A method for determining virtual reflection response in seismic exploration

Abstract

This invention relates to a method for determining virtual reflection responses in seismic exploration, belonging to the field of seismic exploration technology. First, the travel time of each layer above the excitation point is obtained based on the acquired near-surface survey data. Then, the travel time of the excitation point layer is obtained based on the explosion radius and charge length. Finally, the reflection coefficient and quality factor of each layer are obtained based on the near-surface velocity. Based on the travel time, reflection coefficient, and quality factor of each layer, the absorption attenuation and transmission loss of that layer are calculated. The cumulative absorption attenuation and cumulative transmission loss of virtual reflections at each layer interface are then calculated, along with the cumulative propagation attenuation of virtual reflections at the corresponding layer interface. The cumulative travel time of virtual reflections at each layer interface is obtained based on the travel time of each layer. Finally, the frequency response of virtual reflections at each layer interface is calculated based on the cumulative propagation attenuation, cumulative travel time, and reflection coefficient. This method can analyze the frequency response of virtual reflections at any interface above the excitation point and the overall virtual reflection response.

Description

Technical Field

[0001] This invention relates to a method for determining virtual reflection response in seismic exploration, belonging to the field of seismic exploration technology. Background Technology

[0002] In onshore seismic exploration, to improve seismic excitation effectiveness, excitation is typically performed in a high-velocity layer below a low-velocity layer. Due to the significant velocity difference between the high-velocity and low-velocity layers, the interface between them can be considered a strong reflecting surface. The uplifting wave excited by the source reaching this interface is reflected back underground, forming a companion wave to the downlifting wave. This companion wave is called a virtual reflection, and the interface causing this virtual reflection is called the virtual reflection interface. Virtual reflection analysis is fundamental to studying the formation mechanism of excitation wavelets and selecting source depths in seismic exploration, providing quantitative scientific basis for determining optimal excitation well depth and other acquisition parameters. The virtual reflection has a time difference with the directly downlifting seismic wave, causing it to superimpose on the latter part of the downlifting wave. This results in a low-frequency response in the seismic record, reducing the resolution of the seismic profile and posing significant difficulties for seismic data interpretation and inversion. Therefore, further research and in-depth study of virtual reflection are needed.

[0003] Current research and analysis methods for virtual reflections are mainly represented by the literature "The Acquisition of Virtual Reflection Information and Its Formation Mechanism, and Theoretical Discussion on Frequency Response" (Petroleum Geophysical Exploration, No. 6, 1998). This method proposes a method to analyze the impact of virtual reflections generated by the high-velocity layer top interface on seismic signals based on the signal delay superposition principle, and derives the frequency response formula of the impact of virtual reflections on the first downflow wave. This method can effectively guide the design of excitation well depths and has become an important basis for excitation well depth design in subsequent seismic exploration. However, this method only considers the virtual reflections generated by the high-velocity layer top interface and does not consider the virtual reflections of various strata interfaces and the surface above the high-velocity layer top interface. The literature "Determination and Utilization of Virtual Reflection Interfaces in Seismic Exploration" (Petroleum Geophysical Exploration, No. 3, 2002) discusses the impact of virtual reflections on the frequency and energy of excitation seismic waves based on the superposition response of virtual reflections and the first downflow wave. It believes that the distance between the explosive source and the virtual reflection interface should be less than 1 / 8 of the wavelength of the highest frequency signal, and the distance between the explosive and the virtual reflection interface should be greater than the explosion radius. The aforementioned existing technologies are based on the assumption that only one interface at the top of the high-velocity layer is considered, without considering absorption and attenuation losses during propagation, and under the assumption of a point source. This does not match the actual situation where there are often multiple structures near the Earth's surface and seismic waves are affected by absorption and attenuation during propagation. The virtual reflection frequency response obtained by the existing methods has errors compared to the actual virtual reflection frequency response. Summary of the Invention

[0004] The purpose of this invention is to provide a method for determining the virtual reflection response in seismic exploration, in order to solve the problems of existing technologies that only consider the virtual reflection at the top interface of high-velocity layers, and the inaccuracy of virtual reflection analysis caused by errors in calculating the time difference based on point sources.

