Investigation on the Application of Parabolic Reflector in Plasma Logging Source

摘要

Transmitter source is a significant part of a remote-exploration acoustic logging tool. Its power and directional-radiation characteristics are key factors that affect the tool performance. Plasma source features high power and wide band. Thus, it is expected to significantly improve the exploration depth while maintaining the resolution in remote-exploration logging. However, it cannot generate a directional acoustic field, which seriously undermines its advantages as a logging source. Therefore, exploring a suitable method for directional radiation in a plasma source is necessary. In this study, a two-dimensional axisymmetric formation model with a borehole is developed using the finite-element numerical simulation. The characteristics of the plasma source with a small rotating parabolic reflector in an open hole are simulated, such as the energy accumulation and directional radiation. The simulation results reveal that the parabolic reflector in our model can increase the acoustic pressure by more than 10 dB and narrow the - 3dB angle to approximately 60° in a formation 1 m away from the source. This scheme is primarily verified as a feasible method for directional radiation, which can improve the usefulness of a plasma source in remote-exploration acoustic logging.