Development of an efficient Vibration Modeling Technique for Design-Related Optimization of Tools in the Global Drilling Environment

Abstract

Abstract Severe vibrations in drilling systems and bottom-hole assemblies can be caused by cutting forces at the bit or mass imbalances in downhole tools such as mud motors. Vibrations can lead to reduced drilling performance, poor measurement quality and reduced reliability. Models are important to understand the phenomena and predict loads. So far models are established that calculate the dynamic behavior of the drilling system from a global point of view: The drilling system is modeled with simplified geometry and placed in the drilling environment under consideration of the wall contacts with the borehole and the fluid properties. Global models are typically used for optimization of drilling parameters such as the rotary speed or the flow rate with respect to estimated dynamic loads. Global models are not suitable for detailed modeling and analysis for optimization on a tool component level. A system-approach is established to overcome the limitations. A method is developed to connect a detailed 3D-model of a downhole tool with the model of the drilling system and the bit that is placed in the global drilling environment. The method enables new insights into the behavior of downhole tools that can be used to optimize downhole tools with respect to their reliability and their performance: Dynamic loads on tool components such as probes and pockets can be calculated to optimize the tool design and increase reliability. The probe design can be optimized to reduce the dynamic loads on sensor components and significantly increase the measurement quality. In a case study the method is validated with measurements. Herein, torsional eigenfrequencies and corresponding mode shapes which are localized to the bottom-hole assembly as well as the resulting tool stresses and loads are considered. The impact of a dampening tool to mitigate torsional vibrations is discussed. In a second example the capability of the method to capture lateral vibrations under consideration of wall contacts and mass imbalances is shown. The method is used to optimize the design of a downhole tool to decrease the dynamic loads at sensor components that are placed in a probe. The system-approach of the method allows to efficiently simulating the vibrational behavior of tool parts in an arbitrary detail and in a global drilling environment. The new method enables improved tool design for performance and reliability and increased measurement quality.