Research On The Effect Of Internal Stress On Acoustic Propagation Characteristics In Drill String

Process intelligence is the trend of the development of drilling technology.One of the bottlenecks in the realization of intelligent drilling is to build a high-speed and accurate transmission channel of information in the well.Using acoustic wave as carrier and drill string as channel,the downhole information acoustic transmission technology is expected to become the key technology to break through the above bottleneck due to its simple structure,low transmission cost,fast transmission rate and easy directional emission.In the actual drilling process,the drill string bears various loads,and field tests have found that the stress in the drill string is an important factor affecting the stability and reliability of the acoustic signal.In order to clarify the effect of different stress states and stress distributions in the drill string on the acoustic propagation characteristics,an analytical model of sound propagation in loaded drill string was established in this paper,and the experimental devices for acoustic propagation and attenuation characteristics in the drill string with tensile and bending stress were also carried out.These work are aiming to establish the optimization method of acoustic carrier frequency and repeater positions in the development and application of acoustic transmission technology.The influence of different stress states and stress distributions on the sound propagation and attenuation characteristics was clarified with the combination of theoretical research and experimental testing;The sound propagation and attenuation characteristics was analyzed in a complex stressed drill string.An acoustic spectrum evaluation method was established in a loaded drill string,which can realize the quantitative characterization of the spectral characteristics under different loads in drill string with tensile stress;An optimization method of carrier frequency band was established based on the measured noise spectrum characteristics under different drilling conditions;A method for selecting the position of the repeater was set up based on the quantitative relationship between the fitted acoustic attenuation rate and the tensile stress,and the reliability of the application method was verified by the field test data.Aiming at the problem that internal stress was not considered in the past relevant researches for acoustic propagation in the drill string,the theoretical analysis model including the longitudinal wave equation,the dispersion equation and the acoustic propagation transfer matrix were reconstructed based on the linear acoustic theory by introducing the influence of the internal stress of the drill string,to analyze the characteristics of the acoustic propagation in drill string under the bending load.The results show that the axial and bending loads could not change the basic characteristics of acoustic propagation,but it has an impact on the frequency band results.As the axial load increases,the passband and stopband in the tensile drill string shifts to the low frequency,but the passband and stopband of the compressed drill string shifts to the high frequency.The bending load has no obvious effect on the structure of the low frequency band.As the bending load increases,the pass band gradually shifts to the high frequencies,and the shift degree of high frequencies is higher than that of low frequencies.Aiming at the problem that the attenuation was not considered in the acoustic propagation analysis model in loaded drill string,the experimental devices for acoustic propagation and attenuation characteristics in the drill string with tensile and bending stress were established.The experimental test and analysis revealed the effect law that,the tensile and bending load attenuates the acoustic propagation in the drill string,which can confirm the correctness of the calculation results of the model;the difference in the effect of the drill string structure and the acoustic excitation parameters on the acoustic propagation characteristics of the drill string under different loads is found.The tensile stress intensifies the effect of the drill string structure on the frequency spectrum stability.The optimal excitation parameters are different for different tensile stress intervals;the acoustic propagation stability and spectrum difference under different waveforms,transducer installation methods and acoustic excitation methods in tensile drill string,and the difference between axial and circumferential received signals are studied.Aiming at the problems of complex force on drill string and complicated influence of axial load on acoustic attenuation characteristics under actual drilling conditions,the position changing law of the acoustic propagation passband in the complex stressed drill string was analyzed based on the established acoustic propagation transfer matrix analysis model and the experimental results of the effect of the unidirectional force on the acoustic propagation characteristics of the drill string.Introduce an improved radar chart to establish an evaluation method of acoustic wave spectrum characteristics,and selected the lower limit frequency of the passband,bandwidth,peak,peak point frequency and passband energy as the pass band characteristic evaluation index.Then,the evaluation function value of each pass band in the frequency spectrum is used as the evaluation index of spectrum characteristic.This method can realize the quantitative characterization of each pass band in the acoustic wave spectrum in the drill string and the overall characteristic of the spectrum under tensile load.Aiming at the problem that the position of the passband and the attenuation of the acoustic spectrum in the drill string under actual drilling conditions change with the load state,the intensity and frequency spectrum characteristics of the noise under different drilling conditions are analyzed,Then,the optimization method of the frequency band of the acoustic carrier based on the noise spectrum characteristics and the change rule of the passband position with the axial load under different actual drilling conditions.The quantitative relationship between the acoustic attenuation rate and the tensile stress is fitted based on the experimental data.Both the top-down and bottom-up design methods for the repeater were established according to the relationship between the acoustic attenuation rate and the tensile stress.This research content can provide guidance for the realization and promotion of acoustic transmission methods in load-bearing drill strings,and provide theoretical support for the construction of intelligent drilling and efficient information networks.