VSP Upstream and Downstream Wave Separation Method Based on Radon Domain AWT

Abstract

The present invention discloses a VSP up-going and down-going wave separation method based on Radon domain anisotropic wavelet transform, and relates to the field of seismic exploration. The present invention comprises the following steps: using Matlab software to read VSP data; using linear Radon transform to transform VSP data from time-space domain to time intercept-slowness domain; performing anisotropic wavelet transform on Radon domain to obtain decomposition coefficient matrix, and realizing sparse representation of up-going and down-going wave field information in VSP data; dividing and extracting the decomposition coefficient matrix, respectively retaining the coefficient matrix representing up-going and down-going waves, and then reconstructing the coefficient matrix representing up-going and down-going waves on Radon domain by anisotropic wavelet transform, and then performing inverse Radon transform to obtain up-going and down-going wave fields. The present invention can more thoroughly separate the up-going and down-going wave fields in VSP data, and the event axis in the wave field record is clearer and more coherent.

Description

Technical Field

[0001] The present invention relates to the field of seismic exploration, and more specifically to a VSP uplink and downlink wave separation method based on Radon domain anisotropic wavelet transform (AWT). Background Art

[0002] Conventional seismic exploration is a means of exciting seismic waves on the ground and arranging geophones on the ground to receive them. However, with the increasing difficulty of oil field exploration and development, the accuracy of seismic data obtained by conventional seismic exploration is far from meeting the needs of exploration. Therefore, the vertical seismic profile method, referred to as VSP (Vertical Seismic Profile) method, has been developed. It is a refined seismic exploration technology that uses a method of placing geophones vertically downward along the wellbore to receive seismic waves inside the formation. The seismic data obtained by this method has obvious advantages such as high signal-to-noise ratio, high resolution, and rich wave field information. In VSP, because the geophones are placed vertically downward along the wellbore inside the formation, they can receive longitudinal waves, converted waves, and even transverse waves. It can also provide the most direct correspondence between underground structures and ground parameter measurements, provide accurate time-depth conversion and velocity models for ground seismic data processing and interpretation, reliably identify the geological layers of seismic reflection layers, and use the obtained data to study formation lithology and reservoir properties. Therefore, VSP technology is very important both in the field of exploration and in the field of development.

[0003] The original VSP data contains rich wave field information and is relatively complex. It contains both upgoing and downgoing waves, so it is very difficult to interpret the formation directly using VSP data. Therefore, the VSP wave field is separated with high fidelity to fully reflect the wave field characteristics of different waves, so as to better calibrate geological layers, interpret lithology and reservoir properties, etc. Therefore, the separation of upgoing and downgoing waves is the key in VSP data processing, and studying a more effective upgoing and downgoing wave separation method is an important research direction. Existing upgoing and downgoing wave separation methods for VSP data, such as the linear Radon transform separation method and the Curvelet transform separation method, all have certain limitations, which makes the separation effect not very good. Therefore, the present invention aims to study a more effective upgoing and downgoing wave separation method, that is, a VSP upgoing and downgoing wave separation method based on Radon domain AWT. Summary of the invention

[0004] In view of the above reasons, the present invention provides a VSP uplink and downlink separation method based on Radon domain AWT.

[0005] In order to achieve the above object, the present invention adopts the following technical solution:

[0006] A VSP uplink and downlink separation method based on Radon domain AWT includes the following steps:

[0007] Matlab software was used to read VSP data;

[0008] The VSP data were transformed from the time-space tz domain to the time intercept-slowness τ-p domain using a linear Radon transform;

[0009] AWT is performed in the Radon transform domain to obtain the decomposition coefficient matrix, which realizes the sparse representation of the up- and down-going wave field information in the VSP data;

[0010] The Radon domain AWT decomposition coefficient matrix is ​​divided and extracted, and the coefficients representing the upgoing wave field information are retained. The retained coefficients are then reconstructed by AWT, and then the Radon inverse transform is performed to obtain the upgoing wave field.

[0011] Optionally, the method further includes partitioning and extracting the decomposed coefficient matrix, retaining coefficients representing the downlink wave field information, performing AWT reconstruction on the retained coefficients, and then performing inverse Radon transform to obtain the downlink wave field.

