Defining Formation Complexity and Anisotropy With Logging-While-Drilling Dual Ultrasonic Images
Authors:   Schlumberger, Sakiyama Naoki , Blyth Matthew ,   Schlumberger, Yamamoto Hiroaki ,   Schlumberger, Sagara Mizuki ,   Schlumberger, Tan Sarwa ,   Schlumberger, Shrivastava Chandramani ,   Schlumberger, Deger Evgeniya ,   Schlumberger, Nakajima Hiroshi ,   Schlumberger, Barry Andrew ,   Continental Resources, Kittridge Mark G. ,   Occidental
Published: October 2022

A new logging-while-drilling (LWD) dual ultrasonic tool enables the measurement of high-resolution, full-azimuth, ultrasonic pitch-catch compressional and shear (P&S) slownesses, in addition to high-definition pulse-echo images (Blyth et al. 2020). The tool provides a unique capability for near-wellbore rock mechanical property assessment compared to conventional wireline (WL) sonic measurements that have a relatively deeper depth-of-investigation (DOI). This time, P&S slownesses acquired with the ultrasonic pitch-catch method are benchmarked against those acquired with WL sonic tools using field data in order to reveal the applications of the new LWD dual ultrasonic tool. To classify the cases where ultrasonic pitch-catch and sonic slownesses are expected to match or to be different, we leverage the unique features of the data acquired with the new LWD dual ultrasonic tool. This classification uses azimuthal variation of ultrasonic P&S slowness, fractures identified with high-definition pulse-echo images, and calipers. In situations where the formations do not have significant radial slowness variation, within the DOI of sonic tools, the studied field data suggests that ultrasonic pitch-catch P slowness matches WL P slowness to within 1 μs/ft. In the same situations, ultrasonic S slowness measurements within 5 μs/ft from WL S slowness are feasible. Correction of the apparent S slowness for the effect of the pseudo-Rayleigh mode contamination is needed in some situations and not in others, depending on the job conditions. The above benchmark includes formations with intrinsic anisotropy in a horizontal well. Thus, ultrasonic pitch-catch measurements are useful for defining shear anisotropy in the studied case. The current study suggests that the P&S slownesses from the dual ultrasonic tool can be used for applications that require conventional slowness information under the conditions where both measurements can be expected to be the same. When the complexity of the formation makes ultrasonic and sonic slownesses different, due to their different measurement physics, then the tool has unique applications that are not available with conventional sonic tools. Examples of such cases are in azimuthally heterogeneous formations, formations with stress-induced anisotropy, and damaged formations. In the case of azimuthally heterogeneous formations, the existing P&S answers from WL sonic tools do not necessarily have enough information because their measurement principle averages out certain azimuthal information. The dual ultrasonic tool enables a better understanding of these complex cases, using the azimuthal variation of the high-resolution ultrasonic pitch-catch P&S slowness and high-definition ultrasonic pulse-echo images.