A quantitative evaluation method for vertical resolution of broadband seismic result data

Abstract

The application discloses a kind of wideband seismic result data vertical resolution quantitative evaluation method, S1: determining the main frequency and frequency width of the target layer in seismic result data;S2: according to the main frequency of target layer, build wideband zero-phase wavelet;S3: according to the frequency width of target layer, band-pass filter is carried out to wideband zero-phase wavelet, and form band-limited zero-phase pseudo seismic source wavelet;S4: build wedge formation model;S5: using band-limited zero-phase pseudo seismic source wavelet and wedge formation model carries out wave field forward modeling, generates synthetic seismogram profile;S6: from seismic wavelet and seismic record two aspects, carry out seismic vertical resolution analysis.The present application can be used for marine natural gas hydrate and oil and gas seismic data, because the influence of frequency width is considered, the vertical resolution of seismic wavelet and seismic record can be accurately quantitatively evaluated.Provide resolution index for seismic exploration effect evaluation, also provide method means for carrying out the main influencing factor and law of seismic vertical resolution.

Description

Technical Field

[0001] This invention relates to the field of seismic exploration and development technology for marine natural gas hydrates, specifically to a method for quantitative evaluation of vertical resolution of broadband seismic data. Background Technology

[0002] Vertical resolution of seismic data is a crucial indicator for evaluating seismic exploration capabilities and accuracy. Theoretically, vertical resolution depends on layer velocity and the spectrum (amplitude and phase spectra) of the seismic wavelet. When the layer velocity is constant, the zero-phase wavelet has the strongest main lobe amplitude and the highest resolution among all phases. For the zero-phase wavelet, given a dominant frequency, increasing high-frequency components reduces the main lobe width, while increasing low-frequency components reduces the sidelobe ratio (the ratio of sidelobe amplitude to main lobe amplitude). Therefore, increasing the bandwidth improves vertical resolution.

[0003] Marine natural gas hydrates have garnered significant attention due to their importance in energy, atmospheric environment, and seabed geological hazards. Since the 1960s, seismic exploration has been the most important geophysical method for the exploration and evaluation of marine natural gas hydrates. The seismic exploration methods employed have evolved from single-channel seismic exploration in the 1970s, to two-dimensional multichannel seismic exploration in the 1980s, and conventional three-dimensional seismic exploration in the 1990s, to high-resolution seismic exploration represented by the P-Cable three-dimensional seismic method in the 21st century. In P-Cable seismic data, the dominant frequency of the target layer can reach between 120 and 200 Hz, with a maximum bandwidth of 10 to 400 Hz. This high dominant frequency and wide bandwidth give it superior vertical resolution.

[0004] The quantitative evaluation of seismic vertical resolution, widely used in practice today, is based on the Rayleigh criterion, which uses the distance from the wavelet crest to the trough to represent the resolution limit, i.e., the so-called 1. The method is based on the 4-wavelength criterion. However, because it only considers the dominant frequency and layer velocity and ignores the effect of bandwidth, it is applicable to narrow-band seismic data with a bandwidth of approximately 2 to 3 octaves. For wide-band data with a bandwidth of 5 to 6 octaves, the calculation error is relatively large, and it cannot fully reflect the true vertical resolution of shallow seafloor strata containing natural gas hydrates. Summary of the Invention

[0005] To address the limitation of existing Rayleigh criteria in accurately and quantitatively evaluating the vertical resolution of broadband seismic data, this invention provides a method for quantitatively evaluating seismic vertical resolution that considers bandwidth, thereby improving the accuracy of vertical resolution evaluation for broadband seismic data. This invention utilizes zero-phase Rayleigh wavelets and thin-layer tuned resonance amplitudes. Through the construction of broadband and band-limited zero-phase pseudo-source wavelets, wedge-shaped strata modeling, and forward modeling of the seismic wavefield, a method is employed to quantitatively evaluate the vertical resolution of natural gas hydrate seismic data based on the dominant frequency and bandwidth of actual seismic data.

