Study On Ultrasonic Propagation In Borehole And Its Application

The cement ring tightly adheres the casing to the formation as a whole after the cement wells are cemented,which will not only protect the casing from corrosion but also ensure the normal production of oil and gas wells.As the development technology of oil and gas advances,the terrain complexes and drilling types diverse,the development of the oil well cementing technology is also advancing rapidly.For those reasons,the criteria for evaluating the quality of cementing is also becoming extremely stringent.Therefore,it is very important to evaluate the quality of cementing effectively in actual production.The cementing quality inspection is mainly about the cement bond quality inspection.There will be some different degrees defects in the interface due to the interface strain,or the density of cement itself and other reasons.The study of the effect of interface defects on the cementing quality is beneficial for designing the detection scheme more reasonably and improving the accuracy of the test results in the practical problem.The sonic logging is a logging method that studies the geological characteristics of the formation and the quality of the cementing by studying the propagation characteristics of acoustic waves in the down hole formation and in the medium.Based on the ultrasonic propagation characteristics in the borehole and its application in nondestructive evaluation in this paper,the main research contents and results are as follows.(1)The effect of interface defects on the ultrasonic response of casing wells was studied.The finite element software of ANSYS was used to establish the 32 groups of different interface defect size models,and the received ultrasonic echo was analyzed in waveform and converted by spectrum.The results show that the formation echo of good condition cementation is obviously identifiable,and that echoes of the interface defects gradually weakened until it is not obvious with the increase of the defect size.The FFT amplitude peak of the echo from interfacial defects models are increased first and then decreased with the increase of the defect size.When the defects of the interface defects increased to a certain extent,the energy which could reach the cement layer through the casing greatly weakened,and the spectrum of casing structure echo showed its own natural frequency.(2)The influence of the lossing scope of the cement ring on the sound field and the determination of the missing position were studied.The finite element software of ANSYS was used to establish the casing structure with good cementing qualityand 11 groups of cement missing models which loss 30-360 along the x-axis circumferential.The casing wave,the first wave amplitude and the FFT transform peak were analyzed.The results show that the amplitude of the first wave of the good model is the smallest.And with the increase of the missing angle,the amplitude of the first wave amplitude and the amplitude of the echo from different azimuths are increasing.But when the missing angle reach 180° and more,those amplitude decreases sharply and remains stable.Finally,defects in different orientations show different sensitive frequencies.(3)The propagation characteristics and time-frequency analysis of sound field in elliptical casing was studied.The finite element software of ANSYS was used to establish the elliptical well models with ellipticity of 1.1,1.2,1.3,1.4,1.5,and the received echo signal was analyzed by FRFT.The results show that the optimal p value of the circular well is larger that oval wells,and with the increase of ellipticity,the first main peak of the signal in the fractional order domain is getting larger,but the overall amplitude ratio of the signal is becoming smaller and smaller.Through the study of this paper,the ultrasonic detection of casing structure has some reference and guidance significance in theory and practical application.