[0012] Optionally, a linear Radon transform is used to transform the VSP data from the tz domain to the τ-p domain. The specific operation is as follows:

[0013] Assume u(t,z) is the VSP raw data, where t is time and z is offset; U(τ,p) is the τ-p domain data after Radon transformation, where τ = t-pz is the time intercept and p = dt / dz is the ray parameter; the τ-p forward transformation formula is:

[0014]

[0015] Optionally, the AWT formula is as follows:

[0016]

[0017] Where x = [x1 x2] T is the number on the x-axis of the rectangular coordinate plane, b=[b1 b2] T are the displacements in the x1 and x2 directions respectively, a is the scale factor, is the rotation factor; ε is the attenuation factor, φ ε is anisotropic two-dimensional wavelet basis function.

[0018] Optional, anisotropic 2D wavelet basis function φ ε The mathematical expression is as follows:

[0019]

[0020] Wherein, y represents the number on the y-axis of the rectangular coordinate plane.

[0021] Performing AWT on the τ-p domain obtained by Radon transform means substituting the τ-p domain data into formula (3), that is, replacing x and y in formula (3) with τ and p; then substituting the obtained basis function into formula (2), and at this time, f(x) in formula (2) is replaced by U(τ, p), and x is replaced by τ.

[0022] Optionally, the AWT reconstruction formula is as follows:

[0023]

[0024] in, ω is a frequency variable.

[0025] Then, the Radon domain AWT decomposition coefficient matrix is ​​divided, and the coefficient matrices corresponding to the upgoing and downgoing wave field information are extracted respectively. Then, the coefficients representing the upgoing and downgoing waves are reconstructed by AWT according to formula (4), and the τ-p domain data of the upgoing and downgoing waves can be obtained respectively.

[0026] The formula for the inverse Radon transform is as follows:

[0027]

[0028] Then, according to formula (5), the τ-p domain data corresponding to the upgoing wave and the downgoing wave are subjected to inverse Radon transformation respectively, and the tz domain data of the upgoing wave and the downgoing wave can be obtained.

[0029] Through the above technical solutions, it can be known that compared with the prior art, the present invention discloses a VSP up-down and down-going wave separation method based on Radon domain AWT. The method is first applied to the up-down and down-going wave separation processing of simulated VSP data, and compared with the results obtained by the linear Radon transform separation method and the Curvelet transform separation method, it is found that the event axis in the up-down and down-going wave field obtained by the method is clearer and has better continuity. Then it is applied to the separation processing of up-down and down-going waves of actual VSP data, and compared with the separation results of the traditional linear Radon transform method, it is found that the method is superior to the traditional linear Radon transform separation method, and can more thoroughly separate the up-down and down-going wave field in the actual VSP data, and the event axis in the wave field is clearer and more coherent. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0031] Figure 1 It is a schematic diagram of the process of the present invention;

[0032] Figure 2 This is the original record diagram of the model-VSP of the present invention;

[0033] Figure 3 The upgoing wave separated by the linear Radon transform method of the model of the present invention;

[0034] Figure 4 The downlink wave separated by the linear Radon transform method is the model of the present invention;

[0035] Figure 5 The upgoing wave separated by the Curvelet transform method of the model of the present invention;

[0036] Figure 6 The downlink wave separated by the Curvelet transform method of the model of the present invention;

[0037] Figure 7 The upgoing wave separated by the Radon domain AWT method is model 1 of the present invention;

[0038] Figure 8 This is the downlink wave separated by the Radon domain AWT method based on the model 1 of the present invention;

[0039] Fig. 9 This is the original VSP record diagram of Model 2 of the present invention;

[0040] Fig.10 The upgoing wave separated by the model two linear Radon transform method of the present invention;

[0041] Fig.11 It is the downlink wave separated by the model two linear Radon transform method of the present invention;

[0042] Fig.12 The upgoing wave separated by the Curvelet transform method of model 2 of the present invention;

[0043] Fig.13 The downlink wave separated by the Curvelet transform method of model 2 of the present invention;

[0044] Fig.14This is the upgoing wave separated by the Radon domain AWT method based on the model 2 of the present invention;

[0045] Fig.15 This is the downlink wave separated by the Radon domain AWT method based on the model 2 of the present invention;

