Tracking control of rotary steerable toolface in directional drilling

Abstract

This paper presents a detailed tracking based control design for toolface (TF) positioning on a rotary steerable drilling system (RSS). The RSS uses hydro-electromechanical actuators for real-time bit orientation during directional drilling. Key requirements of the RSS are to adjust the TF quickly and smoothly to track the TF command, and to maintain the TF in the presence of external disturbances. Accordingly, a controller with a fast response time and high dynamic stiffness is desired for the RSS. The complexity of the mechanical system and non-linear interaction with the environment creates additional challenges. The required strict feedback nature of the RSS for backstepping control is shown in a detailed mathematical model along with the final control system design. The paper also includes systematic methods to identify various parameters in the RSS equations of motion. Simulations are used to demonstrate the effectiveness of the controller in various operational conditions.