A method for acquiring seismic data along the downdip direction of an X-type fault
By a method of collecting seismic data along the two downward directions of the "X" fault in offshore exploration, the problem of unclear imaging in the "X"-shaped structure of conventional streamer seismic data acquisition is solved, and the effect of improving the image quality of the medium and deep complex structure without increasing costs is achieved.
Patent Information
- Application Number
- CN202411250037.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2024-09-06
- Publication Date
- 2025-06-13
- Estimated Expiration
- 2044-09-06
AI Technical Summary
In offshore exploration, when conventional streamer seismic data acquisition methods encounter "X"-shaped structures, they lead to uneven illumination of the seismic wave field, resulting in unclear imaging, and thus making target evaluation difficult.
A method is adopted to collect seismic data based on the two downward tilt directions of the "X" fault. By designing the acquisition parameters and directions, and combining the actual construction of the "X" development characteristics, another acquisition direction with the same downward tilt direction as the "X" structure is added to obtain reflected wave information and improve the illumination energy of the data.
Without increasing acquisition costs, the imaging quality of the complex structures in the medium and deep layers is improved, the signal-to-noise ratio of tomography is improved, and it is suitable for secondary three-dimensional seismic exploration at sea.
Smart Images
Figure CN119001858B_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of seismic exploration, and particularly relates to a method for collecting marine streamer seismic data, and more particularly to a method for collecting marine streamer seismic data based on two downdip directions along an "X"-type fault. Background Art
[0002] The method for collecting marine streamer seismic data is a conventional and efficient collection method in the ocean. Due to its high efficiency, low cost, and large number of coverage times, etc., it has been widely used in marine oil exploration. As the exploration degree gradually moves towards deep sea, the geological structures in the middle and deep layers of the target exploration area are becoming more and more complex, and the problem of structural imaging urgently needs to be solved. In order to study the characteristics of imaging problems of structures such as faults, Li Xuxuan et al. studied the illumination energy distribution characteristics of seismic waves in different acquisition directions in the deep-water rugged seabed area, and found that the acquisition direction perpendicular to the structural strike is beneficial to the imaging of the structure. However, in the case of being perpendicular to the fault structure strike, when collecting seismic data by conventional marine streamers, when there is an "X"-type structure development in the main exploration target structure, the wave field illumination is uneven when the seismic wave field passes through the two dipping structures, which will cause the imaging of one of the dips to be unclear, making it difficult to evaluate the target.
[0003] In recent years, in order to improve the imaging quality of structures, the conventional marine three-dimensional streamer seismic acquisition method has developed from a narrow azimuth acquisition observation system to a high-coverage, multi-, wide-, and full-azimuth acquisition observation system. According to a large number of exploration application case analyses, multi-, wide-, and full-azimuth observations can better improve the illumination energy of the seismic wave field under complex geological conditions in the middle and deep layers, and have broad application prospects in the fields of complex deep exploration and lithologic and fractured hydrocarbon reservoir exploration. However, due to the limitations of acquisition cost and processing technology for wide-azimuth and full-azimuth seismic acquisition methods, their applications in domestic marine exploration are not many at present. Therefore, on the premise of satisfying the solution to the problem of underground structural imaging, how to achieve cost reduction and efficiency increase in data acquisition is a very urgent problem in the current research on seismic exploration methods and technologies.
[0004] In order to further seek low-cost and efficient exploration means, geophysicists have gradually turned their attention to multi-azimuth acquisition methods. The multi-azimuth acquisition method can make up for the shortcomings of narrow-azimuth acquisition and also has some advantages of wide-azimuth acquisition. It is more reasonable and effective in solving the imaging of complex structures in the middle and deep layers. Moreover, by combining the two-azimuth and high-density acquisition methods, in addition to making up for the narrow-azimuth shortcomings and having some advantages of wide-azimuth acquisition, it can also increase the number of coverage times, and there is a significant improvement in the fault imaging quality and signal-to-noise ratio, which is very suitable for marine secondary three-dimensional seismic exploration. However, the above methods increase the acquisition azimuth or acquisition density on the basis of conventional streamer acquisition, which to a certain extent increases the economic cost and does not conform to the purpose of cost reduction and efficiency increase. Summary of the Invention
[0005] The object of the present invention is to provide a method for acquiring seismic data along the downdip directions of an "X"-type fault. Without increasing the acquisition cost, by combining the actual development characteristics of the "X"-type structure, the acquisition direction is combined with the dip direction of the "X"-type structure to solve the problem of increasing the illumination energy of seismic data and improving the imaging of complex structures in the middle and deep layers, providing a reference for the actual acquisition of seismic data.
