Method for upgoing and downgoing wavefield separation for marine obn data

Abstract

The application discloses a method for up-and-down wave field separation of marine OBN data, which comprises the following steps: step one, performing preliminary pretreatment on original OBN data; step two, introducing a series of incident angles θ, and performing cross-ghost processing on the water-land detection data; step three, transforming the OBN data in the t-x domain to the τ-p domain through τ-p forward transformation, and then obtaining the water-land detection calibration factor related to the incident angle in the τ-p domain; step four, realizing calibration in the τ-p domain to obtain calibrated water-land detection data, and separating the up-and-down wave field based on the calibrated water-land detection data; and step five, transforming the calculation result data obtained in step four to the t-x domain through τ-p inverse transformation, so as to realize the wave field separation of the OBN data in the t-x domain. The application is helpful to realize effective and high-precision separation of the up-and-down wave field of the marine OBN data, and improve the imaging quality based on the marine OBN data.

Description

Technical Field

[0001] This invention relates to the technical field of seismic data processing in petroleum exploration, and specifically to a method for separating uplink and downlink wavefields in marine OBN (submarine node acquisition) data. Background Technology

[0002] In recent years, offshore oil exploration has developed rapidly, and various marine exploration technologies have advanced rapidly. Among them, seabed node (OBN) seismic exploration technology has advantages such as high density, wide azimuth, high coverage, flexible observation system, four-dimensional seismic monitoring, and convenient recovery. It has also solved the problems of traditional offshore towed cable acquisition being affected by seawater flow and towed cable drift. Therefore, OBN acquisition technology has been widely used.

[0003] As is well known, seabed OBN nodes typically use four-component acquisition. The P-component of the water receiver is the pressure wave field received by the pressure detector; the land receiver is a velocity detector, which includes three components: X, Y, and Z, receiving the velocity wave field of the moving particles. Assuming the seabed is horizontal, the X and Y components are parallel to the ground surface, receiving the horizontal velocity wave field of the moving particles, while the Z component is perpendicular to the seabed, receiving the vertical velocity wave field of the moving particles. When a subsurface reflected wave propagates upward and is received by the seabed node, it is called an up-flowing wave; while for seismic reflected waves that propagate from the subsurface to the seabed, continue to propagate upward to the sea surface, are reflected by the sea surface, and then propagate downward again to be received by the seabed node, they are called down-flowing waves.

[0004] Both the P-component of the water detector and the Z-component of the land detector contain ascending and descending waves. Due to the different physical mechanisms of pressure and velocity detectors, they exhibit different responses to the received seismic wavefield. The same seismic wavefield will produce different output results when passed through a vertical velocity detector and a pressure detector, resulting in differences in phase, frequency, and energy between the water and land detector data. Therefore, the water and land detectors (i.e., water detectors and land detectors) must be calibrated before separating the ascending and descending wavefields. By utilizing the different responses of the two types of detectors to the ascending and descending wavefields, the ascending and descending waves are separated. This eliminates virtual reflections at the detector point and, through mirror migration imaging technology, effectively increases the illumination intensity reflected from the subsurface medium, thereby improving imaging quality.

[0005] Currently, there are two main categories of methods for calibration of land and water sensors in marine OBN data processing. The first category is scalar calibration, which only calibrates the amplitude. This is mainly based on the minimum energy method, i.e., amplitude matching of land and water sensor data. This type of method mainly utilizes the principle that the upgoing wave energy is the minimum in the downgoing wave field or the downgoing wave energy is the minimum in the upgoing wave field after wavefield separation. First, the P component of the water sensor and the vertical Z component of the land sensor are analyzed, and a time window containing only upgoing or downgoing waves is selected. Then, the amplitude ratio of the P and Z components within the time window is calculated to obtain the compensation factor. This method is simple and easy to implement, but it has high requirements for the selection of the time window. It is more likely to achieve ideal results in work areas with a certain seabed depth and little seabed variation.

