A method for pure qP wave reverse time migration imaging in three-dimensional ORT medium

Abstract

The embodiment of the specification discloses a pure qP wave reverse-time migration imaging method in three-dimensional ORT medium. Through inputting a three-dimensional velocity field, an anisotropic parameter model, and simultaneously presetting parameters of forward simulation, shot records, boundary wave fields and forward extended source wave fields are obtained after forward simulation; the shot records and the boundary wave fields obtained through the forward simulation are inputted, reverse extension is carried out, and reverse extended receiver point wave fields are obtained; the source normalization cross-correlation imaging condition is applied, zero delay cross-correlation is carried out on the forward extended source wave fields and the reverse extended receiver point wave fields, and single-shot imaging results are obtained; and offset sections of each shot are stacked, and finally, reverse-time migration imaging sections are obtained. Thus, the three-dimensional reverse-time migration imaging is realized by using the pure qP wave equation, and cleaner and complete deep structures can be identified on the imaging sections.

Description

Technical Field

[0001] This manual relates to the field of oil and gas geophysical exploration engineering, and in particular to a method for pure qP-wave reverse time migration imaging in three-dimensional ORT media. Background Technology

[0002] The industry is currently accelerating its transition from isotropic to anisotropic assumptions. Seismic anisotropy is widespread in subsurface media; ignoring this property can lead to erroneous imaging results during migration. When sedimentary basins contain widespread periodic thin interbedded layers and directional fracture systems, such as vertically oriented fractures developing against a thin interbedded background, or two mutually perpendicular directional fracture systems forming within the same stratum under different periods of geostress, the simplest media model that best fits this situation is the Orthothorhombic (ORT) model.

[0003] The coupled pseudoacoustic wave equation based on the acoustic approximation can improve computational efficiency for reverse time migration imaging. However, under the acoustic approximation, shear wave energy is not completely eliminated, resulting in shear wave artifacts in the wave field. Furthermore, it is unstable in areas with drastic changes in tilt angle, leading to a decrease in image quality during reverse time migration.

[0004] Therefore, a higher imaging scheme is needed in three-dimensional ORT media with higher imaging quality. Summary of the Invention

[0005] This specification provides an embodiment of a pure qP-wave reverse time migration imaging method in a three-dimensional ORT medium to solve the following technical problem: the need for an imaging scheme in a three-dimensional ORT medium with higher imaging quality.

[0006] To solve the above-mentioned technical problems, one or more embodiments of this specification are implemented as follows:

[0007] In a first aspect, embodiments of this specification provide a method for reverse time migration imaging of pure qP waves in a three-dimensional ORT medium, comprising:

[0008] Input a three-dimensional velocity field and anisotropic parameter model, and pre-set the parameters for forward modeling. After forward modeling, the shot record, boundary wave field, and forward-extended source wave field are obtained.

[0009] The forward modeling employs the following orthogonal isotropic medium pure qP wave equations:

[0010]

[0011] Where ρ is the density of the medium, V p0 It is the vertical longitudinal wave velocity, v x v y v zε1 and ε2 are the velocity components, u is the wave field, and ε1 and ε2 are the anisotropic parameters.

[0012] Input the shot record and boundary wavefield obtained from forward modeling, and perform inverse time-delay continuation to obtain the receiver point wavefield of the inverse continuation. The inverse time-delay continuation is performed using the following equation:

[0013] Among them, u r It is the backpropagation wave field at the detector point; (x r ,y r ,z r ) represents the coordinates of the receiver point; d obs (x r ,y r ,z r ;t) is the seismic record at time t at the receiver location;

[0014] By applying the source normalized cross-correlation imaging condition, zero-delay cross-correlation is performed on the forward-extended source wavefield and the reverse-extended receiver wavefield to obtain the imaging results of a single shot.

[0015] The offset profiles of each shot are superimposed to obtain the final imaging profile of the reverse time offset.

[0016] In a second aspect, one or more embodiments of this specification provide an electronic device, comprising:

[0017] At least one processor; and,

[0018] A memory communicatively connected to the at least one processor; wherein,

[0019] The memory stores instructions that can be executed by the at least one processor to enable the at least one processor to perform the method as described in the first aspect.

[0020] In a fourth aspect, embodiments of this specification provide a non-volatile computer storage medium storing computer-executable instructions, which, when read by a computer from the storage medium, cause one or more processors to perform the method described in the first aspect.

