A method for improving the accuracy of root mean square velocity in complex structure area

Abstract

The present application belongs to the technical field of seismic data processing, and discloses a method for improving the accuracy of root mean square velocity in a complex structure area, comprising the following processes: S1, establishing a reference root mean square velocity field; S2, interpreting a target layer and then performing along-layer velocity analysis to obtain an along-layer analyzed velocity field; S3, combining the along-layer analyzed velocity field with the reference root mean square velocity field to obtain a target layer controlled root mean square velocity field; S4, using the target layer controlled root mean square velocity field to perform longitudinal high-density root mean square velocity analysis and automatic picking; S5, calculating a difference root mean square velocity field; S6, obtaining a processed difference root mean square velocity field; and S7, obtaining an optimized high-density analysis root mean square velocity field. The present application uses along-layer high-density velocity analysis under the constraint of a geological structure layer to perform vertical high-density velocity analysis, thereby improving the accuracy of the velocity field and achieving the accuracy of complex structure and low-amplitude structure imaging.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of seismic data processing, and is used for improving the precision of velocity field, in particular to a method for improving the precision of root mean square velocity in complex structural area. BACKGROUND

[0002] With the development of technology, oil and gas exploration gradually advances to subtle lithologic traps, low-amplitude structures and deep complex structures. High-quality seismic data imaging is the key to the success of complex oil and gas reservoir exploration, and high-precision root mean square velocity field is the core of obtaining good imaging in pre-stack time migration.

[0003] The velocity involved in seismic data processing includes VSP velocity data, sonic logging velocity, migration velocity spectrum, etc. The accuracy of these velocity data is different, among which the vertical accuracy of VSP velocity and sonic logging velocity is the highest, and the vertical resolution and accuracy of pre-stack time migration velocity in seismic data processing is the lowest. In order to improve the accuracy of pre-stack time migration velocity spectrum, VSP velocity and sonic logging are gradually used to constrain the picking of velocity, or the root mean square velocity of sonic logging is corrected by the root mean square velocity of VSP well to constrain the picking of velocity, and the density of velocity spectrum in space is increased from 1000m*1000m to 500*500m or even to 250m*250m. Meanwhile, the velocity spectrum before and after is used for mutual reference, and strong reflection layer is used to qualitatively constrain the picking of velocity in migration profile, so as to maximize the accuracy of migration velocity in vertical and horizontal directions.

[0004] However, the above method has the following problems: (1) VSP and sonic logging are usually less and have sparse spatial density, which is not conducive to the control of spatial velocity variation; at the same time, due to the influence of cost, VSP and sonic logging are usually only aimed at the target layer, and can only play a trend control role in the complete velocity analysis from top to bottom. (2) Seismic data velocity analysis is a time-consuming and laborious work, and the velocity picking density is developed from 1000m*1000m to 500*500m, 250m*250m or even to the picking of velocity spectrum for each CMP; thus, it is difficult to achieve spatial consistency in velocity analysis work, especially for low-amplitude structure target layer, the accuracy of velocity is required to be high, but the conventional velocity picking method based on the flattening criterion of trace gather is almost difficult to ensure the accuracy of velocity, even if the seismic horizon constraint is used for velocity analysis or the density of velocity analysis is increased, the accuracy of velocity will be affected by noise in trace gather in land data. SUMMARY

[0005] The present application aims to provide a method for improving the accuracy of the root mean square velocity in a complex structure area, which uses high-density velocity analysis along the layer under the constraint of the geological structure horizon to improve the accuracy of the velocity field by performing vertical high-density velocity analysis, so as to improve the accuracy of the complex structure and low-amplitude structure imaging.

[0006] In order to achieve the above-mentioned purpose, the technical solution adopted by the present application is as follows:

[0007] A method for improving the accuracy of the root mean square velocity in a complex structure area is performed in the following order of steps:

[0008] S1, establishing a root mean square velocity field as a reference root mean square velocity field;

[0009] S2, first using the reference root mean square velocity field pre-stack time migration data volume to interpret the target horizon, and then using the CRP gather after pre-stack time migration and reverse dynamic correction to perform velocity analysis along the layer to obtain the velocity field of the along-layer analysis;

[0010] S3, merging the velocity field of the along-layer analysis with the reference root mean square velocity field to obtain the root mean square velocity field controlled by the target layer;

[0011] S4, using the root mean square velocity field controlled by the target layer to perform longitudinal high-density root mean square velocity analysis and automatic picking;

[0012] S5, obtaining the difference root mean square velocity field by subtracting the root mean square velocity field obtained by the longitudinal high-density root mean square velocity analysis and automatic picking from the root mean square velocity field controlled by the target layer;

[0013] S6, suppressing the abnormal velocity values of the difference root mean square velocity field, and then performing smoothing processing at an interval of no more than 10 CMP points or INLINE lines to obtain the processed difference root mean square velocity field;

[0014] S7, merging the processed difference root mean square velocity field and the root mean square velocity field controlled by the target layer to obtain the optimized high-density analysis root mean square velocity field.

