Downhole Attitude-Hold Controller Leads to Automatic Steering of Directional Wells with Improved Accuracy and Reduced Tortuosity

Abstract This paper illustrates the performance of a precise attitude-hold control feature enabled for a new-generation rotary steerable system (RSS) via an intelligent downhole navigation and control system. State-of-the-art downhole navigation sensors and a high-bandwidth pad actuation system are combined with advanced signal processing and control algorithms to ensure tight directional control of RSS along vertical, tangent, and lateral sections, maximizing the pay-zone contact for hydrocarbon extraction. The intelligent downhole navigation and control system blends sensors measuring gravitational and magnetic fields surrounding the RSS to track the propagation of the borehole. The sensory measurements are conditioned by a set of advanced signal-processing techniques prior to being fed to the attitude-hold controller. The controller then generates a control signal to minimize both deviation from a reference trajectory and wellbore tortuosity. Case histories from wells drilled using the automated attitude-hold control feature are presented. The field data include results from vertical, tangent, and lateral sections of wells in various formations from several conventional and unconventional applications. One case suggests significant reduction in generated doglegs upon engaging the attitude-hold controller in a lateral section with a challenging formation. Another case study shows that inclination was maintained within a tight error bound of ±0.1° during a tangent section. An example from a vertical well is also provided, where the vertical-hold control feature was able to hold inclination within 0.1° on average. The ability to tightly lock-in to a desired borehole attitude and to quickly adapt after altering the reference trajectory has proven that the attitude-hold control feature improves wellbore placement accuracy substantially, while minimizing tortuosity.