An Adaptive Reflection Point Encryption Stack-Imaging Method Based on Fresnel Beam Weight Function for Crosswell Seismic

Crosswell seismic VSP-CDP stack imaging method converts common-shot seismic data to common reflection point set when velocity field is known, which is highly dependent on velocity model. Meanwhile, single-channel reflected seismic wave field can only be converted into single-channel common-reflection-point (CRP) field, and the imaging effect is limited in the face of complex geological structures. Therefore, this paper proposes an inverse Fresnel beam stack imaging method based on full waveform inversion (FWI) velocity modeling to convert the single reflected seismic wave field to the multi-channel CRP field in the first Fresnel zone, and adaptively increase the fold times, so as to improve the imaging accuracy. Firstly, an accurate crosswell velocity model is established by FWI method. Secondly, the energy contribution weights of effective rays to the receiver point are calculated through the crosswell seismic Fresnel beam wavefield forward numerical simulation method. Then, the reflected wavefield is dynamically migrated to the reflection points within the first Fresnel zone according to the weight function, and the intensive CRP gather after normal moveout (NMO) correction is generated. Finally, an appropriate bin is selected for stacking. In this paper, the inverse Fresnel beam method is used to decompose the single-channel seismic wavefield into the effective reflection points in the Fresnel zone, which makes the coverage of the reflection point more uniform and improves the imaging accuracy. Actual data processing results proved the validity and robust of this method.