Improved up-down wavefield joint deconvolution method and device

Abstract

The application discloses an improved up-and-down wave field joint deconvolution method and device, and belongs to the technical field of seismic exploration processing. Based on a wave field propagation model which is more in line with the real propagation process of up-and-down wave fields, the application provides an improved up-and-down wave field joint deconvolution method and device, the method comprising the following steps: moving down the up wave field by two water depths of geophones, adaptively subtracting the up wave field from the down wave field, then inverting the above result, and finally folding the above inverse matrix and the up wave field to obtain the formation reflection coefficient. The improved up-and-down wave field joint deconvolution method is simple and easy to implement, can effectively eliminate the noise generated in the traditional method, and improves the signal-to-noise ratio of seismic data. The application can be used in the field of seismic data processing.

Description

Technical Field

[0001] The invention belongs to the field of seismic exploration processing, and relates to an uplink and downlink wave field joint deconvolution method, in particular to an improved uplink and downlink wave field joint deconvolution method and device. Background Art

[0002] Joint uplink and downlink wavefield deconvolution is a water layer multiple attenuation technique in seismic data processing. It is widely used to suppress multiple waves in seismic data from submarine cables (OBCs) or ocean bottom nodes (OBNs). Four-component geophones are typically used to receive OBC or OBN seismic data, which contain water layer multiple waves at both the shot point and the receiver point. The presence of these water layer multiple waves seriously affects the final imaging of the seismic data and, in turn, the final structural interpretation. Dual-detection synthesis is typically used to eliminate water layer multiple waves at the receiver point, while joint uplink and downlink wavefield deconvolution is often used to eliminate water layer multiple waves at the shot point.

[0003] The basic principle of the currently popular uplink and downlink wavefield joint deconvolution technique is that the uplink wavefield is a theoretical model of the convolution of the downlink wavefield and the formation reflection coefficient. The formation reflection coefficient is calculated through joint deconvolution of the uplink and downlink wavefields. Research has found that this model generates a large number of false signals when calculating the formation reflection coefficient, resulting in an inability to accurately describe the propagation characteristics of the wavefield and, consequently, the basic characteristics of the uplink and downlink wavefields received at the receiver. Summary of the Invention

[0004] The present invention is based on the discovery that the upgoing wavefield on the seabed is the convolution of the source wavelet, water depth and formation reflection coefficient, and the downgoing wavefield is the sum of the convolution of the source wavelet and water depth and the water depth of two detection points shifted downward from the upgoing wavefield. The formation reflection coefficient obtained based on this model can overcome the deficiency of the existing joint deconvolution technology of upgoing and downgoing wavefields, which generates a large number of false signals when calculating the formation reflection coefficient.

[0005] Therefore, the object of the present invention is to provide an improved uplink and downlink wavefield joint deconvolution method, which can effectively eliminate the influence of water layer multiple wave interference at the shot point end and improve the signal-to-noise ratio of seismic data.

[0006] Another object of the present invention is to provide a device for applying the improved uplink and downlink wavefield joint deconvolution method, which is conducive to the promotion and application of the improved uplink and downlink wavefield joint deconvolution method.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is:

[0008] An improved uplink and downlink wavefield joint deconvolution method comprises the following steps performed in sequence:

[0009] S1. Separate the upgoing wavefield UP and the downgoing wavefield DOWN in the seismic data;

[0010] S2. Shift the upgoing wave field UP down by two detection points by the water depth H to form UP*(-2H);

[0011] S3. adaptively subtract UP*(-2H) from the downlink wave field DOWN to obtain the matrix Z;

[0012] S4. Find the inverse matrix Z of matrix Z -1 ;

[0013] S5. Set the uplink wave field UP and Z -1 Perform convolution to obtain the formation reflection coefficient R.

[0014] As a first limitation to the invention of an improved method for joint deconvolution of uplink and downlink wave fields,

[0015] In step S1, the seismic data includes submarine cable seismic data or submarine node seismic data;

[0016] The separation method includes separation by double-check synthesis technology.

