Abstract
Drillstring vibrations are a dynamic response of the drillstring to a combination of external forces and initial conditions. Such response is can be measured and recorded by various sensors that are mounted into rigs’ hoisting or rotating systems or directly along the drillstring. Most commonly, the sensors measure dynamic displacements and accelerations and are located either at the surface or downhole. Indisputably, the downhole measurements carry more useful information about the drillstring dyamics than the surface ones, because they are located closer to the vibration sources, like forces from rock-bit interaction, side forces and other mechanical forces. However, in certain cases, for instance, when the transmission capacity is low, serious transmission delay happens or no downhole signal is available, we have to rely on the surface readings, such as torque and RPM (rotational speed), WOB (weight on bit) and SPP (stand-pipe pressure) to monitor the drilling operations.
In this study, we use a small-scale drilling rig, equipped with surface sensors to monitor the dynamics of the drillstring under various conditions as rotation and application of instantaneous force. In addition, a high-speed camera is used to capture downhole dynamics. The study focuses on comparing the sensors’ data, which is achieved by analyzing the key parameters that describe periodic oscillations of the drillstring: frequency, amplitude and damping ratio.
High-speed cameras represent a non-invasive method for detecting and recording displacements, which can be integrated into the rigs’ real-time measurement system. It has been proved to provide accurate and practically noise-free measurements, thus it can be applied as a surface motion detection sensor in various well operations and as a downhole sensor in laboratory conditions for proof-of-concept approaches.
The conducted analysis reveals that the sensors respond differently to the applied load depending on their type and location even in the case of a small-scale experimental rig. This paper provides meaningful interpretation of the measured data and a way to extract the most valuable information from both surface and downhole sensors to enhance the understanding of the drillstring dynamics during drilling operations.
