Stability of drill strings in controlled directional wells

Gulyaev, V. I.; Gorbunovich, I. V.

doi:10.1007/s11223-008-9083-2

Cited by 9 publications

(8 citation statements)

References 13 publications

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“…The structure of equations (4) suggests that the beam rotation has a destabilizing effect too. Indeed, for M z = 0, w ¹ 0 we have If T is preset, the critical value of the angular velocity can be found from (13):…”

Section: Mechanism Of Excitation Of Ds Whirl Vibrationsmentioning

confidence: 99%

“…Dynamics of this section will be modeled based on the theory of compressed-twisted rotating bars [3,4]. For this purpose we specify a fixed coordinate system OXYZ and a coordinate system Oxyz which rotates jointly with the DS, both systems having a common origin O on the support A.…”

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confidence: 99%

“…Substitution of (2) and (3) into (1) gives a resolving equation of dynamics of the DS pipe element [3,4,10],…”

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Wirl vibrations of the drillstring bottom hole assembly

2010

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539.3:622.24 and E. I. BorshchThe paper is focused on a problem of flexural vibrations of a rotating drillstring bottom hole assembly under the action of the friction (cutting) moment. The mechanism of self-excitation of the vibrations has been analyzed. The induced moment is shown to be nonconservative and represents the main source of dynamic instability of the system. The flexural mode shapes of the drillstring bottom hole assembly motion have been plotted for various values of the characteristic parameters.

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Section: Mechanism Of Excitation Of Ds Whirl Vibrationsmentioning

confidence: 99%

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Wirl vibrations of the drillstring bottom hole assembly

2010

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“…One of the important aspects of these efforts is to simulate the deep drill string (DS) behavior in curvilinear well bores at the running and pulling stages. Considering that the cost of well bore laying-out, in view of increasing well depth and distance, has already exceeded US$ 50 million [3] and, according to statistics, one in three wells experiences an accident [4], it becomes clear how important the problem of theoretical prediction of DS critical states is and how much a mistake in such predictions would cost.In our earlier publications, we addressed the stability of a deep-well vertical drill string [5], the problem of self-excitation of torsional oscillations [6], defined and solved the problem of initiation of critical states in directional wells [7,8]. In the present work, we have set and solved the problem of elastic bending of a drill string in a curvilinear well bore with geometrical imperfections.…”

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Sensitivity of drill string drag forces to geometrical imperfections of curvilinear well bore trajectory

Gulyaev

Andrusenko

2011

Strength Mater

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Based on the theory of flexible curvilinear rods, direct and inverse problems of elastic bending of a drill string in a curvilinear well bore have been defined. A procedure for solving the problems has been proposed. Sensitivity of the drill string drag forces to additional geometrical imperfections of the well centerline is studied.Introduction. Nowadays, based on economic considerations, hydrocarbons field conditions, and available process facilities of oil-and gas-producing companies, the wells to be drilled can be vertical, controlled directional, or horizontal ones, running to various depths. Experience of the last decades suggests that the well yield and hydrocarbons withdrawal efficiency can be significantly improved by choosing an appropriate well centerline trajectory; therefore, the current tendency is to give preference to directional and horizontal well bores.The practical implementation of deep-well drilling with a complex spatial orientation of the well trajectory necessitates theoretical modeling of mechanical phenomena encountered during the well operation in order to predict possible critical states [1, 2]. One of the important aspects of these efforts is to simulate the deep drill string (DS) behavior in curvilinear well bores at the running and pulling stages. Considering that the cost of well bore laying-out, in view of increasing well depth and distance, has already exceeded US$ 50 million [3] and, according to statistics, one in three wells experiences an accident [4], it becomes clear how important the problem of theoretical prediction of DS critical states is and how much a mistake in such predictions would cost.In our earlier publications, we addressed the stability of a deep-well vertical drill string [5], the problem of self-excitation of torsional oscillations [6], defined and solved the problem of initiation of critical states in directional wells [7,8]. In the present work, we have set and solved the problem of elastic bending of a drill string in a curvilinear well bore with geometrical imperfections.1. State of the Subject. The currently available methods of physical and mathematical modeling of mechanics of DS in curvilinear wells generally represent a DS as an absolutely flexible inextensible string [9,10]. Such a model can be justified during tentative calculations at a predesigning stage, where the well trajectory is preset in the form of a smooth curve of the simplest outline with large radii of curvature [11]. However, in the course of drilling, especially for a deep well, the designed idealized geometry of the well can not be achieved and there arise local geometrical distortions along the well centerline due to process or tectonic perturbations. These distortions act as imperfections. They can have a form of small-scale three-dimensional spirals of variable diameter and step, plane harmonic waves or rounded bends. Since the curvatures of the well centerline grow sharply at these sections, the DS is subjected to elastic bending there and, consequently, the forces of contact ...