[0005] To achieve the above objectives, the present invention includes:

[0006] The present invention provides a method for determining the virtual reflection response in seismic exploration, comprising the following steps:

[0007] 1) Obtain the explosive charge, explosive length, and near-surface survey data for the target work area. Calculate the explosion radius based on the explosive charge in the target work area. The near-surface survey data includes the velocity and thickness of each near-surface layer.

[0008] 2) Based on the near-surface survey data, the travel time of each layer above the excitation point is obtained. Based on the explosion radius and the length of the explosive charge, the travel time of the excitation point layer is obtained. Based on the near-surface velocity of each layer, the reflection coefficient and quality factor of the corresponding layer incident from top to bottom are obtained. Based on the travel time, reflection coefficient and quality factor of each layer, the absorption attenuation and transmission loss of the corresponding layer are obtained.

[0009] 3) Calculate the cumulative absorption attenuation and cumulative transmission loss of each layer's interface virtual reflection based on the absorption attenuation and transmission loss of each layer. Obtain the cumulative travel time of each layer's interface virtual reflection based on the travel time of each layer. Obtain the cumulative propagation attenuation of the corresponding layer's interface virtual reflection based on the cumulative absorption attenuation and cumulative transmission loss of each layer's interface virtual reflection.

[0010] 4) Calculate the frequency response of virtual reflections at each interface above the excitation point based on the cumulative propagation attenuation, cumulative travel time, and reflection coefficient of each interface. Each interface is the top interface of each layer.

[0011] Beneficial Effects: The seismic exploration virtual reflection response determination method of this invention obtains the frequency response of virtual reflections at each interface above the excitation point based on the reflection coefficient, cumulative propagation attenuation, and cumulative travel time of the corresponding layer. The cumulative propagation attenuation of each interface is derived from the cumulative absorption attenuation and cumulative transmission loss of the corresponding interface. The cumulative absorption attenuation and cumulative transmission loss of each interface can be obtained from the travel time, reflection coefficient, and quality factor of each layer, respectively. When calculating the travel time of each layer, the influence of the explosion radius and explosive charge length on the virtual reflection travel time in the high-velocity layer where the explosive is excitation is also considered. This invention's method considers the frequency response of virtual reflections at multiple interfaces, the attenuation loss during seismic wave propagation, and the influence of the explosion radius on the travel time. It can accurately determine the frequency response characteristics of virtual reflections at each interface and obtain the comprehensive frequency response characteristics of virtual reflections at multiple interfaces, providing better support for excitation well depth design and near-surface seismic wave propagation characteristic research.

[0012] Furthermore, based on the frequency response of the virtual reflections at each interface layer, the combined frequency response of the virtual reflections at all interfaces above the excitation point is obtained.

[0013] Furthermore, the formula for calculating the frequency response of the virtual reflection at each interface above the excitation point is:

[0014]

[0015] In the formula, |H(f) i | is the frequency response of the virtual reflection at the i-th interface, A i Let r be the cumulative propagation attenuation of the virtual reflection at the i-th interface. i Let σ be the reflection coefficient of the i-th interface incident from top to bottom. i Let f be the cumulative travel time of the virtual reflection at the i-th interface, and f be the frequency.

[0016] Furthermore, the combined frequency response of virtual reflections at all interfaces above the excitation point is:

[0017]

[0018] In the formula, |H(f)| is the combined frequency response of virtual reflections from all interlayer interfaces above the excitation point.

[0019] Furthermore, the propagation attenuation of the virtual reflection at the i-th interface is:

[0020] A i =G i T i

[0021] In the formula, G i T represents the cumulative absorption attenuation of the virtual reflection at the i-th interface. i Let be the cumulative transmission loss due to virtual reflection at the i-th interface.