[0017] As a second limitation of the improved uplink and downlink wavefield joint deconvolution method, in step S1, after the separation, the step further includes removing ghost waves at the detection point end.

[0018] As a third limitation of the invention of an improved uplink and downlink wavefield joint deconvolution method, in step S2, the method of moving the two detection points downward by the water depth H includes moving the initial position in the seismic trace to a time of 2H / V and extending the trace head;

[0019] Among them, H is the water depth and V is the propagation speed of the earthquake source in the water.

[0020] As a fourth limitation of the invention of an improved uplink and downlink wavefield joint deconvolution method, in step S5, the formula for obtaining the formation reflection coefficient R is as shown in formulas 1 to 4,

[0021] UP=W*H*R Formula 1

[0022] Z=DOWN-UP*(-2H) Formula 2

[0023] Z*Z -1 =E Formula 3

[0024] R=UP*Z -1 Formula 4

[0025] Where W is the source wavelet, which belongs to the downgoing wavefield; H is the water depth, which provides the time shift; DOWN is the downgoing wavefield; UP is the upgoing wavefield; E is the unit matrix; and R is the formation reflection coefficient.

[0026] The present invention also provides a device for applying the above-mentioned improved upgoing and downgoing wavefield joint deconvolution method, the device comprising an upgoing and downgoing wavefield separation module, an upgoing wavefield downward shift module, an adaptive subtraction module, a matrix inversion module, a formation reflection coefficient determination module and a central control module;

[0027] The upgoing wavefield and downgoing wavefield separation module is used to separate the submarine cable seismic data or the submarine node seismic data into the upgoing wavefield UP and the downgoing wavefield DOWN through the double-detection synthesis technology;

[0028] The upgoing wavefield downward shift module is used to shift the upgoing wavefield UP downward by two detection points water depth H to form UP*(-2H);

[0029] The adaptive subtraction module is used to adaptively subtract UP*(-2H) from the downlink wave field DOWN to obtain a matrix Z;

[0030] The matrix inversion module is used to obtain the inverse matrix Z of the matrix Z -1 ;

[0031] The formation reflection coefficient obtaining module is used to convert the upgoing wave field UP and Z -1 Perform convolution to obtain the formation reflection coefficient R;

[0032] The central control module is used to control the signal flow and data processing in the upgoing wavefield and downgoing wavefield separation module, the upgoing wavefield downward movement module, the adaptive subtraction module, the matrix inversion module and the formation reflection coefficient acquisition module.

[0033] Due to the adoption of the above technical solution, the present invention has the following technical advancements compared with the prior art:

[0034] ① Traditional upgoing and downgoing wavefield joint deconvolution technology is based on a theoretical model where the upgoing wavefield is the convolution of the downgoing wavefield and the formation reflection coefficient. However, the present invention considers the upgoing wavefield to be the convolution of the source wavelet, water depth, and formation reflection coefficient, while the downgoing wavefield is the convolution of the source wavelet and water depth and the sum of the water depths of two detection points shifted down from the upgoing wavefield. Based on this, a new wavefield propagation model is constructed. Compared with the traditional model, the present invention takes the convolution of the source and water depth into account when constructing the downgoing wavefield model, resulting in a model that better reflects the actual propagation process of the upgoing and downgoing wavefields.

[0035] ② Based on a new wavefield propagation model, the present invention establishes a new joint deconvolution method for upgoing and downgoing wavefields. This method shifts the upgoing wavefield down by two detection points, then subtracts it from the downgoing wavefield. The inverse matrix of this result is then calculated. Finally, the inverse matrix is ​​convolved with the upgoing wavefield to obtain the formation reflection coefficient. This method theoretically only produces the formation reflection coefficient, without the extra noise generated by the original model, thus eliminating multiple waves in the water layer at the shot point.