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“…6)-(8) into(5) and including(3), we arrive at the nonlinear ordinary second-order differential equation with delayed argument, Typical diagram of the moment of cutting (friction) torque.…”

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Self-excitation of deep-well drill string torsional vibrations

2009

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539.3: 622.24 and O. V. GlushakovaWe address a problem of self-excitation of elastic torsional vibrations of a rotating drill string due to frictional interaction between the drill bit and rock at the deep well bottom. Using the d'Alembert solution to a wave equation, a mathematical model is constructed for a wave torsional pendulum in the form of a nonlinear ordinary differential equation with delayed argument. Special features of generation of self-excited vibrations of drill strings have been determined through computer simulation.Introduction. Rotary drilling is the most widely accepted method for producing oil and gas wells; it involves rock destruction at the well bottom by means of a drill bit attached to the lower end of the drill string (DS) to which rotation is imparted through the torque applied to the DS top end. In the course of drilling, a drill string experiences a number of mechanical actions the most significant of which are the longitudinally nonuniform DS tension force, torque, centrifugal and compound centrifugal forces induced by the drilling fluid flow inside DS, forces of frictional interaction between the DS and the formation, etc. The factors listed above initiate longitudinal, torsional, and bending vibrations in the string and contribute to its flexural buckling. This may cause a stuck DS, wellbore wall falling in, and overall instability of the system [1-5]. One of the dynamic phenomena that may eventually lead to an emergency occurrence in drilling is the self-excitation of torsional vibration of a rotating DS. Since a DS is a torsional pendulum, where an outflow of energy from the drive to environment occurs at the DS bottom part due to energy-dissipative interaction between the drill bit and the formation, the string may pass from the steady equilibrium rotation to torsional self-excited vibration when the conditions of this energy outflow are upset. To study this phenomena we will use here a wave model of a torsional pendulum, which allows for the effects of the finite-velocity propagation of torsional strains along the DS.Special Features of Processes of Self-Excitation of Torsional Vibration in Long Drill Strings. The effects of self-excitation vibration fundamentally differ from other types of vibration processes in dissipative systems in that no periodic external action is needed for their excitation [6,7]. If a mechanical system's transition from some initial state to self-excited vibration conditions occurs without any addition "push," this is a soft self-excitation. If a vibration starts increasing spontaneously only from some limiting amplitude, this is called the hard self-excitation. To periodic self-excited vibration there corresponds a closed loop path in the phase space, which all neighbor paths tend to; this path has been named the stable limit cycle or the attractor [8].With regard to the phenomena that accompany the DS rotation, a study of generation of the DS self-excited torsional vibration enables one to answer three important questions: (i) at what values of the...

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Stability of drill strings in controlled directional wells

Cited by 9 publications

References 13 publications

Wirl vibrations of the drillstring bottom hole assembly

Wirl vibrations of the drillstring bottom hole assembly

Sensitivity of drill string drag forces to geometrical imperfections of curvilinear well bore trajectory

Self-excitation of deep-well drill string torsional vibrations

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