PASSIVE VIBRATION CONTROL OF PERIODIC DRILL STRING

In this dissertation, the stop and pass bands (i.e. the band gaps) characteristics are determined for gyroscopic systems by developing an approach which is compatible with such class of systems which is based on the concept of Bloch wave propagation in periodic structures. In this approach, the dispersion curves of the periodic gyroscopic systems are determined for different rotational speeds. The obtained characteristics are compared with non-rotating systems in an attempt to quantify the effect of the gyroscopic forces on the “band gap” characteristics. The developed approach is illustrated by a new class of drill strings with passive periodic inserts. These inserts are utilized to filter out the vibration transmission along the drill string. Such mechanical filtering capabilities allow the vibrations to propagate along the periodic drill string only within specific frequency bands called the ‘pass bands’ and completely block it within other frequency bands called the ‘stop bands’. The inserts introduce impedance mismatch zones along the vibration transmission path to impede the propagation of vibration along the drill string. The design and the location of the inserts are optimized to confine the dominant modes of vibration of the drill string within the stop bands generated by the periodic arrangement of the inserts in order to completely block the propagation of the vibrations. A finite element model (FEM) that simulates the operation of this new class of drill strings is developed to describe the complex nature of the vibration encountered during drilling operations. The FEM is used to extract the dispersion characteristics of the gyroscopic unit cell of the drill string in order to determine its stop and pass band characteristics. Experimental prototype of the passive periodic drill string is built and tested to demonstrate the feasibility and effectiveness of the concept of periodic drill string in mitigating undesirable vibrations. The experimental results are used to validate the developed theoretical model in order to develop a scalable design tool that can be used to predict the dynamical behavior of this new class of drill strings

Reliability assessment of drag anchors and drill strings in floating offshore drilling units

As the oil and gas explorations move to deep and ultra-deep water, reliable and economical operation of floating offshore drilling units becomes significantly important. Despite significant improvements achieved in design of all of the components involved in drilling operation, there are still operation failure reports that threaten the vulnerable offshore environment. This, in turn, mandates the reliability assessment of the key elements of these floating drilling units. The station keeping of drilling platform in harsh environment and the structural integrity of the drilling system under both vibrations and environmental loads are the key areas of concern that affect the reliability of these systems. In this study, two crucial elements affecting the overall system reliability was investigated, including the reliability of drag embedment anchors, as a key element of station keeping, and the fatigue reliability of drill strings, as a key element of structural integrity. First, a comprehensive reliability analysis of drag embedment anchors was conducted through the probabilistic modelling of anchor capacity and incorporation of inherent uncertainties. A plastic yield loci was used to characterize the fluke-soil interaction and failure states. The embedded profile and the frictional capacity of the anchor chain at the seabed were also considered in the calculation of ultimate holding capacity. A 3D coupled finite element (FE) model was developed to obtain the characteristic mean and maximum dynamic line tensions for 100 years return period sea states, as well as the design line tension and corresponding line angle at mudline. Catenary mooring system was considered to maximize the vessel motions and approach the worst case scenarios. First order reliability method (FORM) was used through an iterative procedure to obtain the probabilistic failures. The study revealed the 3 sensitivity of the reliability to key components of anchor geometry, seabed soil properties, and the environmental loads. The study revealed that the reliability index depends on the fluke length and is largely irrelevant to the anchor weight. As well, the level of the reliability indices obtained for drag embedment anchors was found to be lower than the other anchoring solutions such as suction caissons. Second, the fatigue reliability assessment of the drill string under stick-slip vibration and first-order vessel motions was comprehensively investigated. An efficient approach for FE modeling of stick-slip vibrations of the full drill strings was developed, and a comprehensive analysis was conducted to observe the influence of the field operating parameters on the structural dynamic response of the full-scaled drill string under stick-slip vibration. The model was developed based on a rate-dependent formulation of bit-rock interaction, for which the cutting process is integrated through the frictional contact. The nonlinear effects of large rotations, the geometrically nonlinear axial-torsional coupling, and the effect of energy dissipation due to the presence of drill mud were taken into account. The performance of the developed numerical model was verified through comparisons with a lumped-parameter model and published field test results. Time-domain analyses were conducted by incorporation of both stick-slip vibration and vessel motion under the environment loads. Then the fatigue reliability assessment of drill string was conducted by damage calculation under different excitation scenarios using the deterministic S-N curve approach and defining the safe, low risk, and high risk damage zones. The points of most severe fatigue damage and the corresponding risk under simultaneous drilling vessel motions and mechanical vibrations were identified. The results showed the significant influence of the rotary table velocity on the stick-slip characteristics 4 of the drill string in comparison with other field operating parameters, i.e., weight-on-bit and damping ratio. It was found that the coexistence of stick-slip vibrations and horizontal vessel motions is detrimental to reliable performance of the drill string and can result in premature fatigue failure of the top-most drill pipe, the drill pipe passing through the BOP, and the lower drill pipe connected to drill collar. Overall, the study provided an in-depth insight into this challenging area of engineering and resulted in developing robust methodologies for reliability assessment of the key components of floating drill systems from station keeping to drill string