[0006] The second type of method is the vector calibration method, which calibrates amplitude, frequency, and phase comprehensively. This type of method is mainly based on matched filtering technology, designing the optimal matched filter to eliminate differences in amplitude, phase, and frequency between land and water samples. It mainly includes adaptive matched filtering, time-domain cross-ghost wave matched filtering, and FK-domain cross-ghost wave matched filtering. Adaptive matched filtering technology is based on Wiener filtering; after filtering the input signal, the output best approximates the desired output in the least squares sense. The key is to find the minimum mean square error filtering factor. Generally, water samples have a higher signal-to-noise ratio, higher dominant frequency, and wider bandwidth than land samples. Therefore, in processing, land sample data is matched to water sample data, and the filter operator is obtained using the least squares principle. The time-domain cross-ghost wave matched filtering method is based on the time-domain cross-ghost wave method for cross-ghost wave-processed land sample data Z. cg Water test data P cg Adaptive matched filtering can be used to obtain the filtering operator. The time-domain cross-ghost wave method is derived based on the assumptions of a one-dimensional model (waves are incident vertically in water and the seabed is horizontal). In actual seismic data, this assumption is too simplistic and its applicability is limited. To expand the applicability of this method and compensate for the algorithm's instability, Amundsen proposed the FK-domain cross-ghost wave matching technique. This technique transforms the pressure wave field and vertical velocity wave field to the FK domain based on the conventional time-domain cross-ghost wave method, and performs matched filtering using the frequency-wavenumber domain cross-ghost wave formula to complete the water-land detection calibration.

[0007] The above-mentioned existing methods all have certain limitations. They are all based on the assumption that seismic waves are incident vertically in water, so they can only be used for calibration with limited near-range gun receivers and cannot be effectively calibrated for far-range gun receivers.

[0008] Therefore, there is an urgent need to design a new method to at least partially alleviate or even eliminate the aforementioned shortcomings and defects of existing methods. Summary of the Invention

[0009] The technical problem to be solved by the present invention is to overcome or alleviate at least some of the deficiencies or defects of the prior art, and to propose a new method for uplink and downlink wavefield separation for ocean OBN data.

[0010] The present invention solves the above-mentioned technical problems by adopting the following technical solution:

[0011] In general, this invention proposes a method to improve wavefield separation by performing cross-ghost wave matched filtering on P-waves and Z-waves in the tp domain.

[0012] This invention provides a method for uplink and downlink wavefield separation in ocean OBN data, characterized in that the method includes the following steps:

[0013] Step 1: Perform preprocessing on the raw OBN data to obtain preprocessed OBN data, where the OBN data includes water inspection data and land inspection data, and the preprocessing includes global calibration of water and land inspection data;

[0014] Step 2: Introduce a series of incident angles θ to perform cross-ghost wave processing on the land and water detection data so that the amplitude, frequency and energy of the processed land and water detection wave field are basically consistent.

[0015] Step 3: Transform the OBN data in the tx domain to the τ-p domain through the τ-p positive transform, where cross-ghost wave processing is performed on each p channel and each specific incident angle, and then the water and land inspection calibration factor related to the incident angle is obtained in the τ-p domain.

[0016] Step 4: Perform calibration in the τ-p domain to obtain calibrated land and water detection data, and separate the uplink and downlink wave fields based on the calibrated land and water detection data;

[0017] Step 5: Transform the calculation results obtained in Step 4 into the tx domain through the inverse τ-p transform, thereby realizing wavefield separation of OBN data in the tx domain.

[0018] According to some embodiments of the present invention, the preprocessing includes data correction and noise suppression based on the instrument response characteristics of the water detector and the land detector.

[0019] According to some embodiments of the present invention, the τ-p positive transformation includes transforming tx domain data into τ-p domain data by superimposing data along straight line trajectories with different slopes in the tx domain based on common shot points or CMP gathers.

[0020] According to some embodiments of the present invention, the cross-ghost wave processing in step two includes adding land-based virtual reflections and water-based virtual reflections to the water-based and land-based data respectively, so as to make the water-based and land-based wave fields consistent.

[0021] According to some embodiments of the present invention, in step three, the water and land inspection calibration factor obtained is the dependent variable of the independent variable, the incident angle.

