I. Introduction to Petroleum Casing for Oil Wells
Petroleum casing for oil wells is a steel pipe used to support the walls of oil and gas wells. Its primary function is to ensure the safety and smooth operation of the drilling process and to guarantee the long-term stable operation of the well after completion. Due to the varying depths and geological conditions of each well, multiple layers of casing are typically required. After the casing is lowered into the well, cementing operations are performed to securely bond it to the formation.
Key Characteristics: Single-Use Consumable
Unlike reusable oil tubing and drill pipes, Petroleum casing for oil wells is a single-use consumable material. As a result, it accounts for over 70% of the total pipe materials used in oil and gas well construction.
II. Structural Composition of Oil Well Casing
i. Casing Body
This is the main body of the casing, providing the primary mechanical strength. It withstands the immense pressure and stress during drilling and production processes. All petroleum casing for oil wells must comply with strict standards, such as the API 5CT casing specification.
ii. Threaded Connections
Both ends of the casing are machined with precision threads. This allows multiple individual casing sections to be connected, forming a continuous pipeline throughout the wellbore. Common thread types include long round threads (LC), short round threads (SC), and partial trapezoidal threads (BC). Different types offer varying connection strengths and sealing capabilities to accommodate diverse well conditions. Some basic models, such as API K55 casing, typically use standard round threads.
iii. Joints
Some casing sections have thicker joints welded or forged at both ends of the pipe body. The purpose of these joints is to enhance the strength and sealing reliability of the threaded connection area. Joints are typically manufactured using the same steel as the pipe body.
iv. Coatings and Corrosion Protection
Depending on the specific well environment, casing may undergo special corrosion protection treatments. For example, in environments containing corrosive gases such as hydrogen sulfide (H₂S) or carbon dioxide (CO₂), surface coatings or special material treatments are critical. This significantly extends the service life of the casing. Some high-petroleum casing for oil wells, such as 140V BJC-II casing, may employ advanced corrosion protection technologies.
III. Petroleum casing specification sheet:
| 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:
Outside Diameter (OD): available in both inches and millimeters for easy reference by international users.
Wall Thickness (WT): adjusted according to application scenarios and steel grades to ensure that different well depths and geological conditions are met.
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.
Remarks: A brief description of the applicable scenarios to help users quickly choose the right product.
IV. Steel grades and properties:
| 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 |
V. Specification and Performance of Petroleum Casing：
1. Weight Calculation
The formula for calculating the weight of petroleum casing is as follows:
Weight per meter (kg/m) = [(O.D.-Wall Thickness)×Wall Thickness]×0.02466
where the unit of O.D. and Wall Thickness are millimeters (mm).
2. Chemical composition
The chemical composition of petroleum casing strictly follows the following standards:
According to SY/T 6194-96: the casing and its joints are made of the same grade of steel, with sulfur content <0.045% and phosphorus content <0.045%.
Sampling according to GB/T 222-84: chemical analysis is carried out according to the relevant part of GB 223.
According to API SPEC 5CT: chemical analysis is made according to the latest version of ASTM E59 and analyzed according to the latest version of ASTM E350.
3. Physical properties
The physical property test of oil casing follows the following standards:
According to SY/T 6194-96: Flattening test (GB 246-97), tensile test (GB 228-2010) and hydraulic test.
According to API SPEC 5CT: Hydrostatic 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 related standards), grain size determination (according to the latest version of ASTM E112 or other methods).
