Seismic reconstruction method based on velocity low-frequency trend modeling

Abstract

The invention provides a seismic reconstruction method based on velocity low-frequency trend modeling. The method comprises the following steps: firstly, reconstructing a logging time domain wave impedance low-frequency component based on generalized S transformation, and calculating a seismic wave impedance low-frequency component based on a seismic velocity data volume and a fitting relation between density and velocity; obtaining a corrected three-dimensional space seismic wave impedance low-frequency component data volume; calculating a wave impedance value of the target layer after decompaction, calculating a wave impedance decompaction coefficient to obtain a three-dimensional seismic compaction coefficient body, and further establishing a mathematical relationship between the multi-channel seismic record and the difference between the seismic wavelets and the multi-channel wave impedance; and a wave impedance inversion objective function after decompaction is established, a seismic record after decompaction correction is obtained by adopting a nonlinear inversion method, and the reconstructed seismic data effectively improves the prediction accuracy of the thin reservoir, the reservoir physical property and the reservoir oiliness of the reservoir in the deep-lying zone.

Description

Technical Field

[0001] The invention relates to the technical field of geophysical exploration and development, and in particular to a seismic reconstruction method based on velocity low-frequency trend modeling. Background Art

[0002] Since the velocity and density of the reservoir in the deep depression zone are affected by compaction, as the burial depth increases and the compaction increases, the velocity and density change characteristics of the three types of reservoirs are directly affected, that is, the wave impedance change characteristics are affected. Affected by compaction, the wave impedance of sandstone and mudstone in different sedimentary phases on the plane is different. The vertical wave impedance difference of sandstone and mudstone in the logging curve gradually decreases with the increase of burial depth, which makes the same type of reservoir not only cause serious cross-overlap of logging lithology wave impedance, but also reduce the difference of wave impedance to produce weak reflection and reduce the seismic identification ability. The difference of wave impedance of the same type of reservoir caused by compaction will directly affect the change of seismic record characteristics, making it difficult to extract the regularity of seismic attribute changes corresponding to the three types of effective reservoirs from the existing seismic records, and it is difficult to select suitable seismic attributes to describe the three types of reservoirs.

[0003] Commonly used formation decompaction correction methods include compaction rate recovery method, compaction coefficient recovery method, decompaction recovery method, formation original thickness recovery plate method, sequence stratigraphic analysis method, vitrinite maximum reflectivity recovery method, geophysical method, etc. The compaction coefficient recovery method is the most commonly used method, among which the compaction coefficient is an important parameter for inverting the burial process of the basin. Considering the difference in wave impedance of the same type of reservoir caused by compaction, it will directly affect the change of seismic record characteristics, and it is also the premise for accurately obtaining the compaction coefficient of mudstone in the normal compaction section. The low-frequency (time domain) or low-wave number (depth domain) component of wave impedance changes with depth, which represents the compaction trend of formation wave impedance. To this end, by extracting the low-frequency or low-wave number component of wave impedance, the formation wave impedance compaction coefficient in the time domain or depth domain can be obtained. Summary of the invention

[0004] In view of the above problems, the present invention is proposed to provide a seismic reconstruction method based on velocity low-frequency trend modeling, which overcomes the above problems or at least partially solves the above problems.

[0005] According to one aspect of the present invention, a seismic reconstruction method based on velocity low-frequency trend modeling is provided, comprising:

[0006] Step S1: convert the logging data into the time domain, perform frequency division processing on the logging wave impedance, and select the low-frequency component that matches the trend as the logging low-frequency component data body;

[0007] Step S2: calculating the seismic wave impedance low-frequency component based on the seismic velocity data volume and the fitting relationship between the well logging density and the velocity, and correcting the seismic wave impedance low-frequency component using the well logging low-frequency component data volume to obtain a corrected three-dimensional space seismic wave impedance low-frequency component data volume;

[0008] Step S3: determining the compaction trend line corresponding to the target layer segment according to the corrected three-dimensional spatial seismic wave impedance low-frequency component data body, calculating the wave impedance value of the target layer after de-compaction, and calculating the wave impedance de-compaction coefficient;

[0009] Step S4: establishing the wave impedance relationship and the mathematical relationship of the reflection coefficient before and after decompaction, and establishing the mathematical relationship between the multi-channel seismic record and the seismic wavelet and the multi-channel wave impedance difference;

[0010] Step S5: Under the constraint of the trend of the low-frequency component of the wave impedance, establish the wave impedance inversion objective function after decompaction, and use the nonlinear inversion method to obtain the compaction-corrected seismic record.

