Imaging near‐borehole structure using directional acoustic‐wave measurement

Abstract

This study shows how to image the structure of a near‐borehole geologic formation and determine its orientation using a directional acoustic measurement tool in the borehole. The advantage of the directional tool over a conventional monopole tool is that the former uses a dipole source and/or receiver to obtain multiple component data that are sensitive to the orientation of the structure. To preserve the orientation information in the presence of tool rotation, the multiple component data are converted from the tool‐frame coordinates into a fixed coordinate system using the recorded tool azimuth. The component data in the fixed coordinates are then used to image the formation structure and determine its orientation. The application of the method and procedure is demonstrated with a four‐component cross‐dipole data set measured in a deviated borehole. Using the directionality of the compressional waves in the dipole data, the method successfully obtains the orientation of bed boundaries crossing the borehole. In addition, the low‐frequency content (about 2–3 kHz) of the data allows for imaging the radial extent of the formation structure up to 15 m, greatly enhancing the penetration depth as compared to that obtained using conventional monopole compressional‐wave data.