Zum statischen und dynamischen Verhalten von Tiefbohrstraengen in raeumlich gekruemmten Bohrloechern

A mathematical model is developed to analyze the static and dynamic behavior of drillstrings in spatially curved boreholes. The model is based on a geometric nonlinear finite element formulation with a three-dimensional beam element. The unilateral constraint of the drillstring by the borehole wall is incorporated at special point elements using a penalty formulation. Assuming a steady state solution with pure rotation of the string, the loading condition of a complete drillstring is analyzed taking into account the friction between the rotating string and the borehole wall. Under the same assumption, some investigations on the directional behavior of several bottom hole assemblies are made on the basis of the bit side forces. An incremental loading procedure enables the analysis of the sinusoidal and helical postbuckling behavior of the drillpipe in a horizontal and a vertical well. The numerical results agree very well with the results of some analytical considerations. The forces acting on the drillstring vibrating in mud are estimated, and - using the linearized equation - the free vibrations of a bottom hole assembly as well as the forced vibrations of a drillstring due to the excitation by a displacement at the bit and due to mass imbalance forces in a downhole motor are calculated. (orig.)Available from TIB Hannover: RR 5346(13) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman