Experimental analysis on acoustic LWD with multipole source

The acoustic logging while drilling (LWD) is an important technology in the petroleum exploration, but the collar waves propagated along the collar from source to receiver make it difficult to measure the P wave and S wave velocities. In this paper, the properties of multipole collar waves are studied from acoustic LWD experiments with a scaled laboratory detector that is built with monopole,dipole and quadrupole modes. We first measure the collar waves with a infinite liquid model when the detector is put in a water tank. The collar waves are recorded with multipole sources. Then we conduct acoustic LWD measurements in sandstone and Lucite borehole models. The frequency responses of collar waves are analyzed and compared with results obtained from the liquid model. Specially, the one and two order collar waves excited by the dipole source are recorded, their influences on the measurements of flexural wave are analyzed later. Based on the full waves measured with monopole and dipole sources, it is found that the relative amplitude of collar waves can be effectively reduced with the increasing source frequency, so that the formation waves can be measured well. This study is useful for the design of LWD detector and the data interpretation.