Ray tracing-free diving wave low-order polynomial tomography method and device

Abstract

The invention relates to a ray tracing-free diving wave low-order polynomial tomography method and device. The method comprises the steps of picking a prestack shot gather, conducting first arrival data sorting on the picked prestack shot gather with a single shot as the unit, and ranking the sorted first arrival data in the offset gradually increasing mode to form first arrival curves within the range between 0 and x; conducting low-order polynomial least square method global fitting on the first arrival curves within the range between 0 and x with the offset as the abscissa and the first arrival time as the ordinate to obtain a polynomial coefficient corresponding to each single-shot first arrival, wherein the polynomial adopted by global fitting is a polynomial obtained through weighted summation of polynomial roots for quick integration; obtaining the slowness curve corresponding to each single-shot first arrival according to the polynomial coefficients; obtaining the speed and depth of the inflexion point of the diving wave corresponding to each selected single-shot first arrival according to the slowness curve of each single-shot first arrival; obtaining a three-dimensional velocity field through interpolation according to the speed and depth of the inflexion point of the diving wave corresponding to each selected single-shot first arrival.

Description

technical field [0001] The invention relates to the technical field of seismic data processing, in particular to a non-ray-tracing low-order polynomial tomography method and device. Background technique [0002] Travel-time tomography is an important method in seismic data processing for velocity imaging of subsurface media using seismic wave travel time. The first step in travel-time tomography is to parameterize the medium velocity field. According to the understanding and simplification of the subsurface structure when the velocity is parameterized, the travel time tomography method is usually divided into three types: [0003] (1) Travel-time tomography method with fully discretized velocity field. This type of method parameterizes the medium velocity field into a discrete grid, and sets the velocity distribution on the discrete grid nodes. The speed between nodes is constant and can also be gradually changed. The advantage of this type of method is that there is no ...

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Problems solved by technology

[0006] For the above three methods, in the actual seismic data, the first-arrival picking error of the low-SNR data will seriously affect the slowness accuracy, and the low-velocity bands that frequently appear in the underground medium and the first-arrival curves of seismic waves caused by sudden changes in velocity The discontinuity also makes the calculation of the derivative of the first arrival curve very difficult

Conventional processing uses local smoothing of the first arrival curve to overcome these problems, but local smoothing makes the first arrival curve deviate from the expected change trend of the continuum, thus making the inversion velocity of the inflection point unreliable; in addition, the integral calculation of the inflection point depth It is very large, which is the key point to reflect the computational efficiency

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