Non-stationary seismic rule noise suppression method and system

Abstract

The application discloses a non-steady-state seismic regular noise suppression method and system, and is applied to oil and gas geophysical exploration. The existing regular interference suppression technology often shows the basic characteristics of "apparent" rules. The "apparent" rule characteristics seriously reduce the regular noise suppression effect based on the steady-state signal theory. The application considers the non-steady-state characteristics of the regular interference in time and space, automatically tracks the spatial track of the noise interference, and uniformly adjusts the energy and the inter-channel time difference. Then, the non-steady-state filtering is performed on the noise interference in the time and space domains, so that the seismic signal contaminated by the noise is effectively recovered. The method of the application adopts the non-steady-state filtering technology to suppress and eliminate the non-steady-state regular noise, and improves the signal-to-noise ratio of the seismic data.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of oil and gas geophysical exploration, and particularly relates to a non-steady-state seismic noise suppression technique. BACKGROUND

[0002] Seismic data regular noise refers to a noise type with a certain spatial trajectory of energy distribution, wherein, surface wave interference is the most widely distributed and the most serious regular interference to seismic signal pollution. Based on the difference between regular interference and effective signal, currently, a variety of regular interference suppression methods have been developed, F-K filtering, apparent velocity filtering, cross arrangement filtering, surface wave simulation based on dispersion and curved wave transformation are currently commonly used regular interference suppression methods. These methods have achieved good noise suppression effect on the theoretical model. But there is a big difference between the actual application effect and the theoretical model. In actual application, not only a lot of noise energy remains, but also the seismic signal is greatly damaged.

[0003] Strictly speaking, the trajectory of regular interference should meet a certain mathematical curve (straight line, parabola and hyperbola, etc.), and its energy and frequency are relatively stable in space. At this time, if its spatial distribution has a large difference with the seismic signal, the current regular interference suppression technology can achieve good suppression effect. However, the actual regular interference is difficult to meet the above mathematical definition, its trajectory, energy and frequency present non-steady-state change in space, and it does not have complete separability with effective signal in the whole space. That is to say, the actual regular interference does not strictly follow the mathematical definition, and it often shows the basic characteristics of "apparent" regularity. This "apparent" regularity seriously reduces the regular noise suppression effect based on the steady-state signal theory.

[0004] In summary, the non-steady-state characteristics of regular interference seriously reduce the application effect of the existing regular interference suppression method. SUMMARY

[0005] To solve the above technical problems, the present application proposes a non-steady-state seismic regular noise suppression method and system, which fully considers the non-steady-state characteristics of the actual regular interference, uses non-steady-state filtering technology to suppress and eliminate the non-steady-state regular noise, and improves the signal-to-noise ratio of seismic data.

[0006] The technical scheme adopted by the present application is as follows: a non-steady-state seismic regular noise suppression method, comprising:

[0007] S1, calculating the dip moveout of seismic data;

[0008] S2, using the surface wave dip moveout to perform flattening processing on local seismic data, and then adjusting the data energy and inter-channel time difference;

[0009] S3, obtain a time domain operator of a f-k filter, and perform time domain f-k filtering on the seismic data processed in step S2;

[0010] S4, perform inverse dynamic moveout adjustment, static moveout adjustment, energy adjustment and inverse flattening processing on the seismic data obtained in step S3, to obtain pure surface wave seismic data;

[0011] S5, subtract the pure surface wave seismic data obtained in step S4 from the original seismic data, to obtain effective signals.

[0012] The second technical solution of the present application is a non-steady-state seismic regular noise suppression system, comprising a seismic data input module, a seismic data dip time difference module, a seismic data forward adjustment module, a filtering module, a seismic data reverse adjustment module and a subtraction module.

[0013] The seismic data forward adjustment module comprises, in series, a flattening processing unit, a data energy adjustment unit and an inter-trace time difference adjustment unit.

[0014] The seismic data reverse adjustment module comprises, in series, an inverse inter-trace time difference adjustment unit, an inverse data energy adjustment unit and an inverse flattening processing unit.

