Research On Three-dimensional Numerical Modeling And Imaging Method Of Single-well Acoustic Reflection Imaging Logging

With the growing demand for exploration and exploitation of resource,the major resource trend to be small hidden oil and gas reservoirs,deep minerals and unconventional oil and gas resources.However,the exploration and exploitation of this kind of energy sources are difficult.The more accurate detection of geological structures,the more detailed description of reservoirs are required.Single-well acoustic reflection imaging logging,which transmits acoustic signals in the well and receives the reflection wave signals generated by the geological mass outside the well,has a deeper investigation depth in the radial direction and a higher vertical and horizontal resolution.This method provides an effective method for the refined detection of the geological structures around the well.According to the acoustic source type and the reflection wave type,the acoustic reflection imaging logging is mainly divided into monopole P wave method and dipole SH wave method.Due to the higher operating frequency and the faster attenuation of the monopole source,its detection depth is limited,and monopole source is a no directional radiation source,so the orientation of the reflector cannot be determined.The use of the dipole acoustic source with the lower operating frequency and the directionality property can overcome the shortcoming of monopole P wave method,mainly in the radial detection depth and azimuth recognition ability.Nevertheless,the use of dipole source in remote sensing was developed in recent years.It need a process to understand the characteristics and shortcomings of this method.Therefore,more researches,such as the simulation of wave field of dipole source,the design of special instrument for remote sensing and data processing methods,are necessary.These researches are of great significance to the development of acoustic logging technology and the exploration and exploitation of resources.This study focused on the basic research of the propagation regularity and response characteristics of wave field.To improve the understanding of acoustic reflection imaging logging technology,this study analyzed and discussed the influence factor of detection depth and the response characteristics of reflection wave of typical geological model.Based on the characteristics of acoustic logging data,this study proposed a data processing flow for processing the reflection imaging logging data.The main research contents and results are summarized as follows:(1)Based on elastic wave theory,the finite difference scheme of three-dimensional staggered grid for wave field simulation is presented.And the discrete form of PML is deduced.the Multithreading parallel computation based on OpenMP standard is adopted to realize the 3-D wave field simulation.By comparing the results of boundary absorption,parallel acceleration and the RAI method,the method of this study is verified to be effective.(2)The regularity of the amplitude of reflection wave and the relative amplitude of borehole mode wave influenced by source type,T-R spacing,source frequency,caliper and so on,are studied.Results demonstrated that the optimum operating frequency range of the dipole shear wave method in fast formation is less than 3 kHz.As the SH reflection wave is stronger when the caliper is smaller,dipole shear wave method can be used for solid minerals detection in small well.The eccentric states of the source not only produce different borehole mode waves,but also influence the amplitude of reflection wave.In slow formation,monopole P wave method can not measure the velocity of shear wave.While the dipole source not only produces SH reflection wave with azimuth recognition ability,but also produces P reflection wave.And the P reflection wave has short duration and is easy to be extracted.The above understanding can provide reference for the design and development of remote detection instruments.(3)Aimed at the complex geological model outside the borehole,the research on wave field simulation and characteristic analysis of dipole source are carried out,and some new understanding of reflection wave are obtained.The complex geological model contain fracture mode,inhomogeneous bodies mode,fault mode,multilayer parallel interfaces mode and non-parallel interfaces mode.By analyzing the characteristics of wave field and reflection wave,results shows that SH wave is more sensitive to open fractures,and also have obvious response characteristics to slaty geological structures such as solid filled fractures and faults.The smaller size of inhomogeneous bodies,the lower amplitude of reflection wave.As to the non-parallel interfaces mode,the maximum effective reflection wave can be obtained by setting the dipole source direction as the strike of the target interface.The above understanding can provide reference for measurement of logging and the data processing method.(4)The wave field in and outside the well with the phased array sources,which are composed of monopole sources and dipole sources respectively,is investigated.By comparing the received wave of the receivers in the well,it can be found that phased array sources will greatly enhanced the amplitude of the reflection wave.And different delay time and number of array elements will have corresponding effects on the amplitude of the reflection wave.The deflection angle of the main lobe can be adjusted by setting the delay time,and the coverage of the main lobe can be controlled by the number of array elements.(5)Based on the characteristics of logging mode,data structure and wave field of acoustic reflection imaging logging data,this study propose an optimal scheme for processing the data.The scheme contains bandpass filtering,deconvolution,compensation,F-K filtering,CMP stack and F-K migration.By processing the measured data,results verified the effectiveness of this scheme.In summary,this study focused on the basic theoretical research of acoustic reflection imaging logging technology.The study of three-dimensional numerical modeling and imaging methods of sing-well acoustic reflection imaging logging,improves the understanding to the superiority of reflection imaging logging and provides reference information for the development and application of this technology.