Design and Implementation of a Miniature Autonomous Drilling Rig for Drillbotics 2018

Abstract

The Society of Petroleum Engineers (SPE) organizes the international student competition Drillbotics. The task is to develop a miniature robotic rig to drill, in a fully autonomous operation, a vertical hole in a 35 cm rock sample with unknown layers – as fast as possible, while maintaining rig integrity and borehole quality. This paper describes the key innovations of the 2nd generation NTNU robotic drilling rig, allowing it to take first place in the 2018 competition. The rig features a wide operational window for WOB and RPM, achieved by a custom-designed non-aggressive bit, improved BHA design, reinforced drill-string connections and improved rig framework. These improvements allow the rig to drill much faster at high WOB and RPM while avoiding drill-string twist-offs due to over-torqueing or fatigue caused by vibrations. An autonomous high-ROP mode was employed on the competition day. The best-fit PID controller tuning enables high performance drilling through both soft- and hard formations. Built-in logics automatically detect and handle over-torqueing and stuck pipe. A novel digitalization framework includes a fit-for-purpose data acquisition and visualization system, data-lake for unified data storage and an automatic well reporting functionality. The system logs all measurements, setpoints and calculations, including WOB, RPM, ROP, drill string torque, stand-pipe pressure, and downhole accelerations and angles (gyroscope). The NTNU drilling rig managed to drill through a 35 cm competition rock consisting of layers of varying hardness, including a hard tile inclined at 45 deg in 3 minutes and 15 seconds, thus proving its ability of efficient and safe autonomous drilling. The drilling time of the nearest competitor was 15 minutes.