Stress Analysis of Drillstrings

Abstract

Abstract Drillstring stress analysis techniques are reviewed with emphasis on the use of torque-drag formulations. Some of the many modifications to torque-drag calculations are reviewed and discussed. The limitations of current results in drillstring dynamics for use in stress analysis calculations are also discussed. Introduction To ensure mechanical integrity of drillstrings, it is necessary to predict the expected loading on each part and then show that these loads do not lead to failure of the drillstring. It is clear that loads should be predicted as accurately as possible to allow safe, economical drillstring designs. This work assumes a well path has been specified and a drillstring has been chosen for evaluation. The procedures and options currently available for this evaluation are reviewed. The central role of torque-drag calculations in this evaluation is well recognized. The next section reviews the standard, elementary method associated with stress analysis of drillstrings using these calculations. String loadings are predicted from well paths and drillstring data using torque-drag calculation procedures. All commonly used torque-drag procedures have as their basis a flexible model for the string. The assumed string is inextensible and has no bending stiffness. The assumption of no bending stiffness has been critically evaluated in the literature.