Characterization of Premium Connections Structural Behavior Under the Presence of Combined Torsional and Axial Loads

Abstract

Abstract During casing installation, especially when running in long horizontal wells, it is common to reach situations in which it is necessary to apply axial and torsional loads simultaneously to move a string that has become stuck. After these complex combined loading modes like pulling out, pushing downwards and twisting, it is possible to find casing internal diameter restrictions, which generate further problems during operations such as the impassability of certain tools. These situations then have to be solved by applying costly remediation strategies. API TR 5C3 provides guidance on how to combine these as mentioned loads for the pipe body; however, no guidance or standard exists to set limits to this type of load combinations in premium connections in order to avoid unintended structural damage to connections. The objective of this work is to provide guidance on the structural behavior of premium connections when subjected to combined axial and torsional loads. The authors developed a specific numerical methodology to evaluate a connection's behavior under combined axial and torsional loads. This methodology is based on validated models used to numerically estimate torques on various premium connections during the design stage and is centered on contact pressure calculations during make up and its variations with axial loading. By using this methodology, variations on connection torsional capacity can be studied in terms of applied axial loads. Additionally, different application load paths were simulated to establish worst-case scenarios for each type of connection. The behavior of connections under combined loading was then studied. After completing numerical evaluations, the authors designed a dedicated full scale testing protocol to validate numerical findings and to check the actual behavior of connections under severe combinations of torsional and axial loads. A specific state of the art testing setup was used to apply simultaneously torsional and axial loads on an instrumented premium connection test article in a laboratory environment. The test article connections were subjected to various load points and load paths for evaluation. Based on finite element models and full scale test result analysis, the response of premium connections to the simultaneous application of axial loads and torsional loads was better understood and characterized technically supporting the development of a criteria to define a safe working envelope for premium connections when operations combining axial and torsional loads are performed. A main observation is that all of the tested specimens successfully completed this very demanding sequence of combined torsional and axial loading, without showing significant structural damage. Novel/Additive Information: By means of this methodology and outputs of this work, operators, manufacturers and laboratories alike, can gain a better understanding of how to try to ensure structural performance and reliability of premium connections, as well as work towards defining limits to safely apply axial and torsional loads minimizing the risk of compromising structural integrity.