A Tectonic Error Correction Method Based on Multiple Iterations of the T0 Trend Surface in Reverse Fault Regions

Abstract

This invention relates to a method for correcting structural errors in reverse fault areas based on multiple iterations of the T0 trend surface, belonging to the field of geophysical exploration technology. The specific steps are as follows: Step 1 is data preparation; Step 2 is the creation of the T0 trend surface; Step 3 is the creation of the velocity surface; Step 4 is the creation of the structural map; Step 5 is the extraction of values ​​corresponding to all well points on the structural map and the calculation of absolute error using the error formula; Step 6 is the gridding of the absolute errors of all well points according to the T0 trend surface, and the addition operation is performed between the gridded data and the structural map from Step 4 to obtain the corrected structural map; Step 7 is the repetition of Steps 5 and 6 until the relative error reaches the threshold value specified by the national standard, at which point the calculation terminates. This invention fully utilizes the T0 trend surface as a trend guide for structural errors and uses the error threshold value as the termination condition for error iteration, thereby minimizing structural errors and effectively improving the accuracy of the structural map.

Description

Technical Field

[0001] This invention relates to a method for correcting tectonic errors in reverse fault areas based on multiple iterations of the T0 trend surface, belonging to the field of geophysical exploration technology. Background Technology

[0002] As oilfield exploration and development gradually enters its middle and late stages, the identification and research of oil and gas reservoirs become increasingly challenging, placing higher demands on the accuracy of seismic exploration technology. Seismic data records the signals reflected back after seismic waves pass through the subsurface medium within a certain time period. After processing, it is usually transmitted to geological interpretation researchers in the time domain. However, most geological research is conducted in the depth domain, necessitating the conversion from the time domain to the depth domain—the time-depth conversion. The main factor affecting the accuracy of the time-depth conversion is the determination of velocity. Typically, when strata are subjected to tensile forces, they undergo twisting deformation or faulting due to the force, forming normal faults, characterized by a subsidence of the hanging wall and an uplift of the footwall. The average velocity of the entire stratum generally increases from shallow to deep. In contrast, reverse faults, corresponding to normal faults, are formed after strata are subjected to compression, primarily characterized by an uplift of the hanging wall and a subsidence of the footwall. Because of the action of reverse faults, the overlying low-velocity layer descends below the high-velocity layer, resulting in a velocity reversal phenomenon in some areas and causing significant 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 underground structural features remains a problem of great concern. Summary of the Invention

[0003] To address the aforementioned problems in existing technologies, this invention discloses a method for correcting structural errors in reverse fault regions based on multiple iterations of the T0 trend surface. In regions containing reverse faults, this method uses the T0 surface as a trend and performs multiple iterations to correct errors, thereby minimizing or even eliminating structural errors while preserving seismic geological structural characteristics.

[0004] The technical solution adopted in this invention is: a tectonic error correction method based on multiple iterations of the T0 trend surface in the reverse fault region, the specific steps of which are as follows:

[0005] Step 1: Data Preparation: 1) Collect seismic stratigraphic 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, and well stratification of the target layer; 3) Collect velocity data of the target layer after well seismic calibration; 4) Understand the seismic reference level in this area;

[0006] Step 2: Creating the T0 trend surface: The seismic horizon interpretation data is gridded and displayed as contour lines. This contour data is the T0 trend surface.

[0007] Step 3: Creating the velocity surface: Grid the velocity data of all wells in the target layer using the T0 trend surface and display it as contour lines. This contour line data is the average velocity of the target layer.

[0008] Step 4: Construction of the plot: Multiply the T0 trend surface obtained in Step 2 with the average velocity obtained in Step 3 to obtain the plot;

[0009] Step 5: Error Calculation: Extract the values ​​corresponding to all well points on the construction 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. The gridded data is added to the construction map in Step 4 to obtain the corrected construction 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, at which point the calculation terminates.

[0012] Furthermore, in step 1, the interpretation of stratigraphic positions in reverse fault areas should be based on a reasonable interpretation scheme formulated according to actual exploration needs. Seismic stratigraphic interpretation data is prepared in the format of x-coordinate, y-coordinate, and z-value (representing the spatial relative position based on geodetic coordinates). Fault data is for planar faults, not cross-sectional fault bars, and its format is x-coordinate, y-coordinate, and fault identifier. If there are deviated wells in the well data, special attention should be paid to ensuring that the x-coordinate and y-coordinate of the deviated wells are the ground coordinates of the target layer corresponding to the well trajectory. The drilling stratification data of the target layer is the vertical depth data of the well stratification, not the depth sounding. Before well-seismic calibration, the seismic reference surface, well coordinates, well trajectory, and well stratification data need to be carefully checked to ensure data accuracy. During the calibration process, stretching and compression functions should be avoided to prevent abnormal velocity after calibration.