[0022] According to some embodiments of the present invention, the amplitude, frequency and energy of the land and water detector fields in step two are basically consistent, defined as the percentage difference between the two not exceeding 10%.

[0023] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of the present invention.

[0024] The positive and progressive effects of this invention are as follows:

[0025] The uplink and downlink wavefield separation method for marine OBN data according to the present invention can overcome the basic assumption of vertical incidence of seismic waves in water, which is the basis of the existing wavefield separation methods mentioned above, and the resulting limitation that calibration can only be performed using a limited near-range, and cannot be effectively performed for far-range.

[0026] The method of the present invention takes into account that seismic waves are directional during actual propagation, that is, they change with the incident angle. Based on this, a method is designed that can effectively improve the accuracy of land and water detection calibration in OBN data and effectively and accurately separate the uplink and downlink wave fields in the data, which helps to improve the imaging quality of marine OBN data. Attached Figure Description

[0027] Figure 1 This is a flowchart illustrating a method for separating uplink and downlink wavefields in marine OBN data according to a preferred embodiment of the present invention.

[0028] Figure 2 This paper presents a common receiver point gather of the water P-component and land Z-component before uplink and downlink wave field separation in the imaged data corresponding to OBN data of an application example.

[0029] Figure 3 This example illustrates the image data corresponding to OBN data in an application instance, showing the common receiver gathers of the uplink and downlink waves after the uplink and downlink fields are separated.

[0030] Figure 4 This paper presents a composite profile of the water P-component and land Z-components of OBN data before uplink and downlink wave field separation, corresponding to an image of an application example.

[0031] Figure 5 This paper presents a graphical representation of OBN data from an application example, showing the superimposed profile of the uplink and downlink waves after the uplink and downlink fields are separated. Detailed Implementation

[0032] The preferred embodiments of the present invention will be further described in detail below with reference to the accompanying drawings. The following description is exemplary and not intended to limit the present invention. Any other similar situations will also fall within the protection scope of the present invention.

[0033] In the following detailed description, directional terms such as "left," "right," "up," "down," "front," and "back" are used with reference to the directions described in the accompanying drawings. Components in various embodiments of the invention may be positioned in a variety of different orientations; the directional terms are for illustrative purposes and not limiting.

[0034] The method of the following preferred embodiments of the present invention is based on the concept that wavefield separation is improved by performing cross-ghost wave matched filtering on P-waves and Z-waves in the tp domain.

[0035] refer to Figure 1-5 As shown, the method for uplink and downlink wavefield separation of ocean OBN data according to a preferred embodiment of the present invention includes the following steps:

[0036] Step 1: Perform preprocessing on the raw OBN data to obtain preprocessed OBN data, where the OBN data includes water inspection data and land inspection data, and the preprocessing includes global calibration of water and land inspection data;

[0037] Step 2: Introduce a series of incident angles θ to perform cross-ghost wave processing on the land and water detection data so that the amplitude, frequency and energy of the processed land and water detection wave field are basically consistent.

[0038] Step 3: Transform the OBN data in the tx domain to the τ-p domain through the τ-p positive transform, where cross-ghost wave processing is performed on each p channel and each specific incident angle, and then the water and land inspection calibration factor related to the incident angle is obtained in the τ-p domain.

[0039] Step 4: Perform calibration in the τ-p domain to obtain calibrated land and water detection data, and separate the uplink and downlink wave fields based on the calibrated land and water detection data;

[0040] Step 5: Transform the calculation results obtained in Step 4 into the tx domain through the inverse τ-p transform, thereby realizing wavefield separation of OBN data in the tx domain.

[0041] According to some embodiments of the present invention, the preprocessing includes data correction and noise suppression based on the instrument response characteristics of the water detector and the land detector.

[0042] The cross-ghost wave processing in step two includes adding land-based and water-based virtual reflections to the water-based and land-based data respectively to ensure consistency between the water-based and land-based wavefields. The τ-p positive transformation in step three involves superimposing the data along straight lines with different slopes in the tx domain, based on a common shot point or CMP gather, thereby transforming the tx-domain data into τ-p-domain data. Furthermore, the water-based and land-based calibration factors obtained in step three vary with the incident angle.

