New imaging and filtering methods: Primary only imaging condition and interferometric migration.

摘要

Two new imaging and filtering methods are formulated and applied to both synthetic and field data. One of the methods, denoted as primary only imaging condition (POIC) migration, discriminates primary reflections from multiple reflections and migrates only the primary reflections using the prestack wavepath migration (WM). The other method is interferometric migration (IM), which can redatum the traces below salt without knowing the velocity model in or above the salt body.; The POIC migration and its practical implementations are presented and applied to both two-dimensional (2-D) synthetic and field marine data for multiple suppression. The key idea is that both the take-off and incidence angles are picked from the seismic data and rays are traced from both the source and the receiver positions along these picked angles. An event is a primary reflection if the intersection point of the rays has a reflection traveltime equal to the observed traveltime. In contrast, an event is a multiple reflection if the intersection point has a reflection traveltime different from the observed traveltime. Test results show that POIC is effective in suppressing the migration artifacts generated by multiple energy in the far-offset data and appears to perform better than the traditional Radon multiple attenuation method in the field test.; The POIC method predicts the multiples in the far-offsets and guides the muting of near-offset multiples in the tau - p domain with a parabolic Radon transform. Synthetic results indicate that the approach is effective in separating the primary reflections from multiple events in the near offset traces.; The POIC method is further combined with the wave-equation based reverse-time datuming (RTD) to better suppress multiples and image the reflectivity distribution below the salt body. The RTD method can extrapolate both primaries and multiples to locations beneath the salt so that the ray-based POIC can suppress multiples in the subsalt areas with a relatively simple velocity model. Synthetic results show that the hybrid approach can eliminate most of multiple artifacts in the subsalt image.; The interferometric migration and the reduced time migration (RTM) are developed and applied to both synthetic and field CDP data. Both IM and RTM use the natural arrival times associated with the reflections from a reference reflector which can be picked from the data. The RTM shifts the data with the time difference between the calculated and natural arrival times of a reference reflection, while IM extrapolates the data to the reference datum with the natural arrival times and then migrates the redatumed data below salt. (Abstract shortened by UMI.)