[0013] Furthermore, in step 2, the T0 trend surface is created using the Zmap module of LandMark software. One important parameter to note is the grid density, which is generally about 1.2 times the interpreted density. The meshed contour lines are often severely curved or contain extreme values, requiring simple filtering and smoothing 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 trend of the results before and after is consistent.

[0015] Furthermore, in step 4, the constructed map is depth data based on the earthquake.

[0016] Furthermore, in step 5, since the well data (well stratification) and seismic data (including seismic stratigraphic interpretation data and fault data) are measured on different surfaces on the Earth's surface, it is necessary to unify their reference surfaces before calculating the error value. The absolute error calculation formula is e. i =F i -B i +a-dep i ; where e i Let F be the error of the i-th well. i B represents the drilling stratification of the i-th well, in meters; i The core elevation of the i-th well is given in meters (m); a is the seismic reference level (constant) in meters (m); dep i Let be the structural depth of the i-th well.

[0017] Furthermore, in step 6, the absolute error of all well points is gridded according to the T0 trend surface to avoid the "bull's eye" phenomenon. The bull's eye phenomenon is a circular phenomenon centered on the interpolation point formed by some data that are too large or too small during the interpolation process, which causes the construction map to deviate from the T0 trend. This ensures the consistency between the construction trend and the T0 trend.

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

[0019] In the formula:

[0020] k i —The relative depth error of the i-th well, expressed as a percentage;

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

[0022] h i —The seismic depth of the i-th well (the distance between the drill core and the reflection interface), in meters (m).

[0023] The relative error threshold value in step 7 must at least meet the relative error standard required by the national standard "Technical Specification for Interpretation of Seismic Exploration Data", as detailed in the relative error threshold value reference table.

[0024] Relative error threshold reference table

[0025]

[0026] This invention discloses a method for correcting structural errors in reverse fault areas based on multiple iterations of the T0 trend surface. Its beneficial effect is that it makes full use of the T0 trend surface as a structural error trend guide and uses the error threshold value as the termination condition for error iteration, thereby minimizing structural errors, effectively improving the accuracy of structural maps, and increasing the success rate of exploration and development. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 The diagram shows the flowchart of the error correction method based on multiple iterations of the T0 trend surface.

[0029] Figure 2 The diagram shown is a schematic representation of normal and reverse faults in the embodiment.

[0030] Figure 3 The diagram shown is a cross-sectional view illustrating the stratigraphy and faults in the embodiment.

[0031] Figure 4 The image shown is a contour map of the T0 level of the bottom surface of the Longtan Formation in the Permian System in the pilot test area 215, as described in the embodiment.

[0032] Figure 5 The figure shown is a contour map of the bottom surface velocity of the Longtan Formation of the Permian System in the pilot test area 215, as described in the embodiment.

[0033] Figure 6 The image shown is a contour map of the Permian Longtan Formation bottom structure in the pilot test area 215, as illustrated in this embodiment.

[0034] Figure 7 The image shows a contour map of the structural error of the Permian Longtan Formation at the bottom of the 215 pilot test area using conventional methods.

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

[0036] Figure 9 The image shown is a contour map of structural errors after conventional method correction of the bottom surface of the Longtan Formation in the Permian System of the 215 pilot test area according to the present invention.

[0037] Figure 10 The image shown is a contour map of structural errors after correction using the conventional method of the present invention, based on the T0 trend surface method at the bottom of the Longtan Formation of the Permian System in the 215 pilot test area.

[0038] Figure 11 The image shown is a contour map constructed after final correction using the T0 trend surface method on the bottom surface of the Longtan Formation of the Permian System in the 215 pilot test area, as described in this invention example. Specific implementation methods

[0039] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] To further understand the invention, the following detailed description, in conjunction with specific embodiments, further illustrates the invention.

[0041] Example 1: It should be noted that the T0 trend surface in the text is an isochronous trend surface, that is, an isochronous diagram of seismic reflection, which can more realistically reflect the basic underground structural morphology.

[0042] Tables 1 and 2 show the data table of the iterative calculation process of the bottom structural error of the Longtan Formation of the Permian in the pilot test area 215 in the example of the present invention.

