Development and Evaluation of Criteria for the Comparison and Optimization of Bottom Hole Assemblies
Research output: Thesis › Master's Thesis › Research
Lateral vibrations pose a major problem in drilling. Bottom Hole Assembly (BHA) failures, for example due to wellbore wall interactions and high bending stresses, can directly be related to vibration phenomena. Downhole measurement and real-time data transmission are also affected by vibrations and pose a problem in drilling performance. Although lateral vibrations can have severe consequences, their nature makes modeling and prediction quite challenging, especially in the pre-well design phase and BHA performance comparison. Lateral vibrations are not recognized at surface. Only downhole measurement systems can provide information about the downhole environment. Dynamic changes in wall contacts alter the vibration system in terms of natural frequencies and mode shapes, leading to different physical deflections. This makes dynamic modeling a difficult process. This thesis demonstrates the impact of stabilization, geometry changes and excitation source variations on lateral BHA vibrations. In a parameter study on a beam structure model, different model configurations are simulated, analyzing the impact of stabilizer placement, bending stiffness and mass on vibration susceptibility. The model utilizes the given transfer matrix method as an analytical approach to compute all modal properties and physical amplitudes. This implementation enables a much faster computation than finite element method simulations, thus more model variations can be conducted in a given time frame. The parameter study proves the importance of appropriate stabilizer placement to mitigate lateral vibration susceptibility. Flex-subs, mainly considered to reduce static bending loads, are found to greatly impact the vibration system, depending on their geometric properties. Moreover, the study identifies the most suitable presentation format for lateral vibrations. The strain energy, coupled with a dynamic-bending-moment-based critical speed analysis, is formed to a key parameter in the BHA optimization process to decrease lateral vibration susceptibility already in the planning phase. The strain energy and dynamic bending moment based dynamic optimization procedure is integrated into an overall drilling performance criterion which incorporates BHA steerability, statics, dynamics and geometric properties. In directional wells, BHA steerability is more important to a drilling project than an optimized static or dynamic load performance. However, every BHA under comparison must not exceed their allowable load limitations. The properties represent ratios between well plan or operation parameters and BHA limitations. The parameter study and optimization criteria are demonstrating the effect of BHA alterations on lateral vibrations and how BHA designs can be optimized and compared.
|Award date||18 Mar 2016|
|State||Published - 2016|