Principal Normal Angle of Borehole Trajectory and Its Equation

Based on the deflection behavior and the characteristics of borehole trajectories, a concept and definition of the principal normal angle of a borehole trajectory was proposed in this paper, and the essential difference between the deflection direction of borehole trajectory and the directional orientation of steering tool was clarified. On this basis, the general equation of the principal normal angle of borehole trajectory was established, and the specific calculation method and formula of the principal normal angle were provided in combination with common borehole trajectory models. The relationships among different deflection parameters were revealed, and the method of characterizing the deflection morphology of a borehole trajectory was established using their characteristic curves. The studies show that the principal normal angle of a borehole trajectory is different from the tool face angle of steering tool. Further, the Cartesian coordinate- polar coordinate coupling based characteristic curve can be used to characterize multiple sets of deflection parameters and their relationships. The research results clarified some fuzzy understandings on the existing theories and techniques, and developed a characterization method for the deflection behavior of borehole trajectories.