Numerical Simulation of Acoustic Field Ahead of Drill Bit in Formation Generated by Multipole Source During Logging While Drilling

The existing acoustic logging instruments do not fulfill the requirements for forward-looking advanced detection. Therefore, research has been undertaken on forward-looking acoustic logging technology utilizing a multipole acoustic source. The finite-difference algorithm was used to simulate the acoustic logging responses of monopole and dipole sources in the presence of a formation interface ahead of the drill bit while drilling. The simulation results indicate that, due to the influence of bottomhole scattering, the wave field of forward-looking acoustic logging is more complex than that of conventional reflected acoustic logging. In contrast to the monopole acoustic radiator, the dipole sound wave exhibits a more robust emission of sound wave energy toward the formation in front of the drill bit. The amplitude of the reflected wave generated at the formation interface is dozens of times greater than that of the monopole reflected wave. Therefore, the dipole sound source proves to be more advantageous for forward detection. Moreover, the comparison of the signal-to-noise ratio for the reflected wave generated by the dipole sound source across different frequencies is further examined. The findings reveal a direct correlation between the primary frequency of the dipole sound source and the signal-to-noise ratio of the reflected wave—specifically, a lower main frequency corresponds to a higher signal-to-noise ratio. In addition, it is observed that the signal-to-noise ratio undergoes periodic changes in magnitude. The research results validate the feasibility of using dipole acoustic logging technology for detecting geological anomalies before drilling. Furthermore, they offer a theoretical base for the subsequent development of industrial prototypes.