[0011] Optionally, the step S1: converting the logging data into the time domain, performing frequency division processing on the logging wave impedance, and selecting the low-frequency component consistent with the trend as the logging low-frequency component data body specifically includes:

[0012] The logging data is used to calculate the time domain logging wave impedance data body, and the generalized S transform time-frequency spectrum analysis is used to determine the low-frequency component range of the wave impedance representing the reservoir compaction trend in the target layer well section;

[0013] The generalized inverse S transform is used to reconstruct the low-frequency component of logging wave impedance and obtain the low-frequency component of logging wave impedance in time domain.

[0014] Optionally, the step S2: calculating the seismic wave impedance low-frequency component based on the seismic velocity data body and the fitting relationship between the well logging density and the velocity, and correcting the seismic wave impedance component using the well logging low-frequency component to obtain the corrected three-dimensional space seismic wave impedance low-frequency component data body specifically includes:

[0015] Based on the seismic migration velocity data and the interpreted main target layer data, the layer-controlled multi-constrained layer velocity inversion MCVI method is used to calculate the seismic layer velocity;

[0016] Analyze the intersection diagram of target layer logging velocity and logging density to obtain the fitting formula of density and velocity, and apply it to convert the seismic layer velocity into formation density and calculate the seismic wave impedance body;

[0017] Use generalized S-transform to obtain low-frequency wave impedance body;

[0018] The low-frequency component of the logging wave impedance is used for correction to obtain a corrected three-dimensional seismic wave impedance low-frequency component data volume.

[0019] Optionally, the step S3: determining the compaction trend line corresponding to the target layer segment according to the corrected three-dimensional spatial seismic wave impedance low-frequency component data body, calculating the wave impedance value of the target layer after decompaction, and calculating the wave impedance decompaction coefficient specifically includes:

[0020] According to the characteristics of low-frequency wave impedance value changing with depth due to compaction, the compaction trend line corresponding to the target layer section is determined, and the wave impedance value of the target layer after de-compaction is calculated;

[0021] The wave impedance compaction coefficient is calculated using the wave impedance values ​​before and after decompaction, and the target layer logging and three-dimensional wave impedance compaction coefficient curves varying with depth are obtained.

[0022] Optionally, in step S3, the difference between the wellbore seismic wave impedance compaction coefficient and the logging wave impedance decompaction coefficient is calculated, and combined with the interpreted layer, the Kriging interpolation correction technology is used to establish a layer-controlled seismic wave impedance compaction coefficient error data body;

[0023] The seismic wave impedance compaction coefficient is corrected to obtain a corrected three-dimensional seismic wave impedance compaction coefficient data volume.

[0024] Optionally, the step S4: establishing the wave impedance relationship and the mathematical relationship of the reflection coefficient before and after decompaction, and establishing the mathematical relationship between the multi-channel seismic record and the seismic wavelet and the multi-channel wave impedance difference specifically includes:

[0025] According to the nonlinear relationship between reflection coefficient and wave impedance and the differential operator, the relationship among reflection coefficient, multi-channel wave impedance difference and seismic record is established.

[0026] Optionally, the step S5: establishing a decompacted wave impedance inversion objective function under the constraint of the wave impedance low-frequency component trend, and using a nonlinear inversion method to obtain a compacted corrected seismic record specifically comprises:

[0027] A low-frequency constraint objective function is established, and the nonlinear inversion method is used to obtain the wave impedance after compaction correction and the reflection coefficient after decompaction correction.

[0028] The seismic wavelets extracted from the wellside data are used to obtain the decompaction-corrected seismic records through convolution.

[0029] Optionally, the nonlinear inversion method in step S5 uses a spectral projection gradient algorithm to solve the wave impedance after compaction correction.

[0030] Optionally, the objective function of the wave impedance inversion after decompaction established in step S5 specifically includes: the multi-channel wave impedance inversion problem is expressed as

[0031]

[0032] in, w is the row vector of the sub-wave time series, X low is the low-frequency component of wave impedance, obtained from logging wave impedance or seismic velocity spectrum; L is the low-pass filter operator; Y is the known multi-channel seismic record, The inverted reflection coefficient time series is sparse and laterally smooth; The synthetic seismic record is consistent with the actual seismic record; X low =LX is the trend constraint of low-frequency component of wave impedance;

[0033] Optionally, the step S5 of establishing the wave impedance inversion objective function after decompaction further includes: the wave impedance inversion problem after decompaction is expressed as

[0034]

[0035] Where C is the matrix composed of compaction coefficients;

[0036] The semi-logarithm of the wave impedance after decompaction is obtained by inversion c ;

[0037] Calculate the multi-channel reflection coefficient R after decompaction using the difference operator c ;

[0038] Calculate the decompacted seismic record Y using the wavelet extracted from the wellbore seismic record c .

