An improved transfer matrix technique as applied to BHA lateral vibration analysis

In previous work on BHA (bottomhole assembly) lateral vibration, the effects of axial loads have often been neglected. In this paper an improved transfer matrix technique is applied to study the dynamics of a BHA system which is always subject to a large axial load. The transfer matrix developed, which is derived directly from the consistent equations of motion of rotating Timoshenko shafts subject to axial loads, includes the effects of rotary inertia, gyroscopic moments, transverse shear and axial load. The mud-drillstring interaction is represented by an added mass coefficient. The influences of rotation speed, weight on bit and added mass coefficient on the lateral vibration are investigated. The buckling loads of horizontal BHA’s are calculated by observing the disappearance of the corresponding eigenfrequencies.