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Current methodologies for analytically determining the onset of buckling of drillstrings within c... more Current methodologies for analytically determining the onset of buckling of drillstrings within curved boreholes are limited. In this paper, the Hypergeometric Model is shown to be an effective model to determine drillstring buckling within curved boreholes. With the Hypergeometric Model, the analysis of drillstring buckling results in curves expressing the local buckling force versus the angle of inclination. The local buckling force alone, however, does not contain all the information required for a practical analysis. From the local buckling force curve, the positional buckling force is derived. The positional buckling force considers the distributed weight of the drillstring and the friction between the drillstring and the borehole wall. From this curve, the point of minimum resistance to buckling of the drillstring is determined. Using the local and positional buckling force curves, experimental results and simulations are presented. When multiple configurations exist (for exam...

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Drill pipe fatigue occurs due to the cyclic loading that takes place at curved sections of the we... more Drill pipe fatigue occurs due to the cyclic loading that takes place at curved sections of the well originated by the rotation of the tubes. The failure caused by the fatigue crack nucleation and propagation is considered the major risk to the integrity of the tubes. The fatigue damage isinitially accumulated as surface plastic strain resulting in slip bands. This highlights the importance of studying the fatigue crack initiation to correctly analyze the fatigue behavior of a material or component and has motivated the project of an experimental system comprising the in situ differential interference contrast optical analysis of the surface fatigue cracks and damage accumulation. A fatigue test rig to perform full-scale fatigue tests under bending and tension combined loading to simulate the physical conditions found at the well was also designed and built. API S – 135 steel samples were machined out of drill pipes used by Petrobras at deep-water oil production. Tensile mechanical p...

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Proceedings of SPE Annual Technical Conference and Exhibition, 2006

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A model for buckling within curved boreholes is important in the drilling of extended reach and h... more A model for buckling within curved boreholes is important in the drilling of extended reach and horizontal wells. It has been noted in drilling operations that a curved borehole increases the buckling resistance of the drillstring compared to a straight borehole. The effects of the curvature, however, cannot be correctly determined from the current buckling models developed for straight boreholes, from where the current models for curved boreholes in the literature borrow their fundamentals. A mathematical model for analyzing buckling of drillstring within curved boreholes has been developed. This model predicts the unloading buckling force of a drillstring. The results show that one can apply higher axial forces at the bit and obtain longer extended reach or horizontal sections without putting the drillstring under risk of helical buckling and the consequent lock-up of the column. The model presented here, called the Hypergeometric Model, uses an analytical method employing an incl...

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