| The progress of downhole oil drilling technology is a significant symbol of the technological development in the field of drilling engineering.With the continuous integration of the cutting-edge technology and the drilling engineering,the intelligent and unmanned drilling technology is an inevitable trend.However,there is still a gap between the development of China’s drilling technology and the world’s advanced level,and the research on core technologies such as the high-speed information transmission between the underground and the ground is not systematic.During the two-way transmission and communication between the ground and the underground,there are interferences such as the collision between the casing and the well wall as well as the vibration caused by the relative rotation of the servo platform.Therefore,it is necessary to possess a stable,real-time,and efficient underground wireless communication technology.Based on the finite element software,this thesis adopts the multi-physical field finite element method to decompose the actual drillstring channel into cascades of the multiple known single drill tool transmission models,establish the three-dimensional model of cascade drillstring with threaded structure,and conduct the numerical simulation solution on the frequency-domain characteristics of the acoustic wave transmission in the drill string channel.In this way,a test system is established through applying a vibration exciter to generate impact excitation signals,taking the drillstring system of the geological drill-pipe cascade structure as the signal transmission channel,and receiving signals measured through the sensor.Specifically,the test data results are collected,and the time-domain is analyzed on the transmission characteristics of the acoustic wave in the drill string.Moreover,the Fourier transform is applied to carry out the time-frequency conversion on test results,and the simulation results with the test results are compared and analyzed,expecting to obtain a finite element method which can effectively analyze the acoustic transmission characteristics of the drillstring system in cascade structure.The results show that in frequency domain response results of the cascade drill column system are consistent with the dispersion characteristics of the sound wave,and the change of the frequency resistance band coincides with the results of the dispersion equation.The simulation results are consistent with the theoretical analysis results,which verifies the reliability of the finite element method to establish the acoustic transmission model.The causes of the signal attenuation in time domain include the abrupt area change at joint,the reflection and refraction at boundary,and the damping effect of the system.The dispersion characteristics of the drill column channel structure will distort the sound signal,and the signal at a certain frequency point can arouse the signal of other frequencies.The experimental results and the simulation results are basically consistent with the amplitude change trend,which verifies that the results of the numerical simulation study are effective and can provide an effective means for subsequent research and analysis. |
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