Stability Analysis of the Rotary Drill-String

Oil and natural gas are major energy sources for modern society. A rotary drilling system is the best known technology to extract them from underground. The vibration and stability of drilling systems have been studied for decades to improve drilling efficiency and protect expensive down-hole components. It is well known that severe drill-string vibrations are caused by many different loads: axial loads such as the hook load and the self-weight of the drill-string, end torques applied by the surface motor and restrained at the bit, the inertial load caused by whirling, the fluid drag force, and the contact force between the borehole wall and the drill-string. The drill-string is usually subjected to a complex combination of these loads. The motivation for this dissertation is the need to understand the complex vibration states and the stability of the drill-string in order to better control its constructive and destructive potential. A mathematical model is proposed to describe the steady-state stability of a long, vertical, rectilinear drill-string. The model accounts for a complex combination of constant and variable loads that affect the behavior of drill-strings. The first critical values of these loads and the corresponding mode shape are obtained by the analytical method and the Rayleigh-Ritz method. COMSOL and ABAQUS are used to validate the numerical results for the cases without analytical solutions. With these results, we see that the Rayleigh-Ritz method gives accurate results and is a good way for us to understand more deeply the dynamics of the drilling process and predict the instability of the drilling system

Nonlinear Drillstring Modeling with Applications to Induced Vibrations in Unconventional Horizontal Wells

A new mathematical model is developed for the nonlinear-static, linearized-dynamic, and fully nonlinear-dynamic behavior of drillstrings in arbitrary wellbore profiles. The formulation is based on a three-dimensional nonlinear finite beam element and accounts for the fully coupled flexibility of the drillstring, geometric nonlinearity (large displacement, small strain), automatic determination of wellbore contact points, friction acting between the drillstring and the wellbore, stabilizer clearance, three-dimensional wellbore profiles, added fluid mass and damping effects from the hydrodynamic forces generated between the drillstring and surrounding fluid, complex tool geometry (including steerable mud motors, rotary steerable systems, and eccentric stabilizers/components), shear beam deformations, lateral rotary inertias, and gyroscopic effects. The resulting model is numerically validated through comparisons with analytical formulas and previous nonlinear models, showing that it can readily be applied to a wide range of drilling engineering problems and used for practical analysis. Additionally, individual contributions of shear deformations, lateral rotary inertias, and gyroscopic effects are definitively shown to be insignificant when calculating the static and dynamic behavior of horizontal drilling assemblies within the rotational speed range of most drilling applications. An initial comparison with field data is also provided, which shows the practicality of the developed algorithms in predicting the characteristics of real drilling scenarios. The model is then adjusted and applied to the specific case of inducing lateral vibrations in unconventional horizontal wells. It is proposed that exciting a lateral resonance in the drill pipe lying on the low side of a horizontal wellbore can induce enough movement to help overcome parasitic axial drag acting on a drillstring. This, in turn, would help to increase weight transfer to the bit while slide-drilling with a steerable mud motor in long lateral sections of a wellbore. The change in this lateral resonant behavior due to variations in weight-on-bit (WOB), inclination, well path curvature, wellbore diameter, fluid properties, and tubular dimensions are clearly shown through linearized-dynamic sensitivity studies. Nonlinear time-domain simulations are also performed to better understand the limitations of linearized-dynamic modeling and to provide a more detailed assessment of how inducing lateral vibration influences the WOB while drilling. It is shown that induced lateral vibrations provide a noticeable dynamic WOB of up to ± 250 lbf about the static value, and a slight increase in the average WOB value of up to 150 lbf. The effects on WOB are dependent on the excitation frequency of the induced lateral vibrations, with the greatest benefits being seen at resonant conditions

