T0 trend surface multi-iteration-based construction error correction method in reverse fault region

Abstract

The invention relates to a T0 trend surface multi-iteration-based structure error correction method in a reverse fault region, and belongs to the technical field of geophysical exploration. The method comprises the following specific steps: step 1, data preparation work; step 2, manufacturing a T0 trend surface; step 3, making a speed surface; step 4, making a construction map; 5, extracting numerical values corresponding to all well points of the structural map, and calculating an absolute error by using an error formula; 6, meshing absolute errors of all well points according to a T0 trend surface, and performing additive operation on the meshed data and the structural map in the step 4 to obtain a corrected structural map; and 7, repeatedly executing the step 5 and the step 6 until the relative error reaches a threshold value limited by the national standard, and ending the calculation. According to the method, the T0 trend surface is fully used as the trend guidance of the construction error, and the error threshold value is used as the termination condition of error iteration, so that the construction error is minimized, and the precision of the construction map is effectively improved.

Description

Technical Field

[0001] The invention relates to a structural error correction method in a reverse fault area based on multiple iterations of a T0 trend surface, and belongs to the technical field of geophysical exploration. Background Art

[0002] As oilfield exploration and development gradually enters the middle and late stages, the difficulty of identifying and studying oil and gas reservoirs gradually increases, and the accuracy requirements for seismic exploration technology also gradually increase. Seismic data is a signal that records seismic waves reflected back after passing through underground media within a certain period of time. After processing, it is usually transmitted to geological interpretation researchers in the form of time domain. Most geological research is carried out in the depth domain mode, which requires converting the time domain into the depth domain, that is, time-to-depth conversion. The main factor for the accuracy of time-to-depth conversion lies in the determination of velocity. Under normal circumstances, when the stratum is subjected to tensile force, the stratum is twisted or dislocated due to the force to produce a normal fault, which is characterized by the descending of the upper plate and the rising of the lower plate. And the average velocity of the entire stratum generally shows a trend of increasing from shallow to deep. The reverse fault corresponding to the normal fault is generated after the stratum is squeezed, which is mainly characterized by the rising of the upper plate and the descending of the lower plate. Due to the effect of reverse faults, the overlying low-velocity layer drops below the high-velocity layer, resulting in velocity reversal in local areas and causing large structural errors. How to eliminate the errors caused by reverse faults and improve the accuracy of structural maps so that they can more accurately describe the true structural characteristics of the underground is still a problem that has attracted much attention. Summary of the invention

[0003] In order to solve the above problems existing in the prior art, the present invention discloses a structural error correction method in a reverse fault area based on multiple iterations of the T0 trend surface, providing a method with the T0 surface as the trend in the reverse fault area, through multiple iterative corrections, while retaining the seismic geological structure characteristics, to achieve the purpose of minimizing or even eliminating the structural error.

[0004] The technical solution adopted by the present invention is: a structural error correction method in a reverse fault area based on multiple iterations of the T0 trend surface, and the specific steps are as follows:

[0005] Step 1: Data preparation: 1) Collect seismic horizon interpretation data and fault data in the reverse fault area; 2) Collect all well data in the target area, including well name, x-coordinate, y-coordinate, core filling, and drilling layer of the target layer; 3) Collect velocity data of the target layer calibrated by well seismic; 4) Understand the seismic datum of the area;

[0006] Step 2: Preparation of T0 trend surface: grid the seismic horizon interpretation data and display them in the form of contour lines. The contour line data is the T0 trend surface;

[0007] Step 3: Velocity surface preparation: Grid the velocity data of all well target layers with T0 trend surface and display them in contour line form. The contour line data is the average velocity of the target layer.

[0008] Step 4: Construction diagram preparation: Multiply the T0 trend surface obtained in step 2 by the average velocity obtained in step 3 to obtain the construction diagram;

[0009] Step 5: Error calculation: extract the values ​​corresponding to all well points in the structural map and calculate the absolute error using the error formula;

[0010] Step 6: Error correction: The absolute errors of all well points are gridded according to the T0 trend surface, and the gridded data are added to the structural map in step 4 to obtain the corrected structural map;

[0011] Step 7: Iterative calculation: If the relative error is greater than the threshold value, repeat steps 5 and 6 until the relative error reaches the threshold value specified by the national standard, and the calculation terminates.

