Ultrasonic Borehole Imaging in the Logging While Drilling Domain in All Mud Types, a Case Study in Offshore Abu Dhabi

Abstract High resolution micro-resistivity imaging has been available in the logging while drilling (LWD) industry for the last 15 years in water-based mud (WBM) systems. However, the recent introduction of LWD ultrasonic technologies means that high-resolution images and associated analysis are now available for both WBM and oil-based mud (OBM) applications. This paper details the deployment of a 4¾-in. LWD ultrasonic imaging service in a mature offshore carbonate field, in Abu Dhabi, and the assessment of images in WBM with micro-resistivity image comparisons. The 4¾-in. ultrasonic service combines borehole size and shape measurements with high-resolution radius and reflection amplitude images. The LWD tool takes advantage of drill string rotation to make a 360-degree scan of the borehole with each transducer. The ultrasonic sensor uses four transducers that operate in a pulse-echo mode. By firing simultaneously, the transducers provide a total of 2,000 traveltime and reflection amplitude measurements each second, enabling the creation of high-resolution images, even at high-logging speeds. The images were used to evaluate the suitability of the LWD ultrasonic measurements to enhance reservoir understanding, along with azimuthal high-resolution resistivity image measurements in WBM applications. The ultrasonic tool was run in tandem with the resistivity imaging tool on a recent well where an inflow control device (ICD) had to be installed. The ultrasonic images showed excellent agreement with the high-resolution resistivity measurements, illustrating bedding, natural fractures, and sedimentological features. The resolution of the reflection amplitude images enables identification of drilling-induced features on the surface of the borehole, highlighting the measurement's value in understanding the impact of bottom hole assembly (BHA) design on the quality of the wellbore in fine detail. The travel-time measurements provide detailed evaluation of the borehole size and shape, with a three-dimensional (3D) visualization of the wellbore illustrating the ability of the tool to identify borehole enlargement and breakout. These findings demonstrate the suitability of the ultrasonic imager to address wellbore stability issues, identify principal stress orientations, and aid completion design in real time by confirming swell packer positions. Comparisons between ultrasonic images and established LWD technologies highlight the suitability of the radius and reflection amplitude images to provide enhanced reservoir characterization in both WBM and OBM applications. Log examples show that high-resolution images can identify bedding features, confirm natural fracture types and provide assessment of borehole size and shape for wellbore stability assessment for better ICD completion design.