scholarly journals Nonlinear Dynamics of Torsional Waves in a Drill-string Model with Spatial Extent

2010 ◽  
Vol 16 (7-8) ◽  
pp. 1049-1065 ◽  
Author(s):  
David A.W. Barton ◽  
Bernd Krauskopf ◽  
R. Eddie Wilson
Keyword(s):  
String Model ◽  
Static Friction ◽  
Drill String ◽  
Numerical Continuation ◽  
Oil Well ◽  
Neutral Delay ◽  
Torsional Mode ◽  
Stick Slip ◽  
Friction Forces ◽  
Torsional Waves

In this paper we investigate the dynamics and bifurcations of an oil-well drill-string model that takes the form of a neutral delay differential equation. We consider the torsional mode of the drill-string and investigate the associated stick-slip motion. To analyze the model we develop numerical continuation routines based on Fourier methods since existing routines based on polynomial approximations are unable to cope with the presence of arbitrarily weakly damped modes. We find “resonance peaks” in the dynamics where a high-frequency mode is superimposed on the underlying periodic behavior, causing large torsional waves in the drill-string. We show that the resonance peaks are robust to small perturbations in the friction parameters but disappear if static friction forces are neglected completely.

A Semi-Analytical Study of Stick-Slip Oscillations in Drilling Systems

2010 ◽  
Vol 6 (2) ◽  
Author(s):  
B. Besselink ◽  
N. van de Wouw ◽  
H. Nijmeijer
Keyword(s):  
Dynamic Analysis ◽  
Limit Cycle ◽  
Analytical Approach ◽  
String Model ◽  
Drill String ◽  
Axial Stiffness ◽  
Torsional Vibrations ◽  
Stick Slip ◽  
Rock Interaction ◽  
Stiffness And Damping

Rotary drilling systems are known to exhibit torsional stick-slip vibrations, which decrease drilling efficiency and accelerate the wear of drag bits. The mechanisms leading to these torsional vibrations are analyzed using a model that includes both axial and torsional drill string dynamics, which are coupled via a rate-independent bit-rock interaction law. Earlier work following this approach featured a model that lacked two essential aspects, namely, the axial flexibility of the drill string and dissipation due to friction along the bottom hole assembly. In the current paper, axial stiffness and damping are included, and a more realistic model is obtained. In the dynamic analysis of the drill string model, the separation in time scales between the fast axial dynamics and slow torsional dynamics is exploited. Therefore, the fast axial dynamics, which exhibits a stick-slip limit cycle, is analyzed individually. In the dynamic analysis of a drill string model without axial stiffness and damping, an analytical approach can be taken to obtain an approximation of this limit cycle. Due to the additional complexity of the model caused by the inclusion of axial stiffness and damping, this approach cannot be pursued in this work. Therefore, a semi-analytical approach is developed to calculate the exact axial limit cycle. In this approach, parametrized parts of the axial limit cycle are computed analytically. In order to connect these parts, numerical optimization is used to find the unknown parameters. This semi-analytical approach allows for a fast and accurate computation of the axial limit cycles, leading to insight in the phenomena leading to torsional vibrations. The effect of the (fast) axial limit cycle on the (relatively slow) torsional dynamics is driven by the bit-rock interaction and can thus be obtained by averaging the cutting and wearflat forces acting on the drill bit over one axial limit cycle. Using these results, it is shown that the cutting forces generate an apparent velocity-weakening effect in the torsional dynamics, whereas the wearflat forces yield a velocity-strengthening effect. For a realistic bit geometry, the velocity-weakening effect is dominant, leading to the onset of torsional vibrations.

Design and HIL Validation of an Effective Super-Twisting Controller for Stick-Slip Suppression in Drill-String Systems

2021 ◽  
Author(s):  
Abdelbasset Krama ◽  
Mohamed Gharib ◽  
Shady S. Refaat ◽  
Alan Palazzolo
Keyword(s):  
Power Plants ◽  
High Efficiency ◽  
Sliding Mode ◽  
Drill String ◽  
Experimental Investigations ◽  
Small Scale ◽  
Oil Well ◽  
Stick Slip ◽  
Rock Interaction ◽  
The Real

Abstract This paper presents a novel controller for drill string systems based on a super-twisting sliding mode theory. The aim is to eliminate the stick-slip vibration and maintain a constant drill string velocity at the desired reference value. The proposed controller inherently attenuates the torsional vibration while ensuring the stability and high efficiency of the drill string. A discontinuous lumped-parameter torsional model of vertical drill strings based on four components (rotary table, drill pipes, drill collars and drill bit) is considered. The Karnopp friction model is adopted to simulate the nonlinear bit-rock interaction phenomena. In order to provide a more accurate evaluation, the proposed drill string controller is implemented with the induction motor, a variable frequency drive and a gearbox to closely mirror the real environment of oil well drill strings. The increasing demand for prototyping and testing high-power plants in realistic and safe environments has led to the advancement of new types of experimental investigations without hurting the real system or building a small-scale prototype for testing. The dynamic performance of the proposed controller has been investigated with MATLAB software as well as in a novel hardware in-the-loop (HIL) testing platform. A power plant is modeled and implemented in the real-time simulator OPAL-RT 5600, whereas the controllers are implemented in the dSPACE 1103 control board. The results obtained through simulation and HIL testing demonstrate the feasibility and high performance of the proposed controller.

