Research on reliability improving of expandable bellow application in crooked holes

Due to the effect of the hole conditions in crooked hole sections, the support technology of expandable bellow hasn’t been formed in China. There are successful application cases abroad, but its application scale is small and its success ratio is low. In this paper, the influential laws of well diameter, hole deviation angle change rate and azimuth angle change rate on the expansion property of expandable bellow were defined in order to determine its applicable hole conditions. A variety of reaming tools were recommended to shorten the hole preparation time and improve the hole quality in sealed intervals. In order to increase the bearing capacity of the welding seams, an end shaping device was developed to keep the shape error of the end less than 1 mm. An automatic welding machine was developed to reduce the effects of artificial factors on the welding quality. By virtue of this device, the welding efficiency is increased by more than 8 times. A weld defect identification method with the maximum identification accuracy of 0.01 mm was developed, and it can be used to determine the critical failure size of different types of defects at different positions. The mechanical expansion tool suitable for slim holes and the milling-expansion integrated tool to deal with downhole complex situations were developed. The construction process of expandable bellow in crooked holes was improved and the risks of pipe string were reduced, e.g. early failure and insufficient expansion. The research results have been successfully applied in 2 wells. It is indicated that the support technology of expandable bellow for sealing the crooked holes in complex formations is formed and it provides a new technology for solving the complex situations in the full hole.