Bending vibration of rotating drill strings

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 1989.Includes bibliographical references (leaves 129-134).by Rong-Juin Shyu.Ph.D

Data-Driven Numerical Simulation and Optimization Using Machine Learning, and Artificial Neural Networks Methods for Drilling Dysfunction Identification and Automation

Providing the necessary energy supply to a growing world and market is essential to support human social development in an environmentally friendly. The energy industry is undergoing a digital transformation and rapidly adopting advanced technologies to improve safety and productivity and reduce carbon emissions. Energy companies are convinced that applying data-driven and physics-based technologies is the economical way forward. In drilling engineering, automating components of the drilling process has seen remarkable milestones with considerable efficiency gains. However, more elegant solutions are needed to plan, simulate, and optimize the drilling process for traditional and renewable energy generation. This work contributes to such efforts, specifically in autonomous drilling optimization, real-time drilling simulation, and data-driven methods by developing: 1) a physics-based and data-driven drilling optimization and control methodologies to aid drilling operators in performing more effective decisions and optimizing the Rate of Penetration (ROP) while reducing drilling dysfunctions. 2) developing an integrated real-time drilling simulator, 3) using data-driven methodologies to identify drilling inefficiencies and improve performance. Initially, a novel drilling control systems algorithm using machine learning methods to maximize the performance of manually controlled drilling while advising was investigated. This study employs feasible non-linear control theory and data analysis to assist in data pre-analysis and evaluation. Further emphasis was spent on developing algorithms based on formation identification and Mechanical Specific Energy (MSE), simulation, and validation. Initial drilling tests were performed in a lab-scale drilling rig with improved ROP and dysfunction identification algorithms to validate the simulated performance. Ultimately, the miniaturized drilling machine was fully automated and improved with several systems to improve performance and study the dynamic behavior while drilling by designing and implementing new control algorithms to mitigate dysfunctions and optimize the rate of penetration (ROP). Secondly, to overcome some of the current limitations faced by the industry and the need for the integration of drilling simulation models and software, in which cross-domain physics are uni-fied within a single tool through the proposition and publication of an initial common open-source framework for drilling simulation and modeling. An open-source framework and platform that spans across technical drilling disciplines surpass what any single academic or commercial orga-nization can achieve. Subsequently, a complementary filter for downhole orientation estimation was investigated and developed using numerical modeling simulation methods. In addition, the prospective drilling simulator components previously discussed were used to validate, visualize, and benchmark the performance of the dynamic models using prerecorded high-frequency down-hole data from horizontal wells. Lastly, machine-learning techniques were analyzed using open, and proprietary recorded well logs to identify, derive, and train supervised learning algorithms to quickly identify ongoing or incipient vibration and loading patterns that can damage drill bits and slow the drilling process. Followed by the analysis and implementation feasibility of using these trained models into a con-tained downhole tool for both geothermal and oil drilling operations was analyzed. As such, the primary objectives of this interdisciplinary work build from the milestones mentioned above; in-corporating data-driven, probabilistic, and numerical simulation methods for improved drilling dysfunction identification, automation, and optimization

A Lyapunov Exponent Approach for Identifying Chaotic Behavior in a Finite Element Based Drillstring Vibration Model