[0046] Fig.16 This is the original VSP record diagram of Model 3 of the present invention;

[0047] Fig.17 The upgoing wave separated by the model trilinear Radon transform method of the present invention;

[0048] Fig.18 It is the downlink wave separated by the trilinear Radon transform method of the model of the present invention;

[0049] Fig.19 The upgoing wave separated by the Curvelet transform method of model 3 of the present invention;

[0050] Fig. 20 It is the downlink wave separated by the Curvelet transform method of model 3 of the present invention;

[0051] Fig.21 This is the upgoing wave separated by the Radon domain AWT method based on the model 3 of the present invention;

[0052] Fig. 22 This is the downlink wave separated by the Radon domain AWT method based on the model 3 of the present invention;

[0053] Fig.23 It is the original record of the actual data of VSP of the present invention;

[0054] Fig.24 The linear Radon transform method is used to process the upgoing wave record of VSP actual data in the present invention;

[0055] Fig.25 The present invention uses the linear Radon transform method to process the down-going wave record of the VSP actual data;

[0056] Fig.26 The present invention uses the Radon domain AWT method to process the upgoing wave records of VSP actual data;

[0057] Fig. 27 The present invention uses the Radon domain AWT method to process the downlink wave record of VSP actual data. DETAILED DESCRIPTION

[0058] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0059] The embodiment of the present invention discloses a VSP uplink and downlink separation method based on Radon domain AWT, such as Figure 1 As shown, the specific steps include:

[0060] Step 1: Use Matlab software to read VSP data;

[0061] Step 2: Use linear Radon transform to transform VSP data from tz domain to τ-p domain;

[0062] Let u(t,z) be the VSP raw data, where t is time and z is offset. Let U(τ,p) be the τ-p domain data after Radon transformation, where τ=t-pz is the time intercept, p=dt / dz is the ray parameter (or apparent slowness), and apparent slowness is the inverse of apparent velocity.

[0063] The τ-p positive transformation is:

[0064]

[0065] Step 3: Perform anisotropic wavelet transform (AWT) in the Radon domain to obtain the decomposition coefficient matrix, which can realize the sparse representation of the up- and down-going wave field information in the VSP data;

[0066] Because: The continuous two-dimensional wavelet transform can usually be defined as

[0067]

[0068] In the above formula, x=[x1 x2] T is the number on the x-axis of the rectangular coordinate plane, b=[b1 b2] T are the displacements in the x1 and x2 directions respectively, a is the scale factor, is the rotation factor; ε is the attenuation factor, φ ε is anisotropic two-dimensional wavelet basis function.

[0069] The attenuation factor ε can make the two-dimensional wavelet basis protrude in any direction, thereby achieving the purpose of anisotropy. The anisotropic two-dimensional wavelet basis function is:

[0070]

[0071] Where y is the number on the y-axis of the rectangular coordinate plane.

[0072] In summary, the formula for AWT is:

[0073]

[0074] Performing AWT on the τ-p domain obtained by Radon transform means substituting the τ-p domain data into formula (3), that is, replacing x and y in formula (3) with τ and p; then substituting the obtained basis function into formula (4), and at this time, f(x) in formula (4) is replaced by U(τ, p), and x is replaced by τ.

[0075] Step 4: Divide and extract the Radon domain AWT decomposition coefficient matrix, retain the coefficient matrices corresponding to the upgoing wave and downgoing wave field information respectively, and then perform AWT reconstruction on the coefficients representing the upgoing wave and downgoing wave respectively, and then perform Radon inverse transform to obtain the upgoing wave and downgoing wave field respectively.

[0076] The AWT reconstruction formula is:

[0077]

[0078] in, ω is a frequency variable.

[0079] Then, after the AWT decomposition coefficient matrix in the Radon domain is divided and extracted into the upgoing wave and downgoing wave field coefficients, the coefficients representing the upgoing wave and downgoing wave are reconstructed by AWT according to formula (5) to obtain the τ-p domain data of the upgoing wave and downgoing wave.

[0080] The formula for the inverse Radon transform is as follows:

[0081]

[0082] Then, the τ-p domain data of the upgoing wave and the downgoing wave are subjected to inverse Radon transformation according to formula (6) to obtain the tz domain data of the upgoing wave and the downgoing wave.