[0006] The technical solution adopted in this invention is as follows:

[0007] A quantitative evaluation method for the vertical resolution of broadband seismic data includes the following steps:

[0008] S1: Determine the dominant frequency and bandwidth of the target layer in the seismic data;

[0009] S2: Construct a broadband zero-phase wavelet based on the target layer's dominant frequency;

[0010] S3: Based on the target layer bandwidth, bandpass filtering is performed on the broadband zero-phase wavelet to form a band-limited zero-phase pseudo-source wavelet;

[0011] S4: Construct a wedge-shaped formation model;

[0012] S5: Wavefield forward modeling is performed using a band-limited zero-phase pseudo-source wavelet and a wedge-shaped stratum model to generate a synthetic seismic record profile;

[0013] S6: Conduct seismic vertical resolution analysis from both seismic wavelet and seismic record perspectives.

[0014] Furthermore, in S1, the dominant frequency and bandwidth of the target layer are determined by performing a Fourier transform on the target layer seismic record to obtain the amplitude spectrum, wherein the target layer seismic record selects the portion of the reflected wavelet starting from the top interface of the target layer and ending at the bottom interface of the target layer.

[0015] Furthermore, in S2, the specific steps for constructing the broadband zero-phase wavelet include:

[0016] S21: Calculate the zero-phase Recker wavelet according to the Recker wavelet calculation formula based on the target layer dominant frequency;

[0017] S22: Calculate the spectrum of the zero-phase Ricker wavelet, and determine the low and high cutoff frequencies and their amplitudes of the effective bandwidth according to the standard of 0.707 times the peak amplitude of the amplitude spectrum;

[0018] S23: Determine the maximum frequency of the broadband zero-phase wavelet based on the ratio of the maximum frequency amplitude to the peak amplitude.

[0019] S24: Extend the amplitude values ​​of the low and high cutoff frequency ranges to the range from 0Hz to the maximum frequency.

[0020] S25: The amplitude values ​​of all frequencies from 0Hz to the maximum frequency range are calculated using interpolation to generate the amplitude spectrum of a broadband zero-phase wavelet.

[0021] S26: Using the phase spectrum of the zero-phase Lake wavelet and the amplitude spectrum of the broadband zero-phase wavelet, perform an inverse Fourier transform to generate a broadband zero-phase wavelet.

[0022] Furthermore, in S3, a bandpass filter is performed using a cosine function border to form a band-limited zero-phase pseudo-source wavelet.

[0023] Furthermore, in S4, well logging and drilling data from the study area are used to statistically analyze water depth, the burial depth and thickness of natural gas hydrates and related strata, and seismic wave velocity information. The formation parameters are determined based on the principle of selecting the average value, and a wedge-shaped formation model with varying target layer thickness and constant thickness of other strata is established.

[0024] Furthermore, in S4, when the target layer is a natural gas hydrate or free gas layer, the surrounding rock parameters are based on actual statistical data; when the target layer is other strata, the thickness of the upper and lower surrounding rocks is based on actual statistical data, but the seismic wave velocities of the upper and lower surrounding rocks are based on the data of the overlying surrounding rocks, so that the wave impedance of the target layer and its upper and lower surrounding rocks exhibits a rhythmic change, resulting in amplitude tuning.

[0025] Furthermore, in S5, the convolution method is used to forward model the self-excited and self-absorbed synthetic seismic record profile corresponding to the target layer thickness.

[0026] Furthermore, in S6, the seismic vertical resolution analysis includes:

[0027] Seismic wavelet vertical resolution analysis: The time resolution of the band-limited zero-phase pseudo-source wavelet is obtained by Rayleigh criterion, Ricker criterion and Wides criterion respectively, and the time resolution is converted into thickness resolution by using the layer velocity of the target layer;

[0028] Vertical resolution analysis of seismic records: Using synthetic seismic records, the vertical thickness resolution of the seismic records is determined by the tuning amplitude based on the thin-layer amplitude effect.

[0029] Furthermore, in S6, the vertical resolution analysis of the seismic wavelet specifically includes: calculating the distance from the peak to the trough of the main lobe of the band-limited zero-phase pseudo-source wavelet, the width between the two inflection points of the main lobe, and 1 / 8 of the dominant frequency wavelength; statistically analyzing the vertical resolution expressed in terms of the two-way travel time of the seismic wave; and converting it into thickness resolution.