[0021] The above-described technical solution adopted in one or more embodiments of this specification can achieve the following beneficial effects: By inputting a three-dimensional velocity field and anisotropic parameter model, and simultaneously pre-setting the parameters for forward modeling, the shot record, boundary wavefield, and forward-extended source wavefield are obtained after forward modeling; the shot record and boundary wavefield obtained from the forward modeling are input and reverse-time extension is performed to obtain the reverse-extended receiver wavefield; the source normalized cross-correlation imaging condition is applied to perform zero-delay cross-correlation on the forward-extended source wavefield and the reverse-extended receiver wavefield to obtain the imaging result of a single shot; the migration profiles of each shot are superimposed to obtain the final imaging profile of the reverse-time migration. This achieves three-dimensional reverse-time migration imaging using the pure qP wave equation, which has higher stability compared to the coupled pseudo-acoustic wave equation under acoustic approximation, can solve the interference of "sheer wave artifacts" in the wavefield, improves the resolution of migration imaging, and can identify cleaner and more complete deep structures on the imaging profile. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments or prior art of this specification, the drawings used in the description of the embodiments or prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this specification. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a flowchart of an embodiment of the present invention;

[0024] Figure 2 The wave field at 0.3s is obtained from the forward modeling of the pseudoacoustic wave equation coupled to an orthogonal anisotropic medium according to an embodiment of the present invention.

[0025] Figure 3 The wave field at 0.3s is obtained from the forward modeling of the pure qP wave equation in an orthogonal anisotropic medium according to an embodiment of the present invention.

[0026] Figure 4 This is a three-dimensional SEG / EAGE salt velocity model according to an embodiment of the present invention;

[0027] Figure 5 This is a three-dimensional anisotropic parameter ε1 model according to an embodiment of the present invention;

[0028] Figure 6 This is a three-dimensional anisotropic parameter ε2 model according to an embodiment of the present invention;

[0029] Figure 7 A gun record according to an embodiment of the present invention;

[0030] Figure 8This is a three-dimensional isotropic medium reverse time migration imaging result according to an embodiment of the present invention;

[0031] Figure 9 This is a three-dimensional VTI medium reverse time migration imaging result according to an embodiment of the present invention;

[0032] Figure 10 This is a three-dimensional ORT medium reverse time migration imaging result according to an embodiment of the present invention;

[0033] Figure 11 This is a schematic diagram of the structure of an electronic device provided in an embodiment of this specification. Detailed Implementation

[0034] This specification provides an embodiment of a method for reverse time migration imaging of pure qP waves in a three-dimensional ORT medium.

[0035] To enable those skilled in the art to better understand the technical solutions in this specification, the technical solutions in the embodiments of this specification will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this specification, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this application.

[0036] Figure 1 This is a schematic flowchart illustrating a method for reverse time migration imaging of pure qP waves in a three-dimensional ORT medium, provided for one or more embodiments of this specification.

[0037] Figure 1 The process may include the following steps:

[0038] S1: Input the three-dimensional velocity field and anisotropic parameter model, and pre-set the parameters for forward modeling. After forward modeling, the shot record, boundary wave field and forward-extended source wave field are obtained.

[0039] The parameters pre-set for the forward modeling here include, but are not limited to, the observation system and model parameters, among which the model parameters include the lateral sampling points N of the three-dimensional velocity field. x and longitudinal sampling points N z Spatial sampling interval dx = dy = dz, temporal sampling interval dt, number of time sampling points N t The dominant frequency is f0. Additionally, the observation system includes the source depth (szbeg), the horizontal position (x-axis) of the first shot (sxbeg) and shot interval (dsx), the y-axis position of the first shot (sybeg) and shot interval (dsy), and the total number of shots (N). s .

