Characterization and Mitigation of Mud Motor Vibrations

Abstract Severe vibrations in drilling systems are one of the main limiting factors for an efficient drilling operation. An adjustment of drilling parameters is necessary to avoid the negative impact of vibrations on reliability, measurement quality, and rate of penetration. The time to drill a well is therefore directly or indirectly affected if vibrations are not properly managed; measurements must be repeated, damaged tools can lead to additional tripping time, and rate of penetration is limited by reduced power that is delivered to the bit and restrictions of operational parameters. Complex well trajectories, a difficult drilling environment, and the extended-reach of wells are additional challenges for drilling operations. The use of a mud motor in the bottom-hole assembly (BHA) is one option to supply power directly to the bit. However, if the mud motor is not properly managed, its operation can lead to lateral vibrations. BHA design and optimization of operational parameters are options to mitigate lateral vibrations. A basic understanding of mud motor vibrations is necessary for this purpose. To characterize mud motor-induced vibrations, a statistical evaluation of averaged vibration measurement data from several runs is conducted. Distributions of the vibrational amplitudes are analyzed, in reference to different designs of the mud motor power section. Analysis continues by reviewing a large quantity of time-based acceleration data with a sampling frequency of 1000 Hz. Special downhole tests are conducted that cover the entire range of operational parameters of the mud motor. High-frequency vibration data with distributed sensors are collected for different motor types and stabilizer configurations. The outcome of the analysis is used to determine the ideal mud motor for a given application. Existing models for drillstring dynamics simulation are fine-tuned. Based on the models, sweet spots for operational parameters that avoid severe vibrations are derived and displayed in an innovative way. The extensive analysis of high-frequency vibration data enables a reliable determination of operational parameters for mud motor applications that correspond to low levels of lateral vibrations. The approach enables efficient drilling with a high rate of penetration and results in increased downhole tool reliability. This ultimately leads to an optimized service delivery for drilling operations.