Non-API oil tube thread types and its failure analysis by CAE technology

In order to meet the sealing and strength requirements of the casing, tubing, and down-hole tools in Shengli oil field, Non-API thread are adopted, which include VAM-TOP thread and FOX thread. The types and advantages of the particular thread are introduced in the paper. The features and sealing design of the special threads are discussed. These two kinds of special threads are applied in about 50 wells of the Shengli oilfield, and the overall effects are good. However, the casing strings of 4 wells failed to seal in the recent operations, which caused serious damages to the productions of these wells. The finite element model of the VAM-TOP thread and FOX thread are developed by the CAE(Computer Assistants Engineering) technology in the paper to find the reasons of failure. The calculating results show the reason of the thread sealing failure is the thread button does not accord with the standards.