[0022] Furthermore, the formula for calculating the travel time of the high-speed layer where the explosive is activated is as follows:

[0023]

[0024] In the formula, τ n For the travel time within the high-velocity layer, d is the distance from the top of the explosive to the top interface of the high-velocity layer, L is the length of the explosive charge, R is the blast radius, and v n This refers to the speed of the high-speed layer.

[0025] Beneficial effects: This invention takes into account the influence of the explosion radius and explosive charge length on the travel time of high-speed seismic waves within the layer during explosive activation, which can reduce errors and improve accuracy when calculating virtual reflection response.

[0026] Furthermore, the cumulative travel time of the virtual reflection at the i-th interface is the travel time of the total propagation process from the excitation location upwards to the i-th interface, and then from the i-th interface back to the excitation location.

[0027] Furthermore, the cumulative absorption attenuation of the virtual reflection from the i-th layer interface is obtained by multiplying the attenuation of the seismic waves reflected from the i-th layer interface to the excitation location upwards from the excitation location. The formula for calculating the absorption attenuation of each layer is as follows:

[0028]

[0029] In the formula, g i Let Q be the absorption and attenuation of the seismic wave at layer i. i Let τ be the quality factor of the i-th layer. i When traveling on the i-th layer.

[0030] Furthermore, the cumulative transmission loss of the virtual reflection at the i-th interface is obtained by multiplying the transmission losses of each layer propagating upward from the excitation position to the i-th interface, and then reflecting back from the i-th interface to the excitation position. The formula for calculating the transmission loss of each layer is as follows:

[0031]

[0032] In the formula, r i Let be the reflection coefficient of the i-th layer interface incident from top to bottom. Attached Figure Description

[0033] Figure 1 This is a flowchart illustrating the implementation process of the method of the present invention.

[0034] Figure 2 This is a schematic diagram of the calculation model in an embodiment of the method of the present invention;

[0035] Figure 3 This is a schematic diagram of near-surface stratification in a work area established in an embodiment of the method of the present invention;

[0036] Figure 4(a) shows the ground virtual reflection frequency response of a certain work area excited 5m below the high-speed layer top interface in an embodiment of the method of the present invention.

[0037] Figure 4(b) shows the virtual reflection frequency response of the deceleration layer top surface excited 5m below the high-speed layer top interface in a certain work area obtained in the embodiment of the method of the present invention.

[0038] Figure 4(c) shows the virtual reflection frequency response of the top surface of the high-speed layer excited 5m below the top interface of the high-speed layer in a certain work area obtained in the embodiment of the method of the present invention.

[0039] Figure 5This is the near-surface virtual reflection composite frequency response of a certain work area excited 5m below the high-speed layer top interface obtained in an embodiment of the method of the present invention;

[0040] Figure 6 This is a comparison of the near-surface virtual reflection comprehensive frequency response of a certain work area excited 5m below the high-speed layer top interface obtained in the embodiment of the method of the present invention with actual data.

[0041] Figure 7 This is a comparison between the near-surface virtual reflection comprehensive frequency response of a certain work area excited 9m below the high-speed layer top interface obtained in the embodiment of the method of the present invention and the actual data. Detailed Implementation

[0042] The present invention will now be described in further detail with reference to the accompanying drawings.

[0043] Example of a method for determining virtual reflection response in seismic exploration:

[0044] like Figure 1 This paper presents a method for determining virtual reflection responses in seismic exploration. It collects data on the amount of excitation charge, charge length, and near-surface survey results for the work area, establishes a near-surface layered data table, calculates the travel time, absorption attenuation, and transmission loss for each layer, considers the influence of charge length and explosion radius on the virtual reflection travel time, and obtains the frequency response of virtual reflections at each interface above the excitation point and the comprehensive frequency response of virtual reflections from all interfaces based on the seismic wave propagation equation and the principle of delay superposition. This embodiment considers the case where the excitation point is within a high-velocity layer. The specific implementation method is as follows:

[0045] 1) Obtain the target work area's initiation charge, charge length, and near-surface survey data. Based on the initiation charge in the target work area, obtain the explosion radius. The near-surface survey data includes the velocity and thickness of each near-surface layer. The layer where the initiation point is located and the overlying layers are numbered from shallow to deep starting from the surface. The interface of each layer refers to its top interface.

