Near-trace residual multiple suppression method

Abstract

According to the near-trace residual multiple suppression method, AVO forward modeling is carried out by adopting a wave equation method according to actual drilling and logging data in a work area, and a near-well synthetic gather is generated. Comparing and analyzing the synthetic gather and the actual gather, evaluating the processing quality level of the actual gather, finding out the residual position and severity of the multiples, and selecting a plurality of CRP gathers with high matching degree with the synthetic gather from middle-far gathers with better multiple suppression effect as standard gathers; fitting a curve that the waveform changes along with the offset according to the waveform characteristics of each event of the standard channel; by means of matching degree analysis, seismic data after suppressing the residual multiples are reconstructed, and the purpose of eliminating the near-trace residual multiples is achieved. The method has the beneficial effects that the near-trace residual multiples are effectively suppressed, the quality of the CRP trace gather is improved, and qualified basic data are provided for AVO attribute analysis and pre-stack inversion; through view comparison of the AVO forward synthetic gather and the well-side actual CRP gather, the basis is sufficient, the quality control means is reasonable, and the processing efficiency is high.

Description

Technical Field

[0001] The present invention relates to the technical field of seismic data processing, and more particularly to a near-path residual multiple wave suppression method. Background Art

[0002] Multiple wave attenuation is a key link in marine seismic data processing, which directly affects the signal-to-noise ratio, fidelity and imaging effect of seismic data processing results.

[0003] There are two main methods for attenuating multiple waves in the existing technology, including filtering method and method based on wave theory. Among them, the methods based on wave theory mainly include wave field extrapolation method, prediction subtraction method and inverse scattering series method. Although such methods can completely attenuate all orders of surface multiple waves in theory, in practical applications, the effect is poor because the restriction conditions do not meet the theoretical assumptions. In addition, such methods have a large amount of calculation and high requirements on hardware equipment, and the application of technology is limited.

[0004] Commonly used filtering methods such as the FK method mainly utilize the difference in apparent velocity between the primary wave and the multiple waves or the periodicity of the multiple waves such as the predicted deconvolution method. Such methods have high computational efficiency, but they can only effectively attenuate the multiple waves when there is a large difference in apparent velocity between the multiple waves and the primary wave.

[0005] In the medium and far offset part of the CRP gather, the time difference between multiple waves and primary waves is large, and the multiple wave attenuation effect is good; in the near offset part, the time difference between multiple waves and primary waves is small and difficult to identify. In order to protect the effective signal, the time difference threshold for distinguishing between primary waves and multiple waves is usually large, resulting in more residual near-track multiple waves, low signal-to-noise ratio and fidelity, which seriously affects the subsequent seismic data imaging processing effect and the quality of AVO attribute analysis and pre-stack inversion technology application results. Summary of the invention

[0006] The present invention overcomes the deficiencies in the prior art and provides a near-path residual multiple wave suppression method.

[0007] The purpose of the present invention is achieved through the following technical solutions.

[0008] The near-channel residual multiple wave suppression method includes the following specific steps:

[0009] S1. Input relevant drilling, logging, interpretation data and CRP gather data;

[0010] Environmental correction and standardization processing are performed on logging data, and coherence, random noise suppression, amplitude compensation, deconvolution, FK method and other multiple wave suppression, pre-stack time migration and gather optimization processing are performed on CRP gathers;

[0011] S2. Establish geological and attribute models based on drilling and logging data, use the wave equation method to carry out AVO forward simulation, and generate wellside synthetic gathers;

[0012] S3. Compare and analyze the wellside synthetic gathers with the actual CRP gathers, and select several CRP gathers with high matching degree with the synthetic gathers from the mid-long distance gathers after multiple wave suppression by the FK method as standard gathers;

[0013] S4, fitting the waveform variation curve with offset distance according to the waveform characteristics of each event axis of the standard trace, and calculating the standard CRP gather excluding multiple waves;

[0014] S5, extrapolating the waveform variation relationship with the offset distance to the near-offset gather, and performing matching analysis between the obtained standard gather excluding multiple waves and the near-offset gather;

[0015] S6. With the help of matching degree analysis, the gather matching reconstruction parameters are optimized, the gather data is reconstructed, and the near-track residual multiple waves are eliminated.