[0039] The invention provides a seismic reconstruction method based on velocity low-frequency trend modeling, comprising: step S1: converting well logging data into a time domain, performing frequency division processing on well logging wave impedance, and selecting a low-frequency component that is consistent with the trend as a well logging low-frequency component data body; step S2: calculating the seismic wave impedance low-frequency component based on the seismic velocity data body and the fitting relationship between well logging density and velocity, and correcting the seismic wave impedance low-frequency component using the well logging low-frequency component data body to obtain a corrected three-dimensional space seismic wave impedance low-frequency component data body; step S3: determining the compaction trend line corresponding to the target layer segment according to the corrected three-dimensional space seismic wave impedance low-frequency component data body, calculating the wave impedance value of the target layer after decompaction, and calculating the wave impedance decompaction coefficient; step S4: establishing a wave impedance relationship and a reflection coefficient mathematical relationship before and after decompaction, and establishing a mathematical relationship between a multi-channel seismic record and a seismic wavelet and a multi-channel wave impedance difference; step S5: under the constraint of the wave impedance low-frequency component trend, establishing a wave impedance inversion target function after decompaction, and using a nonlinear inversion method to obtain a compaction-corrected seismic record. It is used to correct the compaction of deep-sag reservoirs, thereby improving the prediction accuracy of thin reservoirs, reservoir physical properties, and reservoir oil content in deep-sag reservoirs. It is widely used in the exploration of deep oil and gas reservoirs in the western exploration area and even in the Sinopec exploration area.

[0040] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention, it can be implemented according to the contents of the specification. In order to make the above and other purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0042] Figure 1 It is a flow chart of the seismic reconstruction method based on velocity low-frequency trend modeling of the present invention; Figure 2 The components of different frequency bands of a logging wave impedance curve in a specific embodiment 1 of the present invention; Figure 3 It is a schematic diagram of removing low-frequency components from time-domain wave impedance in a specific embodiment 1 of the present invention; Figure 4 It is a schematic diagram of a low-frequency component data volume of a three-dimensional wave impedance in a specific embodiment 1 of the present invention; Figure 5 It is a schematic diagram of the plane distribution of the compaction coefficient and the decompaction coefficient of the target layer in a specific embodiment 1 of the present invention; Figure 6 This is a schematic diagram of earthquake reconstruction in a specific embodiment 1 of the present invention; Figure 7 The components of different frequency bands of a logging wave impedance curve in a specific embodiment 2 of the present invention; Figure 8 It is a schematic diagram of removing low-frequency components from time-domain wave impedance in a specific embodiment 2 of the present invention; Fig. 9 It is a schematic diagram of a low-frequency component data volume of a three-dimensional wave impedance in a specific embodiment 2 of the present invention; Fig.10 It is a schematic diagram of the plane distribution of the compaction coefficient and the decompaction coefficient of the target layer in a specific embodiment 2 of the present invention; Fig.11 It is a schematic diagram of earthquake reconstruction in a specific embodiment 2 of the present invention. DETAILED DESCRIPTION

[0043] The exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0044] The terms "comprises" and "having" and any variations thereof in the description embodiments, claims and drawings of the present invention are intended to cover non-exclusive inclusions, for example, including a series of steps or units.

[0045] The technical solution of the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0046] like Figure 1 As shown, Figure 1 FIG. 1 is a flow chart of a decompaction seismic reconstruction method based on low-frequency trend modeling of the present invention, comprising the following steps:

[0047] Step 101: firstly, the logging data is converted into the time domain, then the logging wave impedance is subjected to frequency division processing, and the low-frequency component consistent with the trend is selected as the logging low-frequency component data body.

[0048] Step 102: Calculate the seismic wave impedance low-frequency component based on the seismic velocity data volume and the fitting relationship between the well logging density and velocity, and use the well logging low-frequency component to correct the seismic wave impedance component to obtain a corrected three-dimensional space seismic wave impedance low-frequency component data volume.

[0049] Step 103: Determine the compaction trend line corresponding to the target layer segment based on the corrected three-dimensional spatial seismic wave impedance low-frequency component data volume, calculate the wave impedance value of the target layer after decompaction, and then calculate the wave impedance decompaction coefficient.

[0050] Step 104: Establish the wave impedance relationship and the mathematical relationship of the reflection coefficient before and after decompaction, and then establish the mathematical relationship between the multi-channel seismic record and the seismic wavelet and the multi-channel wave impedance difference.