[0046] 2) Based on the near-surface survey data, the travel time of each layer above the excitation point is obtained. Based on the explosion radius and the length of the explosive charge, the travel time of the excitation point layer is obtained. Based on the near-surface velocity of each layer, the reflection coefficient and quality factor of the corresponding layer incident from top to bottom are obtained. Based on the travel time, reflection coefficient and quality factor of each layer, the absorption attenuation and transmission loss of the corresponding layer are obtained.

[0047] First, the explosion radius R is calculated based on the amount of ignition charge in the work area, that is:

[0048]

[0049] In equation (1), R is the explosion radius (in meters), c is a coefficient related to the ignition medium in the work area, which is 1.5 in this embodiment, and K is the amount of ignition charge (in kilograms).

[0050] Based on the near-surface survey results, the velocities v of each near-surface layer at each point within the target work area were obtained. i and thickness h i Where i = 1 to n, n is the number of near-surface layers (i = 1 refers to the uppermost layer, i = n refers to the high-velocity layer), when i = n, h n =d, where d is the distance from the top of the explosive to the interface of the high-velocity layer. In this embodiment, at a designated point near the ground surface in a certain actual work area, the velocity of the low-velocity layer v1 = 357 m / s and the thickness h1 = 1.47 m were obtained from the surface survey data, the velocity of the decelerating layer v2 = 1053 m / s and the thickness h2 = 8.73 m, and the velocity of the high-velocity layer v3 = 1654 m / s.

[0051] Based on the velocity v of each layer near the Earth's surface i and thickness h i Calculate the travel time τ for each level. i ,Right now:

[0052] τ i =2h i / v i (2)

[0053] Specifically, for the travel time of the high-velocity layer where the ignition point is located, i.e., the travel time of the virtual reflection within the high-velocity layer, the influence of the explosive charge length and explosion radius on the virtual reflection travel time must be considered during the calculation. The travel time τ within the high-velocity layer where the explosive ignition point is located... n The calculation formula is:

[0054]

[0055] In the formula, d is the distance from the top of the explosive to the top interface of the high-velocity layer, L is the length of the explosive charge, R is the explosion radius, and v n This refers to the speed of the high-speed layer. For example... Figure 2 As shown, the seismic wavelet is formed outside the explosion radius. The propagation distance of the virtual reflection is 2(d+L / 2-R)+2R=2d+L. The travel time of the virtual reflection in the high-speed layer can be calculated according to equation (3).

[0056] Based on the velocities of each near-surface layer, calculate the reflection coefficient r of each layer incident from top to bottom. i Wherein, the reflection coefficient r i The calculation formula is:

[0057]

[0058] In equation (2), ρ i The density of the i-th layer (in g / cm³) 3The density of each layer is calculated based on actual measurements or Gardner's formula, etc.

[0059] The quality factor Q is obtained based on the velocities of each layer in the near-surface layer. i :

[0060]

[0061] Q i Let Q be the quality factor of the i-th layer, where Q is the quality factor. i The quality factor can be obtained from actual measurement or empirical formula. In this embodiment, the quality factor in formula (4) is obtained from Li Qingzhong's empirical formula.

[0062] like Figure 3 As shown in Table 1, this embodiment establishes a near-surface layering data table based on data such as velocity, thickness, reflection coefficient, interlayer travel time, and quality factor of each layer. In Table 1, the high-velocity layer thickness refers to the distance from the top of the explosive to the interface of the high-velocity layer, which is a variable to be analyzed, denoted by d. The subsequent analysis mainly focuses on the virtual reflection response corresponding to different d values, which is of practical significance for guiding the excitation depth.

