Analysis of Coupled Axial-Torsional Drill-String Vibration Based on Fuzzy Bit-Rock Interaction Model Considering Bit Balling Condition

In this article, a coupled axial-torsional drill-string vibration model is established, which considers the influence of bit balling on rock-breaking and drill-string vibration. First, a bit-rock interaction model considering normal drilling and bit balling conditions is established, where the different rock-breaking conditions are classified based on the Gaussian mixture model. The fuzzy method is used to solve clustering inaccuracies problems in the bit balling formation and disappearance phases, and a fuzzy bit-rock interaction model is established in these two phases. The bit-rock interaction modeling method has higher accuracy in describing bit balling than the Real, Ritto, and Karnopp models. Finally, the coupled axial-torsional drill-string vibration model considering bit balling is established based on the established bit-rock interaction model, using the drilling tool parameters of a geothermal well and the bit-rock interaction model parameter identification result. The effectiveness of the modeling method is illustrated by micro-rig experiments and field data verification.