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Oil casing pipe, also known as oil-specific pipe, is mainly used for drilling and oil and gas transportation in oil and gas wells. It includes petroleum drill pipe, oil casing pipe, and oil production pipe. Petroleum drill pipe is mainly used to connect the drill collar and drill bit and transmit drilling power.
Oil casing pipe is mainly used to support the wellbore during drilling and after completion to ensure the normal operation of the entire oil well. The oil production pipe mainly transports the oil and gas at the bottom of the oil well to the surface. Petroleum casing is the lifeline that maintains the operation of oil wells. Due to different geological conditions, the downhole stress state is complex, and tensile, compressive, bending, and torsional stresses act on the pipe body comprehensively, which puts higher requirements on the quality of the casing itself. Once the casing itself is damaged for some reason, it may cause a decrease in production or even scrapping of the entire well.
Oil casing pipe is processed from seamless steel pipes and is supplied in an indefinite length, but still needs to comply with certain rules.
According to SY/T6194-96, the length of domestic casing is indefinite, ranging from 8-13m. However, casing pipes with a length not less than 6m can also be provided, and their quantity should not exceed 20%.
According to API regulations, there are three kinds of lengths : R-1 is 4.88~7.62m, R-2 is 7.62~10.36m, and R-3 is 10.36m or longer.
The inner and outer surfaces of the casing pipe should not have folds, wrinkles, delamination, cracks, rolled edges, or scars. These defects should be completely removed, and the removal depth should not exceed 12.5% of the nominal wall thickness.
According to SY/T6194-96, domestic casing pipe should be strapped with steel wire or steel strip. The exposed parts of each casing and coupling thread should be screwed with protective rings to protect the thread.
The external thick-walled oil casing pipe adopts tapered thread, which is thickened by joints to complete connection and sealing. It is one of the fundamental thread types issued by the Petroleum Association. Its tooth shape is triangular with a circular top and bottom, the tooth angle is 60°, the thread taper is 1:16, and the midpoint of the tooth angle is perpendicular to the axis. After the thread is tightened, the tooth sides on the inner and outer threads form an over-interference fit to achieve sealing, which is easy to process, has sealing ability when used with thread grease, has good joint strength, and is easy to maintain and use on-site.
The joint is strengthened by cold upsetting to improve joint strength.
Without changing the thread shape, the joint is cold-upset to increase its size and improve joint strength, meeting deeper requirements.
The sealing is completed by matching the thread grease.
There is a 0.076mm gap between the tooth top and bottom of the external thick-walled oil casing pipe. When the thread is tightened, the tooth top gap is filled with thread grease. After the thread grease cures, it plugs the leakage channel to achieve sealing effect.
The external thick-walled oil casing pipe has made an indelible contribution to the development of the petroleum industry. As the petroleum industry develops, the geological conditions are getting harsher, and the external thick-walled oil casing pipe thread is constantly advancing to gradually meet the special requirements of formations.
