Drilling automation can replace manual operation with more predictable and consistent computer-controlled drilling process, as well as enhance the digital link between well-site and data center and enable the remote drilling. In this paper, the automation of drilling process is viewed as three hierarchical control loops: the trajectory control loop, the drilling state control loop, and the motor and actuator control loop.

The drilling state control loop, which controls the bit attitude, weight on bit (WOB), etc., is pivotal to the trajectory control, and remains a focus of development. The drilling state control loop is composed of three sub-loops, i.e., the surface loop, the downhole loop and the hybrid loop. The surface loop supervises the torque, pressure, and hook load, controls the WOB, and takes actions in emergencies. This loop is being analyzed in auto driller systems, and in managed pressure drilling. The downhole loop controls the directional drilling tools, and is well realized in rotary steerable systems. The hybrid loop, which connects the prior two loops and reinforces one loop with the other, however, is not well developed.

A slide drilling system is presented as an example, where no downhole loop holds the bit attitude, and the hybrid loop faces sharpest challenge to control the drilling direction from surface. A joint control of top drive and drawworks is developed to perform coupled control of WOB and toolface. The control system takes into account the desired toolface and WOB. Different operating modes of slide drilling systems are identified and applied with specific control algorithm. The shift between modes is controlled by the operator.

The control system is developed and simulated with the aid of multi-body dynamics modelling of the drill string. This drill string simulation model, based on absolute nodal coordinate formulation, receives the control commands for the top drive and drawworks, and outputs the sensor data and the well trajectory. Loads and dynamic response of the drill string are also simulated. Multi-body dynamics method enables real-time full-hole drill string simulation, and is a powerful tool for automated drilling system development.

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