Land ghost reflection suppression method and device

Abstract

The invention discloses a land ghost reflection suppression method and device, and the method sequentially comprises the following steps: S1, determining the development range and frequency characteristics of ghost reflection in a work area based on micro-logging and spectrum analysis; s2, performing tomographic inversion on the near-surface model to obtain the near-surface speed and thickness, and calculating the initial notch frequency of ghost reflection; s3, the initial notch frequency of ghost reflection corresponding to the shot point position is selected, and the deconvolution prediction step length of the shot point position is calculated; and S4, ghost reflection is obtained through variable-step prediction deconvolution backlog, and seismic data of primary reflection are obtained. According to the method, through accurate near-surface survey and high-precision near-surface model inversion, accurate ghost reflection development information is obtained, pressing is carried out through variable-step prediction deconvolution, mature theoretical support and a complete pressing process are achieved, a ghost reflection feature statistical method is innovated, effective pressing of ghost reflection is achieved, and the method has good application prospects. And therefore, the practical problems existing in seismic exploration for many years can be solved.

Description

Technical Field

[0001] The invention belongs to the technical field of petroleum exploration and relates to suppressing ghost reflections, in particular to a method and a device for suppressing ghost reflections on land. Background Art

[0002] In recent years, with the continuous improvement of oil and gas exploration and development technology, the oil and gas exploration field has developed from structural to structural + lithological complex circle. The quality of high-resolution, high-fidelity imaging seismic data is directly related to the success or failure of a series of geophysical technologies such as subsequent structural interpretation, reservoir description, fluid prediction, well location design, and reservoir development. From the perspective of seismology and geology, high-resolution imaging technology for large sets of strata and their internal sequence characteristics is the cornerstone of lithological exploration and a major demand for the development of the company's oil and gas geophysical technology. Therefore, high-quality seismic data is increasingly expected, especially the identification and prediction of lithological exploration targets have very high requirements for the fidelity of seismic data.

[0003] However, during the entire propagation process from excitation to reception, seismic waves are affected by various factors such as the surface and strong reflection interfaces. During the propagation process, the waves will oscillate back and forth between the surface and the strong reflection interface to form multiple reflections. Ghost reflection is one of the multiple reflections. Since it is often accompanied by a primary reflection or mixed with the tail of a primary reflection, it seriously interferes with the phase, frequency and other characteristics of seismic data, restricts the true characterization of wave resistance characteristics, and requires effective methods to suppress it and improve the quality of seismic data.

[0004] The industry has theoretically studied the formation mechanism of such interference and the corresponding suppression technology, but in actual production, such technology is usually used to suppress the ringing of marine data, and its application to land data is relatively rare. The fundamental obstacle is that land seismic data is affected by complex near-surface factors, and the characteristics and range of ghost reflection development are unclear. The difficulties mainly lie in: first, it is difficult to accurately establish the relationship between the actual ghost reflection information and the ghost reflection characteristics on the seismic data; second, there is a lack of scientific methods to distinguish ghost reflections from primary reflections; third, it is difficult to accurately count the development range and characteristics of ghost reflections; fourth, it is difficult to determine the prediction step size of shot-by-shot prediction deconvolution. Summary of the invention

[0005] The purpose of the present invention is to provide a method and device for suppressing ghost reflections on land, so as to solve the problem that the development characteristics and range of ghost reflections in onshore seismic data are unclear.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A method for suppressing ghost reflections on land comprises the following steps performed in sequence:

[0008] S1. Based on micro-well logging and spectrum analysis, determine the development range and frequency characteristics of ghost reflections in the work area;

[0009] S2. Tomographic inversion of the near-surface model, obtaining the near-surface velocity and thickness, and calculating the initial notch frequency of the ghost reflection;

[0010] S3. Select the initial notch frequency of the virtual reflection corresponding to the shot point position, and calculate the deconvolution prediction step size of the shot point position;

[0011] S4. Suppress the ghost reflection through variable step-size prediction deconvolution to obtain the seismic data of one reflection.

