Oil well pipe is connected by threads. Therefore, in addition to the strength of the threaded pipe, it also requires a certain degree of air tightness and durability.
At present, the damages of tubing and casing, which account for most of the development investment, are quite serious, which brings irreparable losses to the development of oil and gas fields. The connecting thread is the weakest link in the whole casing string. In casing damage, the joint failure and seal failure of tubing and casing account for a large proportion.
Failure forms of threaded buckle teeth
The connection strength of threaded buckle teeth of casing joint under various loads mainly refers to the ability of buckle teeth to resist the following failure modes:
Jump buckle: the outer thread jumps out of the internal thread under the axial force, but seldom breaks the buckle.
Broken buckle: the complete buckle of the end of the pipe is broken. The complete buckling strength of the end of the general pipe is the lowest.
Thread cutting: Deduction of buckle from buckle under shear force
Buckling: failure of pipes and coupling under axial compression
In recent years, the failure of casing in use has been increasing at home and abroad, mainly in the form of casing collapse, breakage, serious deformation and serious corrosion.
Casing collapse is mainly caused by crustal stress, poor cementing quality, insufficient casing strength or defects.
Casing fracture is mainly caused by high formation stress, poor cementing quality, insufficient casing strength, unreasonable casing string design, poor thread quality and improper casing operation.
Serious corrosion is mainly due to improper casing design, poor anticorrosion measures, poor corrosion environment, etc.