[0012] Further, in the step 1, the interpretation of the horizon in the reverse fault area should be based on the actual exploration needs to formulate a reasonable interpretation plan. The seismic horizon interpretation data is prepared in the format of x-coordinate, y-coordinate, and z-value (indicating the spatial relative position based on the geodetic coordinates). The fault data is a plane fault, not a profile fault bar, and its format is x-coordinate, y-coordinate, and fault identifier. If there is an inclined well in the well data, it is particularly important to note that the x-coordinate and y-coordinate of the inclined well should be the ground coordinates at the target layer corresponding to the well trajectory, and the drilling layer data of the target layer is the vertical depth data of the well layer, not the depth measurement. Before the well seismic calibration, the seismic datum, well coordinates, well trajectory, and well layer data need to be carefully checked to ensure the accuracy of the data. Avoid using the stretching and compression functions during the calibration process to avoid abnormal velocity after calibration.

[0013] Furthermore, in step 2, the Zmap module of LandMark software is used to produce the T0 trend surface. One important parameter that needs attention is the grid density, which is generally about 1.2 times the interpretation density. The gridded contour lines are usually severely curved or have extreme values, and simple filtering and smoothing are required to obtain a reasonable T0 trend surface.

[0014] Furthermore, in step 3, when the velocity data is gridded, the T0 trend needs to be used as the velocity direction to ensure that the trends of the previous and subsequent results are consistent.

[0015] Furthermore, in step 4, the structural map is depth data based on earthquake as the reference surface.

[0016] Furthermore, in step 5, since the well data (well layers) and seismic data (including seismic horizon interpretation data and fault data) are measured at different surfaces on the surface, it is necessary to unify the reference surfaces of the two and then calculate the error value. The absolute error calculation formula is e i =F i -B i +a-dep i ; where e i is the error of the ith well, F i is the drilling layer of the ith well, in m; B i is the core filling elevation of the ith well, in m; a is the seismic datum (constant), in m; dep i is the structural depth of the ith well.

[0017] Furthermore, in step 6, the absolute errors of all well points are gridded according to the T0 trend surface, which can avoid the "bull's eye" phenomenon. The bull's eye phenomenon is a circular phenomenon with the interpolation point as the center formed during the interpolation process of some large or small data, which causes the structural map to deviate from the T0 trend characteristics, thereby ensuring the consistency of the structural trend with the T0 trend.

[0018] In step 7, the relative error formula is:

[0019] Where:

[0020] k i —Relative error of the depth of the ith well, expressed as a percentage;

[0021] e i —absolute error of the depth of the ith well, in meters (m);

[0022] h i —The seismic depth of the ith well (the distance from the drilling core surface to the reflection interface), in meters (m).

[0023] The relative error threshold value in step 7 at least meets the relative error standard required by the national standard "Technical Code for Interpretation of Seismic Exploration Data", see the relative error threshold value reference table for details.

[0024] Relative error threshold reference table

[0025]

[0026] The present invention discloses a structural error correction method in a reverse fault area based on multiple iterations of a T0 trend surface, which has the beneficial effect of making full use of the T0 trend surface as a structural error trend guide and taking an error threshold value as a termination condition for error iteration, thereby minimizing the structural error, effectively improving the accuracy of the structural map, and improving the success rate of exploration and development. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0028] Figure 1 The figure shows a flow chart of the error correction method based on multiple iterations of the T0 trend surface;

[0029] Figure 2 Shown is a schematic diagram of a normal fault and a reverse fault in an embodiment;

[0030] Figure 3 Shown are the cross-sectional views of the stratigraphic and fault interpretations in the embodiments;

[0031] Figure 4 Shown is a T0 contour map of the bottom of the Longtan Formation of the Permian System in the 215 pilot test area in the embodiment;

[0032] Figure 5 Shown is a velocity contour map of the bottom of the Longtan Formation in the Permian System in the 215 pilot test area in the embodiment;

[0033] Figure 6 Shown is a structural contour map of the bottom surface of the Longtan Formation of the Permian System in the 215 pilot test area in the embodiment;

[0034] Figure 7 Shown is the contour map of the structural error of the conventional method at the bottom of the Permian Longtan Formation in the 215 pilot test area;

[0035] Figure 8 The figure shows the error contour map of the T0 trend surface method at the bottom of the Permian Longtan Formation in the 215 pilot test area;

[0036] Fig. 9 Shown is a contour map of structural errors after conventional correction of the bottom surface of the Longtan Formation of the Permian System in the 215 pilot test area according to the present invention;

[0037] Fig.10 Shown is a structural error contour map after correction of the T0 trend surface method from the bottom of the Permian Longtan Formation in the 215 pilot test area by the conventional method of the present invention;

[0038] Fig.11 Shown is a structural contour map after final correction using the T0 trend surface method for the bottom of the Permian Longtan Formation in the 215 pilot test area in the example of the present invention.

