Study on axial-torsional dynamics characteristics of the drilling robot based on a fluid-structure interaction model

During conventional oil and gas well drilling, weight on bit (WOB) and torque are measured and controlled at the wellhead. However, due to significant transmission lag in thousands of meters long wells, accurate control is unattainable resulting in extremely low drilling efficiency. A novel approach utilizing a coiled tubing drilling (CTD) robot for real-time control of bottom hole WOB and indirect torque regulation via WOB manipulation is proposed. To achieve automatic control, it is imperative to conduct a thorough study of the CTD robot's dynamic characteristics. Through the study, the fluid-structure interaction model of axial torsional dynamics was established for the first time. The factors, including BHA, screw performance, bit performance, rate of penetration (ROP) equation, torque equation, rheological characteristics of drilling fluid and other relevant aspects were comprehensively considered. The effects of drilling fluid displacement (DFD) and WOB fluctuations on the torsional vibration characteristics of the CTD robot system were analyzed. It was found that DFD fluctuation frequency are the main controlling factors affecting the axial torsional dynamic characteristics. By keeping the fluctuation frequency of DFD much higher than 19 Hz, the amplitude and instability of bit vibration can be effectively suppress. This research is beneficial for controlling WOB with CTD robot and suppressing the vibration of the drill bit. •Established an axial-torsional coupled dynamic model based on drilling robot.•Discovered the main control factors of torsional vibration of drilling robot.•Proposed a novel method to suppress the bit torsional vibration with drilling robot.