Research And Application Of Reverse Time Migration Imaging Method Based On Wave Propagation Angle

Seismic exploration is developing towards complex surface,complex structure,complex reservoir and deep oil-gas reservoir exploration.One of the key technologies,which has become increasingly popular in marine seismic survey and field seismic survey,is the broadband,wideazimuth,and high density seismic acquisition.The offset becomes larger,when deep water oilgas is explored in offshore.Under this circumstance,many diving waves and deep refraction waves are observed in the shot gather.Prestack depth migration can not image these types of wave according to the theory of seismic wave migration,so they will cause serious interference to primary reflection,diffraction and scattered wave imaging.In such case,the location of the reservoir and the offshore drilling may be misguided.Suppressing these interference wave fields automatically in the imaging process,rather than dealing with the complex data of mixed waves,is worth studying.In this paper,the reverse time depth migration based on the angle imaging condition is used to suppress the deep refraction waves and the diving waves.It has no limitation on steep dips and can get accurate imaging result even in the presence of severe lateral variation of the velocity.The two-way wave extrapolation is used on both source-side and receiver-side wavefields.Usually the cross-correlation imaging condition is used,but it will lead to lowfrequency artifacts,causing serious interference on shallow structures.These low-frequency artifacts are generated because the imaging condition is satisfied throughout the whole wave path,resulting in interference and reduced imaging accuracy.In essence,the imaging condition should be posed as the correlation of the incident wave field with the reflected wave field at the imaging point.Considering the information of wave propagation angle,the interference waves can be excluded from incident wave and reflected wave.The basic idea of paper that suppress deep refracted wave and diving wave in the imaging process using the reverse time depth migration imaging method based on the imaging condition of wave propagation angle.In the paper,the wavfield direction is calculated by the optical flow method,and then refraction waves and diving waves are automatically suppressed in the imaging process using cross-correlation imaging condition by selecting the appropriate angle range of reflected wave,which is restricted by the estimated propagation angle.Some examples on synthetic data show the effectiveness of this method.