Lateral vibration of non-rotating drill pipe conveying fluid in vertical holes

This dissertation documents a theoretical study on the lateral vibration of non-rotating drillpipe that conveys incompressible drilling fluid in vertical holes. In particular, the interaction between drillpipe and drilling fluid (fluid-pipe coupling forces and fluid excitation forces) near the neutral point has been investigated.; A new mathematical model is developed to predict the behavior of drillpipe conveying incompressible drilling fluid in vertical boreholes. The interaction between drillpipe and drilling fluid is characterized in the model in detailed fashion—to the extent that it is perhaps the most “complete” model published so far. Dimensional analysis is conducted to generalize the approach. A numerical matrix method, utilizing Fourier series functions, is established for the eigensystem analysis/solution. The eigenfrequencies and eigenfunctions are calculated by using Newton-Raphson method and Singular Value Decomposition algorithm, respectively. The linear superposition algorithm is employed to predict the dynamic response of the lateral vibration of non-rotating drillpipe conveying fluid in vertical holes for initial displacement condition problems. In addition, the effects of visco-elastic coefficient of drillpipe, small internal and external flows on drillpipe dynamics are studied theoretically by utilizing the perturbation method.; A computer program was developed with FORTRAN to predict the static and dynamic characteristics of drillpipe that conveys fluid in vertical wellbores. The developed computer program can be used to calculate the critical flow rate that causes drillpipe to buckle, critical buckling length due to the pipe own weight, buckling loads with given system, eigenfrequencies and eigenfunctions of the system, coupling forces between drilling fluid and drillpipe, dynamic displacements of drillpipe and stresses (axial, bending and shear). Moreover, the dynamic transient phenomena at any point along the drillpipe that conveys fluid in a vertical hole can be predicted using this program.; The theoretical results of this study predicts that the interaction between drillpipe and drilling fluid affects drillpipe motions, stresses, eigenfrequencies etc. Therefore, the numerical results that are calculated from the developed computer programs for buckling/vibration should be included in the drillpipe design and drilling operation to reduce drilling costs.