Study On The Time-Frequency Characteristics Of The Numerical Calculation Of Acoustic Logging In Fracture Formations

Acoustic full-wave logging is one of the main methods in geophysical logging,its core is the use of sound waves in the rock spread in different laws,and obtain the petrophysical parameters of the measured rock strata,so as to judge the existence of oil and gas reservoirs and lithology.At present,there are two main ways to deal with the acoustic logging signal: time method and domain method.The core idea is the extraction of slowness,through the slowness of each group of waves with the depth of the curve to determine the nature of the nearby strata.The slow-time extraction method of the time domain starts from the waveform of the signal time domain,including the threshold method,the slow-time correlation method and the energy integration method.The frequency domain method is a Fourier transform of the full wave train of acoustic waves,and finally obtains the spectrum and dispersion curve of each component wave,and then solves the problem of slow extraction of the scattered waves such as Stoneley wave,Including spectral phase analysis,Matrix Pencil algorithm and Prony method.The acoustic signal contains three basic physical quantities: time,frequency and amplitude(energy).The extraction of slowness only reflects one aspect of information,that is,the speed of each component wave,ignoring the spectral characteristics of the signal,although the acoustic logging signal spectrum information can be easily obtained by Fourier transform,but The frequency domain information obtained by Fourier transform will lose time domain information at the same time.If it is necessary to obtain the signal frequency domain characteristics,but also to retain the signal time domain information,it is necessary to introduce time-frequency analysis method.The advantage of the time-frequency analysis method is that it correlates the basicphysical quantity time,frequency and amplitude of the signal to obtain the distribution of energy on the time-frequency coordinate axis.A single time-frequency analysis method is not ideal for the characteristics of the full-wave signal of the acoustic wave,since each component wave may have multiple frequency responses at the same time,and the time and frequency are closer,so it is difficult to distinguish.In this paper,we use the Hilbert-Huang transform,which is the empirical mode decomposition(EMD)and Synchrosqueezing Transform(SST)method in Hilbert-Huang transform.By programming different EMD screening methods It is necessary to obtain a SST for each natural modal function(IMF)to obtain the time-frequency characteristics of the P-wave,S-wave and Stoneley waves.The time-frequency characteristics of different fractured reservoirs are studied.The work of this paper is divided into three parts: Firstly,the empirical mode decomposition(EMD)joint synchronous squeezing wavelet transform(SST)method in Hilbert transform(HHT)is applied.Firstly,The results show that the acoustic signal of the array can be decomposed by the method,and then the wavelet transform is carried out for each natural modal function(IMF).For each IMF,the time-frequency Figure,distinguish between the array of acoustic wave full wave signal in the longitudinal wave,shear wave and Stoneley wave components.The temporal and edge characteristics of the time-frequency distribution and the edge characteristics of the frequency are proposed for the segment processing.The time-frequency characteristics of each component wave are obtained with the depth change rule,and the time-frequency characteristics of the fractures and oil-water layers are evaluated.Secondly,the finite difference method is used to establish the velocity-stress finite difference formula of the wellbore wave equation in the column coordinate system by using the staggered grid technique.The appropriate absorption boundary and sound source function are programmed to simulate the well-Uniform stratigraphic and soft ground strata,including fractured strata and fractures in different layers of fractures,and then the time-frequency analysis is carried out by the method described in the first part to summarize the fractures in the stratum Characteristics of Acoustic Wave Time-frequency for Oil-bearing Water.Thirdly,the data of the acoustic logging of different wellbore arrays are selected.After the data is preprocessed,the data in the depth range is selected by the method described in the first part,and the time-frequency diagram of each IMF is obtained And time edge and frequency edge characteristics,compared with the second part of the time-frequency characteristics,inversion of cracks in the formation of cracks and cracks in the fluid situation.