Abstract: In this paper, we present the calculating model of three-dimentional buckling of lower drill string with multi-stabilizers in beviated-straight borehole. By Laplace transformation,we obtain the solution to the problem. Meanwhile, for the definite design the rules of selecting the string combination and the drilling parameters can be determined according to the condition of drilling straight hole and of corresponding formations by the calculating method in this paper.

Key words: Drill string mechanics, Drill string buckling, Drilling parameters, Directional drilling, String combination, Calculating model