[0036] ③ The improved uplink and downlink wavefield joint deconvolution method provided by the present invention can effectively eliminate the noise generated by the traditional uplink and downlink wavefield joint deconvolution method and improve the signal-to-noise ratio of seismic data.

[0037] ④ The improved uplink and downlink wave field joint deconvolution method provided by the present invention is easy to implement and operate in exploration, and is conducive to promotion and application.

[0038] In summary, based on a wavefield propagation model that more closely reflects the actual propagation process of upgoing and downgoing wavefields, the present invention provides an improved method and apparatus for joint deconvolution of both upgoing and downgoing wavefields. The method involves adaptively subtracting the upgoing wavefield from the downgoing wavefield after shifting it down by two detector depths. The inverse matrix of this result is then calculated, and finally, the inverse matrix is ​​convolved with the upgoing wavefield to determine the formation reflection coefficient. The improved joint deconvolution method for both upgoing and downgoing wavefields provided by the present invention is simple and easy to implement, effectively eliminating noise generated by traditional methods and improving the signal-to-noise ratio of seismic data.

[0039] The present invention provides an improved uplink and downlink wave field joint deconvolution method and device, which can be applied to the field of seismic data processing. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The present invention will be described in further detail below with reference to the accompanying drawings and specific embodiments.

[0041] Figure 1 This is a schematic diagram of the uplink and downlink wave field propagation model proposed by the present invention in Example 1 of the present invention;

[0042] Figure 2 This is a flow chart of an improved uplink and downlink wavefield joint deconvolution method in Example 1 of the present invention;

[0043] Figure 3 This is a schematic diagram of a traditional theoretical model in Example 1 of the present invention;

[0044] Figure 4 Schematic diagram of obtaining formation reflection coefficient using the uplink and downlink wavefield joint deconvolution method constructed based on the traditional theoretical model in Example 1 of the present invention;

[0045] Figure 5Schematic diagram of obtaining formation reflection coefficients for reconstruction using the uplink and downlink wavefield joint deconvolution method constructed based on the traditional theoretical model in Example 1 of the present invention;

[0046] Figure 6 Schematic diagram of the process of obtaining the double-layer reflection coefficient using the uplink and downlink wavefield joint deconvolution method constructed based on the traditional theoretical model in Example 1 of the present invention;

[0047] Figure 7 This is a graph showing the results of obtaining three-layer reflection coefficients using the uplink and downlink wavefield joint deconvolution method based on the traditional theoretical model in Example 1 of the present invention;

[0048] Figure 8 This is a graph showing the results of obtaining three-layer reflection coefficients using the improved uplink and downlink wavefield joint deconvolution method in Example 1 of the present invention;

[0049] Figure 9 This is a seismic single shot record obtained by applying the traditional up- and down-wave field joint deconvolution method in Example 1 of the present invention;

[0050] Figure 10 This is a seismic single shot record obtained by applying the improved uplink and downlink wavefield joint deconvolution method in Example 1 of the present invention;

[0051] Figure 11 This is a structural block diagram of an apparatus using an improved upgoing and downgoing wavefield joint deconvolution method provided in Example 2 of the present invention. In the diagram: 1 - central control module, 2 - upgoing and downgoing wavefield separation module, 3 - upgoing wavefield downward shift module, 4 - adaptive subtraction module, 5 - matrix inversion module, 6 - formation reflection coefficient determination module. DETAILED DESCRIPTION

[0052] The present invention will be further described in detail below by means of specific embodiments in conjunction with the accompanying drawings. It should be understood that the embodiments described are preferred examples of the present invention and are only used to explain the present invention and are not intended to limit the present invention.

[0053] Example 1 An improved uplink and downlink wavefield joint deconvolution method

[0054] (1) The present invention summarizes a new uplink and downlink wave field propagation model by carefully analyzing and studying the seismic waves received by the seabed detector and its propagation process; the schematic diagram of the uplink and downlink wave field propagation model proposed by the present invention is shown in FIG. Figure 1 As shown, the present invention considers that the upgoing wavefield is the convolution of the source wavelet, water depth and formation reflection coefficient, and the downgoing wavefield is the convolution of the source wavelet and water depth and the sum of the water depth of two detection points shifted downward by the upgoing wavefield.