[0040] The forward modeling here uses the pure qP wave equation for orthogonal isotropic media, as shown below:

[0041]

[0042] Where ρ is density; V p0 It is the vertical longitudinal wave velocity (unit: m / s); v x v y v z ε1 and ε2 are the velocity components; u is the wave field; ε1 and ε2 are the anisotropy parameters. Equation (1) is the first-order pure qP wave equation for orthogonal anisotropic media obtained by applying the elliptic approximation. Compared with the general anisotropic coupled pseudoacoustic wave equation, this equation can completely solve the interference of transverse wave artifacts in the forward modeling of coupled pseudoacoustic wave equation, and can remain stable in places where the tilt angle changes drastically. The simulated wave fields of the two equations at 0.3s are as follows: Figure 2 and Figure 3 As shown. Figure 2 It is a wave field simulated by forward modeling of coupled pseudo-acoustic wave equations. There are rhomboid "transverse wave artifacts" inside the wave field, which will affect the imaging results of reverse time migration. Figure 3 It is a clean wave field containing only P waves, obtained by forward modeling of the pure qP wave equation.

[0043] S2, input the shot record and boundary wave field obtained from the forward modeling simulation, perform inverse time extension to obtain the inversely extended receiver wave field.

[0044] The inverse continuation of the receiver wavefield is also based on the wave equation. It involves extending the wavefield in reverse time, starting from the moment of maximum recorded seismic signal. Inverse time continuation is a boundary value problem of solving the wave equation, which is described below:

[0045]

[0046] Among them, u r It is the reverse-extended receiver wavefield; (x r ,y r ,z r ) represents the coordinates of the receiver point; d obs (x r ,y r ,z r ;t) is the seismic record at time t at the receiver location.

[0047] S3. Applying the source normalized cross-correlation imaging condition, zero-delay cross-correlation is performed on the forward-extended source wavefield and the reverse-extended receiver wavefield to obtain the single-shot imaging results.

[0048] Cross-correlation imaging is currently the most widely used imaging condition, possessing good stability and high accuracy. Its expression is:

[0049]

[0050] Where I(x,y,z) is the imaging profile; u s (x,y,z,t) is the source wave field; u r (x,y,z,t) represents the receiver wavefield. This imaging condition utilizes information from both the source and receiver wavefields, enabling imaging of all waves. However, its dimension is the square of the wavefield amplitude, and the resulting imaging profile itself lacks physical meaning. Furthermore, because this imaging condition images all waves, the imaging profile contains significant low-frequency noise. The source-normalized cross-correlation imaging condition used in this invention addresses these shortcomings, and its expression is:

[0051]

[0052] This imaging condition utilizes the illumination intensity of the source wavefield for normalized cross-correlation, which not only removes some low-frequency noise but also reduces the influence of the source intensity on the imaging profile, making the amplitude value of the offset profile have the same dimensions as the reflection coefficient, and is closer to the true reflection coefficient.

[0053] S4. The offset profiles of each shot are superimposed to obtain the final imaging profile of the reverse time offset. The imaging profile of a single shot is difficult to distinguish complete and clear structural information, so it is necessary to superimpose the imaging profiles of each shot to obtain complete structural information.

[0054] By inputting a three-dimensional velocity field and anisotropic parameter model, and pre-setting the parameters for forward modeling, the shot record, boundary wavefield, and forward-extended source wavefield are obtained after forward modeling. The shot record and boundary wavefield obtained from the forward modeling are then input for inverse-time extension to obtain the inverse-extended receiver wavefield. Applying source-normalized cross-correlation imaging conditions, zero-delay cross-correlation is performed on the forward-extended source wavefield and the inverse-extended receiver wavefield to obtain the imaging results for a single shot. The migration profiles of each shot are then superimposed to obtain the final reverse-time migration imaging profile. This achieves three-dimensional reverse-time migration imaging using the pure qP-wave equation, exhibiting higher stability compared to the coupled pseudo-acoustic wave equation under acoustic approximation. It can resolve the interference of "sheer wave artifacts" in the wavefield, improve the resolution of migration imaging, and identify cleaner and more complete deep structures on the imaging profile.

[0055] To illustrate the method of the present invention more specifically, a 3D SEG / EAGE salt model is used as an example.

[0056] Input three-dimensional velocity field (e.g.) Figure 4 (as shown), and anisotropic parameter models (such as) Figure 5 and Figure 6 As shown in the figure, the parameters for the forward modeling were set. The observation system was distributed as follows: 256 shots were evenly distributed in the horizontal and vertical directions at a depth of 10m with an interval of 200 meters. Each shot had 338 receivers in the horizontal and vertical directions, with a receiver interval of 10 meters. The model parameters were as follows: 338 horizontal and 338 vertical sampling points for the velocity field, 200 sampling points in the depth direction, a spatial sampling interval of 10 meters, a time sampling interval of 1 millisecond, 2500 time sampling points, and a dominant frequency of 15 Hz. The shot records (single shot records) obtained after the forward modeling were as follows. Figure 7 As shown; then, the shot record is used as input for reverse time migration to obtain the receiver wavefield. This wavefield is then cross-correlated with the forward-propagating source wavefield using source-normalized cross-correlation imaging conditions to obtain the single-shot imaging profile. Finally, the profiles of each shot are superimposed to obtain the final reverse time migration imaging result (as shown). Figure 10 (As shown).

