Nonlinear Dynamic Response Characteristics of Deep-water Riserless Drilling-string System Under Combined Excitation of Platform Motion and Current

The study develops a model for axial-lateral-torsional (ALT) bidirectional coupling nonlinear vibrations in riserless drill-strings, using energy and finite element methods. The model incorporates environmental factors such as platform motion, sea currents, and wave loads, as well as operational interactions including wellbore contact and the drill-rock interface. Validated with field test results and data from four wells in the South China Sea, the findings emphasize the importance of heave compensation devices in offsetting the effects of sea motions on drilling operations. The analyses indicate that the weight on bit is mainly impacted by heave movements; however, slow drift motions can exacerbate the nonlinearity of bit rotation. Managing the amplitude and frequency of heave motions is crucial to prevent resonances that can arise between the drill-string and the bit, ensuring improved safety and efficiency in deep-water drilling processes.