[0055] By reverse analysis of the propagation model, an improved method for joint deconvolution of uplink and downlink wave fields is obtained. The method specifically includes the following steps:

[0056] S1. On OBC or OBN seismic data, separate the upgoing and downgoing wavefields using dual-detection synthesis technology. After removing ghost waves at the detector end, the upgoing and downgoing wavefields UP and DOWN are obtained.

[0057] S2. Calculate the time 2H / V, where H is the depth of the seawater and V is the propagation velocity of the earthquake source in the seawater;

[0058] Move the initial position in the seismic trace to the time of 2H / V and extend the trace head by at least 2H / V;

[0059] That is, the upgoing wave field UP is shifted down by two detection points by the water depth H to form UP*(-2H);

[0060] S3. adaptively subtract UP*(-2H) from the downlink wave field DOWN to obtain the matrix Z;

[0061] S4. Find the inverse matrix Z of matrix Z -1 ;

[0062] S5. Set the uplink wave field UP and Z -1 Perform convolution to obtain the formation reflection coefficient R;

[0063] The formulas used to calculate the formation reflection coefficient R are shown in formulas 1 to 4.

[0064] UP=W*H*R Formula 1

[0065] Z=DOWN-UP*(-2H) Formula 2

[0066] Z*Z -1 =E Formula 3

[0067] R=UP*Z -1 Formula 4

[0068] Where W is the source wavelet, which belongs to the downgoing wavefield; H is the water depth, which provides the time shift; DOWN is the downgoing wavefield; UP is the upgoing wavefield; E is the unit matrix; and R is the formation reflection coefficient.

[0069] (2) In order to investigate the difference between the improved uplink and downlink wavefield joint deconvolution method provided by the present invention and the uplink and downlink wavefield joint deconvolution method established based on the traditional theoretical model, the following experiment was conducted.

[0070] (1) The impact of different methods on the formation reflection coefficient

[0071] The currently popular up-down wavefield joint deconvolution technology in the industry is mostly based on the theoretical model of the article "Surface multiple attenuation by up-down wavefield deconvolution" published by Brunellière J et al. at the 2004 SEG Annual Meeting. Its basic principle is that the up-down wavefield is the convolution of the down-down wavefield and the formation reflection coefficient, and the formation reflection coefficient is obtained by the joint deconvolution of the up-down wavefield. The traditional theoretical model is shown in the figure below. Figure 3 As shown, the formulas for calculating the formation reflection coefficient based on the theoretical model in the comparison document are shown in Formulas 5 and 6.

[0072] U=D*R Formula 5

[0073]

[0074] Where U is the upgoing wave field; D is the downgoing wave field; and R is the formation reflection coefficient.

[0075] The schematic diagram of the up- and down-wave field joint deconvolution method based on the traditional theoretical model to obtain the formation reflection coefficient is shown in the figure. Figure 4 As shown, the present invention simulates a single layer of stratum by pulse signal, and replays the process of obtaining the stratum reflection coefficient by the up-down wave field joint deconvolution method based on the traditional theoretical model, as shown in the schematic diagram. Figure 5 As shown. Figures 4-5 It can be seen that the single-layer reflection coefficient obtained by the joint deconvolution method of uplink and downlink wave fields constructed based on the traditional theoretical model is correct.

[0076] Because the seabed stratum structure is complex and is not single but multi-layered, the present invention uses pulse signal simulation to expand the original single-layer stratum into double and triple layers, and further obtains the double-layer reflection coefficient and triple-layer reflection coefficient using the up-down wave field joint deconvolution method constructed based on the traditional theoretical model. The schematic diagram of the process of obtaining the double-layer reflection coefficient using the up-down wave field joint deconvolution method constructed based on the traditional theoretical model is shown in the figure. Figure 6 As shown in the figure, the three-layer reflection coefficient is obtained by the joint deconvolution method of uplink and downlink wave fields constructed based on the traditional theoretical model. Figure 7 shown.

