Application Research Of Reverse Time Migration

Complex geologic structures can cause problems with seismic imaging.This is related to complex ray paths,and sharp lateral changes in velocity.Seismic data typically suffer from low amplitude and frequency and are not easily migrated,the lack of good imaging limits seismic interpretation,is not amplitude versus offset(AVO)friendly and adds significant risk to the structural uncertainty in a highly prospective basin.Migration is one of the most important step of determining structural features in the data processing.Prestack depth migration which came up with in recent years is an effective way to imagine complex structure underground.Reverse-time migration(RTM)exhibits great superiority over other imaging algorithms,for example,one-way wave equation migration algorithm and ray migration algorithm,such as Kirchhoff migration algorithms,in handling steeply dipping structures and complicated velocity models.The superiority of reverse-time migration over other imaging algorithms results from the fact that it utilizes the full acoustic wave equation to extrapolate the wavefields.Because this wave equation can accurately simulate wave propagation in all directions,including reflections and transmissions,the resulting imaging algorithm does not suffer from dip limitation and it can even image overturned beds and prismatic waves.However,low-frequency,high-amplitude noises commonly seen in a typical RTM image have been one of the major concerns because they can seriously contaminate the signals in the image if they are not handled properly.In addition,RTM also need large amount of storage and extensive computational cost,therefore,how to effectively remove the low frequency noise to improve the imaging accuracy and operational efficiency is an important topic for the study of reverse time migration.First,we give the physical explanation of the principle of such noises in the conventional RTM image and analyze different low frequency noise suppression methods,and compared the advantages and practicability.In this paper,I derive the high-order staggered grid finite difference wavefield continuation formula,and achieve pre-stack reverse-time migration using this formula.I separate P and S wave using the Helmholtz decomposition and using the source normalized cross-correlation imaging condition.I also do polarity correction to the imaging of multi-component reverse time migration,applications to various synthetic demonstrate its effectively in improving its consistency along an event.Lastly,I apply to various synthetic and real data sets and comparing with other imaging methods,and prove its advantage in processing complex structure model over other imaging algorithms.