Type Curves for Predicting Directional Tendencies of Simple Bottom-Hole Assemblies

Abstract

The paper provides solutions for predicting directional tendencies of slick and single stabilizer bottom-hole assemblies (BHA) in curved boreholes. Solutions are derived in a curvilinear system of coordinates in a dimensionless form. These solutions are presented in the form of type curves. Type curves allow for quick evaluation of directional tendencies of a given BHA by providing values of side force and tilt angle at the bit. Using these values an anticipated direction of bit displacement is evaluated, using concepts of formation anisotropy index (FAI) and bit anisotropy index (BAI). Procedures are illustrated by examples of evaluation of side force and tilt at the bit for a slick and single stabilizer BHA. The resulting bit displacements are calculated assuming formation anisotropy and drill bit directional tendencies (FAI and BAI). The results derived from type curves are in agreement with computer simulated data. The comparison shows that application of graphical solutions (type curves) yields only slight error that can be ignored for practical purposes.