阅读说明：本技术 频率域地震弱信号的增强方法 (Frequency domain seismic weak signal enhancement method ) 是由 杨丰弛 杨巍 王俊杰 于 2021-08-26 设计创作，主要内容包括：本发明公开了一种频率域地震弱信号的增强方法,涉及弱信号增强技术领域,包括：步骤一、对原始地震单道CDP道集S(t)进行快速傅氏变换,得到单道CDP道集的频谱f(t)；步骤二、对所述单道CDP道集的频谱f(t)进行频谱分析,确定弱信号分布频域；步骤三、通过声波测井曲线做弱信号振幅质控,确定所述弱信号分布频域需要增强的幅值；步骤四、基于非线性扩散的导数谱增强模型对需要增强幅值的所述弱信号分布频域进行信号增强,得到增强后的弱信号频谱F-(s)(t)；步骤五、将增强后的所述弱信号频谱F-(s)(t)做快速傅氏逆变换,得到增强后的信号S-(F)(t)。本发明提供的增强弱信号的方法,可以获取更精确、分辨率更高的弱反射界面信息,实现地震弱信号的增强,凸显弱反射界面的反射特征。(The invention discloses a frequency domain seismic weak signal enhancing method, which relates to the technical field of weak signal enhancement and comprises the following steps: firstly, carrying out fast Fourier transform on an original seismic single-channel CDP gather S (t) to obtain a frequency spectrum f (t) of the single-channel CDP gather; secondly, performing spectrum analysis on the frequency spectrum f (t) of the single CDP gather to determine a weak signal distribution frequency domain; thirdly, performing weak signal amplitude quality control through an acoustic logging curve, and determining the amplitude of the weak signal distribution frequency domain to be enhanced; fourthly, signal enhancement is carried out on the weak signal distribution frequency domain needing the amplitude enhancement based on a derivative spectrum enhancement model of the nonlinear diffusion, and the enhanced weak signal spectrum F is obtained s (t); fifthly, the frequency spectrum F of the strengthened weak signal s (t) performing an inverse fast Fourier transform to obtain an enhanced signal S F (t) of (d). The method for enhancing the weak signal can acquire the information of the weak reflection interface with higher accuracy and resolution ratio and realize the purposeAnd the enhancement of the seismic weak signal highlights the reflection characteristics of the weak reflection interface.)

1. A method for enhancing frequency domain seismic weak signals is characterized by comprising the following steps:

firstly, carrying out fast Fourier transform on an original seismic single-channel CDP gather S (t) to obtain a frequency spectrum f (t) of the single-channel CDP gather;

secondly, performing spectrum analysis on the frequency spectrum f (t) of the single CDP gather to determine a weak signal distribution frequency domain;

thirdly, performing weak signal amplitude quality control through an acoustic logging curve, and determining the amplitude of the weak signal distribution frequency domain to be enhanced;

fourthly, signal enhancement is carried out on the weak signal distribution frequency domain needing the amplitude enhancement based on a derivative spectrum enhancement model of the nonlinear diffusion, and the enhanced weak signal spectrum F is obtained_s(t)；

Fifthly, the frequency spectrum F of the strengthened weak signal_s(t) performing an inverse fast Fourier transform to obtain an enhanced signal S_F(t)。

2. The method for enhancing the frequency domain seismic weak signal as claimed in claim 1, wherein in the second step, the determining the weak signal distribution frequency domain comprises:

s21, determining well side channel statistical wavelets w (t) meeting the seismic frequency domain bandwidth based on seismic statistics;

s22, determining a formation reflection coefficient r (t) through an acoustic logging curve;

s23, obtaining a synthetic record S' (t) ═ w (t) × r (t) according to the well bypass statistical wavelets w (t) and the stratum reflection coefficient r (t);

and S24, respectively carrying out spectrum comparison analysis on the original seismic single-channel CDP gather S (t) and the synthetic trace S' (t), and determining a weak signal distribution frequency domain.

