Casing-harmonic-containing vertical seismic profile data interval velocity inversion method

Abstract

The invention relates to a casing-harmonic-containing vertical seismic profile data interval velocity inversion method. The method is used for suppressing casing harmonics by low-pass filtering and F-K filtering in seismic prospection, and includes steps of obtaining amplitude spectrums by means of 15-Hz low-pass filtering, obtaining F-K spectrums by converting the amplitude spectrums in a track direction, clearing all F-K spectrums of up-going waves and down-going waves of the speed higher than 5000 m / s, obtaining a second wave field of time domain by means of inverse Fourier transform, picking a continuous event from the down-going waves of the wave field to obtain first break I of each track, picking the first break on an original interference-less track and translating the same, obtaining the first break II by adding the first break I of each track with the translation value, obtaining the adjacent difference by subtracting the depth of the previous track from the depth of the next track, obtaining the first break difference of the adjacent track by subtracting the record first break of the first track from the record first break II of the next track, and finally dividing the depth difference of the adjacent track by the first break different of the adjacent track. By the method, interference to the interval velocity from the casing harmonics can be avoided, so that accurate first break and interval velocity are acquired. Accordingly, the method is easy and convenient to use, and high in computational efficiency.

Description

technical field [0001] The invention relates to a seismic exploration data processing technology, which is a method for accurately inverting layer velocity by using low-pass filtering in the frequency domain and F-K (frequency-wavenumber domain) filtering to suppress casing harmonics. Background technique [0002] Due to the special acquisition method of vertical seismic profiling (VSP) data, the geophone needs to be placed in the well, and the coupling between the geophone and the cementing casing needs to be good, so that relatively reliable records can be recorded. However, when there is no cementation or poor cementation between the casings or between the casing and the formation, these multi-layer casings will cause high-amplitude ringing, thereby generating casing harmonics related to the natural frequency of the casing. Its energy is hardly attenuated, and the frequency runs through the entire frequency band of the effective wave for the entire recording time, making ...

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Problems solved by technology

[0003] In the field collection, affected by various factors, the method of drilling shallow wells and running casing near the observation well is almost impossible to implement

When the casing harmonic energy is very strong, neither the vertical component nor the horizontal component can pick up the accurate first arrival, so that the accurate time-depth relationship cannot be obtained, let alone the layer velocity

[0004] So far, in VSP data processing, when the harmonic energy of the suppressed casing is relatively strong and the first arrival cannot be picked up, the signal is generally regarded as waste and no longer processed. Therefore, it is impossible to obtain accurate time-depth relationship and layer speed, which greatly reduces the application value of VSP data

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