Velocity Analysis Method Of Reverse Time Migration Study Based On Crosswell Seismic Data

Cross-well angle domain common imaging gathers(ADCIGs)are important data for seismic imaging and interpretation,and play an important role in velocity model building.Focusing on the high resolution and SNR of cross-well seismic acquisition geometry,we can get an accurate image with reverse time migration(RTM)method.But the imaging velocity field of migration have a serious influence on imaging.If there is much difference between velocity model and real velocity field,the final imaging result will be bad.So we need to do velocity analysis to get the model closest to real velocity field.Because that ADCIGs can solve the multi-solution problem caused by propagation way of seismic wave,the velocity analysis method based on ADCIGs is a high-accuracy migration velocity analysis method.Cross-well seismic wave field is complex,so we have analyzed the wave field first,and introduced the cross-well seismic process scheme.Focusing on the particularity of cross-well seismic system,and Considering that Cross-well seismic data contain up-going and down-going reflection data,we have derived the wave extrapolation equation from RTM wave equation,and then discussed the influence of different factors on the method accuracy and calculating efficiency,such as finite difference grid,stability condition,numerical dispersion.We have derived local offset domain common imaging gathers(ODCIGs)based on the wave equation of RTM method,and then have got the angle calculating formula to get ADCIGs.We used correct velocity model data to get the normal ADCIGs which consist of some horizontal lines,and run a test to analyze the influence of velocity error upon ADCIGs.The processing of real seismic data also produces good imaging results.According to the imaging conditions,we have derived the depth residual equation of horizontal interface cross-well reflection ADCIGs,and have built a complete velocity analysis process.Finally,this method was applied the ADCIGs of different velocity model,and did a real data tests.These tests show that the method in this paper is reasonable and feasible.