The Specialty of Push-the-Bit Rotary Steerable Tool Dynamics

Abstract

Abstract Drillstring vibrations are an important cause of premature failure of drillstring components and drilling inefficiency, in particular, torsional vibration is more important. A large amount of research on torsional drillstring vibrations has been conducted in the last few decades. Stick/slip is a severe type of torsional drillstring oscillation that affects the efficiency of the drilling process and can cause bit damage as well as drillstring failure. For rotary steerable system (RSS), the stick-slip vibration is introduced as a new mechanism to explain the large amplitude torsional oscillation of the drillstring. we aim for an improved understanding of the causes for torsional vibrations in RSS and torsional vibrations with and without stick-slip are observed. We show that the RSS implementing agencies pushing the borehole wall caused the drill bit torsional vibration more serious. The results contribute to the better understanding of the dynamics of the push-the-bit RSS. Chaotic vibration is mainly caused by elasticity of the drillstring and changing frictional forces at the bottom tool, static frictional forces are higher than the kinetic frictional forces which make the bit act in a manner where it sticks and then slips, and presents complex dynamic behavior, which makes down-hole dynamic responses difficult to predict. In the Rotary Steerable System (RSS), frictional force between the pads and borehole wall will make the drill bit instantaneous rotational speed reduces. The pads of the implementing agencies in RSS constantly pushed against the borehole wall, making bottom hole by a cycle of nonlinear damping force, which is lead to the bottom drilling tool movement of chaos and disorder.