[0006] The object of the present invention is achieved by the following technical solutions:
[0007] A method for acquiring seismic data along the downdip direction of an X-type fault, comprising the following steps:
[0008] A. Design of marine streamer seismic data acquisition:
[0009] Design the acquisition parameters and acquisition direction. In the case of being perpendicular to the structural strike, establish two observation systems where the acquisition direction is consistent with the downdip direction of the structural dip and the acquisition direction is opposite to the structural dip.
[0010] B. During the process of the marine geophysical exploration ship sailing in circles, evenly thin out the spacing of the sailing at equal intervals.
[0011] C. Obtain seismic data along one of the downdip directions of the X-structure along the sailing route in step B.
[0012] D. The geophysical exploration ship turns around and sails, and evenly supplement the evenly thinned sailing spacing in step B.
[0013] E. Obtain seismic data along the other downdip direction of the X-structure along the sailing route in step D, and obtain the reflection wave information in this acquisition direction to increase the illumination energy of the seismic data in the other direction.
[0014] F. Obtain seismic data along the two downdip directions of the X-structure, and then perform noise and multiple attenuation, velocity analysis, and migration imaging analysis.
[0015] Further, in step A, the design of the acquisition parameters and acquisition direction is specifically as follows: According to the regional geological data, analyze the strike characteristics of the structures in the work area, sort out the strike, dip, and dip angle parameters of the structural characteristics in the work area according to the occurrence, and determine that the acquisition direction of the acquisition observation system is perpendicular to the fault strike according to the occurrence parameters.
[0016] Further, in step A, the establishment of the observation system is specifically as follows: According to the velocity and density geophysical parameters of the actual drilling data, combined with the shallow gently dipping formation, the deep formation with a steeper dip angle, and the steeply dipping fault, the dip angle of the structure is associated with the formation to obtain a theoretical two-dimensional seismic geological model; In the case of being perpendicular to the strike of the structure, an observation system is established with the shot points and geophone points in the same down-dip direction along one of the X-shaped structures; Then, the position relationship between the shot and geophone points is exchanged to establish an observation system with the acquisition direction in the other down-dip direction of the X-shaped structure.
[0017] Further, combining the drilling data, the velocity and density geophysical parameters of this work area are sorted out; Combining the geophysical parameters, using the principle of the wave equation, the shot gather simulation of the two-dimensional geological model in the depth domain is carried out; By establishing the acquisition observation systems along the down-dip direction and the up-dip direction of the structure, the geophysical parameters are applied to the forward modeling of seismic data of the seismic geological model.
[0018] Further, step F is specifically as follows: Conduct velocity analysis and migration imaging on the forward modeled shot gather data, and analyze the imaging differences of the steeply dipping structure when the acquisition is along the down-dip direction and the up-dip direction of the structure.
[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:
[0020] 1. In the case of being perpendicular to the strike of the structure, according to the two observation systems where the acquisition direction is consistent with the down-dip direction of the structure trend and the acquisition direction is opposite to the structure trend, it is found that the acquisition method with the acquisition direction consistent with the down-dip direction of the structure is beneficial to the imaging of the steeply dipping formation;
[0021] 2. The present invention finds that the acquisition direction consistent with the down-dip direction of the structure is beneficial to the structure imaging. By turning around the geophysical exploration ship to increase the acquisition method with the acquisition direction consistent with the other down-dip direction of the structure, the imaging of the structure with the original acquisition direction opposite to the structure trend can be improved;
[0022] 3. On the basis of the original acquisition design, the present invention increases the interval of the acquisition route, turns around once, and supplements the other acquisition direction, supplementing the acquisition azimuth information without increasing the acquisition cost. BRIEF DESCRIPTION OF THE DRAWINGS
[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the embodiments. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can be obtained based on these drawings without creative efforts.
[0024] Figure 1 Establishment of the two-dimensional seismic geological model;
[0025] Figure 2 forward modeling shot gather migration imaging profile, where Figure 2a is the cross-section imaging when the acquisition direction is consistent with the down-dip direction of the fault, Figure 2b is the cross-section imaging when the acquisition direction is opposite to the down-dip direction of the fault;
[0026] Figure 3 Schematic diagram of the acquisition scheme, where Figure 3 a is the conventional clockwise circular acquisition scheme, Figure 3 b is the conventional counterclockwise circular acquisition scheme, Figure 3 c is the acquisition scheme of clockwise interval circular acquisition followed by counterclockwise supplementary circular acquisition after turning the boat around, Figure 3 d is the azimuth information acquisition of conventional clockwise circular acquisition, Figure 3 e is the azimuth information acquisition of conventional counterclockwise circular acquisition, Figure 3 f is the azimuth information acquisition of bidirectional circular acquisition, Figure 3 g is the schematic diagram of conventional clockwise acquisition in the work area, Figure 3 h is the schematic diagram of counterclockwise acquisition in the work area, Figure 3 i is the schematic diagram of bidirectional acquisition in the work area;
[0027] Figure 4 Imaging profile of the actual data acquired to the left;
[0028] Figure 5 Imaging profile of the actual data acquired to the right;
[0029] Figure 6 Imaging profile of the actual data after the data fusion processing of bidirectional acquisition;
[0030] Figure 7 Flowchart of the steps of the streamer seismic data acquisition method based on the down-dip direction of the "X"-type fault. Specific implementation mode
[0031] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It can be understood that the specific embodiments described herein are only used to explain the present invention, rather than limiting the present invention. Additionally, it should be noted that for the convenience of description, only the parts related to the present invention are shown in the accompanying drawings, rather than all the structures.