3. The method for enhancing the frequency domain seismic weak signal according to claim 2, wherein in the step S24, the method comprises:

s241, according to the actual seismic trace beside the well, carrying out amplitude maximum value correction on the synthetic trace S' (t), and determining the amplitude maximum value to be A_MAX；

S242, comparing the frequency spectrum of the synthetic record trace S' (t) with the frequency spectrum of the original seismic single-trace CDP gather S (t), and determining an enhanced region frequency bandwidth as f e [ f [ [ f ]₁,f₂]。

4. The method for enhancing the frequency domain seismic weak signal according to claim 3, wherein in the fourth step, the method comprises:

s41, utilizing a derivative spectrum enhancement model to enable the frequency bandwidth f epsilon [ f ] of the frequency spectrum of the original seismic single-channel CDP gather S (t)₁,f₂]The frequency band of (a) is enhanced to obtain an enhanced spectrum F:

F＝F₀(f)-cF₀ ⁿ(f) (1)；

in the formula: f is the enhanced frequency spectrum; f₀(f) The spectrum of an original seismic single-trace CDP gather S (t); f₀ ⁿ(f) To intercept f₁-f₂The value of the segment; c is a given enhancement coefficient; n is the derivation order;

s42, combining the classical nonlinear diffusion model with the derivative spectrum enhancement model to obtain a signal enhancement model:

wherein:is a diffusion function; λ is a diffusion strength control parameter;

s43, solving the formula (1) by using a finite difference method to obtain a final enhanced weak signal frequency spectrum F_s(t)。

5. The method for enhancing the frequency domain seismic weak signal as claimed in claim 4, wherein the finite difference method comprises an implicit difference method, and the solving of the equation (1) by the implicit difference method comprises:

implicit difference method format:

wherein: k is the number of iterations; i is a serial number; τ is a time step; h is a space discrete step length;

order toThen: u shape^k＝[B^k-1]^-1U^k-1 (4)；

Wherein:

and B^k-1Is reversible;

represents the total number of u after spatial dispersion.

6. The method for enhancing earthquake weak signals in frequency domain according to claim 5, wherein a final enhanced weak signal frequency spectrum F is obtained_sThe specific algorithm of (t) comprises:

s431, giving an enhancement coefficient c, a diffusion intensity control parameter lambda, iteration times N and a time step tau, h, and taking 1;

s432, obtaining the enhanced signal U by using the formula (1)⁰；

S433 according to diffusion functionTo obtain discreteAnd calculate

S434, constructing a matrix B according to the formula (5)^k-1；

S435, obtaining the final enhanced weak signal frequency spectrum F by using the iterative processing of the formula (4)_s(t)。

Technical Field

The invention relates to the technical field of weak signal enhancement, in particular to a frequency domain seismic weak signal enhancement method.

Background

In oil exploration, certain hydrocarbon-bearing reservoirs are subject to strong amplitude disturbances when identified, such as: lithologic abrupt strong amplitude, discontinuous stratum and unconformity strong amplitude, on a seismic section, signals with strong amplitude can shield weak amplitude response, and the weak amplitude corresponds to an oil and gas reservoir, so that a target reservoir is difficult to identify. Therefore, how to enhance the weak signal is a key issue.

Huang proposed a Hilbert-Huang transform method for non-stationary seismic signal analysis in 1998, which is characterized in that an Empirical Mode Decomposition (EMD) method for obtaining an inherent Mode function is used, the method can decompose an original seismic signal into a form of adding a plurality of inherent Mode functions, can well overcome the defect of signal localization in Hilbert transform, and has a very significant effect on processing of a seismic signal containing noise. Reliable empirical mode decomposition results require that signals must satisfy the condition of empirical mode decomposition, but seismic signals, particularly complex reflected seismic signals, often cannot satisfy the decomposition condition. In order to construct seismic signals meeting EMD decomposition conditions, methods such as narrow-band filtering, high-frequency loading and the like are researched, but the method weakens the orthogonality of seismic signal decomposition reconstruction, solves the problem of redundancy of the reconstructed seismic signals and distorts the reconstruction result.

