T he Screw Drill New Cardan Shaft Design and Strength Calculation on the Universal Joint

Abstract

A large number of ultradeep wells, extended wells and horizontal wells are springing up with the exploration and development of oil and gas fields to the deep part of the land and sea. The down- hole guiding drilling tools is normal screw drill, which consists of down- hole motor, cardan shaft and transmission shaft. How to improve screw drill life, avo id fatigue is an urgent problem to be solved. The cardan shaft is important component part of the screw drill and its major function is to convey the rotation rate, torque of the motor and to guide direction. The cardan shaft is easily damaged because of i ts complex stress. Which often leading to drill down and unnecessary tripping accident. Therefore, the cardan shaft working life directly determines the stability and the working life of the screw drill. The new cardan shaft structure was designed based on the analysis of the cardan shaft movement characteristic, and the universal joint strength checking calculation model was established. The 197 mm cardan shaft main damaged parts (universal joint) strength checking values was calculated and analyzed by usi ng finite element analysis software based on the model. The analysis results show that the stress and the strain of the new type cardan shaft are more uniform, which reduces the damage caused by stress concentration. The new cardan shaft spherical gear str ucture load optimal value range is 57.6~81.7MPa, withstanding the torque value range is 1423~2018N.m, which enhances the high torque under working condition. The application in deep wells verified life of the new cardan shaft has increased more than 40% co mpared with that of normal cardan shaft. The results show that the new type cardan shafts has broad application prospects in downhole dynamic drilling tools.