Drillbotics is an international student competition hosted by SPE/DSATS. The 2020/2021 competition challenged student teams to design, build and implement a 1.5″ (3.8cm) hole size, fully autonomous directional drilling rig. The well path had to intersect multiple pre-set targets in a rock sample with up to 30-degree inclination and 15-degree azimuth adjustments from the Kickoff Point (KOP). The Norwegian University of Science and Technology (NTNU) won the competition using a fixed bend Bottom Hole Assembly (BHA) and a simulated mud-motor stator with a rod inside the drill pipe transferring rotational torque from a top drive. The team designed and created a bi-directional hydraulic swivel, BHA, and a custom drill bit. Steering was achieved by changing the fixed bend BHA orientation by rotating the drill pipe. A nonlinear Model Predictive Controller (nMPC) was used to allow long-term trajectory control planning following a pre-planned Bezier-curve well path. Position estimations are derived from movement over time in the direction of the current BHA orientation estimate. Orientation is estimated from a combination of physics-based system model predictions and closed-loop BHA orientation surveys from downhole accelerometer data merged by extended Kalman filter observes. Mechanical capabilities of the rig were demonstrated by drilling a 37-degree inclination well path in 6 minutes in a 60 cm sandstone replica. nMPC trajectory control experiments indicate it may be a viable option for fixed bend BHA trajectory control. However, limited testing makes current results inconclusive if the approach can be used for a general well path with major deviations between the fixed bend angle and well path inclination.

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