Tool Wave in Acoustic Logging While Drilling

A new acoustic well logging while drilling (LWD) was developed with the development of horizontal or declined drilling. The source and receiver transducers are tightly mounted on the drill collar, which is much stiffer than the traditional wireline tool. The acoustic source generates very strong tool waves, which propagate along the collar. The wireline tool applies a technique of "notch" to prevent the source acoustic wave directly propagating from source to the acoustic receivers along the tool directly. The strong tool waves affect the acoustic wave field in the borehole and the measurements of the formation velocities. In this chapter, we investigate the effects of tool waves on the monopole and multipole acoustic well logging with a scaledLWDtool. The experiments show that most of the acoustic source energy propagates along the tool with their tool wave velocities in monopole and dipole cases. Only a very small part of the acoustic energy enters the formation and propagates with the velocities of formation. In the quadrupole case, however, both the quadrupole tool wave and the screw wave with the formation shear velocity can be detected. It is very difficult to eliminate the tool waves propagating along a collar and to measure the formation P-wave and S-wave velocities with the acoustic LWD tool.