The Experts below are selected from a list of 15039 Experts worldwide ranked by ideXlab platform
Emmanuel M Detournay - One of the best experts on this subject based on the ideXlab platform.
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instability regimes and self excited vibrations in deep Drilling systems
2014Co-Authors: Alexandre Depouhon, Emmanuel M DetournayAbstract:Abstract This paper analyzes the stability of the discrete model proposed by Richard et al. (2004 [1] , 2007 [2] ) to study the self-excited axial and torsional vibrations of deep Drilling systems. This model, which relies on a rate-independent bit/rock interaction law, reduces to a coupled system of state-dependent delay differential equations governing the axial and angular perturbations to the stationary motion of the bit. A linear stability analysis indicates that, although the steady-state motion of the bit is always unstable, the nature of the instability depends on the nominal angular velocity Ω 0 of the drillstring imposed at the rig. On the one hand, if Ω 0 is larger than a critical velocity Ω c , the angular dynamics is responsible for the instability. However, on the timescale of the resonance period of the drillstring viewed as a torsional pendulum, the system behaves like a marginally stable one, provided that exogenous perturbations are of limited magnitude. The instability then only appears on a much larger timescale, in the form of slowly growing oscillations that ultimately lead to an undesired Drilling regime such as bit-bouncing or stick-slip vibrations. On the other hand, if Ω 0 is smaller than Ω c , the instability manifests itself on the timescale of the bit motion due to a dominating unstable axial dynamics; perturbations to the steady-state motion then rapidly degenerate into stick-slip limit cycles or bit-bouncing. For typical deep Drilling field conditions, the critical angular velocity Ω c is virtually independent of the axial force acting on the bit and of the bit bluntness. It can be approximated by a power law monomial, a function of known parameters of the Drilling system and of the intrinsic specific energy (a quantity characterizing the energy required to drill a particular rock). This approximation holds on account that the dissipation in the Drilling Structure is negligible with respect to that taking place through the bit/rock interaction, as is typically the case. These findings are further illustrated on an example of deep Drilling and shown to match the trends observed in the field.
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multiple mode analysis of the self excited vibrations of rotary Drilling systems
2009Co-Authors: Christophe Germay, Vincent Denoel, Emmanuel M DetournayAbstract:This paper extends the analysis of the self-excitated vibrations of a Drilling Structure presented in an earlier paper [T. Richard, C. Germay, E. Detournay, A simplified model to explore the root cause of stick-slip vibrations in Drilling systems with drag bits, Journal of Sound and Vibration 305 (3) (2007) 432–456] by basing the formulation of the model on a continuum representation of the drillstring rather than on a characterization of the Drilling Structure by a 2 degree of freedom system. The particular boundary conditions at the bit–rock interface, which according to this model are responsible for the self-excited vibrations, account for both cutting and frictional contact processes. The cutting process combined with the quasi-helical motion of the bit leads to a regenerative effect that introduces a coupling between the axial and torsional modes of vibrations and a state-dependent delay in the governing equations, while the frictional contact process is associated with discontinuities in the boundary conditions when the bit sticks in its axial and angular motion. The dynamic response of the Drilling Structure is computed using the finite element method. While the general tendencies of the system response predicted by the discrete model are confirmed by this computational model (for example that the occurrence of stick-slip vibrations as well as the risk of bit bouncing are enhanced with an increase of the weight-on-bit or a decrease of the rotational speed), new features in the self-excited response of the drillstring can be detected. In particular, stick-slip vibrations are predicted to occur at natural frequencies of the drillstring different from the fundamental one (as sometimes observed in field operations), depending on the operating parameters.
Noel Challamel - One of the best experts on this subject based on the ideXlab platform.
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rock destruction effect on the stability of a Drilling Structure
2000Co-Authors: Noel ChallamelAbstract:Abstract The motion of a Drilling Structure is studied in torsion. The stability of the stationary solution is determined by the direct method of Liapounov, supplemented with results for the linearized method. The stability criterion is firmly based on the form of the boundary condition linked to the rock destruction process. This rock/bit interaction function can be deduced using studies on rock mechanics, based on yield design formalism. Assuming a quasi-static axial evolution, numerical simulations illustrate the instability of the stationary solution: the bit motion can converge on a limit cycle, often called stick–slip. The beam therefore evolves as a complex cone-shaped limit surface. A simple two-degrees-of-freedom system is now considered in both axial and torsional directions, to quantify the quasi-static axial assumption. The instability of the stationary solution is confirmed by the linearized method for the undamped system with the postulated boundary conditions. Even for small damping values the same result is achieved. Even though a limit cycle appears in the axial plane (small amplitude), stick–slip can be described adequately by considering a quasi-static axial evolution.
Christophe Germay - One of the best experts on this subject based on the ideXlab platform.
