Analysis of inaccuracy of determining a directional borehole axis.
Tomasz Topolski, Andrzej Gonet, Stanisław Stryczek
Vol. 32, no. 3 (2015), s. 589-602, 
The development of directional drilling made designers work out numerous measurement devices for spatial location of the borehole axis. The borehole trajectory can be determined on the basis of very accurate calculation methods. The authors present a brief characteristic of devices for measuring dogleg angle and azimuths as well as methods for calculating the spatial placement of borehole axis, i.e.:– average angle method, – tangential method, modified to balanced tangential method, – radius of curvature method (RCM), – minimum curvature method. Calculations and graphical representations of deviations obtained with these four methods were performed for three selected trajectories of borehole axes (2D), increase/decrease of dogleg angle and 3D, increase/decrease of dogleg angle and azimuth with the use of COMPASS software (part of Halliburton Landmark package).