[0030] Furthermore, in S6, the vertical resolution analysis of the seismic record specifically includes: extracting the peak amplitude of the composite reflection wavelet at the top and bottom interfaces of the target layer, creating a curve showing the relationship between the peak amplitude and the thickness of the target layer, and determining the vertical thickness resolution of the seismic record based on the peak value of the curve.

[0031] The present invention has the following technical effects:

[0032] The present invention provides a quantitative evaluation method for the vertical resolution of broadband seismic data, which quantitatively evaluates the vertical resolution based on the dominant frequency and bandwidth of the seismic data. It considers the influence of bandwidth on vertical resolution, overcomes the shortcomings of conventional methods, and has no limitation on bandwidth. This method is implemented under noise-free conditions, and the obtained resolution value should represent the vertical resolution limit achievable by actual seismic data.

[0033] The method of this invention can be used not only for marine natural gas hydrate seismic data, but also for oil and gas seismic data, including conventional two-dimensional and three-dimensional seismic data, high-resolution two-dimensional and three-dimensional seismic data, and extremely high-resolution P-Cable three-dimensional seismic data.

[0034] The method of this invention can quantitatively evaluate the vertical resolution of seismic wavelets and seismic records. It can provide resolution indicators for evaluating the performance of seismic exploration systems, the quality of seismic acquisition, processing and interpretation, and other aspects of seismic exploration. It also provides methods and means for studying the main influencing factors and laws of seismic vertical resolution. Attached Figure Description

[0035] The present invention includes the following figures:

[0036] Figure 1 A flowchart illustrating the implementation of a quantitative evaluation method for the vertical resolution of broadband seismic data.

[0037] Figure 2 The waveform and amplitude spectrum of the zero-phase Ricker wavelet (dominant frequency 200Hz) corresponding to the South China Sea hydrate layer.

[0038] Figure 3 The broadband zero-phase wavelet waveform and amplitude spectrum corresponding to the South China Sea hydrate layer.

[0039] Figure 4 The waveform and amplitude spectrum of the band-limited zero-phase pseudo-seismic source wavelet corresponding to the South China Sea hydrate layer.

[0040] Figure 5 These are parameters for wedge-shaped formations.

[0041] Figure 6 This is a wedge-shaped stratigraphic model showing variations in hydrate layer thickness.

[0042] Figure 7This is a composite seismic record profile.

[0043] Figure 8 This is the vertical resolution data for seismic wavelet.

[0044] Figure 9 This is the vertical resolution analysis curve for the seismic record. Detailed Implementation

[0045] The steps of the present invention will be further described in detail below with reference to the accompanying drawings and test examples.

[0046] like Figure 1 As shown, this invention provides a method for quantitatively evaluating the vertical resolution of broadband seismic data, specifically including:

[0047] Step 1: Determine the dominant frequency and bandwidth of the target layer in the seismic data.

[0048] Perform spectral analysis on the reflected wave from the target layer to determine the dominant frequency. With low cutoff frequency of effective bandwidth and high cutoff frequency .

[0049] Step 2: Construct a broadband zero-phase wavelet based on the target layer dominant frequency.

[0050] Statistically analyze the dominant frequency and wavelet length of the target layer in seismic data, based on the dominant frequency of the actual data. Given the wavelet length L, the seismic wavelet is calculated using the zero-phase Ricker wavelet formula. The value of the seismic wavelet at time point t... Represented as:

[0051]

[0052] After Fourier transform, the spectrum of the zero-phase Ricker wavelet is obtained. The phase spectrum is kept unchanged. Based on the dominant frequency amplitude... The low cutoff frequency of the effective frequency band is determined by using a standard that is 0.707 times the standard. and high cutoff frequency and its amplitude spectrum value and By using the minimum limit of the given amplitude spectrum value. Determine the high-frequency limit Then, maintain the main frequency. and its spectral values and arbitrary frequency points With the spectral values ​​unchanged, the 0Hz and high-frequency limits are set. As the low and high cutoff frequencies, their amplitude spectrum values ​​are assigned as follows: and The linear interpolation method is used to calculate the frequency corresponding to the original amplitude spectrum value, and then the interpolation method is used again to calculate the amplitude spectrum value of any frequency. Amplitude spectrum values Represented as:

[0053]

[0054] Thus, while keeping the dominant frequency constant, the amplitude spectrum within the effective frequency band is extended to the entire frequency band, generating a broadband zero-phase seismic wavelet spectrum. After inverse Fourier transform, the broadband zero-phase seismic wavelet is obtained.