[0051] Step 105: Under the constraint of the trend of the low-frequency component of the wave impedance, establish the wave impedance inversion objective function after decompaction, and use the nonlinear inversion method to obtain the compaction-corrected seismic record.

[0052] In step 101, firstly, the logging data can be used to calculate the time domain logging wave impedance data body, and the range of the low-frequency component of the wave impedance representing the reservoir compaction trend of the target layer section is determined by generalized S transform time-frequency analysis, and then the generalized S inverse transform is used to reconstruct the low-frequency component of the logging wave impedance to obtain the low-frequency component of the logging wave impedance in the time domain.

[0053] In step 102, based on the seismic migration velocity data body and the interpreted main target layer data, the layer-controlled multi-constrained layer velocity inversion (MCVI) method is used to calculate the seismic layer velocity; secondly, the target layer logging velocity and logging density intersection diagram analysis is performed to obtain the density and velocity fitting formula, which is applied to the seismic layer velocity to convert the formation density, calculate the seismic wave impedance body, and also use the generalized S transform to obtain the low-frequency wave impedance body. Finally, the low-frequency component of the logging wave impedance is used for correction to obtain the corrected three-dimensional space seismic wave impedance low-frequency component data body.

[0054] In step 103, according to the characteristics that the low-frequency wave impedance value varies with depth due to compaction, the compaction trend line corresponding to the target layer segment is determined, and then the wave impedance value of the target layer after decompaction is calculated; then, the wave impedance compaction coefficient is calculated using the wave impedance values ​​before and after decompaction, thereby obtaining the target layer segment logging and three-dimensional wave impedance compaction coefficient variation with depth curve.

[0055] In step 103, the difference between the wellbore seismic wave impedance compaction coefficient and the logging wave impedance decompaction coefficient is calculated, and combined with the interpretation layer, the Kriging interpolation correction technology is used to establish the layer-controlled seismic wave impedance compaction coefficient error data body, and then the seismic wave impedance compaction coefficient is corrected to obtain the corrected three-dimensional space seismic wave impedance compaction coefficient data body.

[0056] In step 104, firstly, the relationship between the reflection coefficient, multi-channel wave impedance difference and seismic record is established according to the nonlinear relationship between the reflection coefficient and the wave impedance and the differential operator.

[0057] In step 105, the wave impedance after compaction correction is obtained by using the established low-frequency constrained objective function and the nonlinear inversion method, and then the reflection coefficient after decompaction correction is obtained. The seismic wavelet extracted from the wellside data is used to obtain the seismic record after decompaction correction through convolution.

[0058] In step 105, in the nonlinear inversion method, a spectral projection gradient algorithm is used to solve the wave impedance after compaction correction.

[0059] Calculation of low frequency component of logging wave impedance

[0060] The time domain logging wave impedance data volume can be calculated based on the logging data. The range of low-frequency components of the wave impedance representing the reservoir compaction trend in the target layer well section can be determined through generalized S transform time-frequency analysis. Then, the generalized S inverse transform is used to reconstruct the low-frequency components of the logging wave impedance to obtain the low-frequency components of the logging wave impedance in the time domain.

[0061] Calculation of low-frequency components of three-dimensional seismic wave impedance

[0062] The calculation of the decompaction coefficient of seismic wave impedance requires the low-frequency component of seismic wave impedance. For this purpose, based on the seismic offset velocity, the layer-controlled multi-constrained layer velocity inversion method is used to calculate the seismic layer velocity. The low-frequency velocity field is obtained by frequency division calculation. The density and velocity intersection diagram is used to obtain the fitting formula of density and velocity. Then, the formation density is converted using the seismic layer velocity to obtain the low-frequency component of seismic wave impedance. Finally, the low-frequency component of the well logging wave impedance is used for correction to obtain the corrected three-dimensional space seismic wave impedance low-frequency component data body, which can be obtained by using the matrix X low express.

[0063] Among them, the layer-controlled multi-constrained layer velocity inversion method improves the calculation accuracy of layer velocity. This method can convert the sparse and irregularly distributed velocity spectrum points in the vertical and horizontal directions into regular and fine layer velocity bodies after geological constraints, overcoming the errors in velocity spectrum analysis caused by artificially picking velocity spectra and drastic changes in the vertical and horizontal directions of the structure. This technology makes the root mean square velocity converted from the inverted layer velocity and the input root mean square velocity fit best in the least square sense under the trend constraints and damping constraints of the vertical and horizontal changes in velocity.