[0043] The above methods will be explained and illustrated in more detail below.

[0044] The PZ calibration technique for cross-ghost waves is widely used. Its basic principle is to incorporate land-based and water-based virtual reflections into the water and land-based receiver data respectively, ensuring consistency between the land and water wavefields, and then perform calibration to determine the factor. The underlying principles are as follows:

[0045] Let P and Z represent the seabed pressure field and the seabed vertical velocity field, respectively. Then the signals received by the pressure detector and the vertical velocity detector are respectively:

[0046] S P =ω(t) H P

[0047] S V =ω(t) G Z

[0048] Where S P The signal received by the pressure detector, S V Let ω(t) be the signal received by the vertical velocity detector. H For the pressure detector's impulse response and coupling factors, ω(t) G The pulse response and coupling factors of the vertical velocity detector.

[0049] Near the seabed:

[0050] P = U + D

[0051] Z = UD

[0052] D≈-O z U

[0053] Where D is the down-going wave field, U is the up-going wave field, (1-O z (1+O) represents the virtual reflection response of the pressure detector. z ) represents the virtual reflection response of the vertical velocity detector, O z Let be the two-way propagation operator for the water layer. Then:

[0054] P = (1-O) z )U

[0055] Z = (1 + O)z )U

[0056] Therefore, we can obtain:

[0057] S P =ω(t) H (1-O z )U

[0058] S V =ω(t) G (1+O z )U

[0059] (1-O) z ) and (1+O z By convolving Z with Z and P respectively, the cross-ghosting land detection Z can be obtained. cg and cross-ghost wave water detection P cg ,Right now:

[0060] Z cg =ω(t) G (1+O z )U*(1-O z )

[0061] P cg =ω(t) H (1-O z )U*(1+O z )

[0062] It can be seen that after cross-ghosting, land-based and sea-based inspections are basically the same.

[0063] Both the time domain and the FK domain assume that seismic waves are incident perpendicularly in the water. Therefore, calibration can only be performed using limited near-range gun-receiver calibration, and cannot be effectively calibrated at far-range gun-receiver calibration. Furthermore, seismic waves have a direction during actual propagation, which changes with the angle of incidence. Therefore, the angle of incidence must be considered to improve the accuracy of water-to-land calibration.

[0064] The principle of implementing land-water inspection calibration and solving the incident angle problem in the τ-p domain is as follows.

[0065] In this application, the τ-p transformation, also known as tilt superposition, is to superimpose data along straight lines with different slopes (Δt / Δx) on common shot points or CMP gathers in the tx domain (i.e., the time-space domain), thereby converting the data in the time-space domain tx to the data in the τ-p domain. In the τ-p domain, each trace corresponds to a specific incident angle, and it is easy to obtain the water and land inspection calibration factor that varies with the incident angle.

[0066] Let the incident angle be θ. After cross-ghosting, the land inspection and water inspection records are as follows:

[0067] Zcg =Z*(1-O z (θ))

[0068] P cg =P*(1+O z (θ))

[0069] The above formula can be easily solved for the filter factor in the τ-p domain. That is, the data in the tx domain is transformed to the τ-p domain through a forward τ-p transform:

[0070]

[0071] Each path in the τ-p domain corresponds to a specific incident angle, i.e.:

[0072]

[0073] Among them, v w This represents the speed at which seismic waves propagate in seawater.

[0074] Let the vertical propagation time in the water layer be T. w Then the propagation time of the seismic wave in the water layer for each p channel is:

[0075]

[0076] Use afterwards replace By performing cross-ghosting as a delay operator, the calibration factor related to the incident angle can be obtained, and calibration and wavefield separation can be achieved in the τ-p domain. Finally, the tx domain data can be obtained by performing an inverse τ-p transform.

[0077]

[0078] The uplink waves received by the P-component of the water detector and the Z-component of the land detector have the same polarity, while the downlink waves have opposite polarities. Therefore, this characteristic can be used to separate the uplink and downlink waves. The uplink wave data can be obtained by summing the calibrated water and land detector data, and the downlink wave data can be obtained by subtracting them.

