Numerical and field data analysis of drill stem vibration

Drill stem vibration is a major cause of premature failure of drill stem components and drilling inefficiency. In severe cases, drill stem vibration may lead to wellbore instability that could lead to increased operational cost. Drill stem vibrations are affected by design decisions and the drilling environment. Examples are; bottom hole assembly configurations, selection of operational parameters, and frequent changes in lithology. Vibration modeling, analysis of vibration data, and specialized vibration reduction tools are methods in use to prevent and mitigate severe vibrations. A drill stem vibration model was created using nonlinear strain formulation which couples the axial, lateral and torsional vibration of the entire drill stem. The model includes the effect of geometric stiffening arising from the applied axial load, two new developed vibration reduction tools used to reduce drill stem vibrations and fluid flow inside and outside the drill stem taking into account two different fluid rheological models. The obtained equation of motion was assembled using the finite element analysis which was solved numerically in Matlab®. The sensitivity analysis using Euler-Bernoulli and Timoshenko models, showed that the Euler-Bernoulli assumption is satisfactory when modeling drill stem vibrations at typical drilling conditions. Analyzing three adjacent wells in the North Sea with different bottom hole assembly and recorded vibration data, revealed that including drill stem vibration reduction tools reduces drill stem vibration and decreases stick-slip tendency. Including drilling fluid circulation, by imposing dynamic pressures on the inside and outside of the drill stem, affect lateral natural frequencies. High flow rate and wrong selection of total flow area at the drill bit could lead to vibrations --Abstract, page iii