[0015] As a limitation, it further includes step S8, using the optimized high-density analysis root mean square velocity field to perform target line pre-stack time migration, and repeating S6 and S7 until the CRP gather is completely flattened according to the migration effect and the flatness of the CRP gather, that is, the final root mean square velocity field is obtained.

[0016] As a second limitation, the step S2 is performed in the following order of steps:

[0017] S21, for each velocity point, calculating the travel time with different test values and giving a similarity function as the maximum target function of the search;

[0018] S22, determining the search space according to the given time range, speed range and anisotropy range, and taking the speed corresponding to the maximum value of the search target function as the final result of the optimization of the root mean square speed, thereby obtaining the speed field along the layer analysis.

[0019] As a third limitation, the process of merging in step S3 with the reference root mean square speed field is carried out according to the following step sequence:

[0020] S31, the speed along the layer analysis is centered on the target layer, and the speed field along the layer analysis in the time window of 15 milliseconds above and below the target layer is used to replace the speed value at the corresponding position of the reference root mean square speed field;

[0021] S32, within 16 milliseconds to 50 milliseconds from the center of the target layer, the proportion of the speed field along the layer analysis is linearly changed from 80% to 0%, and the proportion of the reference root mean square speed field is linearly changed from 20% to 100%, and the speed field obtained at this time is the root mean square speed field controlled by the target layer.

[0022] Compared with the prior art, the technical progress achieved by the present application is that:

[0023] (1) The present application uses the high-density speed analysis along the layer under the constraint of the geological structure layer, performs vertical high-density speed analysis, improves the accuracy of the speed field, and thus improves the accuracy of complex structure and low-amplitude structure imaging;

[0024] (2) Based on the establishment of the root mean square speed field using near-surface investigation and well speed constraint, through the along-layer speed analysis of the target layer, high-density speed analysis, abnormal value removal and smoothing, the speed field in the shallow, medium and deep layers is more consistent with the geological regularity change, the longitudinal and lateral accuracy and resolution of the root mean square speed field are ensured, the accuracy of pre-stack time migration in solving the imaging of geological bodies with small structure amplitude is improved, the consistency of well and seismic is improved, and technical support is provided for improving the success rate of drilling;

[0025] (3) The present application is aimed at the single-point precision deficiency of seismic velocity, but the plane distribution density is large, and the lateral variation trend of velocity is well reflected, while other velocity sources mainly depend on the number of drilling and logging, and can only be used as control points for plane velocity variation; in the velocity research and mapping method, gradually developing into using seismic velocity to build a field, grasping the lateral variation of velocity, and using drilling and logging velocity to constrain the formation mapping velocity model; in view of the characteristics of rapid phase change of seismic data, sparse velocity picking points and spatial interpolation cannot meet the accuracy of imaging, the formation mapping velocity model is used to constrain the velocity picking in processing in turn, and the along-layer velocity updating is carried out on the purpose layer, the high-density velocity analysis is carried out on the premise of considering efficiency and effect, and the accuracy of pre-stack time migration velocity analysis in time direction and space direction is improved.

[0026] The present application belongs to the technical field of seismic data processing, and can improve the accuracy of complex structure and low-amplitude structure imaging. BRIEF DESCRIPTION OF DRAWINGS

[0027] The accompanying drawings are included to provide a further understanding of the present application, and constitute a part of the specification, and are used together with embodiments of the present application to explain the present application, and do not constitute a limitation on the present application.

[0028] In the drawings:

[0029] Figure 1 It is a reference root mean square velocity field of the embodiment of the present application;

[0030] Figure 2 It is the final result of root mean square velocity optimization in step S2 of the embodiment of the present application;

[0031] Figure 3 It is the purpose layer controlled root mean square velocity field obtained in step S3 of the embodiment of the present application;

[0032] Figure 4 It is a schematic diagram of the optimal velocity value obtained in step S4 of the embodiment of the present application;

[0033] Figure 4 a is a position map of high-density velocity analysis points in step S4 of the embodiment of the present application; wherein the asterisk represents the time of velocity picking;

[0034] Figure 4 b is the velocity spectrum and the CMP gather after velocity dynamic correction of two CMP positions before and after velocity optimization in step S4 of the embodiment of the present application;

[0035] Figure 5 It is the difference root mean square velocity field obtained in step S5 of the embodiment of the present application;

[0036] Figure 6The processed difference root mean square velocity field obtained in step S6 of the embodiment of the present application;

[0037] Figure 7 The final root mean square velocity field obtained in step S8 of the embodiment of the present application;

[0038] Figure 8 a is the CRP gather of pre-stack time migration using the root mean square velocity field obtained in the embodiment of the present application by direct high-density velocity analysis;

[0039] Figure 8 b is the CRP gather of pre-stack time migration using the final root mean square velocity field obtained in the embodiment of the present application. DETAILED DESCRIPTION

[0040] The preferred embodiments of the present application will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present application, and are not used to limit the present application.

