| Summary: | Oil and gas exploration and development often encounter deep wells, ultra-deep wells, and special wells in complex formation. In these wells, the threaded joint of expandable casing face two problems: low connection strength and poor sealing effect. To solve the problems, this paper explores how the mechanical properties of expandable casing change dynamically downhole through corrosion test and tensile test. Based on the test results, the dynamic expansion of expandable casing was modelled, and used to analyze the mechanical behavior of threads in the expansion process. The analysis indicates that matching mode of thread joint affects the connection strength and sealing effect of the threads on expandable casing. Then, different matching modes, namely, interference fit and clearance fit, were subjected to sensitivity analysis. After that, a three-stage special thread joint was designed for expandable casing, and proved feasible through contrastive experiments. The research results provide a good reference for the thread design of expandable casing, and the application of expandable casing under complex conditions downhole.
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