TYPE CURVES FOR PREDICTING DIRECTIONAL TENDENCIES OF SIMPLE BOTTOM-HOLE ASSEMBLIES

The paper provides solutions for predicting directional tendencies of slick and single stabilizer bottom-hole assemblies (BHA) in curved bor eholes. Solutions are derived in a curvilinear system of coordinates i n a dimensionless form. These solutions are presented in the form of t ype curves. Type curves allow for quick evaluation of directional tend encies of a given BHA by providing values of side force and tilt angle at the bit. Using these values an anticipated direction of bit displa cement is evaluated, using concepts of formation anisotropy index (FAI ) and bit anisotropy index (BAI). Procedures are illustrated by exampl es of evaluation of side force and tilt at the bit for a slick and sin gle stabilizer BHA. The resulting bit displacements are calculated ass uming formation anisotropy and drill bit directional tendencies (FAI a nd BAI). The results derived from type curves are in agreement with co mputer simulated data. The comparison shows that application of graphi cal solutions (type curves) yields only slight error that can be ignor ed for practical purposes.