Nonlinear modeling for analysis of directional drilling processes

Directional drilling allows for the drilling of boreholes with complex shapes, which are needed to reach unconventional reservoirs of oil, gas and mineral resources. Figure 1 shows a sketch of a directional drilling system. The drillstring is a hollow slender pipe with most of it is in tension under its own weight, except for the bottom hole assembly (BHA),\u3cbr/\u3ewhich is in compression. The BHA contains several stabilizers ensuring centering of the BHA inside the borehole, a bit penetrating the rock formation and a rotary steerable system (RSS), being a robotic actuator, steering the BHA. In practice, directional drilling often results in spiraled boreholes, see Figure 2 for an illustration. These are unwanted selfexcited oscillations in the borehole geometry which negatively influence the drilling process and the borehole qualit