[0079] Figure 2-3 The illustration schematically shows the P and Z common detector gathers before uplink and downlink field separation and the common detector gathers of uplink and downlink waves after separation, corresponding to the image data of OBN data based on the above-described preferred embodiment, as a reference. Figure 4-5 This schematically illustrates the image data corresponding to OBN data in this application example, showing the P and Z common detector gathers before uplink and downlink field separation / the superimposed profile of uplink and downlink waves after separation.

[0080] refer to Figure 2-5It should be understood that, through the uplink and downlink wave field separation method of the present invention, the uplink and downlink waves in the P and Z components are separated to the greatest extent, laying the foundation for subsequent uplink imaging, downlink mirror imaging, and joint deconvolution of uplink and downlink wave fields.

[0081] The preferred embodiment of the present invention, as a whole, achieves wavefield separation of OBN data in the time and space domains through the following process: "1) performing cross-ghost wave processing on the land and water survey data; 2) obtaining the calibration factor related to the incident angle and separating the wavefield in the τ-p domain; 3) transforming to the tx domain through inverse τ-p transform to achieve wavefield separation." This method primarily achieves efficient and accurate determination of the calibration factor while considering the incident angle factor through one forward transform and one inverse transform.

[0082] The method for separating uplink and downlink wavefields in marine OBN data according to the above-described embodiments of the present invention takes into account that seismic waves have a direction during actual propagation, that is, they change with the incident angle. Based on this, a method is designed that can effectively improve the accuracy of land-sea detection calibration in OBN data and effectively separate the uplink and downlink wavefields in the data with high precision, which helps to improve the imaging quality of marine OBN data.

[0083] While specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples, and the scope of protection of the present invention is defined by the appended claims. Those skilled in the art can make various changes or modifications to these embodiments without departing from the principles and essence of the present invention, and all such changes and modifications fall within the scope of protection of the present invention.

Claims

1. A method for uplink and downlink wavefield separation in ocean OBN data, characterized in that, The method includes the following steps: Step 1: Perform preprocessing on the raw OBN data to obtain preprocessed OBN data, where the OBN data includes water inspection data and land inspection data, and the preprocessing includes global calibration of water and land inspection data; Step 2: Introduce a series of incident angles θ to perform cross-ghost wave processing on the land and water detection data so that the amplitude, frequency and energy of the processed land and water detection wave field are basically consistent. Step 3: Transform the OBN data in the tx domain to the τ-p domain through the τ-p positive transform, where cross-ghost wave processing is performed on each p channel and each specific incident angle, and then the water and land inspection calibration factor related to the incident angle is obtained in the τ-p domain. Step 4: Perform calibration in the τ-p domain to obtain calibrated land and water detection data, and separate the uplink and downlink wave fields based on the calibrated land and water detection data; Step 5: Transform the calculation results obtained in Step 4 into the tx domain through the inverse τ-p transform, thereby realizing wavefield separation of OBN data in the tx domain; In step two, the amplitude, frequency, and energy of the land and water detector fields are basically consistent, defined as the percentage difference between the two not exceeding 10%.

2. The method for uplink and downlink wavefield separation of marine OBN data as described in claim 1, characterized in that, The preprocessing includes data correction and noise suppression based on the instrument response characteristics of the water and land detectors.

3. The method for uplink and downlink wavefield separation of marine OBN data as described in claim 1, characterized in that, The τ-p positive transformation includes transforming tx domain data into τ-p domain data by superimposing data along straight line trajectories with different slopes in the tx domain based on common shot points or CMP gathers.

4. The method for uplink and downlink wavefield separation of marine OBN data as described in claim 1, characterized in that, The cross-ghost wave processing in step two includes adding land-based virtual reflections and water-based virtual reflections to the water-based and land-based data, respectively, so as to make the water-based and land-based wave fields consistent.

5. The method for uplink and downlink wavefield separation of marine OBN data as described in claim 1, characterized in that, In step three, the water and land inspection calibration factor is the dependent variable of the incident angle as the independent variable.

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