[0064] Calculation of compaction coefficient of three-dimensional seismic wave impedance

[0065] According to the characteristics of low-frequency wave impedance value changing with depth due to compaction, the compaction trend line corresponding to the target layer is determined, and then the wave impedance value of the target layer after decompaction is calculated; then the wave impedance compaction coefficient is calculated using the wave impedance values ​​before and after decompaction. According to the difference between the wellside seismic wave impedance compaction coefficient and the logging wave impedance decompaction coefficient, combined with the interpretation layer, the Kriging interpolation correction technology is used to establish the layer-controlled seismic wave impedance compaction coefficient error data body, and then the seismic wave impedance compaction coefficient is corrected to obtain the corrected three-dimensional space seismic wave impedance compaction coefficient data body. The multi-channel compaction coefficients form a matrix C.

[0066] Establishment of wave impedance inversion equation after decompaction

[0067] The change in wave impedance of the same type of reservoir caused by compaction will directly affect the change in seismic record characteristics. Therefore, multi-channel absolute wave impedance inversion with low-frequency impedance trend constraints can obtain corrected wave impedance and seismic records. This method overcomes the problem that traditional single-channel wave impedance inversion does not consider the law of lateral gradual change of wave impedance. Secondly, the inversion objective function considers the constraint of low wave number component of wave impedance.

[0068] The multi-channel impedance inversion problem is expressed as

[0069]

[0070] In the formula, w is the row vector of the wavelet time series, X lowis the low-frequency component of wave impedance, which can be obtained from logging wave impedance or seismic velocity spectrum; L is the low-pass filter operator; Y is the known multi-channel seismic record, It means that the inverted reflection coefficient time series is sparse and lateral (along the formation) smooth; represents the constraint that the synthetic seismic record matches the actual seismic record; X low =LX represents the trend constraint of the low-frequency component of wave impedance.

[0071] The wave impedance inversion problem after decompaction can be expressed as

[0072]

[0073] Where C is the matrix composed of compaction coefficients.

[0074] The semi-logarithm of the wave impedance after decompaction is obtained by inversion c , and then use the difference operator to calculate the multi-channel reflection coefficient R after decompaction c Finally, the wavelet extracted from the wellside seismic record is used to calculate the decompacted seismic record Y c .

[0075] Reconstructed seismic records after decompaction correction

[0076] According to the established low-frequency constrained objective function, the nonlinear inversion method is used to obtain the wave impedance after compaction correction, and then the reflection coefficient after de-compaction correction is obtained. The seismic record after de-compaction correction is obtained by convolution using the seismic wavelet extracted from the wellside data.

[0077] The present invention discloses a seismic reconstruction method based on velocity low-frequency trend modeling. The seismic wave impedance low-frequency component is calculated through the seismic velocity data body and the fitting relationship between density and velocity; the seismic wave impedance low-frequency component is corrected by using the logging low-frequency component to obtain the corrected three-dimensional space seismic wave impedance low-frequency component data body; the compaction trend line corresponding to the target layer segment is determined, the wave impedance value of the target layer after decompaction is calculated, and the wave impedance decompaction coefficient is calculated to obtain a three-dimensional seismic compaction coefficient body; then the wave impedance relationship and the reflection coefficient mathematical relationship before and after decompaction are established, and then the mathematical relationship between the multi-channel seismic record and the seismic wavelet and the multi-channel wave impedance difference is established; finally, under the constraint of the wave impedance low-frequency component trend, the wave impedance inversion objective function after decompaction is established, and the seismic record after decompaction correction is obtained by using a nonlinear inversion method. The invention is used to correct the compaction effect of deep-sag reservoirs, thereby improving the prediction accuracy of thin reservoirs, reservoir properties, and reservoir oil content of deep-sag reservoirs. It is widely applicable to the exploration of deep oil and gas reservoirs in the quasi-medium-deep layers of the western exploration area and even in the Sinopec exploration area.

[0078] Embodiment 1:

[0079] In a specific embodiment 1 of the present invention, the seismic reconstruction method based on velocity low-frequency trend modeling of the present invention includes the following steps:

[0080] Step 1: Establish the low-frequency component of logging wave impedance

[0081] The generalized S transformation of the W1 logging wave impedance variation over time in the W1 work area is obtained Figure 2 The wave impedance curve of the well with different frequency band components is shown. It can be seen that the low-frequency energy of the target layer wave impedance in the range of 0-3Hz represents the formation compaction trend. Therefore, 0-3Hz is selected as the low-frequency component of the target layer of the well to simulate the formation compaction effect. Subtracting the low-frequency component from the original wave impedance can obtain the high-frequency component curve of the wave impedance without compaction, as shown in Figure 3 As shown, it can be seen that the difference between sand bodies at different depths is not obvious after removing the low-frequency component, and the numerical trends of sand body wave impedance are consistent.