[0063] Table 1

[0064]

[0065] 3) Based on the travel time, reflection coefficient, and quality factor of each layer, obtain the corresponding layer absorption attenuation and transmission loss. Calculate the cumulative absorption attenuation and cumulative transmission loss of virtual reflections at each layer's interface based on the absorption attenuation and transmission loss of each layer. Obtain the cumulative travel time of virtual reflections at each layer's interface based on the travel time of each layer. Obtain the cumulative propagation attenuation of virtual reflections at the corresponding layer's interface based on the cumulative absorption attenuation and cumulative transmission loss of virtual reflections at each layer's interface.

[0066] The cumulative propagation attenuation of virtual reflections at each interface (the top interface of each layer in this embodiment) is calculated based on the cumulative absorption attenuation and cumulative transmission loss of the virtual reflections at the corresponding interface. The cumulative absorption attenuation of virtual reflections at each interface is calculated based on the absorption attenuation of each layer through which the seismic wave propagates, and the cumulative transmission loss of virtual reflections at each interface is obtained based on the transmission loss of each interface through which the seismic wave propagates. Specifically:

[0067] Based on the near-surface layer data table, the absorption attenuation of each layer was calculated, i.e.:

[0068]

[0069] Among them, g i Let Q be the absorption and attenuation of the seismic wave at layer i. i Let τ be the quality factor of the i-th layer.i For the travel time of the i-th layer, the absorption attenuation of each layer is obtained according to equation (5), and the cumulative absorption attenuation of the corresponding interface virtual reflection is:

[0070]

[0071] In equation (6), G i This represents the cumulative absorption attenuation of the virtual reflection at the i-th interface, which is the absorption attenuation of the entire propagation process from the excitation position upwards to the i-th interface, and then reflected downwards back to the excitation position.

[0072] Based on the near-surface layer data table, the transmission loss t of each layer was calculated. i ,Right now:

[0073]

[0074] In equation (7), t i Let r be the transmission loss of the i-th layer. i Let T be the reflection coefficient of the i-th interface. Based on the transmission loss obtained from equation (7), the cumulative transmission loss of the virtual reflection at the i-th interface can be calculated, which is the transmission loss during the total propagation process from the excitation position upwards to the i-th interface, and then reflected downwards back to the excitation position. The cumulative transmission loss T of the virtual reflection at the i-th interface is... i The calculation formula is:

[0075]

[0076] In equation (8), when i = n, which is the high-speed layer, the cumulative transmission loss T i The value is 1, meaning there is no transmission loss in this case.

[0077] Considering the far-field effect of seismic exploration and neglecting the spherical diffusion effect in seismic wave propagation, the propagation attenuation A of virtual reflections at each interface is... i The calculation formula is:

[0078] A i =G i T i (9)

[0079] A i G represents the cumulative propagation attenuation of the virtual reflection at the i-th interface. i T represents the cumulative absorption attenuation of the virtual reflection at the i-th interface, obtained from formula (6). i The cumulative transmission loss of the virtual reflection at the i-th interface is calculated by formula (8).

[0080] The cumulative travel time σ of the virtual reflection at the i-th interface layer iThe travel time of the total propagation process from the excitation location upwards to the i-th interface, and then reflected downwards back to the excitation location, is obtained by summing the travel times of each layer obtained from equation (2) and the high-speed layer travel time obtained from equation (3). The cumulative travel time σ of each interface is calculated as follows: i The calculation formula is:

[0081]

[0082] Based on the cumulative travel time of virtual reflections at each interface obtained from equation (10), the calculation model is as follows: Figure 3 As shown, virtual reflection analysis is performed on each layer of the multi-layer model, while also considering the influence of the charge length and explosion radius on the virtual reflection travel time.

[0083] 4) Based on the cumulative propagation attenuation, cumulative travel time, and reflection coefficient of each interface virtual reflection, calculate the frequency response of each interface virtual reflection above the excitation point, and obtain the comprehensive frequency response of all interface virtual reflections above the excitation point based on the frequency response of each interface virtual reflection above the excitation point.