Draft: Stick-Slip Motions of a Rotor-Stator System

2013 ◽  
Vol 136 (2) ◽  
Author(s):  
Nicholas Vlajic ◽  
Chien-Min Liao ◽  
Hamad Karki ◽  
Balakumar Balachandran
Keyword(s):  
Dry Friction ◽  
Torsional Oscillation ◽  
Flexible Structures ◽  
Oil Well ◽  
Torsional Vibrations ◽  
Dimensional Model ◽  
Torsional Mode ◽  
Stick Slip ◽  
Finite Dimensional ◽  
Motion State

In the current study, the authors examine the torsional vibrations of a rotor enclosed within a stator subjected to dry friction. Through the experiments, it is demonstrated that forward whirling of the rotor occurs while in contact with the stator, backward whirling occurs with contact, as well as impacting motions, which are characterized by nonsynchronous whirling with rotor-stator collisions. While undergoing these motions, the torsional oscillations are excited by stick-slip interactions. Experimental data are presented to show the presence of a stable torsional mode dominated motion while subjected to stick-slip forces during dry-friction whirling. In this motion state, the torsional oscillation response occurs at a combination of frequencies including drive and whirl frequencies. A finite dimensional model is constructed and simulations carried out by using this model are able to capture the system dynamics, including the torsional responses observed during dry-friction whirling. Numerical results obtained by using this model are consistent with experimental observations. The findings of this study are relevant to whirling motions experienced by rotating, long flexible structures, such as drill strings used in oil-well explorations.

scholarly journals Stick-slip and Torsional Friction Factors in Inclined Wellbores

2018 ◽  
Vol 148 ◽  
pp. 16002 ◽  
Author(s):  
Ulf Jakob F. Aarsnes ◽  
Roman J. Shor
Keyword(s):  
High Frequency ◽  
String Model ◽  
Drill String ◽  
Distributed Model ◽  
Dynamic Friction ◽  
Stick Slip ◽  
Rock Interaction ◽  
Interaction Field ◽  
Friction Factors ◽  
Start Ups

Stick slip is usually considered a phenomenon of bit-rock interaction, but is also often observed in the field with the bit off bottom. In this paper we present a distributed model of a drill string with an along-string Coulomb stiction to investigate the effect of borehole inclination and borehole friction on the incidence of stick-slip. This model is validated with high frequency surface and downhole data and then used to estimate static and dynamic friction. A derivation of the torsional drill string model is shown and includes the along-string Coulomb stiction of the borehole acting on the string and the ‘velocity weakening’ between static and dynamic friction. The relative effects of these two frictions is investigated and the resulting drillstring behavior is presented. To isolate the effect of the along-string friction from the bit-rock interaction, field data from rotational start-ups after a connection (with bit off bottom) is considered. This high frequency surface and downhole data is then used to validate the surface and downhole behavior predicted by the model. The model is shown to have a good match with the surface and downhole behavior of two deviated wellbores for depths ranging from 1500 to 3000 meters. In particular, the model replicates the amplitude and period of the oscillations, in both the topside torque and the downhole RPM, as caused by the along-string stick slip. It is further shown that by using the surface behavior of the drill-string during rotational startup, an estimate of the static and dynamic friction factors along the wellbore can be obtained, even during stick-slip oscillations, if axial tension in the drillstring is considered. This presents a possible method to estimate friction factors in the field when off-bottom stick slip is encountered, and points in the direction of avoiding stick slip through the design of an appropriate torsional start-up procedure without the need of an explicit friction test.

scholarly journals An introduction to the mechanics of the lasso

2014 ◽  
Vol 470 (2171) ◽  
pp. 20140512 ◽  
Author(s):  
Pierre-Thomas Brun ◽  
Neil Ribe ◽  
Basile Audoly
Keyword(s):  
Boundary Layer ◽  
Horizontal Plane ◽  
Laboratory Experiments ◽  
String Model ◽  
Line Tension ◽  
Static Friction ◽  
The Other ◽  
Numerical Continuation ◽  
The World ◽  
Small Loop

Trick roping evolved from humble origins as a cattle-catching tool into a sport that delights audiences all over the world with its complex patterns or ‘tricks’. Its fundamental tool is the lasso, formed by passing one end of a rope through a small loop (the honda) at the other end. Here, we study the mechanics of the simplest rope trick, the Flat Loop , in which the rope is driven by the steady circular motion of the roper's hand in a horizontal plane. We first consider the case of a fixed (non-sliding) honda. Noting that the rope's shape is steady in the reference frame rotating with the hand, we analyse a string model in which line tension is balanced by the centrifugal force and the rope's weight. We use numerical continuation to classify the steadily rotating solutions in a bifurcation diagram and analyse their stability. In addition to Flat Loops , we find planar ‘coat-hanger’ solutions, and whirling modes in which the loop collapses onto itself. Next, we treat the more general case of a honda that can slide due to a finite coefficient of friction of the rope on itself. Using matched asymptotic expansions, we resolve the shape of the rope in the boundary layer near the honda where the rope's bending stiffness cannot be neglected. We use this solution to derive a macroscopic criterion for the sliding of the honda in terms of the microscopic Coulomb static friction criterion. Our predictions agree well with rapid-camera observations of a professional trick roper and with laboratory experiments using a ‘robo-cowboy’.