[0082] Step 2: Establishment of low-frequency component data volume of three-dimensional seismic wave impedance

[0083] According to the characteristics of wave impedance value changing with depth, the range of low-frequency component of wave impedance representing reservoir compaction trend in the target layer is determined by generalized S transform time-frequency analysis. Then, the low-frequency component of seismic wave impedance is reconstructed by generalized S inverse transform to obtain the data volume of low-frequency component of seismic wave impedance. Then, it is corrected by logging low-frequency component. The schematic diagram of low-frequency section through the well is shown in the figure below. Figure 4 .

[0084] Step 3: Establishment of decompaction coefficient of three-dimensional seismic wave impedance

[0085] According to the characteristics of low-frequency wave impedance value changing with depth due to compaction, the compaction trend line corresponding to the target layer section is determined, and then the wave impedance value of the target layer after decompaction is calculated; then the wave impedance values ​​before and after decompaction are used to calculate the wave impedance compaction coefficient and decompaction coefficient. The schematic diagram of the plane distribution of the target layer is shown in the figure. Figure 5 .

[0086] Step 4: Decompact seismic data reconstruction

[0087] The decompaction-corrected seismic impedance is inverted by establishing a low-frequency constrained inversion objective function, and then the decompaction-corrected reflection coefficient is obtained. The seismic record after decompaction correction is obtained by convolution using the seismic wavelet extracted from the wellside data. Figure 6 a is the original seismic profile of the target layer of the three wells. The target layers of the three wells are all fine sandstones with similar thickness, but the reflection characteristics are completely different. The difference in event axis reflection makes it difficult to accurately predict the sand bodies between wells. The seismic de-compaction correction and reconstruction are carried out by the above method. The reconstructed profile is shown in the figure. Figure 6b, The reflection amplitude of the sand bodies in the target layer near wells W2 and W4 has been enhanced, and the reflection characteristic responses of the sand bodies in the target layers of the three wells are similar.

[0088] Embodiment 2:

[0089] In a specific embodiment 2 of the present invention, the seismic reconstruction method based on velocity low-frequency trend modeling of the present invention includes the following steps:

[0090] Step 1: Establish the low-frequency component of logging wave impedance

[0091] The generalized S transformation of the time-varying value of the W11 logging wave impedance in the W10 work area is obtained Figure 7 The wave impedance curve of the well with different frequency band components is shown. It can be seen that the low-frequency energy of the target layer wave impedance in the range of 0-3Hz represents the formation compaction trend. Therefore, 0-3Hz is selected as the low-frequency component of the target layer of the well to simulate the formation compaction effect. Subtracting the low-frequency component from the original wave impedance can obtain the high-frequency component curve of the wave impedance without compaction, as shown in Figure 8 As shown, it can be seen that the difference between sand bodies at different depths is not obvious after removing the low-frequency component, and the numerical trends of sand body wave impedance are consistent.

[0092] Step 2: Establishment of low-frequency component data volume of three-dimensional seismic wave impedance

[0093] According to the characteristics of wave impedance value changing with depth, the range of low-frequency component of wave impedance representing reservoir compaction trend in the target layer is determined by generalized S transform time-frequency analysis. Then, the low-frequency component of seismic wave impedance is reconstructed by generalized S inverse transform to obtain the data volume of low-frequency component of seismic wave impedance. Then, it is corrected by logging low-frequency component. The schematic diagram of low-frequency section through the well is shown in the figure below. Fig. 9 .

[0094] Step 3: Establishment of decompaction coefficient of three-dimensional seismic wave impedance

[0095] According to the characteristics of low-frequency wave impedance value changing with depth due to compaction, the compaction trend line corresponding to the target layer section is determined, and then the wave impedance value of the target layer after decompaction is calculated; then the wave impedance values ​​before and after decompaction are used to calculate the wave impedance compaction coefficient and decompaction coefficient. The schematic diagram of the plane distribution of the target layer is shown in the figure. Fig.10 .

[0096] Step 4: Decompact seismic data reconstruction

[0097] The decompaction-corrected seismic impedance is inverted by establishing a low-frequency constrained inversion objective function, and then the decompaction-corrected reflection coefficient is obtained. The seismic record after decompaction correction is obtained by convolution using the seismic wavelet extracted from the wellside data. Fig.11a is the original seismic profile of the target layer of the two wells. The target layers of the two wells are fine sandstone with similar thickness, but the reflection characteristics are completely different. The difference in event axis reflection makes it difficult to accurately predict the sand body between the wells. The seismic de-compaction correction and reconstruction are carried out by the above method. The reconstructed profile is shown in the figure. Fig.11 b, The reflection amplitude of the sand body in the target layer near Well W11 has been improved. The reflection characteristic responses of the sand bodies in the target layers of the two wells are close, and the amplitude characteristics of the intermediate layers have also been significantly improved.

