Browsing by Subject "Vibration suppression"
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Item Inverse problems in drill-string torsional vibration(2020-08) Alrasheed, Abdulmalik; Gray, Kenneth E., Ph. D.In this study, a method is developed to better model drill-string torsional vibration by using data to calibrate a Partial Differential Equation (PDE) based model. Drill-string vibration is a complex phenomenon that is widely studied with several approaches to model the complexities encountered in real life. Sensors are now more widely available that can acquire high frequency data needed for the approach described in this study. The goal of this study is to use synthetic data to calibrate a PDE torsional model by using an inverse problem approach as a proof of concept to implementation on real data. The outcome of this approach is a calibrated model that can be used in control systems which can be implemented in the field to mitigate severe torsional vibration. Torsional drill-string vibration was simulated using finite element method under different conditions of drill-string stiffness coefficients and damping coefficients varying along the entire length of the drill-string. Newmark beta method was used to perform the time stepping in the simulation giving us a more stable implicit formulation for time stepping which reduces the errors. Numerical methods were used to generate drill-string displacement data for the simulation time interval, which were then stored to act as input for subsequent processing to simulate input data from sensors. Adjoint based method was used to calculate the gradients of the optimization problem. Using gradient descent, we incrementally update the parameters to better approximate the synthetic data until the original parameters were recoveredItem Modeling and control of drillstring dynamics for vibration suppression(2019-05) Feng, Tianheng; Chen, Dongmei, Ph. D.; Djurdjanovic , Dragan; Beaman , Joseph; Longoria , Raul; Kinnas , SpyrosDrill-string vibrations could cause fatigue failure to downhole tools, bring damage to the wellbore, and decrease drilling efficiency; therefore, it is important to understand the drill-string dynamics through accurately modeling of the drill-string and bottom-hole assembly (BHA) dynamics, and then develop controllers to suppress the vibrations. Modeling drill-string dynamics for directional drilling operation is highly challenging because the drill-string and BHA bend with large curvatures. In addition, the interaction between the drill-string and wellbore wall could occur along the entire well. This fact complicates the boundary condition of modeling of drill-string dynamics. This dissertation presents a finite element method (FEM) model to characterize the dynamics of a directional drill-string. Based on the principle of virtual work, the developed method linearizes the drill-string dynamics around the central axis of a directional well, which significantly reduced the computational cost. In addition, a six DOF curved beam element is derived to model a curved drill-string. It achieves higher accuracy than the widely used straight beam element in both static and dynamic analyses. As a result, fewer curved beam elements are used to achieve the same accuracy, which further reduces the computational cost. During this research, a comprehensive drill-string and wellbore interaction model is developed as the boundary condition to simulate realistic drilling scenarios. Both static and dynamic analyses are carried out using the developed modeling framework. The static simulation can generate drill-string internal force as well as the drilling torque and drag force. The dynamic simulation can provide an insight of the underlying mechanism of drilling vibrations. Top drive controllers are also incorporated as torsional boundary conditions. The guidelines for tuning the control parameters are obtained from dynamic simulations. Drill-string vibrations can be suppressed through BHA configuration optimization. Based on the developed modeling framework, the BHA dynamic performance is evaluated using vibration indices. With an objective to minimize these indices, a genetic algorithm is developed to optimize the BHA stabilizer location for vibration suppression. After optimization, the BHA strain energy and the stabilizer side force, two of the vibration indices, are significantly reduced compared to the original design, which proves the BHA optimization method can lead to a significant reduction of undesirable drilling dynamics. At the end of this dissertation, reduced order models are also discussed for fast simulation and control design for real time operation