For the Hilbert-huang model, the existing signal enhancement method comprises an improved empirical mode decomposition-based seismic weak signal enhancement processing method, an inverse Q filtering method and the like, wherein the EMD method is introduced for signal decomposition, any basis function does not need to be preset, and the time scale characteristics of data are utilized for signal decomposition. Compared with short-time Fourier transform, wavelet decomposition and other methods, the method is intuitive, direct, posterior and adaptive. However, the biggest and inevitable disadvantage of the EMD decomposition process is the generation of modal aliasing effects, i.e. signals containing other IMF components in the IMF component signal of a certain decomposition. Therefore, the former people improve the method for many times, and compared with the conventional EMD decomposition method, the improved EMD decomposition method has obvious improvements in the aspects of the reliability of the decomposition result, the decomposition precision, the nonlinear weak signal time-frequency analysis capability and the like.

Therefore, in view of the defects in the prior art, an urgent need exists in the art for providing a method capable of enhancing frequency domain seismic weak signals and acquiring more accurate and higher-resolution weak reflection interface information.

Disclosure of Invention

In view of this, the invention provides a frequency domain seismic weak signal enhancement method, which enhances a weak signal in a seismic section and solves the problem of identification of a target reservoir seismic response characteristic near a strong reflection interface.

In order to achieve the above purpose, the invention provides the following technical scheme:

a method for enhancing frequency domain seismic weak signals comprises the following steps:

firstly, carrying out fast Fourier transform on an original seismic single-channel CDP gather S (t) to obtain a frequency spectrum f (t) of the single-channel CDP gather;

secondly, performing spectrum analysis on the frequency spectrum f (t) of the single CDP gather to determine a weak signal distribution frequency domain;

thirdly, performing weak signal amplitude quality control through an acoustic logging curve, and determining the amplitude of the weak signal distribution frequency domain to be enhanced;

fourthly, signal enhancement is carried out on the weak signal distribution frequency domain needing the amplitude enhancement based on a derivative spectrum enhancement model of the nonlinear diffusion, and the enhanced weak signal spectrum F is obtained_s(t)；

Fifthly, the frequency spectrum F of the strengthened weak signal_s(t) performing an inverse fast Fourier transform to obtain an enhanced signal S_F(t)。

According to the frequency domain seismic weak signal enhancement method disclosed by the technical scheme, the original seismic signal is subjected to Fourier forward transform to obtain a frequency spectrum, then the frequency spectrum is enhanced by using a derivative spectrum method, the enhanced frequency spectrum is used as an initial frequency spectrum of a nonlinear diffusion model, and a smooth enhanced weak signal is obtained through diffusion and inverse Fourier transform, so that the problem of identification of the seismic response characteristic of a target reservoir layer close to a strong reflection interface is solved.

Preferably, in the second step, determining a weak signal distribution frequency domain includes:

s21, determining well side channel statistical wavelets w (t) meeting the seismic frequency domain bandwidth based on seismic statistics;

s22, determining a formation reflection coefficient r (t) through an acoustic logging curve;

s23, obtaining a synthetic record S' (t) ═ w (t) × r (t) according to the well bypass statistical wavelets w (t) and the stratum reflection coefficient r (t);

and S24, respectively carrying out spectrum comparison analysis on the original seismic single-channel CDP gather S (t) and the synthetic trace S' (t), and determining a weak signal distribution frequency domain.

