The Cement Bonding Quality Detection In Double-Casing Wellbores With Ultrasonic Flexural Lamb Waves

At present,the research on cementing quality detection at home and abroad mainly evaluates the cementing quality of single-casing wells,that is to say,the two interfaces of casing-cement interface and cement-formation interface are mainly concerned.In recent years,the application of double-casing wells cementing technology has increased.This technology is to put two coaxial casings of different diameter in the same well.Its purpose is mainly embodied in two aspects:(1)repairing and reinforcing the original single-casing wells;(2)meeting the higher requirements of cementing quality for deep well exploitation.So cementing quality testing needs to evaluate the cementing quality of two layers cement and four interfaces.Obviously,the cementing quality testing of double-casing wells is more difficult than that of single-casing wells.There have been studies on the application of acoustic amplitude-variable density logging method in double-casing wells in China.It can be used to judge whether there are fluid layers at the four interfaces by inner and outer casing waves and formation longitudinal and shear waves.However,this method can only evaluate cementing quality qualitatively and azimuthally,and can not provide radial and azimuthal information,distinguish instrument eccentricity,and accurately interpret data in azimuth.Aiming at oblique incidence ultrasonic logging technology,this paper simulates its logging process in double-casing wells,studies the propagation characteristics of bend Lamb wave in cased wells,analyses the feasibility of its application in cementing quality detection of double-layer cased wells,and puts forward the basis and method of detection.The main contents of this paper include:Firstly,the implementation process of finite difference time domain method(FDTD)in Cartesian coordinate system(including the application of non-splitting perfectly matched layer condition and the method of simulating line source with point source)and parallel computing for plane layered model are briefly described.Secondly,Fortran 90 program is compiled to simulate the cementing quality testing process of double cased wells.Firstly,the program is degraded and the cementing quality test of single-casing wells is simulated,which verifies the correctness of theoretical derivation and programming.Then the cementing quality test of double-casing wells with low,medium and high acoustic impedance cement is simulated.It is found that only double-casing wells with medium acoustic impedance cement can judge the cementing quality of four interfaces by flexural Lamb waves received by oblique incidence ultrasonic logging technology.Thirdly,for the double-casing wells with medium acoustic impedance cement,the situation of channeling with different thickness at each interface is simulated,and the quantitative detection effect of this logging method on the thickness of channeling at four interfaces is analyzed and discussed,and the basis and method of detection are put forward.Finally,the case of using cement with different acoustic impedance for inner and outer cement is simulated,and the basis and method of using oblique incidence ultrasonic logging technology in cementing quality detection are discussed by analyzing the received full wave.This paper simulates and analyses various situations of different cement,different interfaces and different channeling thicknesses,which has positive theoretical guidance value for logging methods and log interpretation of double-casing wells.