Acoustic Logging Scattering Effect Basic Application Research In Complex Formation

Scattering due to small-scale heterogeneities,such as the hydraulically created fracture,in the rock formation surrounding a wellbore can significantly change the acoustic waveform from a logging measurement which in turn can be used to characterize the formation heterogeneities.In this paper,from two aspects of numerical simulation and data processing we study acoustic logging,especially the dipole acoustic logging,scattering effect in the heterogeneities formation.According to the coda wave attenuation characteristics,a method is presented to evaluate the formation heterogeneities and anisotropy which were used to characterize dipole acoustic data logged before and after fracturing a reservoir interval.The full text is divided into the following three parts :In the first part,elastic wave scattering in the heterogeneous mediun was studied.We first deduce the scattering wave expressions based on Born approximation.On this basis,we calculate the scattering wave field of different heterogeneous model using Born approximation,image the scattering wave,and analyze the imageing characteristics of different types heterogemeous medium model.This part work provides the theory guidance for the data processing and interpretation of single-well imaging.In the second part,we focus on the acoustic logging scattering effect using three-dimensional finite difference time domain in the complex heterogeneous formation.First of all,based on the elastic medium scatterer distribution in statistical sense and random process theory,we establish three-dimensional random medium models to characterize heterogeneity around the borehole.On this basis,monopole and dipole acoustic logging response characteristics were simulated in the isotropic heterogeneous formation.The results show that significant coda waves are generated in both monopole and dipole waveforms and the dipole coda is dominated by S-to-S scattering.Further,dipole acoustic logging scattering effect were simulated in the anisotropy heterogeneous formation,and we analyze the characteristics of different azimuth coda wave envelope.In addition,we studied the effect of small-scale heterogeneities around the borehole on the high angle reflector imaging.According to the characteristics of scattered wave,waveform array could be used to eliminate the influence of stochastic signal,and to obtain high signal–to-noise ratio of the reflected wave signal.In the third part,the data processing methods of the acoustic logging scattering effect are studied.First,we analyze the frequency wavenumber domain features of both scattering waves propagating along the borehole and caused due to heterogeneities outside well,and preprocess the acoustic logging data using f-k filtering to eliminate the influence of scattering signal propagating along the borehole.On this basis,we analyze the dipole acoustic logging scattering wave attenuation characteristics using the short-time fourier transform.One thing worth nothing is that the frequency of the coda wave decreases gradually over time.A method is presented to evaluate the formation heterogeneities which were used to characterize dipole acoustic data logged before and after fracturing a reservoir interval.The result show that significant coda wave in the after-fracturing data indicate fracturing-induced heterogeneous property change in the rock volume surrounding the borehole.Compared with microseismic fracture monitoring technology,this method can greatly save oil and gas drilling time and economic costs,the use of acoustic logging data for the future fracturing evaluation of unconventional reservoirs,such as shale reservoir,provides a new train of thought.In addition,coda wave Energy-Flux model is utilized to extract the heterogeneous formation of scattering attenuation and scattering attenuation may quantitatively evaluate formation heterogeneity,multi-component dipole acoustic logging data can identify differences between the azimuth of scattering attenuation heterogeneous anisotropic.