Preferably, the S24 includes:

s241, according to the actual seismic trace beside the well, carrying out amplitude maximum value correction on the synthetic trace S' (t), and determining the amplitude maximum value to be A_MAX；

S242, comparing the frequency spectrum of the synthetic record trace S' (t) with the frequency spectrum of the original seismic single-trace CDP gather S (t), and determining an enhanced region frequency bandwidth as f e [ f [ [ f ]₁,f₂]。

Preferably, in the fourth step, the method includes:

s41, utilizing a derivative spectrum enhancement model to enable the frequency bandwidth f epsilon [ f ] of the frequency spectrum of the original seismic single-channel CDP gather S (t)₁,f₂]The frequency band of (a) is enhanced to obtain an enhanced spectrum F:

F＝F₀(f)-cF₀ ⁿ(f) (1)；

in the formula: f is the enhanced frequency spectrum; f₀(f) The spectrum of an original seismic single-trace CDP gather S (t); f₀ ⁿ(f) To intercept f₁-f₂The value of the segment; c is a given enhancement coefficient; n is the derivation order;

s42, combining the classical nonlinear diffusion model with the derivative spectrum enhancement model to obtain a signal enhancement model:

wherein:is a diffusion function; λ is a diffusion strength control parameter;

s43, solving the formula (1) by using a finite difference method to obtain a final enhanced weak signal frequency spectrum F_s(t)。

Preferably, the finite difference method includes an implicit difference method, and solving equation (1) by using the implicit difference method includes:

implicit difference method format:

wherein: k is the number of iterations; i is a serial number; τ is a time step; h is a space discrete step length;

order toThen: u shape^k＝[B^k-1]^-1U^k-1 (4)；

Wherein:

and B^k-1Is reversible;

and m is F/h and represents the total number of spatially dispersed u.

Preferably, a final enhanced weak signal spectrum F is obtained_sThe specific algorithm of (t) comprises:

s431, giving an enhancement coefficient c, a diffusion intensity control parameter lambda, iteration times N and a time step tau, h, and taking 1;

s432, obtaining the enhanced signal U by using the formula (1)⁰；

S433 according to diffusion functionTo obtain discreteAnd calculate

S434, constructing a matrix B according to the formula (5)^k-1；

S435, obtaining the final enhanced weak signal frequency spectrum F by using the iterative processing of the formula (4)_s(t)。

Compared with the prior art, the method for enhancing the frequency domain seismic weak signal has the following beneficial effects that:

(1) the method for enhancing the frequency domain seismic weak signal can accurately enhance the underground target horizon to be enhanced by combining the acoustic logging curve, and ensures that the enhanced weak signal can reflect the underground condition more truly and cannot be distorted when a specific limit value of enhanced amplitude is given;

(2) the frequency domain seismic weak signal enhancement method utilizes a derivative spectrum enhancement model based on partial differential equation, can effectively enhance the characteristics of the upper peak of the frequency spectrum, and increases the components of the weak reflection signal.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.

FIG. 1 is a flow chart of the frequency domain seismic weak signal enhancement method of the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

The embodiment of the invention discloses a frequency domain seismic weak signal enhancing method, which comprises the following steps of:

firstly, carrying out fast Fourier transform on an original seismic single-channel CDP gather S (t) to obtain a frequency spectrum f (t) of the single-channel CDP gather;

secondly, performing spectrum analysis on the frequency spectrum f (t) of the single CDP gather to determine a weak signal distribution frequency domain;

thirdly, performing weak signal amplitude quality control through the acoustic logging curve, and determining the amplitude value to be enhanced of a weak signal distribution frequency domain;

fourthly, signal enhancement is carried out on the weak signal distribution frequency domain needing the enhanced amplitude value based on the derivative spectrum enhancement model of the nonlinear diffusion, and the enhanced weak signal spectrum F is obtained_s(t)；

Step five, the frequency spectrum F of the enhanced weak signal_s(t) performing an inverse fast Fourier transform to obtain an enhanced signal S_F(t)。

In an embodiment, the determining the weak signal distribution frequency domain in the second step includes:

s21, determining well side channel statistical wavelets w (t) meeting the seismic frequency domain bandwidth based on seismic statistics;

s22, determining a formation reflection coefficient r (t) through an acoustic logging curve;

s23, obtaining a synthetic record S' (t) ═ w (t) × r (t) according to the well bypass statistical wavelets w (t) and the stratum reflection coefficient r (t);

and S24, respectively carrying out spectrum comparison analysis on the original seismic single channel CDP gather S (t) and the synthetic trace S' (t) to determine a weak signal distribution frequency domain.