[0032] It should be noted that: similar reference numerals and letters represent similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings. At the same time, in the description of the present invention, the terms "first", "second", etc. are only used for distinguishing descriptions, and cannot be understood as indicating or implying relative importance.
[0033] The present invention provides a method for increasing the azimuth information of seismic data without increasing the acquisition cost during the acquisition of towed streamer seismic data. By thinning the acquisition spacing of the acquisition ship's navigation and then changing the acquisition direction to densify the acquisition spacing, information in another acquisition direction is obtained. Based on a conventional towed streamer, combined with the actual "X"-type development characteristics of the structure, another acquisition direction identical to the down-dip direction of the "X"-type structure is added to obtain the reflected wave information in this acquisition direction, that is, to increase the illumination energy of seismic data in another direction, so as to improve the imaging of complex structures in the middle and deep layers.
[0034] The method for acquiring towed streamer seismic data based on the down-dip direction of the "X"-type fault according to the present invention, based on the "X"-type development characteristics of the fault, the faults in the work area include two down-dip directions, and the towed streamer seismic data acquisition in both down-dip directions of the faults is taken into account, including the following steps:
[0035] 1. Design an observation system, acquisition parameters for conventional marine towed streamer seismic data acquisition, and an acquisition direction perpendicular to the strike of the structure.
[0036] 2. During the process of the marine geophysical exploration ship sailing in a circle, thin the sailing spacing at equal intervals.
[0037] 3. Obtain seismic data along one of the down-dip directions of the "X" structure from this sailing route.
[0038] 4. The geophysical exploration ship turns around and sails, and supplement the sailing spacing thinned at equal intervals in step 2 at equal intervals.
[0039] 5. Obtain seismic data along the other down-dip direction of the "X" structure from this sailing route.
[0040] 6. Obtain seismic data along two down-dip directions of the "X" structure, and then perform noise and multiple attenuation, velocity analysis, and migration imaging analysis.
[0041] Specifically, it includes the following steps:
[0042] Step 1: According to the regional geological data, analyze the strike characteristics of the structures in the work area, sort out the strike, dip direction, and dip angle parameters of the structural characteristics in the work area according to the occurrence, and determine that the acquisition direction of the acquisition observation system is perpendicular to the fault strike according to the occurrence parameters.
[0043] Step 2: According to the geophysical parameters such as velocity and density of the actual drilling data, combine the shallow gently dipping strata, the deep strata with steeper dip angles, and the steeply dipping faults, associate the dip angle of the structure with the strata to obtain a theoretical two-dimensional seismic geological model. In the case of being perpendicular to the strike of the structure, establish an observation system with the direction of the shot points and geophone points along one of the down-dip directions of the "X"-type structure; then, exchange the position relationship between the shot and geophone points to establish an observation system with the acquisition direction along the other down-dip direction of the "X"-type structure.
[0044] Step 3: Combine the drilling data to sort out geophysical parameters such as velocity and density in this work area. Based on the geophysical parameters, apply the principle of wave equation to conduct shot gather simulation on the 2D geological model in the depth domain. By establishing acquisition observation systems along the downdip direction and updip direction of the structure, apply the geophysical parameters to the forward modeling of seismic data for the seismic geological model.
[0045] Step 4: Migrate image the forward modeled shot gather data, and analyze the imaging differences of steeply dipping structures when the acquisition is along the downdip direction and updip direction of the structure. The analysis results show that collecting along the downdip direction of the structure is more conducive to the imaging of steeply dipping faults.
[0046] Step 5: In the work area where the "X" structure develops, conduct acquisitions along the two dip directions of the "X" structure. After data processing and imaging, the results show that the data collected along the downdip direction of one of the structures has better imaging than that of the other dip structure; when the two are combined for processing and imaging, the imaging of both dip structures can be improved.