[0055] Step 3: Based on the target layer bandwidth, perform bandpass filtering on the broadband zero-phase wavelet to generate a band-limited zero-phase pseudo-source wavelet.

[0056] Based on the bandwidth of the actual data, i.e., the low cutoff frequency and high cutoff frequency Bandpass filtering of the broadband zero-phase wavelet generates a band-limited zero-phase wavelet, i.e., a pseudo-source wavelet. Frequency domain filtering factor. Represented as:

[0057]

[0058] This invention employs cosine function flanging for bandpass filtering, which can effectively reduce signal distortion in the frequency band transition region and preserve the phase consistency and amplitude spectrum integrity of the broadband zero-phase wavelet to the greatest extent.

[0059] Step 4: Construct a wedge-shaped formation model.

[0060] Using drilling and logging data from the study area, we statistically analyzed the water depth, the burial depth and thickness of natural gas hydrates and related strata, and seismic wave velocity. Based on the principle of selecting average values, we determined parameters such as the velocity and depth of the seawater layer, the burial depth and velocity of the hydrate layer, and the burial depth, thickness, and velocity of related strata. We then established a wedge-shaped geological model with constant thickness in other strata and varying thickness in the target layer. To ensure a tuning phenomenon after interference of reflected wave amplitudes at the top and bottom interfaces of the target layer, the wave impedance of the target layer and its overlying and underlying surrounding rock strata needs to exhibit a rhythmic variation. Therefore, when the target layer is a natural gas hydrate or free gas layer, the surrounding rock parameters are based on actual statistical data; when the target layer is other strata, the thickness of the overlying and underlying surrounding rock strata is based on actual statistical data, but the seismic wave velocities of both the overlying and underlying surrounding rock strata are based on data from the overlying surrounding rock strata.

[0061] Step 5: Wave field forward modeling.

[0062] Using the wedge-shaped stratigraphic model established in step 4 and the band-limited zero-phase pseudo-source wavelet generated in step 3, the self-excited and self-absorbed synthetic seismic record profile corresponding to the target layer thickness is simulated by forward modeling of the seismic record convolution model.

[0063] Step 6: Seismic vertical resolution analysis.

[0064] Seismic vertical resolution analysis was conducted from both seismic wavelet and seismic record perspectives.

[0065] 1) Vertical resolution analysis of seismic wavelet. Using the band-limited zero-phase pseudo-source wavelet generated in step 3, the distance from the peak to the trough of the main lobe, the width between the two inflection points of the main lobe, and 1 / 8 of the dominant frequency wavelength are calculated according to the Rayleigh criterion, Ricker criterion, and Widess criterion, respectively. The vertical resolution of the source wavelet, expressed as the two-way travel time of the seismic wave, is then statistically analyzed. The statistical time is converted into thickness using the layer velocity of the target layer.

[0066] 2) Vertical resolution analysis of seismic records. Based on the synthetic seismic records generated in step 5, the peak amplitude (maximum absolute amplitude) of the main lobe of the composite reflection wavelet at the top and bottom interfaces of the target layer is extracted using the thin-layer amplitude effect. The vertical resolution of the seismic records is determined according to the principle of maximum peak amplitude, i.e., the target layer thickness corresponding to the tuning amplitude.

[0067] Specific Implementation Example 1: Taking the high-resolution three-dimensional marine natural gas hydrate seismic data of short cable in Area A of the South China Sea as an example, combined with... Figure 1 The flowchart illustrates the process for quantitatively evaluating vertical resolution.

[0068] like Figure 1 As shown, it includes the following steps.

[0069] Step 1: Determine the dominant frequency and bandwidth of the target layer in the seismic data. Through spectral analysis, the dominant frequency of the hydrate layer in the high-resolution 3D marine natural gas hydrate seismic data of the short cable in Area A of the South China Sea is determined. Hz, with an effective bandwidth of 10-390Hz.

[0070] Step 2: Construct a broadband zero-phase wavelet. Determine the wavelet length L = 64 ms, and calculate the seismic wavelet using the zero-phase Ricker wavelet formula. Figure 2 ); broaden the effective bandwidth of the seismic wavelet to generate a broadband zero-phase wavelet ( Figure 3 ).