[0039] Specific implementation methods

[0040] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0041] In order to further understand the content of the present invention, the present invention is further described below in conjunction with specific implementation methods.

[0042] Example 1: It should be noted that the T0 trend surface in this article is an isochronous trend surface, that is, a seismic reflection isochronous diagram, which can more truly reflect the basic underground structural form.

[0043] Tables 1 and 2 show the data tables of the iterative calculation process of the structural error of the bottom surface of the Longtan Formation of the Permian System in the 215 pilot test area in the examples of the present invention;

[0044] Table 1

[0045] well F(m) B(m) a(m) t0(ms) v(m / ms) FY1 2840.40 323.07 400.00 1546.50 1.88255 Z1 2381.00 320.00 400.00 1311.00 1.88257 H52-2 2930.00 359.86 400.00 1508.78 1.96504 H53 2863.20 359.86 400.00 1500.38 1.93240 H59 2930.00 359.86 400.00 1508.04 1.96630 Zi215 2863.00 359.86 400.00 1504.27 1.92683 Zi215H1-1 2846.00 357.44 400.00 1500.39 1.92245 Zi215H3-1 2804.00 328.52 400.00 1478.09 1.94319 Zi304 2937.00 335.90 400.00 1557.63 1.92177

[0046] Table 2

[0047] well dep(m) er(m) C_dep(m) C_er(m) T_dep(m) T_er(m) FY1 2911.36 5.94 2916.8 0.5 2917.5 -0.2 Z1 2468.04 -7.04 2462.8 -1.8 2462.7 -1.7 H52-2 2964.82 5.28 2967.5 2.6 2966.7 3.4 H53 2899.34 3.96 2902.1 1.2 2902.5 0.8 H59 2965.26 4.84 2961.1 9 2969.7 0.4 Zi215 2898.48 4.62 2901.1 2 2900.9 2.2 Zi215H1-1 2884.42 4.18 2888.8 -0.2 2888.8 -0.2 Zi215H3-1 2872.2 3.3 2870.8 4.7 2873.4 2.1 Zi304 2993.4 7.7 2999.2 1.9 2999.4 1.7

[0048] like Figures 1 to 11 As shown in the figure, the structural error correction method in the reverse fault area based on multiple iterations of the T0 trend surface is as follows:

[0049] Step 1: Preparation of main materials before drawing

[0050] The present invention takes the bottom surface of the Longtan Formation of the Permian System in the 215 pilot test area of ​​the Zigong block in southern Sichuan as an example;

[0051] Figure 1 A simple schematic diagram is made to facilitate the understanding of the meaning of normal faults and reverse faults. Figure 2This is the profile of the interpretation of the stratigraphic faults. Due to the influence of the Xi-III plate orogeny in the late deposition of the Longtan Formation of the Permian System in Zigong, southern Sichuan, the region was subjected to a large compression force, resulting in reverse faults mostly in the northwest and northeast directions. The reverse faults are of different sizes, different plane lengths, and a large number of them. They are complex and cannot be interpreted by fault blocks. In order to avoid the influence of repeated formations near the reverse faults, combined with the actual exploration and development needs, to ensure the accuracy of the high points and areas of the trap structure, the best interpretation scheme based on the overlap of the upper wall of the reverse fault to the fault is comprehensively considered in the process of stratigraphic interpretation. In this profile, the velocities of the two wells Zi304 and Zi215H1-3 in the target layer are 1.92177m / ms and 1.94319m / ms, respectively. From t0 in Table 1, it can be seen that the time of the two wells in the target layer is 1557.63ms and 1478.09ms, respectively. It can be concluded that there is an obvious velocity reversal problem in the two wells, which will inevitably lead to large errors.

[0052] Collect the interpreted bottom layer and fault data of the Longtan Formation in the target area, collect all well data in the target area, including well name, x-coordinate, y-coordinate, core filling, drilling layer of the bottom of the Longtan Formation, collect the velocity data of the bottom of the Longtan Formation calibrated by well seismic, and the seismic base data of the area. The well data are shown in Table 1, where the coordinate data does not participate in the calculation and is not shown here.

