Bending stresses for dillpipe subjected to axial loads in a dogleg and its use in drillpipe fatigue analysis

Failure due to fatigue is a very costly problem in oil and gas industry. Many investigators have previously addressed this problem, but its frequency of occurrence is still excessive. Torque and tension can be correctly predicted but computations of fatigue duration are still approximate. Regarding the fatigue failure of drillstring, prediction and calculation of fatigue duration are stated. Fatigue may occur when drillstring is crooked and rotated. Bending stresses for drillstring subjected to axial loads in a dogleg are discussed. In order to reduce fatigue failure, mechanical stresses in drillpipe and unusual conditions, such as horizontal well, bending in dogleg, bending in buckled area rotating, etc., predicted as accurately as possible. A high level architecture of the simulator for fatigue management of drillpipe is presented. A computational scheme is also developed based on the presented formulation using MATLAB.