[0083] Combination Figure 2—27 It can be seen that the Radon domain AWT up-down wave separation method was verified by applying VSP theoretical model experiments under different conditions such as horizontal formations, inclined formations and cross-well seismic, and compared with the linear Radon transform method and Curvelet transform method in traditional separation methods. The results show that the linear Radon transform method is affected by the false frequency and truncation effect, the τ-p domain energy will diverge, and the up-down wave energy will affect each other, which will eventually lead to incomplete separation of VSP up-down waves and affected the clarity and continuity of the event axis; although the Curvelet transform method can separate the up-down waves, the event axis is blurred compared with the original VSP record, the effective signal is down-converted, and the event axis of the up-down waves has a more serious distortion phenomenon; the Radon domain AWT method can not only more thoroughly separate the VSP up-down wave field, but also better retain the event axis information, so that the event axis of the up-down waves is clear and coherent. Therefore, the method proposed in this patent is superior to the traditional linear Radon transform method and Curvelet transform method in the up-down wave separation effect. Finally, this method is applied to the separation of upgoing and downgoing waves in actual VSP data, and by comparing the separation results with the traditional linear Radon transform method, it can be found that this method is superior to the traditional linear Radon transform method, that is, it can more thoroughly separate the upgoing and downgoing wave fields in actual VSP data, and the wave field characteristics are more obvious, and the upgoing and downgoing wave events are clearer and more coherent. Both the simulation data experiment and the actual data processing have verified the superiority of this method in the separation of VSP upgoing and downgoing waves.

[0084] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0085] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A VSP uplink and downlink separation method based on Radon domain AWT, characterized in that: The following steps are involved: Matlab software was used to read VSP data; The VSP data were transformed from the time-space domain to the time intercept-slowness domain using a linear Radon transform; Anisotropic wavelet transform (AWT) is performed in the Radon domain to obtain the decomposition coefficient matrix, which realizes the sparse representation of the up-and-down wave field information in the VSP data. The coefficient matrix obtained by AWT decomposition in Radon domain is divided and extracted, and the coefficients representing the upgoing wave field information are retained. Then, the retained coefficients are reconstructed by AWT, and then the inverse Radon transform is performed to obtain the upgoing wave field. It also includes partitioning and extracting the decomposed coefficient matrix, retaining the coefficients representing the downlink wave field information, and then performing AWT reconstruction on the retained coefficients, followed by Radon inverse transformation to obtain the downlink wave field; The linear Radon transform is used to transform the VSP data from the time-space domain to the time intercept-slowness domain as follows: Assume u(t,z) is the VSP raw data, where t is time and z is offset; U(τ,p) is the τ-p domain data after Radon transformation, where τ = t-pz is the time intercept and p = dt / dz is the ray parameter; the τ-p forward transformation formula is: The AWT formula is as follows: Where x = [x1 x2] T is the number on the x-axis of the rectangular coordinate plane, b=[b1 b2] T are the displacements in the x1 and x2 directions respectively, a is the scale factor, is the rotation factor; ε is the attenuation factor, φ ε is anisotropic two-dimensional wavelet basis function; Anisotropic 2D wavelet basis function φ ε The mathematical expression is as follows: To perform AWT on the τ-p domain obtained by Radon transform, the τ-p domain data is substituted into formula (3), that is, x and y in formula (3) are replaced by τ and p; then the obtained basis function is substituted into formula (2), and at this time f(x) in formula (2) is replaced by U(τ, p), and x is replaced by τ; The AWT reconstruction formula is as follows: in, ω is the frequency variable; Then, the coefficient matrix obtained by AWT decomposition in the Radon domain is divided, and the coefficient matrices corresponding to the upgoing and downgoing wave field information are extracted respectively. Then, the coefficients representing the upgoing and downgoing waves are reconstructed by AWT according to formula (4), and the τ-p domain data of the upgoing and downgoing waves can be obtained respectively. The formula for the inverse Radon transform is as follows: Then, according to formula (5), the τ-p domain data corresponding to the upgoing wave and the downgoing wave are subjected to inverse Radon transformation respectively, and the tz domain data of the upgoing wave and the downgoing wave can be obtained.

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