[0053] Step 2: Preparation of T0 trend surface: Grid the interpreted horizon of the bottom of Longtan Formation, that is, calculate the scattered data of the horizon into representative values ​​in a regular grid according to the sliding average method or Kriging method, and display it in the form of contour lines, that is, T0 trend surface. Figure 4 As shown in the figure, the background colors red-yellow-blue represent the gradual process of values ​​changing from large to small; the red line represents the fault, the blue line represents the contour line, and the black dot represents the well point location; the map is displayed in a standard orientation mode with the top as north, the bottom as south, the left as west, and the right as east; all the following maps involving these features have the same meaning and will not be repeated. Figure 1 It can be seen that the T0 trend surface gradually decreases from southwest to northeast, and presents the smallest trend characteristics in the southeast and northwest; the t0 values ​​of the corresponding well points on the T0 trend surface are extracted as shown in the t0 column in Table 1.

[0054] Step 3: Velocity surface preparation: Using the velocity data of all wells on the bottom of the Longtan Formation, i.e., column v in Table 1, the T0 trend surface is gridded and displayed in the form of contour lines, as shown in Figure 2. Figure 5 As shown, it can be seen that the speed trend is similar to the T0 trend.

[0055] Step 4: Construction diagram preparation: Multiply the T0 trend surface obtained in step 2 with the velocity surface obtained in step 3 to obtain the construction diagram, such as Figure 6The trend of the structural map is basically consistent with the trend of T0, and the dep values ​​of the corresponding well points on the structural map are extracted as shown in the dep column in Table 2.

[0056] Step 5: Error calculation: According to the absolute error formula e i =F i -B i +a-dep i The absolute error calculated for each well is shown in the er1 column of Table 2.

[0057] Step 6: Grid the absolute errors of all well points. The error contours after conventional gridding are as follows: Figure 7 As shown, according to the T0 trend surface grid error contour line is as follows Figure 8 As shown in the figure, the error contour lines after conventional gridding have obvious characteristics of circling the well points, that is, the bull's eye phenomenon. However, the error contour lines after gridding according to the T0 trend surface are more similar to the T0 trend.

[0058] The error gridded data of the two algorithms are added to the structural map in step 4 to obtain the corrected structural map, as shown in Fig. 9 and Fig.10 , it can be seen from the two figures that the structural map after conventional error correction inherits the defect of the conventional error grid drawing circles around the well points ( Figure 7 and Fig. 9 Black box), and according to the comparative analysis of the four columns of data in Table 2, namely, C_dep column (contour line value of the structural map after conventional grid error correction), C_er column (error value of the structural map after conventional grid error correction), T_dep column (contour line value of the structural map after T0 trend surface error correction), and T_er column (error value of the structural map after T0 trend surface error correction), it can be seen that the error value of the structural map after conventional grid error correction is too large; while the error value of the structural map after T0 trend surface error correction is small, and the structural map after T0 trend surface correction is consistent with the T0 trend, which is more in line with the law of seismic geology.

[0059] Step 7: According to the relative error standard required by the national standard "Technical Code for Interpretation of Seismic Exploration Data", this area belongs to the plain and other areas, and meets the requirements of every 100km 2 There are two or more wells that meet the requirements of 3D seismic results with acoustic logging, so the relative error threshold is less than or equal to 1.5%. In combination with the actual exploration needs of the region, the relative error threshold is increased from less than or equal to 1.5% to less than or equal to 1.5‰ based on the national standard requirements. By comparing the relative error with the threshold value, steps 5 and 6 are iterated repeatedly until the relative error of all well points is less than the threshold value of 1.5‰. The final corrected structural map is shown in the figure below. Fig.11 As shown, the error meets the accuracy requirements, the trend is consistent with the T0 trend, and it is in line with the laws of seismic geology.

[0060] Since the 215H1-2 well is located near the reverse fault, the above method is used to make the structural map of the bottom of the Longtan Formation. After the conventional error correction, the structural contour value at the well is 2870.6m, and after the T0 trend surface correction, the structural contour value at the well is 2876.2m. The drilling layer of the bottom of the Longtan Formation obtained by later actual drilling is 2838.76m, the core is 359.86m, the seismic base surface is 400m, and the drilling layer after converting the drilling platform surface to the seismic platform surface is 2878.9m. The absolute structural error of the conventional correction method is 8.3m, and the relative error is 2.88‰. The absolute structural error of the T0 trend surface correction method is 2.7m, and the relative error is 0.94‰. It can be seen that the T0 trend surface correction method has significantly improved the structural accuracy compared with the conventional correction method, and meets the error standard of actual drilling accuracy within 1.5‰.

