State Dependent Delayed Drill-string Vibration : Theory, Experiments and New Model

L.J. Pei would like to acknowledge NNSF of China (No. 11372282) and China Scholarship Council.Peer reviewedPublisher PD

Instability regimes and self-excited vibrations in deep drilling systems

peer reviewe

Modeling and experimental identification of drill string torsional dynamics under uncertainties

This D.Sc. thesis proposes new perspectives for modeling drill string torsional dynamics under uncertainties. This work develops a novel stochastic hysteretic (nonreversible) bit-rock interaction model. Firstly, a new nominal interaction model, which depends not only on the bit speed, but also on the bit acceleration is developed. Then, a new stochastic model for the bit-rock interaction, taking into account the inherent fluctuations during the drilling, is also proposed. Furthermore, a new test-rig is proposed to analyze drill string dynamics and bit-rock interaction, which is able to reproduce stick-slip phenomena while drilling a rock sample using standard masonry bits, as well as to validate bit-rock interaction models. An original strategy for modeling uncertainties globally, based on terms of the nonparametric probabilistic approach, considering a simple torsional model for a drill string, is also proposed. This strategy allows to control the dispersion level of each interior and interface DOFs of each drill string substructure independently, which can provide more information to improve the operational safety.Esta tese de doutorado propõe novas formas de modelar a dinâmica torciona de uma coluna de perfuração de petróleo considerando incertezas. Este trabalho propõe um novo modelo estocástico de interação broca-rocha histerético (não-reversível). Primeiramente, um novo modelo nominal de interação o qual depende não somente da velocidade angular da broca, mas também de sua aceleração é proposto. Então, um novo modelo estocástico para a interação broca-rocha levando em consideração as flutuações inerentes é também proposto. Além disso, uma nova bancada experimental é proposta para analisar a dinâmica da coluna de perfuração de petróleo e interação broca-rocha, a qual é apta para reproduzir o fenômeno do stick-slip enquanto perfura uma amostra de rocha utilizando broca de concreto comercial, assim como validar modelos de interação broca-rocha Uma estratégia original para modelar incertezas em nível global baseada em termos da abordagem probabilística não-paramétrica considerando um modelo torcional simples para uma coluna de perfuração de petróleo é também proposta. Esta estratégia permite controlar o nível de dispersão para cada grau de liberdade interno e na interface de cada subestrutura de forma independente, a qual pode prover mais informações para melhorar a segurança operacional

Hybrid Modelling and Optimisation of Oil Well Drillstrings

The failure of oil well drillstrings due to torsional and longitudinal stresses caused by stick-slip phenomena during the drilling operation causes great expense to industry. Due to the complicated and harsh drilling environment, modelling of the drillstring becomes an essential requirement in studies. Currently, this is achieved by modelling the drillstring as a torsional lumped model (which ignores the length of the drillstring) for real-time measurement and control. In this thesis, a distributed-lumped model including the effects of drillstring length was developed to represent the drillstring, and was used to simulate stick-slip vibration. The model was developed with increasing levels of detail and the resultant models were validated against typical measured signals from the published literature. The stick-slip model describes the friction model that exists between the cutting tool and the rock. Based on theoretical analysis and mathematical formulation an efficient and adaptable model was created which was then used in the application of a method of species conserving genetic algorithm (SCGA) to optimise the drilling parameters. In conclusion, it was shown that the distributed-lumped model showed improved detail in predicting the transient response and demonstrated the importance of including the drillstring length. Predicting the response of different parameters along the drillstring is now possible and this showed the significant effect of modelling the drillcollar. The model was shown to better represent real system and was therefore far more suited to use with real time measurements.Iraqi Government, Ministry of Higher Education and Scientific Research

The effect of well path, tortuosity and drillstring design on the transmission of axial and torsional vibrations from the bit and mitigation control strategies