[0084] According to formula (9), the cumulative propagation attenuation A i The cumulative travel time σ obtained from formula (10) i and reflection coefficient r i Calculate the frequency response of the virtual reflection at each interface above the excitation point, i.e.:

[0085]

[0086] Where, |H(f) i This is the frequency response of the virtual reflection at the i-th interface, which is obtained in this embodiment using the principle of delay superposition.

[0087] According to formula (11), as shown in Figure 4(a), when i=1, the frequency response of the virtual reflection on the ground is obtained. As shown in Figure 4(b), when i=2, the frequency response of the virtual reflection on the top surface of the deceleration layer is obtained. As shown in Figure 4(c), when i=3, the frequency response of the virtual reflection on the top surface of the high-speed layer is obtained. Due to the severe attenuation of the low-speed layer, even though the surface reflection coefficient is very large, the amplitude of the virtual reflection frequency response it produces is weak and within 10%. However, the amplitude of the virtual reflection frequency response produced by the interface between the deceleration layer and the top surface of the high-speed layer can reach 30%, which is the virtual reflection interface that needs to be considered and utilized.

[0088] The formula for calculating the combined frequency response of virtual reflections from all interfaces above the excitation point is:

[0089]

[0090] The combined frequency response of all interface virtual reflections above the excitation point is obtained from formula (12), as follows: Figure 5As shown, the black line represents the combined frequency response of all interfaces above the excitation point. Its shape is more complex and includes some notch bands. The frequency response of the high-velocity top interface is similar to the results obtained by existing analysis methods.

[0091] This embodiment uses an actual target work area as an example. Figure 6 The figure shows a comparison between the near-surface virtual reflection comprehensive frequency response excited 5m below the high-speed layer top interface in a certain work area and the actual data spectrum. As can be seen from the figure, the actual data spectrum and the near-surface virtual reflection comprehensive frequency response obtained by the method of this embodiment are similar in shape, and both have notch characteristics at around 40Hz. Figure 7 This paper compares the near-surface virtual reflection composite frequency response excited 9m below the high-speed layer top interface in a certain work area with the actual data spectrum. The actual data spectrum is quite similar to the near-surface virtual reflection composite frequency response obtained by the method of this embodiment, exhibiting notch characteristics around 30Hz. This indicates that the near-surface virtual reflection composite frequency response obtained by the method of this embodiment is largely consistent with the actual data spectrum, verifying the correctness of the method.

[0092] contrast Figure 6 and Figure 7 As the excitation depth increases below the high-velocity layer, high-frequency components are suppressed, which is not conducive to improving seismic resolution. Therefore, selecting a smaller excitation depth below the high-velocity layer is beneficial to acquiring a wider frequency band, providing guidance and basis for optimizing the excitation well depth for seismic acquisition in the target area.

