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Analysis techniques for cyclic loading of oil field drill strings

Vaz, Murilo Augusto; (1994) Analysis techniques for cyclic loading of oil field drill strings. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Demand for cost reduction in offshore hydrocarbon field developments has driven drilling technology research into two areas. The first of these is concerned with using highly deviated drilling to access larger reservoir volumes from fewer platforms whereas the second aims at employing drill pipes more efficiently, that is, close to their fatigue limits. This work has two principal objectives - firstly to develop analysis methodologies to calculate cyclic loading in drill strings and secondly to carry out a preliminary investigation of software associated with existing hardware to implement a working drill floor based system. As part of this work, analytical solutions for the buckling of vertical drill strings when subjected to self weight and to both self weight and torque are presented. These solutions are an extension of Lubinski's¹ pioneering work in the 1950's when he presented a solution for vertical drill strings under self weight only and hinged at both ends. This work also uses a power series solution technique to account for self weight with different boundary conditions and with self weight and torque. It is shown that drill string buckling characteristics for the case of self weight only are significantly altered by the boundary condition applied at the bit. In the case of both self weight and torque, a three-dimensional buckling shape with a spiral drill string geometry also significantly changes buckling characteristics. The analytical results are presented in a form that can be readily transferred to computer programs for drill string buckling calculations. In addition, Galerkin's method is applied to some typical problems in drill string mechanics. The technique is used to determine drill string dynamic stability in vertical holes and drill string static deflection in curved and straight inclined holes. In the first case, critical loads and natural frequencies for lateral vibration are calculated assuming that the drill string is hinged at both ends. In the latter case, emphasis is placed on the particular conditions of low weight on bit and large drill string pendulum length for which other solution techniques run into difficulties. Results from Galerkin's technique compare well with those from other semi-analytical solutions and it is shown that the technique offers a simple and easily programmable alternative for analysis of deviated drill strings. Cyclic loading on oil field drill strings due to longitudinal, torsional and lateral vibrations is investigated and compared with the "statical" cyclic loading caused by a deviated string at a dog-leg. Numerical dynamic analyses of longitudinal and torsional vibrations together with quasi-static models for lateral vibration and dog-legs are used to compare the cyclic loading induced separately by each of these effects. A linear damage law (i.e., Miner's rule) is used to calculate the resultant fatigue damage from the cyclic loading. The results show that longitudinal and torsional vibrations may induce significant cyclic loading comparable to that from typical dog-legs whereas the influence of lateral vibration is small. The longitudinal and torsional vibrations are strongly influenced by rotary speed and damping coefficients and can induce significant cyclic loading and rapid accumulation of fatigue damage on drill pipes and collars. The above analysis have been used to develop software for the automated monitoring of cyclic loading and accumulated fatigue damage in oil field drill strings. This software estimates cyclic loading to yield both the expended and remaining service lives of drill pipe segments. The software operates in conjunction with existing drill pipe tagging hardware to identify each drill pipe segment and determine its respective cyclic loading history.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Analysis techniques for cyclic loading of oil field drill strings
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Thesis digitised by ProQuest.
Keywords: Applied sciences; Offshore drilling
URI: https://discovery.ucl.ac.uk/id/eprint/10104816
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