[0047] Step 6: On the basis of the original acquisition method, thin out the navigation interval of the geophysical exploration ship by half, and then insert gaps in the reverse direction at the thinned positions. This way, it not only does not increase the acquisition cost, but also adds another acquisition direction, improving the imaging of the "X"-type faults.
[0048] In the case of being perpendicular to the strike of the structure, according to two observation systems where the acquisition direction is consistent with the downdip direction of the structure tendency and the acquisition direction is opposite to the structure tendency, combined with geophysical parameters, apply the principle of wave equation to conduct shot gather simulation on the 2D geological model in the depth domain, as Figure 1 shown. For the velocity analysis and migration imaging of the simulated shot gather, it can be known that the acquisition method where the acquisition direction is consistent with the structure tendency is more conducive to the imaging of steeply dipping formations, as shown in Figure 2.
[0049] According to the analysis results, combined with the characteristics of the towing cable acquisition in circles, the interval of the acquisition route can be increased on the basis of the original acquisition design, and then turn around once to supplement another acquisition direction. This way, it not only supplements the acquisition azimuth information, but also does not increase the acquisition cost, as Figure 3 shown.
[0050] Example 1
[0051] A method for collecting seismic data of towed cables based on the downward dip direction of X-shaped faults. According to the characteristics of the "X"-shaped fault development, for a certain sea area, the seismic data collected by the conventional towed cable method along two different acquisition dip directions are subjected to the same noise removal, multiple wave removal, etc. processing, and then velocity analysis is carried out, and imaging analysis is carried out using the same migration velocity to compare the differences between the two; through imaging analysis, it can be seen that the acquisition direction consistent with the structural dip is beneficial to structural imaging; the data in the two directions are combined so that the same data contains the azimuth information of the two structural dips, and the same processing flow and velocity imaging are adopted. It can improve the imaging of structures with the acquisition direction opposite to the structural dip, such as Figures 4 to 6 shown.
[0052] Note that the above is only the preferred embodiment of the present invention and the technical principles applied. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described here, and various obvious changes, re-adjustments and substitutions can be made by those skilled in the art without departing from the protection scope of the present invention. Therefore, although the present invention has been described in more detail through the above embodiments, the present invention is not limited to the above embodiments only. Without departing from the concept of the present invention, it can also include more other equivalent embodiments, and the scope of the present invention is determined by the scope of the appended claims.
Claims
1. A method for collecting seismic data along the downdip direction of an X-shaped fault, characterized in that: The following steps are involved: A. Offshore streamer seismic data acquisition design: Design the acquisition direction, and establish two observation systems: one with the acquisition direction consistent with the structural inclination and the other with the acquisition direction opposite to the structural inclination, in the case of being perpendicular to the structural inclination. The design of the acquisition direction is as follows: according to the regional geological data, the strike characteristics of the structure in the work area are analyzed, and the structural characteristics of the work area are sorted out into strike, dip and occurrence parameters according to the occurrence parameters. According to the occurrence parameters, the acquisition direction of the acquisition observation system is determined to be perpendicular to the fault strike; The establishment of the observation system is as follows: according to the velocity and density geophysical parameters of the actual drilling data, combined with the shallow gentle strata, the deep strata with relatively steep dip angles and the steep dip faults, the structural inclination is associated with the strata to obtain a theoretical two-dimensional seismic geological model; in the case of being perpendicular to the structural strike, an observation system is established in which the directions of the shot points and the receiver points are consistent along one of the down-dip directions of the X-shaped structure; then, the positional relationship between the shot and receiver points is exchanged to establish an observation system in which the acquisition direction is consistent with the other down-dip direction of the X-shaped structure; Combined with the drilling data, the velocity and density geophysical parameters of the work area were sorted out; combined with the geophysical parameters, the principle of wave equation was used to simulate the two-dimensional geological model in the depth domain; by establishing an acquisition observation system along the two down-dip directions of the X-shaped structure, the geophysical parameters were applied to the forward seismic data of the seismic geological model; B. During the process of circling the offshore geophysical exploration vessel, the interval of sailing is evenly spaced; C. Acquire seismic data along one of the down-dip directions of the X structure along the navigation route of step B; D. The geophysical exploration ship turns around and sails, supplementing the sparse sailing intervals in step B at equal intervals; E. Acquire seismic data in another down-dip direction along the X structure along the navigation route of step D, and obtain reflection wave information in the acquisition direction to increase illumination energy of seismic data in another direction; F. Obtain seismic data in two down-dip directions along the X structure, and then perform noise and multiple wave attenuation, velocity analysis, and migration imaging analysis; specifically: perform velocity analysis and migration imaging on the forward shot gather data, and analyze the differences in steep-angle structure imaging when collecting along the down-dip and up-dip directions of the structure.