[0012] As a limitation, the step S1 specifically includes:

[0013] According to the near-surface velocity and thickness data in the micro-well logging, the notch frequency of the virtual reflection is calculated using the following formula, and the location of the micro-well logging where the virtual reflection occurs is determined by spectrum analysis. All micro-well logging in the work area are counted to determine the spatial location and frequency range of the virtual reflection:

[0014]

[0015] Where f is the notch frequency of the virtual reflection; k is the period parameter; τ is the vertical two-way travel time of the seismic wave; v is the near-surface velocity; and h is the near-surface thickness.

[0016] As another limitation, step S2 specifically includes:

[0017] According to the initial arrival time, the near-surface model tomography inversion is performed, and the near-surface velocity and thickness of the work area are obtained by using the micro-logging data for constraints. The frequency component of the first reflection corresponding to the ghost reflection signal in the work area is calculated according to the following formula as the initial notch frequency of the ghost reflection:

[0018]

[0019] Where f0 is the initial notch frequency of the virtual reflection; v is the near-surface velocity; h is the near-surface thickness.

[0020] As a third limitation, the deconvolution prediction step length of the shot point position in step S3 is determined by the periodic characteristics of the ghost reflection, and its value is equal to the near-surface vertical two-way travel time of the seismic wave at the position, and the calculation formula is:

[0021]

[0022] Where τ is the vertical two-way travel time of the seismic wave; v is the near-surface velocity; and h is the near-surface thickness.

[0023] The present invention also discloses a land ghost reflection suppression device, comprising:

[0024] The ghost reflection determination module is used to determine the development range and frequency characteristics of ghost reflections in the work area based on micro-well logging and spectrum analysis;

[0025] The first calculation module is used to obtain the near-surface velocity and thickness through tomographic inversion of the near-surface model and calculate the initial notch frequency of the ghost reflection;

[0026] The second calculation module is used to select the initial notch frequency of the virtual reflection corresponding to the shot point position and calculate the deconvolution prediction step length of the shot point position;

[0027] The ghost reflection suppression module is used to suppress ghost reflections through variable step-size prediction deconvolution to obtain seismic data of a single reflection.

[0028] Due to the adoption of the above technical solution, the present invention has the following technical advances compared with the prior art:

[0029] ① The invention provides a method and device for suppressing ghost reflections on land, which integrates and applies the field measured micro-logging data and the near-surface velocity model information of micro-logging constrained tomography inversion based on the initial arrival time, fully considers the problem that the development range and characteristics of ghost reflections are not obvious due to the lateral changes of the near-surface, obtains the real near-surface information based on the field micro-logging data, reduces the influence of errors caused by the seismic data statistical method, and can suppress ghost reflections according to the real situation of near-surface changes and ghost reflection development;

[0030] ② The invention provides a method and device for suppressing ghost reflections on land, which suppresses ghost reflections shot by shot, and avoids the situation where the suppression effect is not obvious through the variable step-size predictive deconvolution technology, while ensuring the real waveform characteristics of a single reflection;

[0031] ③ The onshore ghost reflection suppression method and device provided by the present invention ensure that the reflection levels of the imaging results are clear and the wave group characteristics are obvious, and can provide higher quality seismic data for lithological exploration.

[0032] The present invention obtains relatively accurate information on the development of ghost reflections through accurate near-surface investigation and high-precision near-surface model inversion, and suppresses them through variable-step predictive deconvolution. On the one hand, it has mature theoretical support and a complete suppression process, and on the other hand, it innovates the statistical method of ghost reflection characteristics, thereby achieving effective suppression of ghost reflections and solving practical problems that have existed in seismic exploration for many years. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Schematic diagram of the physical mechanism of the development of ghost reflection in an embodiment of the present invention;

[0034] Figure 2 is a micro-logging data diagram in an embodiment of the present invention, wherein Figure 2a. Figure 2 b are micro-well logging at two different locations;

[0035] Figure 3 is a typical seismic single shot diagram with developed ghost reflections in the embodiment of the present invention, wherein Figure 3 A. Figure 3 B is respectively Figure 2 a. Figure 2 b) Single shot 1 and single shot 2 corresponding to the micro-logging position;

[0036] Figure 4 In the embodiment of the present invention, Figure 3 First arrival leveling and spectrum analysis performed on single shot 1 in A;

[0037] Figure 5 In the embodiment of the present invention, Figure 3 First arrival leveling and spectrum analysis performed by single shot 2 in B;