[0016] In step S5, the matching degree F is calculated using the following formula:

[0017]

[0018] In the formula, is a standard CRP gather that does not contain multiple waves.

[0019] In step S6, the seismic data after reconstructing and suppressing the remaining multiple waves is specifically constructed using the following formula:

[0020]

[0021] In the formula, is a standard CRP gather that does not contain multiple waves.

[0022] The beneficial effects of the present invention are:

[0023] The present invention effectively suppresses near-track residual multiple waves, improves the quality of CRP gathers, and provides qualified basic data for AVO attribute analysis and pre-stack inversion; through the comparison between AVO forward modeling synthetic gathers and actual CRP gathers near the well, the favorable angle range is determined, and with the help of matching degree analysis, gather matching reconstruction parameters are optimized, with sufficient basis and reasonable quality control means; and the overall calculation amount of the scheme is small and the processing efficiency is high. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a flowchart of the multiple wave suppression process of the present invention;

[0025] Figure 2 It is a comparison chart of AVO forward modeling, synthetic gathers and actual gathers;

[0026] Figure 3 It is the profile of the gathers before and after the conventional method of the theoretical model and the multiple wave suppression of the present invention;

[0027] Figure 4 This is a comparison chart of the effects of three multiple wave suppression methods in actual gathers;

[0028] Figure 5 It is the superposition profile of the actual gather before and after multiple wave suppression in the FK method and this embodiment. DETAILED DESCRIPTION

[0029] The technical solution of the present invention is further described below through specific embodiments.

[0030] Example

[0031] The present invention uses the wave equation method to carry out AVO forward modeling based on the actual drilling and logging data in the work area to generate a synthetic gather near the well. The synthetic gather has no noise interference, and the waveform changes are regular and orderly. It is the standard seismic response of the formation at the wellbore position. By comparing and analyzing the synthetic gather with the actual gather, it is possible to evaluate the processing quality level of the actual gather, find out the residual position and severity of the multiple waves, and select several CRP tracks with high matching degree with the synthetic gather from the middle-long track with better multiple wave suppression effect as the standard track, and fit the waveform change curve with the offset distance according to the waveform characteristics of each phase axis of the standard track; with the help of matching degree analysis, the seismic data after suppressing the remaining multiple waves is reconstructed to achieve the purpose of eliminating the residual multiple waves of the near track.

[0032] The specific steps of the near-channel residual multiple wave suppression method include:

[0033] like Figure 1 As shown, step S1, input drilling, logging data and CRP gather data in the work area, wherein the logging data is subjected to environmental correction and standardization processing, and the CRP gather is subjected to coherent random noise suppression, amplitude compensation, deconvolution, multiple wave suppression such as FK method or τ–ρ method, prestack time migration and gather optimization processing;

[0034] like Figure 2 As shown, step S2 establishes geological and attribute models based on drilling and logging data, uses the wave equation method to carry out AVO forward simulation, and generates wellside synthetic gathers;

[0035] Step S3, comparing and analyzing the wellside synthetic gathers with the actual CRP gathers, and selecting several CRP gathers with high matching degree with the synthetic gathers from the mid-long distance gathers with good multiple wave suppression effect as standard gathers;

[0036] like Figure 3-5 As shown, step S4, fitting the waveform variation curve with the offset distance according to the waveform characteristics of each event axis of the standard track;

[0037] In the CRP gathers after NMO dynamic correction, the relationship between the sampling value of the seismic signal and the shot offset at any time t can be expressed by an even-order polynomial, that is,

[0038]

[0039] Where: x n is the offset distance of the nth track, A(x n ) is the amplitude value of the nth track at time t, a0, a1, …a m is a constant coefficient, r(x n ) is the higher-order error.

[0040] Ignoring the errors of higher-order terms, equation (1) can be expressed by a vector matrix:

[0041]

[0042] It can also be written as:

[0043] A=Xa (3)

[0044] Then the least squares estimate of the polynomial coefficient a is

[0045]

[0046] Where W = (X T X) -1 X T =Y -1 X T

[0047] If the polynomial fit uses only the quartic terms, then

[0048]

[0049] The mid-to-long offset traces with good multiple wave suppression in the trace gather are selected for calculation, and the Right now

[0050]

[0051] The amplitude value of the seismic trace at time t can be approximately calculated by the following formula:

[0052]

[0053] where x n is the offset

[0054] Thus, the standard CRP gather without multiple waves is obtained.

