Unlock the Potential of High-Resolution Ultrasonic Imaging and Caliper Measurements for Large Borehole Sections

Abstract Obtaining high-resolution ultrasonic caliper measurements and amplitude images in oil-based and water-based mud from logging-while-drilling (LWD) tools has become a common practice for hole sizes up to 14.75-in. in diameter. This paper introduces a new LWD high-resolution ultrasonic caliper/imager tool designed for hole sizes up to 19 in. in diameter. The insight gained with smaller ultrasonic tools has revealed that a 9.5-in. tool would require a distinct ultrasonic transducer to account for larger standoff distances in larger boreholes. The new 9.5-in. tool utilizes an ultrasonic transducer with a lower nominal frequency than the smaller tools. Laboratory and field trials confirmed the 9.5-in. tool's capability to capture high-resolution borehole images and caliper measurements in boreholes up to 19 in. with varying mud weights. The tool's eccentricity-corrected amplitudes and radius images improved borehole geometry analysis and geological feature identification. The high firing rate of the transducers and four-transducer design allows for obtaining an average caliper size while tripping out of the hole without rotation and enables accurate cement volume calculation. Additionally, while reaming out of the hole, the borehole shape can be evaluated to understand its behavior over time after drilling, providing valuable information for the operator. The data collected during field trials was analyzed and compared with wireline ultrasonic tools from the same area to validate the results. The interpretation of the borehole images (amplitude and travel time) for both borehole geometry and geologic features confirmed a spot resolution of 0.2-in. while drilling with different logging and rotary speed combinations. The development of a new 9.5-in. LWD high-resolution ultrasonic caliper/imager tool has resolved the challenge of obtaining caliper measurements and borehole images in larger borehole sections. This innovative tool will significantly enhance operators' ability to perform cement volume calculations and accurately identify unstable formations in larger boreholes.