.259) |
59.61 (2.347) 56.62 (2.229) 54.99 (2.165) |
88.9 (3.500) | Round Thread | J55 N80 |
8.5m-9.5m (27.9-31.2) |
| 88.9 (3-1/2) | 11.47 (7.70) 15.19 (10.20) |
5.49 (0.216) 7.34 (0.289) |
77.9 (3.067) 76.0 (2.992) |
74.25 (2.923) 71.04 (2.797) |
107.95 (4.250) | Round Thread | J55 N80 |
8.5m-9.5m (27.9-31.2) |
| 114.3 (4-1/2) | 18.77 (12.60) | 6.88 (0.271) | 100.5 (3.957) | 97.37 (3.833) | 132.08 (5.200) | Round Thread | J55 N80 |
8.5m-9.5m (27.9-31.2) |
Structure of petroleum casing:
I. Tubing Body
The tubing body of petroleum casing for oil wells provides essential structural support to withstand the pressures and stresses encountered during drilling and production operations。
II. Threaded Connection
Both ends of the casing feature threaded connections used to join multiple pieces of casing into a complete wellbore. Thread types include Long Circular Thread (LC), Short Circular Thread (SC), and Biased Trapezoidal Thread (BT), which are designed to meet varying strength and sealing requirements。
III. Couplings
Couplings enhance the strength and sealing of the connections, typically made from the same steel grade as the tubing body. This ensures compatibility and reliability in harsh environments。
IV. Coating or Anti-Corrosion Treatment (Optional)
For petroleum casing for deep-sea drilling, coatings or anti-corrosion treatments are often applied. These treatments protect the casing from corrosive environments, such as those containing hydrogen sulfide (H₂S) or carbon dioxide (CO₂), thereby extending the service life of the casing。
Weight calculation:
Weight per metre of petroleum casing (kg/m) = [(OD – wall thickness) x wall thickness] x 0.02466
Where OD and wall thickness are in millimetres (mm).
Chemical composition:
a. According to SY/T 6194-96: Casing and its joints are made of the same steel grade with sulphur content <0.045% and phosphorus content <0.045%.
b. Sampling according to GB/T 222-84: Chemical analysis according to relevant parts of GB 223.
c. According to API SPEC 5CT: Chemical analysis according to the latest version of ASTM E59 and analysis according to the latest version of ASTM E350.
Physical properties:
a. According to SY/T 6194-96: flattening test (GB 246-97), tensile test (GB 228-2010) and hydraulic test.
b. According to API SPEC 5CT: Hydraulic test, flattening test, sulfide stress corrosion cracking test, hardness test (according to the latest version of ASTM E18 or E10), tensile test, transverse impact test (according to the latest version of ASTM A370, ASTM E23, and other relevant standards), and particle size determination (according to the latest version of ASTM E112 or other methods). .