[0077] Depend on Figures 6-7 It can be seen that when the traditional uplink and downlink wave field joint deconvolution method is used to obtain the two-layer reflection coefficient or the three-layer reflection coefficient, the obtained double-layer reflection coefficient and the three-layer reflection coefficient both have a lot of noise, which cannot accurately describe the propagation characteristics of seismic waves, and thus cannot truly reflect the seabed geological structure.

[0078] By using pulse signal simulation, the original single-layer stratum is expanded into double and triple layers, and the improved up-down wave field joint deconvolution method proposed in this invention is applied to obtain the double-layer reflection coefficient and triple-layer reflection coefficient. Figure 8 As shown. Figure 8 It can be seen that the formation reflection coefficient obtained by the improved uplink and downlink wavefield joint deconvolution method proposed in the present invention does not have noise, which is consistent with the uplink and downlink wavefield propagation characteristics at the detection point end.

[0079] Depend on Figures 7-8 Comparison of the results shows that the improved uplink and downlink wavefield joint deconvolution method proposed in the present invention effectively eliminates the noise generated by the traditional method, improves the signal-to-noise ratio of seismic data, and also shows that the theoretical model of this method can well describe the propagation characteristics of seismic waves.

[0080] (2) The impact of different up- and down-wave field joint deconvolution methods on seismic processing results

[0081] The formation reflection coefficient obtained by the traditional up- and down-going wave field joint deconvolution method contains residual tails (such as Figure 7 The seismic single shot record obtained by this method is shown in Figure 9 As shown;

[0082] The formation reflection coefficient (such as Figure 8 As shown in Figure 2, this method truly restores the formation reflection coefficient without any extra noise. The seismic single shot record obtained by this method is shown in Figure 2. Figure 10 shown.

[0083] Depend on Figures 9-10 It can be seen that the seismic single-shot record obtained by applying the traditional uplink and downlink wavefield joint deconvolution method has residual multiple waves, resulting in false phase axes; while the seismic single-shot record obtained by applying the improved uplink and downlink wavefield joint deconvolution method proposed in the present invention can effectively avoid the defects of residual multiple waves or false phase axes.

[0084] Example 2: A device using an improved uplink and downlink wavefield joint deconvolution method

[0085] This embodiment provides a device that applies an improved uplink and downlink wavefield joint deconvolution method. The block diagram of the device is as follows: Figure 11 As shown, it includes an upgoing wavefield and downgoing wavefield separation module 2, an upgoing wavefield downward shift module 3, an adaptive subtraction module 4, a matrix inversion module 5, a formation reflection coefficient calculation module 6 and a central control module 1, which are specifically as follows:

[0086] (1) The upgoing wavefield and downgoing wavefield separation module 2 is used to separate the upgoing wavefield and the downgoing wavefield from the submarine cable seismic data or the submarine node seismic data by using the double detection synthesis technology, and after removing the ghost waves at the detection point end, the upgoing wavefield UP and the downgoing wavefield DOWN are obtained;

[0087] (2) The upgoing wave field downward shift module 3 is used to shift the upgoing wave field UP downward by two detection points water depth H to form UP*(-2H);

[0088] (3) The adaptive subtraction module 4 is used to adaptively subtract UP*(-2H) from the downlink wave field DOWN to obtain the matrix Z;

[0089] (4) The matrix inversion module 5 is used to obtain the inverse matrix Z of the matrix Z -1 ;

[0090] (5) Formation reflection coefficient calculation module 6 is used to calculate the upgoing wave field UP and Z -1 Perform convolution to obtain the formation reflection coefficient R. The formulas used to obtain the formation reflection coefficient R are shown in formulas 1 to 4.