Further, the specific operations in S24 include:

s241, according to the actual seismic channel beside the well, carrying out amplitude maximum value correction on the synthetic recording channel S' (t), and determining the amplitude maximum value to be A_MAX；

S242, comparing the frequency spectrum of the synthetic trace S' (t) with the frequency spectrum of the original seismic single-trace CDP gather S (t), and determining an enhanced region frequency bandwidth as f ∈ [ f [ f [ ]₁,f₂]。

In one embodiment, the step four of enhancing the weak signal includes:

s41, utilizing a derivative spectrum enhancement model to enable the frequency bandwidth f epsilon [ f ] of the frequency spectrum of the original seismic single-channel CDP gather S (t)₁,f₂]The frequency band of (a) is enhanced to obtain an enhanced spectrum F:

F＝F₀(f)-cF₀ ⁿ(f) (1)；

in the formula: f is the enhanced frequency spectrum; f₀(f) The spectrum of an original seismic single-trace CDP gather S (t); f₀ ⁿ(f) To intercept f₁-f₂The value of the segment; c is a given enhancement coefficient; n is the derivation order;

s42, combining the classical nonlinear diffusion model with the derivative spectrum enhancement model to obtain a signal enhancement model:

wherein:is a diffusion function; λ is a diffusion strength control parameter;

s43, solving the formula (1) by using a finite difference method to obtain a final enhanced weak signal frequency spectrum F_s(t)。

Further, the finite difference method includes an implicit difference method, and solving equation (1) by using the implicit difference method includes:

implicit difference method format:

wherein: k is the number of iterations; i is a serial number; τ is a time step; h is a space discrete step length;

order toThen: u shape^k＝[B^k-1]^-1U^k-1 (4)；

Wherein:

and m is F/h and represents the total number of spatially dispersed u.

Obtaining the final enhanced weak signal frequency spectrum F_sThe specific algorithm of (t) comprises:

s431, giving an enhancement coefficient c, a diffusion intensity control parameter lambda, iteration times N and a time step tau, h, and taking 1;

s432, obtaining the enhanced signal U by using the formula (1)⁰；

S433 according to diffusion functionTo obtain discreteAnd calculate

S434, constructing a matrix B according to the formula (5)^k-1；

S435, usage formula (4) Iterative processing to obtain the final enhanced weak signal frequency spectrum F_s(t)。

The method for enhancing the frequency domain seismic weak signal obtains a frequency spectrum after Fourier forward transformation is carried out on a part needing to be enhanced on a synthetic record trace, quality control is carried out on the part in the frequency domain by combining an acoustic logging curve, a frequency band area needing to be enhanced is enhanced on the basis of a signal enhancement model utilizing a nonlinear diffusion equation, and finally Fourier inverse transformation is carried out on the frequency band area, so that an enhanced seismic signal is obtained, and the enhanced seismic signal is superposed with other original unprocessed section planes to obtain a final seismic section plane. The method can accurately enhance the frequency band region to be enhanced by combining the acoustic logging curve, and when a specific enhanced amplitude limit value is given, the enhanced weak signal can reflect the real underground condition and ensure that the enhanced signal is not distorted; on the other hand, the derivative spectrum enhancement model based on the partial differential equation can effectively enhance the characteristics of the peaks on the frequency spectrum, so that the components of the weak reflection signals are increased.

The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other. The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.