Method For Drill Collar Wave Suppression And Formation Signal Extraction In LWD

As acoustic logging technology to gradually development,acoustic logging while drilling in recent years become the hot subject,compared with the traditional wireline acoustic logging,the acoustic logging while drilling can get the formation information in the process of drilling.Through the analysis of the measured acoustic logging data,we can adjust the drilling direction,making drill collar accurately drilling through the reservoir,improve the production efficiency of oil and gas.But when the sound source make excitation,because of the existence of drilling collar,there will be collar wave propagating along drill collar.The collar wave interferes with formation wave signal in the data of acoustic logging,making the formation information is difficult to extract.So suppressing collar signal become one of the important problems in the study of acoustic logging while drilling.The common practice at present is periodically groove on the drill collar,to cut off the collar wave propagation path.But the acoustic insulation effect of grooving is not obvious in complex logging environment,and the collar wave still exists.In this paper,a weight-based ?-p transform processing method is presented to suppress collar wave interference and improve the signal-to-noise ratio of formation signal,so as to accurately extract useful formation information.This paper first used concentric layered medium to simulate the formation structure in and around the well.We use the theoretical model described above to theoretically deduce the acoustic field of LWD acoustic logging,and analysis the full waveform characteristics after simulation.Then,waveform correlation method,frequency-wave number correlation method,waveform interference method and energy threshold method are used to process the theoretical data of LWD acoustic logging.The results show that the above four methods have some limitations in certain casesIn order to overcome the shortcomings of the above conventional data processing methods,this paper presents an array acoustic logging processing method based on weight?-ptransform principle.Basing on ?-p transform principle,We convert the time domain acoustic data to the ?-p domain for processing.The he traditional linear ?-p transform will produce truncation effect(energy trailing divergence phenomenon),the using of least square method can reduce the divergence characteristics.Due to the existence of downhole noise and the limitation of the number of receivers on the array instrument,the energy of the formation wave field is still diverging.According to the collar wave and the formation wave distribution characteristics in?-p field,we create suitable weights,weighting each elements in the ?-p field,that can suppress the wave field energy of collar,and the formation wave energy of wave field convergence concentrated,achieving the goal of improving formation signal SNR.This method is used to process the theoretical data of LWD acoustic logging,and the theoretical data processing results verify that the new method can suppress the drill collar wave and improve the signal-to-noise ratio of formation signals and extract the formation sound velocity.The application of this method to the actual acoustic logging data shows remarkable results.This paper provides a new processing method for array acoustic logging in LWD.