[0041] Embodiment: a method for improving the accuracy of root mean square velocity in a complex structure area

[0042] The present application is performed according to the following steps in sequence:

[0043] S1, establish a root mean square velocity field as a reference root mean square velocity field;

[0044] The velocity field established by combining the conventional picked root mean square velocity and the structure mapping velocity is more consistent with the geological regular variation of shallow, medium and deep layer velocities, which is of great benefit to the accuracy and continuity of pre-stack time migration imaging, reduces the phenomenon of well-seismic inconsistency, and the structure map obtained by variable velocity mapping is accurate, reducing the exploration risk. The velocity field at this time is the reference root mean square velocity field, as shown in Figure 1 ;

[0045] In this step, the root mean square velocity field is established by using the method provided in the Chinese invention patent with the patent number ZL201611122830.7;

[0046] S2, the interpreter first interprets the target layer on the data volume subjected to pre-stack time migration using the reference root mean square velocity field, and then extracts the root mean square velocity values from the reference root mean square velocity field at intervals less than 100 meters using these layers, and performs along-layer velocity analysis on the CRP gather subjected to pre-stack time migration and deconvolution correction in a time window of 50 milliseconds above and below the target layer, to obtain the along-layer analyzed velocity field;

[0047] Specifically, when performing along-layer velocity analysis,

[0048] Firstly, for each velocity point, the travel time is calculated with different test values, and a similarity function is given as the maximum objective function of the search; wherein the different test values include time, velocity, anisotropy parameter;

[0049] Then, the search space is determined according to the given time range, velocity range, and anisotropy range, and the velocity corresponding to the maximum value of the search objective function is the final result of the root mean square velocity optimization, as shown in Figure 2 Accordingly, the velocity field of the along-layer analysis is obtained;

[0050] S3, the along-layer analysis velocity field and the reference root mean square velocity field are combined to obtain the root mean square velocity field controlled by the target layer;

[0051] Specifically, first, the velocity obtained by the along-layer analysis is centered on the target layer, and the velocity field of the along-layer analysis in the time window of 15 milliseconds above and below the target layer is replaced with the velocity value at the corresponding position of the reference root mean square velocity field;

[0052] Then, within 16 milliseconds to 50 milliseconds from the center of the target layer, the proportion of the along-layer analysis velocity field linearly transitions from 80% to 0%, and the proportion of the reference root mean square velocity field linearly transitions from 20% to 100%, and the velocity field obtained at this time is the root mean square velocity field controlled by the target layer, as shown in Figure 3 ;

[0053] S4, using the root mean square velocity field controlled by the target layer, performing longitudinal high-density root mean square velocity analysis and automatic picking;

[0054] In this step, the target function is roughly calculated by twice the grid size determined by the determination parameter to find the optimization point position, and then fine grid calculation is performed near the optimization point to determine the optimal velocity value, as shown in Figure 4 , which is a schematic diagram of the optimal velocity value obtained in this step. Among them Figure 4 a is a position map of high-density velocity analysis points; Figure 4 The asterisk in a indicates the velocity picking time; Figure 4 b is the velocity spectrum and the CMP gather after the velocity dynamic correction corresponding to the velocity before and after the velocity optimization of the two CMP positions in step S4 of the embodiment of the application. As can be seen from the figure, using the method provided by the embodiment, the velocity spectrum points are encrypted, the accuracy of the velocity spectrum is higher, the picking is more accurate, and the dynamic correction gather is more flat;

[0055] S5, the root mean square velocity field obtained by the longitudinal high-density root mean square velocity analysis and automatic picking is subtracted from the root mean square velocity field controlled by the target layer to obtain the difference root mean square velocity field, as shown in Figure 5 ; from Figure 5As can be seen, due to the influence of residual noise in the trace collection, the automatically picked root mean square velocity will have the largest target value at the location of the noise, directly resulting in a large velocity difference between adjacent locations. This is unreasonable in both time and space, and the differential root mean square velocity field needs to be processed.