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multiple mode analysis of the self excited vibrations of rotary Drilling systems
2009Co-Authors: Christophe Germay, Vincent Denoel, Emmanuel M DetournayAbstract:This paper extends the analysis of the self-excitated vibrations of a Drilling Structure presented in an earlier paper [T. Richard, C. Germay, E. Detournay, A simplified model to explore the root cause of stick-slip vibrations in Drilling systems with drag bits, Journal of Sound and Vibration 305 (3) (2007) 432–456] by basing the formulation of the model on a continuum representation of the drillstring rather than on a characterization of the Drilling Structure by a 2 degree of freedom system. The particular boundary conditions at the bit–rock interface, which according to this model are responsible for the self-excited vibrations, account for both cutting and frictional contact processes. The cutting process combined with the quasi-helical motion of the bit leads to a regenerative effect that introduces a coupling between the axial and torsional modes of vibrations and a state-dependent delay in the governing equations, while the frictional contact process is associated with discontinuities in the boundary conditions when the bit sticks in its axial and angular motion. The dynamic response of the Drilling Structure is computed using the finite element method. While the general tendencies of the system response predicted by the discrete model are confirmed by this computational model (for example that the occurrence of stick-slip vibrations as well as the risk of bit bouncing are enhanced with an increase of the weight-on-bit or a decrease of the rotational speed), new features in the self-excited response of the drillstring can be detected. In particular, stick-slip vibrations are predicted to occur at natural frequencies of the drillstring different from the fundamental one (as sometimes observed in field operations), depending on the operating parameters.
Vincent Denoel - One of the best experts on this subject based on the ideXlab platform.
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multiple mode analysis of the self excited vibrations of rotary Drilling systems
2009Co-Authors: Christophe Germay, Vincent Denoel, Emmanuel M DetournayAbstract:This paper extends the analysis of the self-excitated vibrations of a Drilling Structure presented in an earlier paper [T. Richard, C. Germay, E. Detournay, A simplified model to explore the root cause of stick-slip vibrations in Drilling systems with drag bits, Journal of Sound and Vibration 305 (3) (2007) 432–456] by basing the formulation of the model on a continuum representation of the drillstring rather than on a characterization of the Drilling Structure by a 2 degree of freedom system. The particular boundary conditions at the bit–rock interface, which according to this model are responsible for the self-excited vibrations, account for both cutting and frictional contact processes. The cutting process combined with the quasi-helical motion of the bit leads to a regenerative effect that introduces a coupling between the axial and torsional modes of vibrations and a state-dependent delay in the governing equations, while the frictional contact process is associated with discontinuities in the boundary conditions when the bit sticks in its axial and angular motion. The dynamic response of the Drilling Structure is computed using the finite element method. While the general tendencies of the system response predicted by the discrete model are confirmed by this computational model (for example that the occurrence of stick-slip vibrations as well as the risk of bit bouncing are enhanced with an increase of the weight-on-bit or a decrease of the rotational speed), new features in the self-excited response of the drillstring can be detected. In particular, stick-slip vibrations are predicted to occur at natural frequencies of the drillstring different from the fundamental one (as sometimes observed in field operations), depending on the operating parameters.
Alexandre Depouhon - One of the best experts on this subject based on the ideXlab platform.
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instability regimes and self excited vibrations in deep Drilling systems
2014Co-Authors: Alexandre Depouhon, Emmanuel M DetournayAbstract:Abstract This paper analyzes the stability of the discrete model proposed by Richard et al. (2004 [1] , 2007 [2] ) to study the self-excited axial and torsional vibrations of deep Drilling systems. This model, which relies on a rate-independent bit/rock interaction law, reduces to a coupled system of state-dependent delay differential equations governing the axial and angular perturbations to the stationary motion of the bit. A linear stability analysis indicates that, although the steady-state motion of the bit is always unstable, the nature of the instability depends on the nominal angular velocity Ω 0 of the drillstring imposed at the rig. On the one hand, if Ω 0 is larger than a critical velocity Ω c , the angular dynamics is responsible for the instability. However, on the timescale of the resonance period of the drillstring viewed as a torsional pendulum, the system behaves like a marginally stable one, provided that exogenous perturbations are of limited magnitude. The instability then only appears on a much larger timescale, in the form of slowly growing oscillations that ultimately lead to an undesired Drilling regime such as bit-bouncing or stick-slip vibrations. On the other hand, if Ω 0 is smaller than Ω c , the instability manifests itself on the timescale of the bit motion due to a dominating unstable axial dynamics; perturbations to the steady-state motion then rapidly degenerate into stick-slip limit cycles or bit-bouncing. For typical deep Drilling field conditions, the critical angular velocity Ω c is virtually independent of the axial force acting on the bit and of the bit bluntness. It can be approximated by a power law monomial, a function of known parameters of the Drilling system and of the intrinsic specific energy (a quantity characterizing the energy required to drill a particular rock). This approximation holds on account that the dissipation in the Drilling Structure is negligible with respect to that taking place through the bit/rock interaction, as is typically the case. These findings are further illustrated on an example of deep Drilling and shown to match the trends observed in the field.