[0071] Step 3: Generate a band-limited zero-phase pseudo-source wavelet. This is based on the bandwidth of the hydrate layer in the seismic data, i.e., the low cutoff frequency. and high cutoff frequency Bandpass filtering is performed on the broadband zero-phase wavelet to form a band-limited zero-phase pseudo-source wavelet. Figure 4).

[0072] Step 4: Establish a wedge-shaped stratigraphic model of the hydrate layer. Collect drilling and logging data for the study area, and statistically analyze and select average values ​​to determine the burial depth, thickness, seismic wave propagation velocity, and other stratigraphic parameters of the seawater layer, hydrate layer, and related strata, as well as the maximum range of variation in the hydrate layer thickness. Figure 5 Using the determined parameters, a wedge-shaped stratigraphic model was established with varying hydrate layer thickness (0-30m, increments of 0.5m) and constant thickness of the upper and lower surrounding rocks. Figure 6 ).

[0073] Step 5: Wavefield forward modeling. Based on the wedge-shaped stratigraphic model established in Step 4 and the band-limited zero-phase pseudo-source wavelet generated in Step 3, the self-excited and self-absorbed synthetic seismic record profile corresponding to the hydrate layer thickness is forward modeled using the convolution method. Figure 7 ).

[0074] Step 6: Seismic vertical resolution analysis.

[0075] 1) Vertical resolution analysis of the seismic wavelet. For the band-limited zero-phase pseudo-source wavelet generated in step 3, the vertical resolution of the seismic wavelet is calculated using the Rayleigh, Ricker, and Wides criteria, respectively. Figure 8 ).

[0076] 2) Vertical resolution analysis of seismic records. From the synthetic seismic records generated in step 5, the peak amplitude (maximum absolute amplitude) of the main lobe of the composite reflection wavelet at the top and bottom interfaces of the hydrate layer is extracted using the thin-layer amplitude effect. Based on the principle of maximizing the peak amplitude (maximum absolute amplitude), the vertical resolution of the seismic records is statistically analyzed. Figure 9 ).

[0077] In this embodiment, according to the conventional Rayleigh criterion, the vertical resolution of the natural gas hydrate layer is 2.81m, while the calculation result of the broadband vertical resolution quantitative method of this invention is 2.0m. Figure 8 The vertical resolution was improved by 40.5%.

[0078] The proposed method for quantitatively evaluating the vertical resolution of broadband seismic data is a method that quantitatively evaluates the vertical resolution of seismic data based on the dominant frequency and bandwidth of actual seismic data. It has no limitation on the bandwidth of the seismic data and is applicable to both broadband high-resolution marine natural gas hydrate seismic data and narrow-band conventional two- and three-dimensional marine natural gas hydrate and oil and gas seismic data. This method can simultaneously quantitatively assess the vertical resolution of seismic wavelets and seismic records; the difference between the two can provide a basis for revealing the impact of changes in the internal structure or physical properties of the target layer on the vertical resolution. Because it considers the influence of bandwidth, this method can obtain high-precision vertical resolution. It not only provides resolution indicators for evaluating the performance, acquisition, processing, and interpretation quality of seismic exploration systems, but also provides a technical means for in-depth research on the main influencing factors and patterns of seismic vertical resolution.

[0079] The above embodiments are for illustrative purposes only and are not intended to limit the scope of this invention. Those skilled in the art can make various changes and modifications without departing from the essence and scope of this invention. Therefore, all equivalent technical solutions also fall within the scope of this invention, and the patent protection scope of this invention should be defined by the claims. Content not described in detail in this specification is prior art known to those skilled in the art.

