Comparing Open-Source Drill String Models: Establishing Test Cases and Methods

Abstract This paper presents a foundational guide for comparing drilling dynamics models, emphasizing the establishment of methodologies rather than just results. We assess two open-source soft-string dynamic models: the distributed, torsional model by Aarsnes and Shor, and the lumped-mass, coupled axial-torsional model by Dixit et al. Both models are evaluated through six progressively complex test cases designed to enhance methodology development for future model comparisons. Despite their different assumptions and mathematical foundations, both models demonstrated similar responses in drill string vibrations and stick-slip behaviors, with minor differences attributed to the use of distinct friction models (Coulomb versus Stribeck). The study also illustrates the benefits of open-source software in drilling dynamics, such as ease of modification and problem-solving speed, highlighting its potential for improving productivity and insights when combined with collaborative efforts from various industries and academic entities. This work lays the groundwork for further research and robust comparisons of drilling dynamics models, enhancing confidence in both open and closed-source models.