Bridging the Gap Between Geologists and Drillers: LWD Ultrasonic Imaging Goes That Extra Mile

Advanced logging-while-drilling (LWD) ultrasonic images provide 0.2 in. resolution, the highest possible resolution for well logs, enabling detailed reservoir characterization at the borehole wall of key geological events. In this paper, we demonstrate how this plethora of information provided by such imagers can be used to identify borehole wall features, but to also specify drilling dynamics. Optimal drilling can be considered as being the efficient transfer of available energy from the surface to the drill bit. When this energy transfer is compromised, drilling rates decrease, hole condition might suffer, and drilling accessories can fail. These problems often lead to poor directional control and compromise the drilling objective itself. The instantaneous kinetics of the drilling bottomhole-assembly (BHA) transparently reveals how efficiently mechanical energy is used to drill a well. This paper presents an application able to understand high-resolution BHA motion from the ultrasonic sensors in an LWD imager. Essentially, information from four pulse-echo ultrasonic sensors is combined using an inversion method to resolve the instantaneous position of the center of the tool, the hole shape as well as the mud slowness. The inversion algorithm was validated by experimental measurements where a tool was immersed in drilling mud and the transit-time data were extracted using a peak detection method applied to the received ultrasonic waveforms. The inversion showed that the computed caliper image and mud slowness were matching the parameters of the experimental setup, and that the tool center of mass moved in x and y directions, as the tool entered into lateral resonance. The inversion was applied on field data to retrieve the history of the tool position in wells after drilling completion. The BHA kinetics from these borehole images highlighted the type and number of lateral movements compared with the hole size and helped to identify improvements in future drilling operations. A comparison of the BHA vibrations simulations during the pre-job planning with the post-drilling dynamics has also provided insights for subsequent wells. The real-time definition of a more optimal workflow was made possible by streaming computed results to the surface. Using the LWD ultrasonic imager as a tool for high-resolution BHA dynamics analysis is an innovative approach with a potential to identify multiple drilling-related issues downhole, in addition to the existing applications of high-resolution borehole imaging. The LWD ultrasonic imager appears to bridge the gap between geologists and drillers with both providing meaningful inputs to each other.