A Simulation Study On ANL Electrode Characteristics Of Plasma Impulse Sound Source While Drilling

Because the monopole sound source,dipole sound source and phased array sound source have defects such as limited emission power and inability to take into account high and low frequencies,however,the impulse sound source while drilling has the advantages of high shock wave intensity,wide frequency band and controllable parameters,which just make up for the shortcomings of the current sound source.Therefore,in the deep detection technology of the impulse sound source while drilling,the emission source is the impulse sound source while drilling.Since the electrode structure is a very important part of the impulse sound source while drilling,this paper studies the following four aspects for the electrode structure of the impulse sound source while drilling:(1)First,the present status of research on the acoustic depth detection technology while drilling,the impulse acoustic source while drilling and the electrode structure of the impulse acoustic source while drilling both in China and abroad are summarized;The shock wave generation mechanism and theoretical process of the impulse sound source while drilling are analyzed,and the judgment condition of the pre-breakdown time is obtained,in other words,the boundary water temperature of the electrode structure reaches the boundary boiling temperature(773.15K),and the average electric field strength of the electrode water gap reaches 8kV/cm,the pre-breakdown time when the two conditions are satisfied at the same time is the time that meets the judgment conditions,and the shock wave intensity under different electrode structures is calculated by using the plasma control equation.(2)Secondly,the finite element simulation software COMSOL is used to model and simulate the electrodes of the known experiments to confirm the correctness of the simulation method and model in this paper.Then needle-needle electrodes(N-type electrodes),needlering electrodes(L-type electrodes),and needle-ring array electrodes(A-type electrodes)structures were constructed.When the peripheral circuit remains unchanged,by comparing the pre-breakdown time,leakage energy,deposition energy,shock wave intensity and conversion efficiency of the three electrodes,It is concluded that the L-type electrode has a shorter pre-breakdown time,less leakage energy,more deposition energy in the channel,stronger shock wave intensity,and higher electro-acoustic conversion efficiency,Therefore,the L-type electrode is more suitable for the electrode structure of the impulse sound source while drilling.(3)Next,the effects of electrode gap,charging voltage,and ring radius on the characteristics of L-type electrodes were investigated.With the increase of charging voltage,the pre-breakdown time is shortened,and the shock wave intensity increases linearly,but the electroacoustic conversion efficiency decreases;when the optimal electrode gap is 5mm and the ring radius is 2mm,the shock wave intensity and electroacoustic conversion Efficiency is the best.(4)Finally,under the condition of optimal electrode gap and ring radius,the structure of L-type electrode is micro-optimized.Compared with the electrode before optimization,the pre-breakdown time of the optimized electrode is shortened by 67.58 μs,the leakage energy is reduced,the deposition energy is increased,and the shock wave intensity at a distance of 8cm from the discharge center is increased by 0.6 MPa.The conversion efficiency is improved by 0.13%.Therefore,the optimized electrode improves the shock wave intensity and electroacoustic conversion efficiency of the impulse sound source while drilling,and the electrode structure size is suitable for small downhole spaces,which provides a theoretical basis for the sound source design of the sound source depth detection tool for the impulse while drilling.