[0056] S6. For the differential root-mean-square velocity field, anomaly values ​​are suppressed using a multi-channel identification and single-channel noise reduction approach. Then, smoothing is performed at intervals no greater than 250 meters (i.e., no more than 10 CMP points or INLINE lines) to ensure the rationality of the differential root-mean-square velocity field, resulting in the processed differential root-mean-square velocity field, as shown below. Figure 6 As shown;

[0057] S7. Combine the processed differential root mean square velocity field with the root mean square velocity field controlled by the target layer to obtain the optimized high-density analytical root mean square velocity field.

[0058] S8. Utilize the optimized high-density root-mean-square velocity field to perform pre-stack time migration of the target line. Based on the migration effect and the flatness of the CRP gather, repeat steps S6 and S7 until the CRP gather is completely flattened or the remaining time difference is less than 1%, thus obtaining the final root-mean-square velocity field. Figure 7 As shown.

[0059] In step S8, the final pre-stack time offset is as follows: Figure 8 As shown, where Figure 8 'a' is a CRP gather obtained from the pre-stack time migration of the root mean square velocity field obtained directly from high-density velocity analysis. Figure 8 b is the final root mean square velocity field obtained from the pre-stack time-migrated CRP gather. Figure 8 a and Figure 8 The comparison shows that the final root mean square velocity field obtained from the pre-stack time-migrated CRP gather is flatter at mid-to-long-range migrations, resulting in higher imaging accuracy.

Claims

1. A method for improving the root mean square velocity accuracy in complex structural regions, characterized in that, Follow these steps in sequence: S1. Establish the root mean square velocity field as a reference root mean square velocity field; S2. First, the target layer is interpreted using the data volume of the pre-stack time migration of the reference root mean square velocity field. Then, the velocity along the layer is analyzed using the CRP gather after reaction correction following the pre-stack time migration, and the velocity field of the analysis along the layer is obtained. S3. Combine the velocity field analyzed along the layer with the reference root mean square velocity field to obtain the root mean square velocity field controlled by the target layer. S4. Utilize the root mean square velocity field controlled by the target layer to perform longitudinal high-density root mean square velocity analysis and automatic picking. S5. Calculate the difference root mean square velocity field between the longitudinal high-density root mean square velocity analysis, the automatically picked root mean square velocity field and the root mean square velocity field controlled by the target layer. S6. Suppress the abnormal velocity values ​​of the differential root mean square velocity field, and then smooth it at intervals of no more than 10 CMP points or INLINE lines to obtain the processed differential root mean square velocity field. S7. Combine the processed differential root mean square velocity field with the root mean square velocity field controlled by the target layer to obtain the optimized high-density analytical root mean square velocity field.

2. The method for improving the root mean square velocity accuracy in complex structural regions according to claim 1, characterized in that, The process also includes step S8, which involves using the optimized high-density analysis root mean square velocity field to perform pre-stack time migration of the target line. Based on the migration effect and the flatness of the CRP gather, steps S6 and S7 are repeated until the CRP gather is completely flattened, thus obtaining the final root mean square velocity field.

3. A method for improving the root mean square velocity accuracy in complex structural regions according to claim 1 or 2, characterized in that, In step S2, the process of performing the layer velocity analysis is carried out in the following order: S21. For each velocity point, calculate the travel time using different experimental values, and use a similarity function as the maximum objective function for the search. S22. Determine the search space based on the given time range, velocity range, and anisotropy range. Take the velocity at the position corresponding to the maximum value of the search objective function as the final result of the root mean square velocity optimization, and obtain the velocity field along the layer analysis accordingly.

4. A method for improving the root mean square velocity accuracy in complex structural regions according to claim 1 or 2, characterized in that, In step S3, the process of merging with the reference root mean square velocity is performed in the following order: S31. Replace the velocity values ​​at the corresponding positions of the reference root mean square velocity field with the velocity field obtained by the layer analysis within a time window of 15 milliseconds above and below the target layer. S32. Within 16 to 50 milliseconds from the center of the target layer, the proportion of the velocity field analyzed along the layer linearly transitions from 80% to 0%, while the proportion of the reference root mean square velocity field linearly transitions from 20% to 100%. The velocity field obtained at this time is the root mean square velocity field controlled by the target layer.

5. The method for improving the root mean square velocity accuracy in complex structural regions according to claim 3, characterized in that, In step S3, the process of merging with the reference root mean square velocity is performed in the following order: S31. Replace the velocity values ​​at the corresponding positions of the reference root mean square velocity field with the velocity field obtained by the layer analysis within a time window of 15 milliseconds above and below the target layer. S32. Within 16 to 50 milliseconds from the center of the target layer, the proportion of the velocity field analyzed along the layer linearly transitions from 80% to 0%, while the proportion of the reference root mean square velocity field linearly transitions from 20% to 100%. The velocity field obtained at this time is the root mean square velocity field controlled by the target layer.

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