[0038] Figure 6 It is a near-surface model of micro-logging constrained tomographic inversion in the working area in an embodiment of the present invention;

[0039] Figure 7 is the initial notch frequency within the ghost reflection development range in the embodiment of the present invention;

[0040] Figure 8 is the deconvolution prediction step length within the ghost reflection development range in the embodiment of the present invention;

[0041] Fig. 9 In the embodiment of the present invention, Figure 3 The single gun in the middle performs a virtual reflection suppression diagram, in which Fig. 9 A. Fig. 9 B is respectively Figure 3 A. Figure 3 In B, single gun 1 and single gun 2 are used for ghost reflection suppression;

[0042] Fig.10 It is a data comparison diagram after prestack time migration imaging in an embodiment of the present invention. DETAILED DESCRIPTION

[0043] The present invention is further described in detail below by specific examples. It should be understood that the described examples are only used to explain the present invention, and are not intended to limit the present invention.

[0044] Embodiment A method and device for suppressing ghost reflection on land

[0045] The present invention is applied in a certain area in North China. The main exploration targets in this area are the third segment of the sandstone and its deep layers. The surface of the study area is mainly plains, and the surface structure is relatively simple. However, the bottom interface of the weathering layer forms a strong reflection interface with the ground. Figure 1As shown in the figure, when the source is excited, the sub-wave first reaches the ground and is reflected, then propagates downward and reflects from the underground interface, forming a virtual reflection. The virtual reflection forms a companion wave after the normal primary wave that propagates directly downward from the source and is reflected by the underground interface, which seriously interferes with the waveform characteristics of the normal reflection wave. The problem of virtual reflection leads to poor overall seismic reflection characteristics in the area, chaotic reflections, and low signal-to-noise ratio, which brings difficulties to the deep sequence division and regional stratigraphic comparison of the third section of Shahejie and below; the wave group characteristics of seismic data in the deep lateral layer are not obvious, the breakpoint position is difficult to accurately interpret, and there are multiple solutions, which brings certain difficulties to the precise implementation of complex fault blocks.

[0046] This embodiment mainly includes the following steps performed in sequence:

[0047] S1. Based on micro-well logging and spectrum analysis, determine the development range and frequency range of ghost reflections in the work area

[0048] like Figure 2 As shown in the figure, two micro-logging data at different locations are counted. According to the near-surface velocity and thickness data in the micro-logging, the notch frequencies of the virtual reflections at the corresponding locations are calculated using the following formula: (7Hz, 14Hz, 21Hz...) and (5Hz, 10Hz, 20Hz...):

[0049]

[0050] Where f is the notch frequency of the virtual reflection; k is the period parameter; τ is the vertical two-way travel time of the seismic wave; v is the near-surface velocity; and h is the near-surface thickness.

[0051] like Figure 3 As shown in Figure 2, through waveform investigation, it can be determined that both single shots have ghost reflections, and the ghost reflection development waveform characteristics are different, that is, the micro-logging data at these two locations also have ghost reflection effects, such as Figure 4 , Figure 5 As shown in the figure, by performing initial flattening and spectrum analysis on single shot 1 and single shot 2, it can be determined that the notch frequencies of the ghost reflections are (7Hz, 14Hz, 21Hz...) and (5Hz, 10Hz, 20Hz...), respectively, which are consistent with the calculated values. After mastering the ghost reflection development characteristics (mainly notch frequencies), the ghost reflection development range in the construction area can be statistically analyzed based on all micro-logging data in the work area, thereby determining the spatial location and notch frequency range of the ghost reflection. The ghost reflection occurrence rate in this work area is higher than 80%, and the initial notch frequency range is 5-15Hz, so ghost reflection suppression is required.

[0052] S2. Tomographic inversion of the near-surface model to obtain the near-surface velocity and thickness, and calculate the frequency component of the first reflection wave corresponding to the ghost reflection signal in the work area as the initial notch frequency of the ghost reflection

[0053] The near-surface model tomography inversion was performed based on the initial arrival time and constrained by micro-logging data to obtain the following Figure 6 The near-surface velocity model in the work area is shown in Figure 1, so as to obtain the near-surface velocity and thickness of the work area, and calculate the initial notch frequency of the virtual reflection in the work area according to the following formula:

[0054]

[0055] Where f0 is the initial notch frequency of the virtual reflection; v is the near-surface velocity; h is the near-surface thickness.