Lubricant Performance in Magnetic Thin Film Disks With Carbon Overcoat—Part I: Dynamic and Static Friction

1991 ◽  
Vol 113 (1) ◽  
pp. 22-31 ◽  
Author(s):  
J. L. Streator ◽  
B. Bhushan ◽  
D. B. Bogy
Keyword(s):  
Thin Film ◽  
Film Thickness ◽  
Static Friction ◽  
Disk Surface ◽  
Stick Slip ◽  
Sliding Speed ◽  
Friction Coefficients ◽  
Friction Forces ◽  
Strong Adhesion ◽  
Lubricant Viscosity

Static and dynamic friction coefficients are presented for an Al2O3·TiC slider in contact with 130 mm carbon-coated rigid thin film disks lubricated with several different perfluoropolyether lubricants. The lubricants tested include three nonpolar liquid lubricants and one polar liquid lubricant with dihydroxyl end groups. The effects of lubricant film thickness, disk surface topography, sliding speed and lubricant viscosity are investigated. In many cases, the interfaces exhibited a sharp increase in the dynamic and static friction coefficients after a certain film thickness was reached, due to strong adhesion in the interface. In most cases, the lubricant thickness for the onset of high friction forces was found to increase with increasing disk surface roughness, lubricant viscosity and sliding speed. Under certain conditions stick/slip of the slider occurred during which the static friction increased with time of contact. The various data suggest that the rate at which strong adhesion develops depends on the lubricant viscosity.

Analysis of Friction-Induced Limit Cycling in an Experimental Drill-String System

2004 ◽  
Vol 126 (4) ◽  
pp. 709-720 ◽  
Author(s):  
N. Mihajlovic´ ◽  
A. A. van Veggel ◽  
N. van de Wouw ◽  
H. Nijmeijer
Keyword(s):  
Steady State ◽  
Oil And Gas ◽  
Static Friction ◽  
Friction Model ◽  
Drill String ◽  
Torsional Vibrations ◽  
State Behavior ◽  
Rotary Drilling ◽  
Stick Slip ◽  
Predictive Quality

In this paper, we aim for an improved understanding of the causes for torsional vibrations that appear in rotary drilling systems used for the exploration of oil and gas. For this purpose, an experimental drill-string setup is considered. In that system, torsional vibrations with and without stick-slip are observed in steady state. In order to obtain a predictive model, a discontinuous static friction model is proposed. The steady-state behavior of the drill-string system is analyzed both numerically and experimentally. A comparison of numerical and experimental bifurcation diagrams indicates the predictive quality of the model. Moreover, specific friction model characteristics can be linked to the existence of torsional vibrations with and without stick-slip.

scholarly journals Nonlinear Self-Excited Vibration Mechanism for Under-Actuated Oil-Well Drilling System with Stick-Slip Vibration

2019 ◽  
Vol 37 (4) ◽  
pp. 802-808
Author(s):  
Meng Fu ◽  
Jianghong Li ◽  
Aiqi Zhao ◽  
Yafeng Wu ◽  
Zuhao Chen ◽  
...  
Keyword(s):  
Friction Model ◽  
Drill String ◽  
Oil Well ◽  
Damping Force ◽  
Stick Slip ◽  
Equivalent Damping ◽  
Excited Vibration ◽  
Vibration Mechanism ◽  
Drilling System ◽  
Damping Torque

Exploration of oil or gas wells is usually carried out by using drilling system. When the kilometers of drilling system is externally disturbed, the drilling system is prone to undesired stick-slip vibration of the drill-string. The stick-slip vibration of the drill-string belongs to the nonlinear self-excited vibration. In order to study the vibration mechanism, the model for the nonlinear torque on the bit by using Karnopp friction model and the two degrees of freedom model for drilling system were established. The equivalent damping torque formula and the energy variation formula of the drilling system were proposed. The mechanism of the nonlinear self-excited vibration of the drilling system was explained. The simulation results indicated that the stick-slip vibration of the drill-string was caused by the negative value of the equivalent damping force of the drilling system. The equivalent damping torque made the positive work on the system, so that the system absorbed the vibration energy from the outside, which destroyed the stability of the system equilibrium point. The feedback effect in the speed of the drill-bit regulates the system energy to maintain constant vibration without attenuation. In each vibration cycle, the energy input by the system is equal to the energy dissipated by the system. The energy absorbed by the drilling system is mainly converted into the potential energy.

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