[0098] In summary, the present invention studies a seismic reconstruction method based on velocity low-frequency trend modeling. The method first reconstructs the low-frequency component of the well logging time domain wave impedance based on the generalized S transform, and calculates the low-frequency component of the seismic wave impedance based on the seismic velocity data body and the fitting relationship between density and velocity; then the low-frequency component of the seismic wave impedance is corrected by the low-frequency component of the well logging to obtain the corrected three-dimensional space seismic wave impedance low-frequency component data body; the compaction trend line corresponding to the target layer segment is determined, the wave impedance value of the target layer after decompaction is calculated, and the wave impedance decompaction coefficient is calculated to obtain a three-dimensional seismic compaction coefficient body; then the wave impedance relationship and the reflection coefficient mathematical relationship before and after decompaction are established, and then the mathematical relationship between multi-channel seismic records and seismic wavelets and multi-channel wave impedance differences is established; finally, under the constraint of the trend of the wave impedance low-frequency component, the wave impedance inversion objective function after decompaction is established, and the seismic record after decompaction correction is obtained by using the nonlinear inversion method. The reconstructed seismic data can effectively improve the prediction accuracy of thin reservoirs, reservoir properties, and reservoir oil content of deep depression reservoirs.

[0099] Beneficial effect: A seismic reconstruction method based on velocity low-frequency trend modeling. The method first reconstructs the low-frequency component of the well logging time domain wave impedance based on the generalized S transform, and calculates the low-frequency component of the seismic wave impedance based on the seismic velocity data body and the fitting relationship between density and velocity; then the low-frequency component of the seismic wave impedance is corrected by the low-frequency component of the well logging to obtain the corrected three-dimensional space seismic wave impedance low-frequency component data body; the compaction trend line corresponding to the target layer segment is determined, the wave impedance value of the target layer after decompaction is calculated, and the wave impedance decompaction coefficient is calculated to obtain a three-dimensional seismic compaction coefficient body; then the wave impedance relationship and the reflection coefficient mathematical relationship before and after decompaction are established, and then the mathematical relationship between multi-channel seismic records and seismic wavelets and multi-channel wave impedance differences is established; finally, under the constraint of the trend of the wave impedance low-frequency component, the wave impedance inversion objective function after decompaction is established, and the seismic record after decompaction correction is obtained by using the nonlinear inversion method. The reconstructed seismic data effectively improves the prediction accuracy of thin reservoirs, reservoir properties, and reservoir oil content of deep depression reservoirs.

[0100] The above specific implementation methods further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are only specific implementation methods of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A seismic reconstruction method based on velocity low-frequency trend modeling, characterized in that: The reconstruction method comprises: Step S1: convert the logging data into the time domain, perform frequency division processing on the logging wave impedance, and select the low-frequency component that matches the trend as the logging low-frequency component data body; Step S2: calculating the seismic wave impedance low-frequency component based on the seismic velocity data volume and the fitting relationship between the well logging density and the velocity, and correcting the seismic wave impedance low-frequency component using the well logging low-frequency component data volume to obtain a corrected three-dimensional space seismic wave impedance low-frequency component data volume; Step S3: determining the compaction trend line corresponding to the target layer segment according to the corrected three-dimensional spatial seismic wave impedance low-frequency component data body, calculating the wave impedance value of the target layer after de-compaction, and calculating the wave impedance de-compaction coefficient; Step S4: establishing the wave impedance relationship and the mathematical relationship of the reflection coefficient before and after decompaction, and establishing the mathematical relationship between the multi-channel seismic record and the seismic wavelet and the multi-channel wave impedance difference; Step S5: Under the constraint of the trend of the low-frequency component of the wave impedance, establish the wave impedance inversion objective function after decompaction, and use the nonlinear inversion method to obtain the compaction-corrected seismic record.

2. The seismic reconstruction method based on velocity low-frequency trend modeling according to claim 1, characterized in that: The step S1: converting the logging data into the time domain, performing frequency division processing on the logging wave impedance, and selecting the low-frequency component that matches the trend as the logging low-frequency component data body specifically includes: The logging data is used to calculate the time domain logging wave impedance data body, and the generalized S transform time-frequency spectrum analysis is used to determine the low-frequency component range of the wave impedance representing the reservoir compaction trend in the target layer well section; The generalized inverse S transform is used to reconstruct the low-frequency component of logging wave impedance and obtain the low-frequency component of logging wave impedance in time domain.