As well designs become increasingly complicated, a complete understanding of drillstring vibrations is key to maximize drilling efficiency, to reduce drillstring dysfunction and to minimize drillstring, tool, and borehole damage. Torque and drag models exist that seek to quantify the effects of borehole inclination and tortuosity on static friction along the drillstring; however, the effects on dynamic friction remains poorly understood. This dissertation begins with a review of the past fifty years of work on drillstring dynamics models, an overview of the proposed control strategies and a summary deployed vibration mitigation applications within the drilling industry. Derivations from first principles of a series of computationally efficient axial and torsional drillstring models in both the frequency and time domains are then presented and verified with field data. The transfer matrix approach is used to predict the severity of axial vibrations along the drillstring and is verified using a series of case studies using field data. Harmonic axial vibrations within drillstrings are either induced intentionally, in the case of axial oscillation tools midway along the drillstring, or unintentional, in the case of bit bounce. Two case studies of bit bounce are first evaluated to ensure model validity for a harmonic excitation at a the bit and the model is found to accurately predict bit bounce based on surface rotation rates. Induced axial oscillations, generated by axial oscillation tools, are then investigated to quantify friction reduction and drilling efficiency improvements. Optimal placement is found to depend on wellbore geometry, but is usually restricted to periodic regions of the drillstring. These optimizations are then verified using field trials and suggest that improved placement can result in 20% or more reduction in friction along the drillstring. Two applications of torsional drillstring vibrations are then investigated -- stick slip mitigation and drillstring imaging. The time domain form of the torsional drillstring model is used first to evaluate the effectiveness of three types of top drive controllers -- stiff controllers, tuned PI controllers and impedance matching controllers -- in mitigating stick slip oscillations. Then, the transfer matrix method is applied to evaluate the effect of wellbore geometry on drillstring mobility to conclude that higher order modes of stick slip may become dominant in non-vertical wellbores. The feasibility of drillstring imaging using torsional signals from surface is then investigated to identify inputs and methods that show promise in three setups of varying complexity -- a hanging beam, a laboratory drillstring model and a drilling rig. Two techniques show promise -- white noise injection and model fitting of a step response -- in identifying larger features, including drillstring length and BHA location. However, low sampling frequencies and low bandwidth inputs reduce the ability to image small features such as friction points along the wellpath.Petroleum and Geosystems Engineerin

Control Method to Suppress Stick-slip in Drill-strings Featuring Actuation Delay and Constraints

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Internal mechanics of anti stick–slip tool

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Torsional stick-slip vibrations and multistability in drill-strings

This is the final version. Available on open access from Elsevier via the DOI in this recordData accessibility: The datasets generated and analysed during the current study are available from the corresponding author on reasonable request.The generalized lumped-parameter model of the drill-string system is studied in this paper to provide a fundamental understanding of the torsional stick-slip vibrations in downhole drilling. Our investigation focuses on analysing the cause of three coexisting states: bit sticking, stick-slip vibration, and constant rotation. A critical region of multistability is identified based on the lumped-parameter model, and the conditions for switching between these multiple stable states are discussed. Special attention is given to the bifurcation structure of the considered drill-string model, which is obtained via path-following methods for nonsmooth dynamical systems. The bifurcation scenario is compared to the case when a longer drill-string is considered, which amounts to drilling deeper. It is found that the main features of the bifurcation picture persist under variation of the drill-string length, with certain numerical differences regarding for instance the window of multistability.Engineering and Physical Sciences Research Council (EPSRC)National Natural Science Foundation of ChinaChina Scholarship Counci

Modeling and Control of Axial and Torsional Stick-Slip Oscillations in Drill String

A drill string is the transmission component of rotary drill-rig system used for mining petroleum and natural gas resources. The drill string system is essentially a long slender structure whose length can be in kilometers. Additionally, the drill-string is subjected to discontinuous forces from interactions with the wellbore, which can cause erratic torsion oscillations and stick-slip motions. Throughout this report, all the information that is needed to execute this project will be explain in chapter 1 which is introduction that consist of background of the project, the problem statement of the project and the objectives of doing this project. The literature review of this project will be explained after the introduction. All the studies about this project in order to gain insights into the drill string dynamics and reduce order model have been stated in the literature review. In chapter 3, the methodology in doing this project will be explained which consists of project flow, Gantt chart and the key milestone of doing this project. Furthermore, the results and discussion during this Final Year Project have been concluded and the findings are presented in chapter 4 in this report. These findings provide the simulation code in forms of MATLAB code. This report effort provides clues to how the drive speed can be used as a control parameter to move the system out of regions of undesired and how the drill-string motions can be influenced to keep them close to the borehole center