Investigation of the mitigation effect of an anti-stall tool on stick-slip vibrations of drill strings

The anti-stall tool (AST) is a downhole tool used to mitigate stick-slip vibrations during drilling. It has the ability to adjust the cutting depth of the drill bit and is characterized by an axial spring and a screw pair. In this paper, the dynamic characteristics and working mechanism of the AST are studied by modeling and parametric analysis. Based on the lumped-mass model, torsional dynamic models of the drill string without and with the AST are built and simulated. The simulation results of the drill string model indicate that there is an upper limit on the weight on bit (WOB) (148 kN) and a lower limit on the rotary table speed (84 RPM) to avoid stick-slip vibration, and that a stick-slip vibration cycle can be divided into five phases. The simulation results of the model with the AST indicate that the AST can mitigate the stick-slip vibration and stabilize the bit angular velocity effectively for a large range of WOBs (120-200 kN) and rotary table speeds (40-120 RPM). The AST spring strength and helical angle have important influences on AST performance. Reasonable values for these two parameters should be determined to ensure AST effectiveness while avoiding other adverse effects. This work can provide guidance for AST applications and improve drilling efficiency and safety.