AN IMPROVED TRANSFER-MATRIX TECHNIQUE AS APPLIED TO BHA LATERAL VIBRATION ANALYSIS

In previous work on BHA (bottomhole assembly) lateral vibration, the e ffects of axial loads have often been neglected. In this paper an impr oved transfer matrix technique is applied to study the dynamics of a B HA system which is always subject to a large axial load. The transfer matrix developed, which is derived directly from the consistent equati ons of motion of rotating Timoshenko shafts subject to axial loads, in cludes the effects of rotary inertia, gyroscopic moments, transverse s hear and axial load. The mud-drillstring interaction is represented by an added mass coefficient. The influences of rotation speed, weight o n bit and added mass coefficient on the lateral vibration are investig ated. The buckling loads of horizontal BHA's are calculated by observi ng the disappearance of the corresponding eigenfrequencies. (C) 1995 A cademic Press Limited