LWD Sonic Tool Design for High‐Quality Logs

The design of a logging‐while‐drilling (LWD) sonic tool is always a challenge; the acoustic propagation along the tool cannot be ignored, nor can effects on measurements due to tool presence. It is well known that collar arrivals can interfere with compressional waves in fast formations. The interaction of the collar with other modes such as Stoneley and quadrupole must also be considered while designing an LWD acoustic tool. Because the LWD tool occupies a significant area of the borehole cross section, it is known that the presence of a sonic tool in a borehole shifts a dispersion curve in the slowness frequency domain. In this paper, we present an approach to optimize tool design for minimizing tool effects on measurements or making tool presence effects predictable for enabling a broadband use of the acquired data. Experimental results validate the design of the tool, and real log examples illustrate the quality of the acquired waveforms.