Acoustic Logging While Drilling (LWD): Experimental Studies with Anisotropic Models

Abstract

A model LWD tool (0.16" ID, 0.4" OD) was built to investigate its operation in an anisotropic formation. The tool consists of a dipole source and six dipole receivers capable of operating at several hundred kHz. The formation was a block of delabole slate with a borehole of 1.27 cm diameter. In an anisotropic °uid-¯lled borehole with a dipole source and dipole receiver ori- ented along the principal directions, dipole (°exural) modes are mainly observed. Weak compression and shear refracted arrivals are also discernable when they were not ob- scured by stronger arrivals. Further, modes corresponding to fast shear direction are evident in the slow shear direction measurement. With a model LWD tool in the °uid-¯lled borehole, and oriented in the fast and slow directions, the main arrivals were the corresponding °exural modes. Modes cor- responding to the fast shear direction are no longer evident in the slow shear direction measurments. These preliminary experiments suggest that, with an LWD tool in an anisotropic formation, arrivals sensitive to formation properties can be discerned.