The purpose of this work is to present a methodology to predict vibrations of drilllstrings for oil recovery service. The work extends a previous model of the drill collar between two stabilizers in the literature to include drill collar flexibility utilizing a modal coordinate condensed, finite element approach. The stiffness due to the gravitational forces along the drillstring axis is included. The model also includes the nonlinear effects of drillstring-wellbore contact, friction and quadratic damping. Bifurcation diagrams are presented to illustrate the effects of speed, friction at wellbore, stabilizer clearance and drill collar length on chaotic vibration response. Their effects shifts resonance peaks away from the linear natural frequency values and influences the onset speed for chaos. A study is conducted on factors for improving the accuracy of Lyapunov Exponents to predict the presence of chaos. This study considers the length of time to steady state, the number and duration of linearization sub-intervals, the presence of rigid body modes and the number of finite elements and modal coordinates. The Poincare map and frequency spectrum are utilized to confirm the prediction of Lyapunov exponent analysis. The results may be helpful for computing Lyapunov exponents of other types of nonlinear vibrating systems with many degrees of freedom. Vibration response predictions may assist drilling rig operators in changing a variety of controlled parameters to improve operation procedures and/or equipment

Modeling, Optimization, and Control of Down-Hole Drilling System

This dissertation investigates dynamics modeling, optimization, and control methodologies of the down-hole drilling system, which can enable a more accurate and reliable automated tracking of drilling trajectory, mitigating drilling vibration, improving the drilling rate, etc. Unlike many existing works, which only consider drilling control in the torsional dimension, the proposed research aims to address the drilling dynamics modeling and control considering both coupled axial and torsional drill string dynamics. The dissertation will first address optimization and control for vertical drilling, and then resolve critical modeling and control challenges for the directional drilling process. In Chapter 2, a customized Dynamic Programming (DP) method is proposed to enable a computationally efficient optimization for the vertical down-hole drilling process. The method is enabled by a new customized DP searching scheme based on a partial inversion of the dynamics model. Through extensive simulation, the method is proved to be effective in searching for an optimal drilling control solution. This method can generate an open-loop optimal control solution, which can be used as a guide for drilling control or in a driller-assist system. In Chapter 3, to enable a closed-loop control solution for the vertical drilling, a neutral- delay differential equations (NDDEs) model based control approach is proposed, specifically to address an axial-torsional coupled vertical drilling dynamics capturing more transient dynamics behaviors through the NDDE. An equivalent input disturbance (EID) approach is used to control the NDDEs model by constructing the Lyapunov-Krasovskii functional (LKF) and formulating them into a linear matrix inequality (LMI). The control gains can be obtained to effectively mitigate the undesired vibrations and maintain accurate trajectory tracking performance under different control references. The works on Chapter 2 and Chapter 3 are mostly for vertical drilling, and the remaining of the dissertation will focus on modeling and control for directional drilling. Chapter 4 proposes a dual heuristic programming (DHP) approach for automated directional drilling control. By approximating the derivative of the cost-to-go function using a neural network (NN), the DHP approach solves the “curse of dimensionality” associated with the traditional DP. The result shows that the proposed controller is robust, computationally efficient, and effective for the directional drilling system. To validate the DHP based control method using a high-fidelity directional drilling model, a hybrid drilling dynamics model is proposed in Chapter 5. The philosophy of the proposed modeling approach is to use the finite element method (FEM) to describe curved sections in the drill string and use the transfer matrix method (TMM) to model straight sections in the drill string. By integrating different methods, we can achieve both modeling accuracy and computational efficiency for a geometrically complex structure. Compared to existing directional drilling models used for off-line analysis, this model can be used for real-time testbeds such as software-in-the-loop (SIL) system and hardware-in-the-loop (HIL) system. Finally, a software-in-the-loop real-time simulation testbed is built to test the designed DHP based controller in Chapter 6. A higher-order hybrid model of directional drilling is implemented in the SIL. The SIL results demonstrate that the designed DHP based controller can effectively mitigate harmful vibrations and accurately track the desired references