Claims

1. A method for quantitatively evaluating the vertical resolution of broadband seismic data, characterized in that, Includes the following steps: S1: Determine the dominant frequency and bandwidth of the target layer in the seismic data; S2: Based on the target layer dominant frequency, calculate the zero-phase Ricker wavelet and its spectrum, and determine the low cutoff frequency of the effective frequency band. and high cutoff frequency and its amplitude spectrum values; Set high frequency limit To maintain the phase spectrum, dominant frequency, and amplitude spectrum values ​​unchanged, a bilinear interpolation method is used to adjust the effective frequency band. ~ The amplitude spectrum extends from 0 Hz to the high-frequency limit. Constructing a broadband zero-phase wavelet; S3: Based on the target layer bandwidth, bandpass filtering is performed on the broadband zero-phase wavelet to form a band-limited zero-phase pseudo-source wavelet; S4: Based on the actual burial depth, seismic wave velocity and thickness of the strata, construct a depth-domain rhythmic wedge-shaped stratum model with constant surrounding rock thickness and varying target layer thickness; S5: Wavefield forward modeling is performed using a band-limited zero-phase pseudo-source wavelet and a depth-domain rhythmic wedge-shaped strata model to generate a synthetic seismic record profile; S6: Quantitative analysis of seismic vertical resolution is carried out from both seismic wavelet and seismic record aspects; Specifically, for the vertical resolution analysis of the seismic wavelet: using the band-limited zero-phase pseudo-source wavelet generated by S3, the distance from the peak to the trough of the main lobe, the width between the two inflection points of the main lobe, and 1 / 8 of the dominant frequency wavelength are calculated according to the Rayleigh criterion, Ricker criterion, and Wides criterion, respectively, to obtain the vertical resolution of the source wavelet expressed in terms of the two-way travel time of the seismic wave; using the layer velocity of the target layer, the statistical time is converted into thickness resolution; For the vertical resolution analysis of seismic records: the composite seismic records generated by S5 utilize the thin-layer amplitude effect to extract the peak amplitude of the main lobe of the composite reflection wavelet at the top and bottom interfaces of the target layer. Based on the principle of maximum peak amplitude, i.e., the thickness of the target layer corresponding to the tuning amplitude, the vertical thickness resolution of the seismic records is determined.

2. The method as described in claim 1, characterized in that, In S1, the dominant frequency and bandwidth of the target layer are determined by performing a Fourier transform on the target layer seismic record to obtain the amplitude spectrum, wherein the target layer seismic record selects the portion of the reflected wavelet that starts from the top interface of the target layer and ends at the bottom interface of the target layer.

3. The method as described in claim 1, characterized in that, In S2, the specific steps for constructing the broadband zero-phase wavelet include: S21: Calculate the zero-phase Recker wavelet according to the Recker wavelet calculation formula based on the target layer dominant frequency; S22: Calculate the spectrum of the zero-phase Ricker wavelet, and determine the low and high cutoff frequencies and their amplitudes of the effective bandwidth according to the standard of 0.707 times the peak amplitude of the amplitude spectrum; S23: Determine the maximum frequency of the broadband zero-phase wavelet based on the ratio of the maximum frequency amplitude to the peak amplitude. S24: Extend the amplitude values ​​of the low and high cutoff frequency ranges to the range from 0Hz to the maximum frequency. S25: The amplitude values ​​of all frequencies from 0Hz to the maximum frequency range are calculated using interpolation to generate the amplitude spectrum of a broadband zero-phase wavelet. S26: Using the phase spectrum of the zero-phase Lake wavelet and the amplitude spectrum of the broadband zero-phase wavelet, perform an inverse Fourier transform to generate a broadband zero-phase wavelet.

4. The method as described in claim 1, characterized in that, In S3, a bandpass filter is performed using a cosine function border to form a band-limited zero-phase pseudo-source wavelet.

5. The method as described in claim 1, characterized in that, In S4, well logging and drilling data from the study area are used to statistically analyze water depth, the burial depth and thickness of natural gas hydrates and related strata, and seismic wave velocity information. The formation parameters are determined by selecting the average value, and a depth domain wedge-shaped formation model with varying target layer thickness and constant thickness of other strata is established.

6. The method as described in claim 5, characterized in that, In S4, when the target layer is a natural gas hydrate or free gas layer, the surrounding rock parameters are based on actual statistical data; when the target layer is other strata, the thickness of the upper and lower surrounding rocks is based on actual statistical data, but the seismic wave velocity of the upper and lower surrounding rocks is based on the data of the overlying surrounding rocks, so that the wave impedance of the target layer and its upper and lower surrounding rocks exhibits a rhythmic change, resulting in amplitude tuning.

7. The method as described in claim 1, characterized in that, In S5, the convolution method is used to forward model the self-excited and self-absorbed synthetic seismic record profile corresponding to the target layer thickness.

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