Claims

1. A method of determining a seismic survey ghost response, characterized by, Includes the following steps: 1) Obtain the explosive charge, explosive length, and near-surface survey data for the target work area. Calculate the explosion radius based on the explosive charge in the target work area. The near-surface survey data includes the velocity and thickness of each near-surface layer. 2) Based on the near-surface survey data, the travel time of each layer above the excitation point is obtained. Based on the explosion radius and the length of the explosive charge, the travel time of the excitation point layer is obtained by taking the additional propagation distance of the virtual reflection compared to the first downward wave as 2(d+L / 2-R)+2R. Based on the near-surface velocity of each layer, the reflection coefficient and quality factor of the corresponding layer incident from top to bottom are obtained. Based on the travel time, reflection coefficient, and quality factor of each layer, the absorption attenuation and transmission loss of the corresponding layer are obtained. The excitation point layer is a high-velocity layer, where d is the distance from the top surface of the explosive charge to the top interface of the high-velocity layer, L is the length of the explosive charge, and R is the explosion radius. 3) Calculate the cumulative absorption attenuation and cumulative transmission loss of each layer's interface virtual reflection based on the absorption attenuation and transmission loss of each layer. Obtain the cumulative travel time of each layer's interface virtual reflection based on the travel time of each layer. Obtain the cumulative propagation attenuation of the corresponding layer's interface virtual reflection based on the cumulative absorption attenuation and cumulative transmission loss of each layer's interface virtual reflection. 4) Calculate the frequency response of virtual reflections at each interface above the excitation point based on the cumulative propagation attenuation, cumulative travel time, and reflection coefficient of each interface. Each interface is the top interface of each layer. The formula for calculating the frequency response of the virtual reflection at each interface above the excitation point is: wherein is the frequency response of the virtual reflection at the ith interface, is the cumulative propagation attenuation of the virtual reflection at the ith interface, is the reflection coefficient of the ith interface for an upward incidence, is the cumulative travel time of the virtual reflection at the ith interface, f is the frequency, is the cumulative absorption attenuation of the virtual reflection at the ith interface, is the cumulative transmission loss of the virtual reflection at the ith interface; The cumulative transmission loss of the virtual reflection at the i-th interface is obtained by multiplying the transmission losses of each layer propagating upward from the excitation position to the i-th interface, and then reflecting back from the i-th interface to the excitation position. The formula for calculating the transmission loss of each layer is as follows: The formula for calculating the cumulative transmission loss of the virtual reflection at the i-th interface is: In the formula, n is the high-speed layer.

2. The method for determining the virtual reflection response in seismic exploration according to claim 1, characterized in that, The method also includes obtaining the combined frequency response of virtual reflections of all interfaces above the excitation point based on the frequency response of virtual reflections of each interface.

3. The method for determining the virtual reflection response in seismic exploration according to claim 1, characterized in that, The combined frequency response of virtual reflections from all interfaces above the excitation point is: In the formula, This represents the combined frequency response of virtual reflections from all interfaces above the excitation point. Let be the cumulative propagation attenuation of the virtual reflection at the i-th interface. Let be the reflection coefficient of the i-th interface incident from top to bottom. Let f be the cumulative travel time of the virtual reflection at the i-th interface, and f be the frequency.

4. The method for determining the virtual reflection response in seismic exploration according to claim 2, characterized in that, The formula for calculating the travel time of the high-speed layer where the explosive is activated is: In the formula, For travel within the high-speed layer, L is the distance from the top surface of the explosive to the top interface of the high-velocity layer, R is the length of the explosive charge, and R is the blast radius. This refers to the speed of the high-speed layer.

5. The method for determining the virtual reflection response in seismic exploration according to claim 1, characterized in that, The cumulative travel time of the virtual reflection at the i-th interface is the travel time of the total propagation process from the excitation location upwards to the i-th interface, and then from the i-th interface back to the excitation location.

6. The method for determining the virtual reflection response in seismic exploration according to claim 3, characterized in that, The cumulative travel time of the virtual reflection at the i-th interface is the travel time of the total propagation process from the excitation location upwards to the i-th interface, and then from the i-th interface back to the excitation location.

7. The method for determining the virtual reflection response in seismic exploration according to claim 1, characterized in that, The cumulative absorption attenuation of the virtual reflection from the i-th interface is obtained by propagating upwards from the excitation location to the i-th interface, and then by multiplying the attenuation of the seismic waves reflected from the i-th interface to the excitation location from each layer. The formula for calculating the absorption attenuation of each layer is as follows: In the formula, Let be the absorption and attenuation amount of the seismic wave at layer i. Let be the quality factor of the i-th layer. When traveling on the i-th layer.

8. The method for determining the virtual reflection response in seismic exploration according to claim 1, characterized in that, The travel time of each layer above the layer containing the excitation point is calculated using the following formula: in, v represents the thickness of each near-surface layer at various points within the target work area. i The velocity of each point near the surface at each layer within the target work area. The travel time of each layer above the layer where the trigger point is located.

Images