Application of expansion joints to expandable casing operation

To decrease the expansion pressure during expandable casing operation is important to ensure successful expandable casing path. For hydraulic expansion, smaller expandable pressure could reduce operation risk. Through the analysis of the pressure variation of expandable casing during downhole expansion, it is put forward that the gravity of tubing string may lead to the additional pressure that is insurmountable during initial anchoring, expansion jonints could be used to remove additional expansion pressure and improve anchoring. Through field operation, the use of expansion joints at the stage of expansion casing anchoring that is difficult to master, i. e. the stage of the highest expansion pressure, the pressure during expansion increases less as compared to lab test. Expansion joints could not only decrease the maximum pressure during expansion, also improve anchoring effect. They are easy to operate, especially applicable to deep well expansion.