[0057] From the imaging results, the reverse time migration results of the isotropic acoustic wave equation (ISO) (such as...) Figure 8 As shown, the imaging of the upper part of the salt dome structure is relatively blurry and has low-frequency noise. Accurate imaging of structures below 1.5 km is impossible, and some structures are not clearly imaged. The reverse time migration results of the pure qP equation for VTI (transversely isotropy with a vertical symmetry axis) medium (e.g.) Figure 9 The imaging effect of the method shown is slightly better than that of reverse time migration based on the acoustic equation, but deep structural information is still missing; while the reverse time migration achieved by the method of this invention (as shown) Figure 10 (As shown) This method suppresses imaging noise, resulting in cleaner and clearer imaging of the structure and improved imaging resolution. Therefore, compared with existing methods, the method of this invention improves computational efficiency while ensuring equation accuracy, and enhances the imaging quality of 3D reverse time migration, which is of great significance for imaging of 3D exploration areas.

[0058] In the second aspect, such as Figure 11 As shown, Figure 11 This is a schematic diagram of the structure of an electronic device provided in an embodiment of this specification. The device includes:

[0059] At least one processor; and,

[0060] A memory communicatively connected to the at least one processor; wherein,

[0061] The memory stores instructions that can be executed by the at least one processor to enable the at least one processor to perform the method as described in the first aspect.

[0062] The foregoing has described specific embodiments of this specification. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps recited in the claims may be performed in a different order than that shown in the embodiments and may still achieve the desired result. Furthermore, the processes depicted in the drawings do not necessarily require the specific or sequential order shown to achieve the desired result. In some embodiments, multitasking and parallel processing are possible or may be advantageous.

[0063] The above description is merely one or more embodiments of this specification and is not intended to limit this specification. Various modifications and variations can be made to the one or more embodiments of this specification by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of one or more embodiments of this specification should be included within the scope of the claims of this specification.

Claims

1. A method for reverse time migration imaging of pure qP waves in a three-dimensional ORT medium, comprising: Input a three-dimensional velocity field and anisotropic parameter model, and pre-set the parameters for forward modeling. After forward modeling, the shot record, boundary wave field, and forward-extended source wave field are obtained. The forward modeling employs the following orthogonal isotropic medium pure qP wave equations: Where ρ is the density of the medium, V p0 It is the vertical longitudinal wave velocity, v x v y v z ε1 and ε2 are the velocity components, u is the wave field, and ε1 and ε2 are the anisotropic parameters. Input the shot record and boundary wavefield obtained from forward modeling, and perform inverse time-delay continuation to obtain the receiver point wavefield of the inverse continuation. The inverse time-delay continuation is performed using the following equation: Among them, u r It is the reverse-extended receiver point wavefield; (x r ,y r ,z r ) represents the coordinates of the receiver point; d obs (x r ,y r ,z r ;t) is the seismic record at time t at the receiver location; By applying the source normalized cross-correlation imaging condition, zero-delay cross-correlation is performed on the forward-extended source wavefield and the reverse-extended receiver wavefield to obtain the imaging results of a single shot. The offset profiles of each shot are superimposed to obtain the final imaging profile of the reverse time offset.

2. The method as described in claim 1, wherein, Zero-delay cross-correlation was performed on the forward-extended source wavefield and the reverse-extended receiver wavefield, including: Cross-correlation is performed in the following manner: Where I(x,y,z) is the imaging result of a single shot; u s (x,y,z,t) is the positively extended source wave field; u r (x,y,z,t) is the detector point wavefield of the inverse continuation.

3. An electronic device, comprising: At least one processor; as well as, A memory communicatively connected to the at least one processor; wherein, The memory stores instructions that can be executed by the at least one processor, such that the at least one processor can perform the method as described in any one of claims 1 to 2.

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