Computer simulation of resistance force mitigation through curvature bridging in extended bore-holes

As is shown in scientific literature, the curvature discontinuity of a bore-hole trajectory can be one of the most influential factors in generation of friction forces resisting to motion of drill strings. To avoid the curvature discontinuities between the bore-hole sections, curvature-bridge curves in the shape of clothoid spirals were proposed for their smoothing. In this paper, it is shown that if the transient clothoid curve is short, the cubic parabola bridge can be substituted for it. As demonstrated below with the use of the elaborated stiff string drag and torque model, this curve has simpler geometry and is suitable for use of spline approximations. The impact of the curvature break smoothing on the resistance forces reduction is investigated for tripping in and out operations and different regimes, simulating drilling procedure. The cases of pure sliding, pure rotation and their combinations are considered for the 2D and 3D models of the bore-hole trajectories.