An Improved Model to Characterize Drill-String Vibrations in Rotary Drilling Applications

Abstract

A specific model is elaborated for stick-slip and bit-bounce vibrations, which are dangerous dynamic phenomena typically encountered in the context of rotary drilling applications. Such a model takes into account two coupled degrees of freedom of drill-string vibrations. Moreover, it assumes a state-dependent time delay and a viscous damping for both the axial and torsional vibrations and relies on a sawtooth function to account for the cutting force fluctuation. In the frame of this theoretical approach, the influence of rock brittleness on the stability of the drill string is calculated via direct integration of the model equations. The results show that the rock brittleness has a great influence on the rotational speed and bit depth.

Study on settling characteristics of rock cuttings from terrestrial high clay shale in power-law fluid

“…A large number of experimental studies on the settlement law of spherical particles in Newtonian fluid have been carried out all over the world (Cheng, 2008;Barati et al, 2014), and a relatively high-precision prediction model has been obtained. However, the shape of shale cuttings is highly irregular, and most drilling fluids belong to non-Newtonian fluids with certain shear dilutions (Mengbo et al, 2014;Wang and Liu, 1996). Whether the previous model for predicting the settling drag coefficient of spherical particles in Newton fluid is suitable for predicting the settling drag coefficient of irregular shale cuttings in non-Newtonian fluid is questionable (Guo et al, 2010;Wang et al, 2010).…”