[0015] The present application has the following advantages: the present application fully considers the non-steady-state characteristics of actual regular interference, suppresses and eliminates non-steady-state regular noise, and improves the signal-to-noise ratio of seismic data; compared with the conventional technology, the present application can better suppress non-steady-state regular interference; effectively restores the seismic signals contaminated by noise, improves the signal-to-noise ratio of seismic data, and improves the quality of seismic data processing. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 is a flowchart of the method of the present application;

[0017] Figure 2 is the input seismic data of block A provided by the embodiment of the present application;

[0018] Figure 3 is the result of the seismic data of block A provided by the embodiment of the present application after suppressing surface waves by the present application;

[0019] Figure 4 is the suppressed surface waves of block A provided by the embodiment of the present application;

[0020] Figure 5 is the input seismic data of block B provided by the embodiment of the present application;

[0021] Figure 6 is the result of the seismic data of block B provided by the embodiment of the present application after suppressing surface waves by the present application;

[0022] Figure 7 The B block suppressed surface wave provided by the embodiment of the present application. DETAILED DESCRIPTION

[0023] In order to make the skilled in the art understand the technical content of the present application, the content of the present application is further explained below in combination with the drawings.

[0024] Embodiment 1

[0025] The embodiment of the present application is further explained below in combination with the embodiment of an oilfield A block and the accompanying drawings. Figures 2-4 The embodiment of the present application is further explained below in combination with the embodiment of an oilfield A block and the accompanying drawings.

[0026] As Figure 1 shown is the scheme flowchart of the present application, which specifically includes the following steps in the embodiment:

[0027] (1) input the original seismic data as d(t,x), t=1,2,…n s ; x=1,2,…n c , t represents a time point, and x represents a seismic trace; in the embodiment, the number of time points n s =3000, and the number of seismic traces n c =160;

[0028] (2) the seismic data dip time difference σ is obtained, specifically including the following steps:

[0029] (2.1) the regular interference velocity v 0 is picked up from the seismic data d 0 (t,x) of the same arrangement of shot points and geophones, and the apparent velocity v * of the shot points and geophones not in the same arrangement is calculated

[0030]

[0031] Wherein, θ is the azimuth angle. The arrangement of shot points and geophones is the existing known technology, which is not described in detail herein;

[0032] (2.2) the seismic data surface wave dip time difference σ is calculated,

[0033]

[0034] Wherein, dt=0.002 and dx=50 are respectively the time sampling interval and the space sampling interval.

[0035] (3) the local seismic data is flattened by using the surface wave dip time difference, and the surface wave is adjusted by the data energy and the inter-trace time difference to make the surface wave more comply with the definition of linear event in the mathematical sense; the step specifically includes the following steps:

[0036] (3.1) In this embodiment, the window is 201x101, and the flattened seismic data in the window is and the middle trace is selected as the reference trace x r = 51;

[0037] (3.2) The seismic trace in the window is adjusted by Root Mean Square (RMS) to be consistent with the energy of the reference trace;

[0038]

[0039] wherein q is the number of time sampling points;

[0040] (3.3) The correlation between each trace in the window and the reference trace is calculated, and the maximum correlation between the seismic trace and the reference trace is taken as the inter-trace static time difference for adjustment, so that the lateral consistency is better. The calculation formula of the correlation between each trace and the reference trace is:

[0041]

[0042] wherein x r is the reference trace, l is the static time difference between the seismic trace x and the reference trace x r , and ξ = l*dt is the inter-trace static time difference adjustment;

[0043] (3.4) The phase filter h1(t, x) is obtained to adjust the dynamic time difference of each trace in the window to the reference trace, i.e. phase adjustment, to weaken the inherent dispersion characteristics of the surface wave.

[0044]

[0045] wherein obj is the objective function, x r is the reference trace, and F() is the Fourier transform;

[0046] (4) The f-k filter time domain operator is obtained, and the seismic data is subjected to time domain f-k filtering. This step specifically includes the following sub-steps:

[0047] (4.1) The filter time domain expression is known as:

[0048]

[0049] wherein the cutoff frequency f N = 40, and the apparent velocity v = 2000.

[0050] (4.2) The seismic data is filtered:

[0051]

[0052] wherein Represents a two-dimensional convolution operator;

[0053] (5) Earthquake data Perform anti-dynamic time difference adjustment, static time difference adjustment, energy adjustment and anti-flattening to obtain seismic data D(t,x). This process is the reverse of step (3).

[0054] (6) After the above steps, the seismic data of pure surface waves are obtained. Then, the effective signal is obtained by subtracting it from the original seismic data, thereby achieving the purpose of removing the interference of non-steady surface waves.

[0055] Seismic data after suppressing surface wave interference through the above steps were plotted using conventional techniques. Figure 2 The results of suppressing surface waves using the present invention are shown. The broom-shaped high-energy surface wave interference is well suppressed, and the seismic signal contaminated by surface waves is clearly recovered. Figure 3 As can be seen from the suppressed surface wave, no reflected wave remains. This invention suppresses unsteady surface waves without damaging the effective signal.