[0091] UP=W*H*R Formula 1

[0092] Z=DOWN-UP*(-2H) Formula 2

[0093] Z*Z -1 =E Formula 3

[0094] R=UP*Z -1 Formula 4

[0095] Where W is the source wavelet, which belongs to the downgoing wavefield; H is the water depth, which provides the time shift; DOWN is the downgoing wavefield; UP is the upgoing wavefield; E is the unit matrix; and R is the formation reflection coefficient.

[0096] (6) The central control module 1 is used to control the signal flow and data processing in the upgoing wavefield and downgoing wavefield separation module 2, the upgoing wavefield downward movement module 3, the adaptive subtraction module 4, the matrix inversion module 5 and the formation reflection coefficient calculation module 6.

[0097] The above description is merely an optional embodiment of the present disclosure and is not intended to limit the present disclosure. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present disclosure shall be included in the scope of protection of the present disclosure.

Claims

1. An improved uplink and downlink wavefield joint deconvolution method, characterized in that: The method comprises the following steps performed in sequence: S1. Separate the upgoing wavefield UP and the downgoing wavefield DOWN in the seismic data; S2. Shift the upgoing wave field UP down by two detection points by the water depth H to form UP*(-2H); S3. adaptively subtract UP*(-2H) from the downlink wave field DOWN to obtain the matrix Z; S4. Find the inverse matrix Z of matrix Z -1 ; S5. Set the uplink wave field UP and Z -1 Perform convolution to obtain the formation reflection coefficient R; Among them, in step S2, The method of shifting the water depth H of the two detection points downwards comprises shifting the initial position in the seismic trace to a time of 2H / V and extending the trace head; wherein H is the water depth of the detection point and V is the propagation velocity of the earthquake source in water; In step S5, the formula for obtaining the formation reflection coefficient R is shown in formulas 1 to 4. UP=W*H*R Formula 1 Z=DOWN-UP*(-2H) Formula 2 Z*Z -1 =E Formula 3 R=UP*Z -1 Formula 4 Where W is the source wavelet, which belongs to the downgoing wavefield; H is the water depth of the receiver point, which provides the time shift; DOWN is the downgoing wavefield; UP is the upgoing wavefield; E is the unit matrix; and R is the formation reflection coefficient.

2. The improved uplink and downlink wavefield joint deconvolution method according to claim 1, characterized in that: In step S1, the seismic data includes submarine cable seismic data or submarine node seismic data; The separation method includes separation by double-check synthesis technology.

3. The improved uplink and downlink wavefield joint deconvolution method according to claim 1, characterized in that: In step S1, after the separation, the ghost waves at the detection point end are removed.

4. The device using the improved uplink and downlink wavefield joint deconvolution method according to any one of claims 1 to 3, characterized in that: The device includes an upgoing wave field and a downgoing wave field separation module, an upgoing wave field downward movement module, an adaptive subtraction module, a matrix inversion module, a formation reflection coefficient obtaining module and a central control module; The upgoing wavefield and downgoing wavefield separation module is used to separate the submarine cable seismic data or the submarine node seismic data into the upgoing wavefield UP and the downgoing wavefield DOWN through the double-detection synthesis technology; The upgoing wavefield downward shift module is used to shift the upgoing wavefield UP downward by two detection points water depth H to form UP*(-2H); The adaptive subtraction module is used to adaptively subtract UP*(-2H) from the downlink wave field DOWN to obtain a matrix Z; The matrix inversion module is used to obtain the inverse matrix Z of the matrix Z -1 ; The formation reflection coefficient obtaining module is used to convert the upgoing wave field UP and Z -1 Perform convolution to obtain the formation reflection coefficient R; The central control module is used to control the signal flow and data processing in the upgoing wavefield and downgoing wavefield separation module, the upgoing wavefield downward movement module, the adaptive subtraction module, the matrix inversion module and the formation reflection coefficient acquisition module.

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