[0056] S3. Select the initial notch frequency of the virtual reflection corresponding to the shot point position and calculate the deconvolution prediction step length of the shot point position

[0057] like Figure 7 As shown, the initial notch frequency of the shot point position where the ghost reflection occurs is counted, and the deconvolution prediction step length of the shot point position where the ghost reflection occurs is calculated according to the following formula. The result is as follows Figure 8 As shown:

[0058]

[0059] Where τ is the vertical two-way travel time of the seismic wave; v is the near-surface velocity; and h is the near-surface thickness.

[0060] S4. Suppress the ghost reflection by predicting deconvolution with variable step size and obtain the seismic data of one reflection

[0061] The ghost reflection of single shot 1 and single shot 2 is suppressed by predicting the anti-fold with variable step length. The results are as follows: Fig. 9 As shown, it can be seen that predictive deconvolution with different step lengths for different single shots can effectively suppress ghost reflections, make primary reflections clearer, eliminate notch points, and broaden the effective frequency band.

[0062] S5. Prestack Time Migration Imaging

[0063] The pre-stack time migration imaging data before and after ghost reflection suppression in the work area are compared, such as Fig.10 As shown in the figure, after the ghost reflection is suppressed, the reflection levels of the imaging data are clear and the wave group characteristics are obvious.

Claims

1. A method for suppressing ghost reflections on land, characterized in that: The process includes the following steps: S1. Based on micro-well logging and spectrum analysis, determine the development range and frequency characteristics of ghost reflections in the work area; S2. Tomographic inversion of the near-surface model, obtaining the near-surface velocity and thickness, and calculating the initial notch frequency of the ghost reflection; S3. Select the initial notch frequency of the virtual reflection corresponding to the shot point position, and calculate the deconvolution prediction step size of the shot point position; S4. Suppress the ghost reflection through variable step-size prediction deconvolution to obtain the seismic data of one reflection.

2. A method for suppressing ghost reflections on land according to claim 1, characterized in that: The step S1 specifically includes: According to the near-surface velocity and thickness data in the micro-well logging, the notch frequency of the virtual reflection is calculated using the following formula, and the location of the micro-well logging where the virtual reflection occurs is determined by spectrum analysis. All micro-well logging in the work area are counted to determine the spatial location and frequency range of the virtual reflection: Where f is the notch frequency of the virtual reflection; k is the period parameter; τ is the vertical two-way travel time of the seismic wave; v is the near-surface velocity; and h is the near-surface thickness.

3. A method for suppressing ghost reflections on land according to claim 1, characterized in that: The step S2 specifically includes: According to the initial arrival time, the near-surface model tomography inversion is performed, and the near-surface velocity and thickness of the work area are obtained by using the micro-logging data for constraints. The frequency component of the first reflection corresponding to the ghost reflection signal in the work area is calculated according to the following formula as the initial notch frequency of the ghost reflection: Where f0 is the initial notch frequency of the virtual reflection; v is the near-surface velocity; h is the near-surface thickness.

4. A method for suppressing ghost reflections on land according to any one of claims 1 to 3, characterized in that: The deconvolution prediction step length of the shot point position in step S3 is determined by the periodic characteristics of the ghost reflection, and its value is equal to the near-surface vertical two-way travel time of the seismic wave at the position, and the calculation formula is: Where τ is the vertical two-way travel time of the seismic wave; v is the near-surface velocity; and h is the near-surface thickness.

5. A land ghost reflection suppression device, characterized in that: include: The ghost reflection determination module is used to determine the development range and frequency characteristics of ghost reflections in the work area based on micro-well logging and spectrum analysis; The first calculation module is used to obtain the near-surface velocity and thickness through tomographic inversion of the near-surface model and calculate the initial notch frequency of the ghost reflection; The second calculation module is used to select the initial notch frequency of the virtual reflection corresponding to the shot point position and calculate the deconvolution prediction step length of the shot point position; The ghost reflection suppression module is used to suppress ghost reflections through variable step-size prediction deconvolution to obtain seismic data of a single reflection.

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