3. The seismic reconstruction method based on velocity low-frequency trend modeling according to claim 1, characterized in that: The step S2: calculating the seismic wave impedance low-frequency component based on the seismic velocity data body and the fitting relationship between the well logging density and the velocity, and correcting the seismic wave impedance component using the well logging low-frequency component to obtain the corrected three-dimensional space seismic wave impedance low-frequency component data body specifically includes: Based on the seismic migration velocity data and the interpreted main target layer data, the layer-controlled multi-constrained layer velocity inversion MCVI method is used to calculate the seismic layer velocity; Analyze the intersection diagram of target layer logging velocity and logging density to obtain the fitting formula of density and velocity, and apply it to convert the seismic layer velocity into formation density and calculate the seismic wave impedance body; Use generalized S-transform to obtain low-frequency wave impedance body; The low-frequency component of the logging wave impedance is used for correction to obtain a corrected three-dimensional seismic wave impedance low-frequency component data volume.

4. The seismic reconstruction method based on velocity low-frequency trend modeling according to claim 1, characterized in that: The step S3: determining the compaction trend line corresponding to the target layer segment according to the corrected three-dimensional spatial seismic wave impedance low-frequency component data volume, calculating the wave impedance value of the target layer after de-compaction, and calculating the wave impedance de-compaction coefficient specifically includes: According to the characteristics of low-frequency wave impedance value changing with depth due to compaction, the compaction trend line corresponding to the target layer section is determined, and the wave impedance value of the target layer after de-compaction is calculated; The wave impedance compaction coefficient is calculated using the wave impedance values ​​before and after decompaction, and the target layer logging and three-dimensional wave impedance compaction coefficient curves varying with depth are obtained.

5. The seismic reconstruction method based on velocity low-frequency trend modeling according to claim 1, characterized in that: In step S3, the difference between the wellbore seismic wave impedance compaction coefficient and the logging wave impedance decompaction coefficient is calculated, and the layer-controlled seismic wave impedance compaction coefficient error data body is established by using the Kriging interpolation correction technology in combination with the interpretation layer; The seismic wave impedance compaction coefficient is corrected to obtain a corrected three-dimensional seismic wave impedance compaction coefficient data volume.

6. The seismic reconstruction method based on velocity low-frequency trend modeling according to claim 1, characterized in that: The step S4: establishing the wave impedance relationship and the reflection coefficient mathematical relationship before and after decompaction, and establishing the mathematical relationship between the multi-channel seismic record and the seismic wavelet and the multi-channel wave impedance difference specifically includes: According to the nonlinear relationship between reflection coefficient and wave impedance and the differential operator, the relationship among reflection coefficient, multi-channel wave impedance difference and seismic record is established.

7. The seismic reconstruction method based on velocity low-frequency trend modeling according to claim 1, characterized in that: The step S5: establishing a decompacted wave impedance inversion objective function under the constraint of the wave impedance low-frequency component trend, and using a nonlinear inversion method to obtain a compacted corrected seismic record specifically comprises: A low-frequency constraint objective function is established, and the nonlinear inversion method is used to obtain the wave impedance after compaction correction and the reflection coefficient after decompaction correction. The seismic wavelets extracted from the wellside data are used to obtain the de-compaction corrected seismic records through convolution.

8. The seismic reconstruction method based on velocity low-frequency trend modeling according to claim 1, characterized in that: The nonlinear inversion method in step S5 adopts a spectral projection gradient algorithm to solve the wave impedance after compaction correction.

9. The seismic reconstruction method based on velocity low-frequency trend modeling according to claim 1, characterized in that: The step S5 in which the wave impedance inversion objective function after decompaction is established specifically includes: The multi-channel impedance inversion problem is expressed as in, w is the row vector of the wavelet time series, X low is the low-frequency component of wave impedance, obtained from logging wave impedance or seismic velocity spectrum; L is the low-pass filter operator; Y is the known multi-channel seismic record, The inverted reflection coefficient time series is sparse and laterally smooth; The synthetic seismic record is consistent with the actual seismic record; X low =LX is the trend constraint of the low-frequency component of wave impedance.

10. The seismic reconstruction method based on velocity low-frequency trend modeling according to claim 1, characterized in that: The step S5 of establishing the wave impedance inversion objective function after decompaction also includes: The wave impedance inversion problem after decompaction is expressed as Where C is the matrix composed of compaction coefficients; The semi-logarithm of the wave impedance after decompaction is obtained by inversion c ; Calculate the multi-channel reflection coefficient R after decompaction using the difference operator c ; Calculate the decompacted seismic record Y using the wavelet extracted from the wellbore seismic record c .

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