Investigation Acoustic Variable Density Logging For Well-Cementating Interpretation

The main method to evaluate and carry out cement bond quality in cased borehole is CBL-VDL logging information,it can provide the quality and condition of cementation aboutâ… ,â…¡interfaces.Through extracting energy value of casing wave and formation wave from variable density logging waveform,calculating BI ofâ… ,â…¡interfaces,furthermore,we can evaluate bond quality by using CBL-VDL logging data.At present,the best result was obtained through using VDL as the main method to carry out bond quality in domestic oil field,but there are still some problems need to be improved related logging data interpretation.In addition,there are some methods by using comprehensive interpretation method or SGDT to identify micro-gap.According to present situation of VDL logging,in this article,discussed the methods and standard of evaluatingâ… interface.This article mainly applies 3'CBL and using amplitude compare method and the method of cement bond index.In addition,in this article,evaluate the parameter of cement filling and strength of cement by using CBLcurve.We can evaluate the bond quality ofâ… interface not only by using cement filling and strength of cement but using thickness of fluid annular.When evaluated the bond quality ofâ…¡interface,this article used formation wave and Complex-Mode Wave which picked-up from VDL data to discuss and carry out the attenuation correction and interference correction,furthermore find the energy parameter and calculate the BI ofâ…¡interface.Besides using attenuation correction and interference correction,this article set up the method of acoustic impedance differences to remove the influence of formation outside the tube.Through academic forward modeling simulation,investigated the quality relationship ofâ…¡interface among arise of Complex-Mode Wave,arrive time and amplitude of head wave;compared the method for evaluating bond quality ofâ…¡interface by using Complex-Mode Wave and formation wave,tried to find the difference between that two ways,find the relationship between bond quality ofâ…¡interface and arise of Complex-Mode Wave and arrive timeand amplitude of head wave.This will provide evidence for using calculation model which based on the bond quality ofâ…¡interface.Moreover, Complex-Mode Wave will be effected when bond quality ofâ… interface becoming low because of superposition with Complex-Mode Wave and casing wave.Therefore,It's necessary to investagete the attenuation of Complex-Mode Wave when extracting amplitude of Complex-Mode Wave.Based on this point,this article calculated the amplitude of Complex-Mode Wave and extracting the attenuation coefficient of amplitude of Complex-Mode Wave to distinguish casing wave and Complex-Mode Wave.There is no shear coupling between casing and fluid annular,result in high amplitude of casing wave although fluid annular does not affect aroduction layer's hydraulic sealing.The character is almost same between fluid annular and channelling interface in VDL curve, namely,casing wave and formation wave have above medium amplitude,it seems as good bond quality and easy to be misjudgment.For comparing fluid annular and bad bond quality ofâ… interface,this article set up a distinguishing method by evaluating the character of length of fluid annular,VDL,gamma-density logging. whereas mentioned above,it seems that,we got some successes for evaluating bond quality ofâ… ,â…¡interfaces,but there are still some problems need to be clarified,for example,the relationship between amplitude of formation wave andâ…¡interface coupling,forming the slide wave in soft formation,mechanism of 5'and 3'CBL ratio,we can further study these problems with Forward Numerical Simulation method.