Real-Time Wellbore Stability Assessment Using a New Generation Ultrasonic Logging-While-Drilling Imaging Technique
Authors: Khan K. , Alidi R. , Taher A. , Fouda M. , Hussein M. , Al Maimani A. 
Published: February 2024

A stable and good-quality wellbore in oil and gas drilling serves various critical purposes including minimizing drilling difficulties, obtaining high-quality open hole log data, running completions successfully, and reducing well integrity risks during stimulation. A properly built pre-drill geomechanical model to predict safe mud weight and real-time wellbore stability monitoring are two main components of wellbore stability management. Real-time wellbore stability monitoring includes surface indicators of drilling difficulties or excess cavings observed during drilling. It's further enhanced by downhole measurements from logging-while-drilling (LWD) tools. These tools provide information about the extent and severity of unstable intervals along the logged section. Recently, high-resolution ultrasonic LWD tools have been used, which provide advanced capabilities to monitor wellbore breakouts (compressive wellbore wall failure) or drilling induced fractures (tensile wellbore wall failure).

LWD technologies has been traditionally used for petrophysical analysis and well placement applications. In addition, several tools have been used to calculate average hole diameter while drilling in real time. Tools having multiple detectors with multiple depths of investigation have been used to identify hole deterioration by analyzing effects on the sensor measurements. LWD tools with azimuthal sensitivity can indicate the direction of wellbore breakout. Utilizing the newly developed azimuthal high-resolution ultrasonic sensor can provide an accurate definition of breakout width and the mapping of thin drilling-induced fractures. Ultrasonic amplitude images can be used in real time to monitor wellbore deterioration and proactively take decisions to adjust drilling fluid density or drilling parameters.

Incorporating LWD data into workflows to maintain wellbore stability enabled accurate determination of wellbore deterioration mechanisms. Advanced workflows integrated density, resistivity, and ultrasonic data for real-time decision-making and post-well analysis. Real-time density images from multiple detectors gave an indication of hole deterioration while drilling. Real-time ultrasonic amplitude images provided a solution for monitoring the development of breakouts and taking decisions proactively to mitigate risk while drilling. High-resolution ultrasonic memory images provided accurate measurement of breakout severity and induced fracture azimuth, enabling advanced post-well analysis. In addition, time-lapse analysis comparison between multiple logging passes while drilling and while pulling out of the hole indicated time-lapse wellbore deterioration. Integrating data from different sources led to informed decisions and proactive planning for upcoming drilling and completions operations. This paper presents a comparative study of different LWD technologies utilized for wellbore stability evaluation including successful utilization of the ultrasonic LWD high-resolution imaging tool in comparison with results using conventional tools.