Influence of Rotary-Steerable-System Design on Borehole Spiraling

Abstract

The paper investigates the influence of the design of push-the-bit rotary-steerable systems (RSSs) on the tendency to drill spiraled boreholes by analyzing the directional stability of the bit trajectory. In this model, differences in RSS designs are accounted for conceptually by assigning a lateral stiffness to the RSS pads. This simple device, which introduces a dependence of the force on the pads upon the deflection of the bottomhole assembly (BHA) relative to the borehole axis, enables exploration of the influence of the actuation mechanism, with the RSS behaving at the ends of the spectrum either as a soft or as a stiff node of the drilling structure.According to this analysis, low pad stiffness has little consequence on the general behavior of the system. However, as the pad stiffness increases, any perturbation in the borehole geometry sensed by the pads alters the drilling direction of the bit and triggers, under certain conditions, self-excited oscillations in the borehole geometry. By increasing the transverse rigidity of the BHA in the vicinity of the bit, stiff RSS pads thus enhance the propensity of a drilling structure to drill spiraled holes and generate, if the system is directionally unstable, borehole oscillations with pitch that corresponds to the distance between the bit and the pads. In contrast, a directionally unstable BHA equipped with RSS characterized by a low stiffness produces spiraled holes with a wavelength corresponding to the distance between the bit and the first stabilizer.

Robust output‐feedback control of 3D directional drilling systems

“…This oscillatory behavior was observed in the works of Marck et al, 4 Perneder and Detournay, 18 Detournay et al, 26 and Marck and Detournay, 27 and one of the main goals of this work is avoiding the borehole spiraling effect displayed in Figure 4 by means of control. These results highlight the fact that open-loop actuation cannot guarantee the desired behavior of the directional drilling system and motivates the design of a feedback control system.…”

“…The exact values of these coefficients can be found in Appendix A. Note that after the linearization, the nonlinear perturbation vector P cl , as in the nonlinear dynamics in (23), only yields terms that affect theĀ 0c ,Ā 1c , andĀ 2c matrices above and does not introduce a perturbation term in the linearized dynamics in (27).…”

“…We start the analysis by noting that the main diagonals ofĀ ocl ,Ā 1cl , andĀ 2cl in (27) have the same structure for both the inclination and azimuth dynamics. The matricesĀ 0c ,Ā 1c , andĀ 2c couple the azimuth dynamics with the inclination dynamics, but this coupling is only present in terms of the inclination observer error and the integral action of the inclination observer.…”

“…Cascaded structure of the linearized nominal (left) error dynamics in (27) and the linearized robust (right) error dynamics in (47) Using this analysis of the cascaded decomposition of the error dynamics, the stability of the total ( -dependent) error dynamics can be guaranteed by the stability of the ( -independent) subsystems corresponding to the azimuth observer, and the tracking error dynamics (as in Figure 6) can be guaranteed without considering the perturbation terms (ie, using a cascaded systems argument).…”

Analysis and optimization of control algorithms for RSSTSP for horizontal well drilling

“…This article focuses on three static push-the-bit (RSS TSP ) like AutoTrak systems. RSS TSP have three stretching pads, which press against the well bore thereby causing the bit to press on the opposite side resulting in a direction change (Niu et al 2013;Wang et al 2014, Marck andDetournay 2016). Steering control algorithm plays an important role in any RSS TSP , and a robust control algorithm is the key factor to achieve the desired control effects (Seifabad and Ehteshami 2013;Hakam et al 2014;Kremers et al 2015).Because many of these techniques are not available to the public, the research papers for control algorithm for RSS TSP are very few in the published literature.…”