[0055] Step S5: Extrapolate the waveform variation with offset to the near-offset gathers, and use the following formula to calculate the gathers obtained by formula (7): Perform matching analysis with the close offset gather S(t).

[0056] The matching degree F is simply defined as:

[0057]

[0058] The larger the matching value calculated by equation (8), the higher the matching degree between the calculated CRP trace and the actual seismic trace. It can be seen that the matching value decreases as the offset distance decreases.

[0059] Step S6, after obtaining the matching degree between the calculated seismic trace and the actual seismic trace, the seismic data after suppressing the remaining multiple waves are reconstructed using the following formula:

[0060]

[0061] That is, a matching threshold is set, the actual CRP gathers with high matching degree are retained, and the gathers with low matching degree are replaced with the standard CRP gathers S * (t), thereby achieving the purpose of eliminating the near-path residual multiple waves.

[0062] like Figure 3 As shown in the figure, from left to right are a schematic diagram of a three-layer theoretical model, a schematic diagram of a forward modeling of a theoretical model, a profile diagram of a gather after suppressing multiple waves using the FK method, a profile diagram of a gather after suppressing multiple waves using the τ–ρ method, and a profile diagram of a gather after suppressing multiple waves in this embodiment.

[0063] It can be clearly seen from the figure that compared with the FK method and the τ–ρ method, the gather profile after suppressing multiple waves in this embodiment shows that the residual multiple waves in the near channels from the 2nd to the 6th layers are completely eliminated.

[0064] Further, if Figure 4 As shown in the figure, from left to right are the effect diagram of multiple wave suppression of the actual gather by the FK method, the effect diagram of multiple wave suppression of the actual gather by the τ–ρ method, and the effect diagram of multiple wave suppression of the actual gather of this embodiment. As shown in the figure, it can be clearly seen that the multiple wave suppression effect of the actual gather using the method of this embodiment is significantly better.

[0065] like Figure 5 As shown, the left side of the figure is the superimposed cross-sectional diagram of the actual gather after multiple wave suppression of the FK method, and the right side of the figure is the superimposed cross-sectional diagram of the actual gather after multiple wave suppression of this embodiment. It can be clearly seen from the figure that the multiple wave suppression effect in this embodiment is better.

[0066] The embodiments of the present invention are described in detail above, but the contents described are only preferred embodiments of the present invention and cannot be considered to limit the scope of implementation of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the patent coverage of the present invention.

Claims

1. A near-path residual multiple wave suppression method, characterized in that: The specific steps include: S1. Input relevant drilling, logging, interpretation data and CRP gather data; Environmental correction and standardization processing are performed on logging data, and coherence, random noise suppression, amplitude compensation, deconvolution, FK method and other multiple wave suppression, pre-stack time migration and gather optimization processing are performed on CRP gathers; S2. Establish geological and attribute models based on drilling and logging data, use the wave equation method to carry out AVO forward simulation, and generate wellside synthetic gathers; S3. Compare and analyze the wellside synthetic gathers with the actual CRP gathers, and select several CRP gathers with high matching degree with the synthetic gathers from the mid-long distance gathers after multiple wave suppression by the FK method as standard gathers; S4, fitting the waveform variation curve with offset distance according to the waveform characteristics of each event axis of the standard trace, and calculating the standard CRP gather excluding multiple waves; S5, extrapolating the waveform variation relationship with the offset distance to the near-offset gather, and performing matching analysis between the obtained standard gather excluding multiple waves and the near-offset gather; S6. With the help of matching degree analysis, the gather matching reconstruction parameters are optimized, the gather data is reconstructed, and the near-track residual multiple waves are eliminated.

2. The near-path residual multiple suppression method according to claim 1, characterized in that: In step S5, the matching degree F is calculated using the following formula: In the formula, is a standard CRP gather that does not contain multiple waves.

3. The near-path residual multiple suppression method according to claim 1, characterized in that: In step S6, the seismic data after reconstructing and suppressing the remaining multiple waves is specifically constructed using the following formula: In the formula, is a standard CRP gather that does not contain multiple waves.

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