Application Of Pre-stack Reverse Time Migration Technology In Reflected Acoustic Logging

Pre-stack reverse time migration is a technique for imaging the comple x geological structure near the well by propagating the wave field and obtaining the full wave field based on the bidirectional wave dynamic equation.This method retains the vector characteristics of the wave and is relatively limited by the dip Angle of the underground structure.It can provide accurate imaging results for arbitrarily complex stratigraphic models and small geological structures.The application of pre-stack reverse time migration technology in reflected acoustic logging solves the problem that the existing acoustic logging technology is difficult to image the complex formation structures(such as fractures,large dip Angle structures,etc.)near the well.The purpose of this thesis is to explore the imaging effect and influencing factors of the pre-stack reverse time migration technique,and to compare the imaging effect with the F-K migration technique,so as to further discuss the application of this technique in acoustic logging and make preparations for its future application.First,this thesis derived the two-dimensional acoustic wave equation of second order and high order staggered grid finite difference formula,and using the method to realize the forward modeling of layer around the model,through the modeling of the factors affecting the method of grid dispersion is analyzed,by using perfectly matched layer absorbing boundary well to eliminate the influence of boundary reflection wave,for reverse-time migration method based on the study laid a good foundation.The pre-stack reverse time migration technique and F-K migration technique are used to simulate the formation model and obtain the imaging profile.In order to observe the imaging effect of pre-stack reverse time migration technique in simple stratum and the imaging accuracy of multilayer interface when the local layer interface is increased,the horizontal and oblique homogeneous medium stratigraphic models are designed.In order to simulate the imaging effect of pre-stack reverse time migration technique when the dip Angle of the local layer gradually increases,the fault model and the barrier and graben models with different degrees of inclination are designed.A very small geological anomaly body model is designed to simulate the imaging effect of pre-stack reverse time migration technique on small geological structures.In order to observe the imaging effect of this method,the single and multiple emission of sound source under the same model were designed.In addition,by using f-k migration imaging technology for all model,analysis and comparison of pre-stack reverse-time migration technology characteristics and influencing factors.Compared with F-K migration,the reverse time migration technology has higher imaging accuracy,is less affected by sound attenuation,can c learly image the multi-layer interface,and has a good imaging effect on small geological structures.However,this technique has a long computational time,low efficiency and high requirements on storage strategy.It is also affected by incident Angle,lo w-frequency noise and reflected wave energy.Generally speaking,the reverse time migration technology has a good application prospect,but to learn from the seismic migration method and apply it to logging,it should be adjusted according to the logging data structure.In addition,further research is needed to improve the calculation rate of this method.