[0056] Example 2

[0057] This embodiment is an application example of Block B in an oilfield. Figure 4 The seismic data input for this embodiment was severely contaminated by broom-shaped high-energy surface wave interference, which polluted the seismic signals within a medium shot-receiver distance. Figure 5 This is the result of using the present invention to suppress unsteady surface waves; surface wave interference has been well suppressed. Figure 6 The surface wave suppressed using this invention contains no obvious reflected wave signal. This invention has a stronger ability to suppress surface waves and recover effective signals.

[0058] Those skilled in the art will recognize that the embodiments described herein are intended to help the reader understand the principles of the invention, and should be understood that the scope of protection of the invention is not limited to such specific statements and embodiments. Various modifications and variations can be made to the invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the invention should be included within the scope of the claims of the invention.

Claims

1. A method for suppressing regular noise from unsteady earthquakes, characterized in that, include: S1. Calculate the dip time difference of the original seismic data; S2. Flatten the local seismic data using surface wave dip time difference, and then adjust the data energy and inter-trace time difference; S3. Obtain the time domain operator of the fk filter and perform time domain fk filtering on the seismic data processed in step S2. S4. Perform reverse inter-trace time difference adjustment, reverse energy adjustment, and reverse flattening on the seismic data obtained in step S3 to obtain pure surface wave seismic data. S5. Subtract the pure surface wave seismic data obtained in step S4 from the original seismic data to obtain the effective signal.

2. The method for suppressing regular noise from unsteady earthquakes according to claim 1, characterized in that, Step S1 specifically includes the following sub-steps: S11. Seismic data where the shot point and receiver point are in the same arrangement is denoted as d. 0 (t,x), from d 0 The speed at which regular disturbances are picked up on (t,x) is v. 0 And calculate the apparent velocity v when the shot point and receiver point are not in the same arrangement. * : Where t represents the time point, x represents the seismic trace, and θ is the azimuth angle; S12. Calculate the surface wave dip angle time difference in seismic data: Where dt and dx are the time sampling interval and the spatial sampling interval, respectively.

3. The method for suppressing regular noise from unsteady earthquakes according to claim 2, characterized in that, Step S2 specifically includes the following sub-steps: S21. Record the flattened seismic data within the window as follows: And select the middle lane as the reference lane x r ; S22. Adjust the root mean square energy of the seismic traces within the window to match the energy of the reference trace: Where q is the number of time sampling points; S23. Calculate the correlation between each trace and the reference trace within the calculation window, and take the point of maximum correlation between the seismic trace and the reference trace as the inter-trace static time difference for adjustment. Better lateral consistency; the calculation formula related to the reference track for each track within the window is: Where, x r Let l be the reference trace and l be the earthquake trace x and the reference trace x. r The static time difference that needs to be adjusted between them; S24. Find the phase filter h1(t,x) so that each channel in the window can dynamically adjust the time difference to the reference channel, i.e., adjust the phase, in order to weaken the inherent dispersion characteristics of the surface wave. Where obj is the objective function, x r Let F be the reference channel, and F() be the Fourier transform.

4. The method for suppressing regular noise from unsteady earthquakes according to claim 3, characterized in that, Step S3 specifically includes the following sub-steps: S31. The time-domain expression of the filter is: Among them, f N Where is the cutoff frequency, and v is the apparent velocity; S32. Filtering seismic data: in, This represents a two-dimensional convolution operator.

5. A non-steady-state seismic regular noise suppression system, characterized in that, include: The system includes a seismic data dip time difference module, a seismic data forward adjustment module, a filtering module, a seismic data reverse adjustment module, and a subtraction module. The seismic data forward adjustment module consists of, in series: a flattening processing unit, a data energy adjustment unit, and an inter-trace time difference adjustment unit. The seismic data reverse adjustment module consists of, in series: a reverse inter-trace time difference adjustment unit, a reverse data energy adjustment unit, and a reverse flattening processing unit. The seismic data dip time difference module is used to calculate the surface wave dip time difference of raw seismic data; The seismic data forward adjustment module flattens the seismic data based on dip time difference, and then performs data energy adjustment and inter-trace time difference adjustment; The seismic data processed by the forward seismic data adjustment module is used as the input of the filtering module, and the output of the filtering module is used as the input of the reverse seismic data adjustment module. The output of the seismic data inverse adjustment module is pure surface wave seismic data; The raw seismic data and the pure surface wave seismic data are used as inputs to the subtraction module, and the output of the subtraction module is the valid signal.

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