Heaved earth surface collected seismic data direct prestack time migration method

Abstract

The invention relates to a direct prestack time migration method for the seismic data acquired under the undulant ground surface. The method is applied to reflection seismic data processing during earthquake exploration and is a prestack migration imaging method aiming at the seismic data acquired under the undulant ground surface. The method can be directly applied to the seismic data which is acquired under the undulant ground surface and is acquired at shot points and demodulation points of different heights. Accordingly, the method can avoid errors caused by field static correction processing as well as correct the speed of a speed reducing belt in a migration process. The method can self-adaptively determine time-varying migration aperture and can correctly compensate geometric spreading effect of seismic waves during an imaging process so as to obtain an amplitude-preserved common reflection point gather. The core of the method is to use a one-way wave theory and a stable phase point principle to analyze so that the travel time and the amplitude of the seismic waves, which depend on the speed and thickness of the speed reducing belt, the heights of the shot points and the demodulation points, and stacking speed based on a floating datum plane, are obtained. The method has important application value for the explorations of oil, gas and mineral resources in areas with complex ground surfaces.

Description

A Direct Prestack Time Migration Method for Seismic Data Acquired Under Undulating Surfaces technical field The invention belongs to the technical field of reflection seismic data processing in seismic exploration, relates to the technical category of pre-stack migration imaging in the process of seismic data processing, and is a pre-stack time migration method for seismic data collected under undulating surfaces. Background technique In the process of seismic data processing, prestack migration imaging is the most critical link, and prestack time migration is an important method in prestack migration imaging. The pre-stack time migration method can better image a kind of geological structures with complex dip angles and faults but less severe lateral velocity changes. Compared with the pre-stack depth migration method, in addition to its higher computational efficiency, its main advantage is that it only needs to use stacked velocities; in this way, an appropriate velocit...

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Problems solved by technology

The former is simple but the amount of static correction is too large, so the error is also relatively large; the latter is currently used more

Although the use of floating datum can reduce the static correction error by reducing the amount of static correction and mutual error cancellation, there are still several problems in this technology: First, when a high-speed layer (old formation) is exposed, the vertical incidence and The conditions for the application of static correction for exit are no longer established, and continuing to use the static correction method will bring large errors; second, the errors of low-velocity layer stripping and velocity replacement are difficult to completely offset; third, the amount of static correction is completely dependent on the known near-surface velocity model, cannot correct for low-speed zone velocities during imaging

The determination of the migration aperture is important for prestack time migration. A smaller aperture can reduce the amount of migration calculations, but there is a risk that the image cannot be constructed correctly for steep dip angles. An excessively large aperture brings migration noise and large computational load; better determination of the offset aperture is still a research problem

The current prestack time migration is based on the double square root equation, and its imaging conditions actually use the relevant imaging conditions of prestack depth migration, so the imaging does not compensate for the geometric diffusion effect of seismic wave propagation, that is, it does not preserve amplitude

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