[0061] This method was used to carry out experimental research on the bottom of the Permian Longtan Formation in the Zigong 215 pilot test area in southern Sichuan. Through multiple iterations of the structural error correction method on the T0 trend surface, the problem of large errors caused by velocity reversal in the reverse fault area was eliminated. Ultimately, the accuracy of 25 wells in the entire area was reduced from the original 4.8‰ to within 0.5‰, and the accuracy of subsequent actual drilling was guaranteed to be controlled within 1.5‰, which improved the success rate of exploration and development to a certain extent.

[0062] The above established structural error correction method based on multiple iterations of the T0 trend surface in the reverse fault area first collects seismic and logging data, uses seismic layer data to produce the T0 trend surface, and uses the velocity after well-seismic calibration to produce the average velocity surface. The two are multiplied to calculate the structural map, and the drilling data is compared with the values ​​of the corresponding well point data on the structural map to obtain the absolute error value. The error is gridded according to the T0 trend surface as the error trend direction to obtain the error surface, and then the structural map and the error surface are added to achieve error correction. Through the continuous iteration of the absolute error and the termination condition of the relative error threshold value, the purpose of minimizing or even eliminating the error value is achieved. This correction method effectively improves the accuracy of the structural map. The method is simple and highly operable, and it has great guiding significance for improving the success rate of exploration and development.

[0063] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A structural error correction method in a reverse fault area based on multiple iterations of the T0 trend surface, characterized in that: The following steps are involved: Step 1: Data preparation: 1) Collect seismic horizon interpretation data and fault data in the reverse fault area; 2) Collect all well data in the target area, including well name, x-coordinate, y-coordinate, core filling, and drilling layer of the target layer; 3) Collect velocity data of the target layer calibrated by well seismic; 4) Understand the seismic datum of the area; Step 2: Preparation of T0 trend surface: grid the seismic horizon interpretation data and display them in the form of contour lines. The contour line data is the T0 trend surface; Step 3: Velocity surface preparation: Grid the velocity data of all well target layers with T0 trend surface and display them in contour line form. The contour line data is the average velocity of the target layer. Step 4: Construction diagram preparation: Multiply the T0 trend surface obtained in step 2 by the average velocity obtained in step 3 to obtain the construction diagram; Step 5: Error calculation: extract the values ​​corresponding to all well points in the structural map and calculate the absolute error using the error formula; Step 6: Error correction: The absolute errors of all well points are gridded according to the T0 trend surface, and the gridded data are added to the structural map in step 4 to obtain the corrected structural map; Step 7: Iterative calculation: If the relative error is greater than the threshold value, repeat steps 5 and 6 until the relative error reaches the threshold value specified in the national standard "Technical Code for Interpretation of Seismic Exploration Data", and the calculation is terminated.

2. The structural error correction method based on multiple iterations of the T0 trend surface in the reverse fault area according to claim 1 is characterized in that: In step 1, the seismic layer interpretation data is prepared in the format of x-coordinate, y-coordinate, and z-value; the fault data is a planar fault, and its format is x-coordinate, y-coordinate, and fault identifier; the drilling layer data of the target layer is the vertical depth data of the well layer; before well seismic calibration, the seismic datum, well coordinates, well trajectory, and well layer data need to be carefully checked.

3. The structural error correction method based on multiple iterations of the T0 trend surface in the reverse fault area according to claim 1 is characterized in that: In step 2, the T0 trend surface is produced with the help of the Zmap module of the LandMark software. One parameter that needs to be paid attention to during the production process is the grid density, which is 1.2 times the interpretation density.

4. The structural error correction method based on multiple iterations of the T0 trend surface in the reverse fault area according to claim 1 is characterized in that: In step 3, when the velocity data is gridded, the T0 trend needs to be used as the velocity direction.

5. The structural error correction method based on multiple iterations of T0 trend surface in reverse fault areas according to claim 1 is characterized in that: In step 4, the structural map is the depth data based on the earthquake reference surface.

6. The structural error correction method based on multiple iterations of T0 trend surface in reverse fault areas according to claim 1 is characterized in that: In step 5, the error formula is e i =F i -B i +a-dep i ; where e i is the error of the ith well, F i is the drilling layer of the ith well, in m; B i is the core filling elevation of the ith well, in m; a is the seismic datum, in m; dep i is the structural depth of the ith well.

7. The structural error correction method based on multiple iterations of T0 trend surface in reverse fault areas according to claim 1 is characterized in that: In step 7, the relative error formula for calculating the relative error is: Where: k i —Relative error of the depth of the ith well, expressed as a percentage; e i —absolute error of the depth of the ith well, in meters (m); h i —The seismic depth of the ith well (the distance from the drilling core surface to the reflection interface), in meters (m).

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