Standard formulation and coverage
API 5CT is a standard for oil casing developed by the American Petroleum Institute. It not only specifies the thickness standard of casing, but also covers the dimensions, weight, technical requirements and inspection methods of different grades of casing.
Thickness specification range
Common thickness range: The wall thickness specification requirements of API 5CT casing vary according to the well depth and formation environmental conditions, generally between 4.24 mm (0.167 inches) and 22.23 mm (0.875 inches).
Examples of wall thickness of casing with different outer diameters: For example, the outer diameter of oil casing is 139.7 mm (5-1/2 inches), and the common wall thickness is 6.20 mm, 7.72 mm, etc.; the outer diameter of casing is 244.5 mm (9-5/8 inches), and the wall thickness is 7.92 mm, 8.94 mm, etc.
Select thickness according to well conditions
Shallow wells and low-pressure wells: For shallow wells or wells with low formation pressure, thinner casings, such as 4.24 mm to 8 mm, can be used to reduce costs while meeting the basic requirements of well wall support and fluid transportation.
Deep wells and high-pressure wells: In deep wells, ultra-deep wells or high-pressure oil and gas wells, in order to withstand higher pressures, temperatures and complex formation stresses, thicker casings, such as 10 mm to 22.23 mm, are required to ensure the strength and sealing of the casing and prevent well wall collapse and oil and gas leakage.
Thickness requirements in special environments
Highly corrosive environment: If there are corrosive media in the well, such as hydrogen sulfide, carbon dioxide, etc., in addition to considering the wall thickness to meet the strength requirements, it is also necessary to select a material with good corrosion resistance, and the wall thickness may need to be increased to increase the corrosion resistance life of the casing.
Complex geological conditions: In areas with complex geological conditions, such as faults and fracture zones, the casing needs to withstand greater extrusion and friction. At this time, the wall thickness needs to be appropriately increased to ensure the stability and reliability of the casing.