[0043] Table 1

[0044] 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

[0045] Table 2

[0046] 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

[0047] like Figures 1-11 As shown, the method for correcting tectonic errors in reverse fault regions based on multiple iterations of the T0 trend surface includes the following specific steps:

[0048] Step 1: Preparation of key data before drawing

[0049] This invention takes the bottom surface of the Longtan Formation of the Permian System in the Zigong Block of Southern Sichuan (Zigong 215 pilot test area) as an example;

[0050] Figure 1 A simplified diagram to help understand the meaning of normal and reverse faults. Figure 2This is a cross-section diagram for the stratigraphic fault interpretation. Due to the influence of the Xisan orogeny during the late deposition of the Permian Longtan Formation in the Zigong area of ​​southern Sichuan, the region experienced significant compressional forces, resulting in numerous reverse faults trending northwest and northeast. These reverse faults vary in size and length, are numerous, and complex, making block-based interpretation impossible. To avoid the influence of overlapping strata near the reverse faults, and considering the actual exploration and development needs, as well as ensuring the accuracy of the trap's structural high points and area, the optimal interpretation scheme was determined to be based primarily on the connection between the hanging wall of the reverse fault and the fault itself. In this cross-section diagram, the velocities of wells Zi304 and Zi215H1-3 in the target layer are 1.92177 m / ms and 1.94319 m / ms, respectively. From t0 in Table 1, the times in the target layer for the two wells are 1557.63 ms and 1478.09 ms, respectively. This indicates a significant velocity reversal problem between the two wells, inevitably leading to substantial errors.

[0051] We collected the interpreted stratigraphic and fault data of the bottom surface of the Longtan Formation in the target area, as well as all well data in the target area, including well names, x-coordinates, y-coordinates, cores, and drilling strata of the bottom surface of the Longtan Formation. We also collected the well-calibrated velocity data of the bottom surface of the Longtan Formation and the seismic reference surface data for the region. The well data are shown in Table 1. The coordinate data is not used in the calculations and is not shown here.

[0052] Step 2: Creating the T0 trend surface: The interpretation stratigraphic layers of the Longtan Formation are gridded, which involves converting the dispersed data of the stratigraphic layers into representative values ​​within a regular grid using the moving average or kriging method, and displaying this as contour lines, i.e., the T0 trend surface. For example... Figure 4 As shown, the background color in the image, red-yellow-blue, represents the gradual change in numerical values ​​from large to small; red lines represent faults, blue lines represent contour lines, and black dots represent well point locations; the map is displayed in a standard orientation mode with north at the top, south at the bottom, west on the left, and east on the right; all subsequent maps using these features have the same meaning and will not be elaborated further. Figure 1 It can be seen that the T0 trend surface generally decreases from southwest to northeast, and shows the smallest trend in southeast and northwest; the t0 values ​​of the corresponding well points on the T0 trend surface are shown in the t0 column of Table 1.

[0053] Step 3: Creating the velocity surface: Using the velocity data from all wells at the bottom of the Longtan Formation, i.e., column v in Table 1, the data is gridded using the T0 trend surface and displayed as contour lines, as shown below. Figure 5 As shown, the speed trend is quite similar to the T0 trend.

[0054] Step 4: Constructing the Diagram: Multiply the T0 trend surface obtained in Step 2 with the velocity surface obtained in Step 3 to obtain the constructed diagram, such as... Figure 6As shown in the figure, the trend of the construction diagram is basically consistent with the T0 trend. The dep values ​​of the corresponding well points on the construction diagram are extracted as shown in the dep column of Table 2.

[0055] Step 5: Error Calculation: Calculated using the absolute error formula e i =F i -B i +a-dep i The absolute error for each well was calculated and is shown in column er1 of Table 2.

[0056] Step 6: Grid the absolute errors of all well points. The error contour lines after conventional gridding are shown below. Figure 7 As shown, the error contour lines after the T0 trend surface grid are as follows: Figure 8 As shown, the error contour lines after conventional meshing exhibit a clear characteristic of circling around the well points, known as the bullseye phenomenon. However, the error contour lines after meshing according to the T0 trend surface are more similar to the T0 trend.

[0057] The data after error gridding from both algorithms are added to the constructed graph in step 4 to obtain the corrected constructed graph, as shown below. Figure 9 and Figure 10 As can be seen from the two figures, the construction diagram after conventional error correction inherits the defect of drawing circles around the well points in the conventional error grid. Figure 7 and Figure 9 (Black box) Furthermore, based on the comparative analysis of the four columns of data in Table 2—C_dep (contour values ​​of the structural map after conventional grid error correction), C_er (error values ​​of the structural map after conventional grid error correction), T_dep (contour values ​​of the structural map after T0 trend surface error correction), and T_er (error values ​​of the structural map after T0 trend surface error correction)—it can be seen that the error values ​​of the structural map after conventional grid error correction are relatively large; while the error values ​​of the structural map after T0 trend surface error correction are relatively small, and the structural map after T0 trend surface correction is consistent with the T0 trend, which is more in line with the seismic geological laws.

[0058] Step 7: According to the relative error standard required by the national standard "Technical Specification for Interpretation of Seismic Exploration Data", this area belongs to plains and other areas, and meets the requirement of relative error per 100km. 2 For wells with two or more wells and 3D seismic data meeting the requirements for acoustic logging, the relative error threshold is less than or equal to 1.5%. Based on the actual exploration needs of the region and in accordance with national standards, the relative error threshold is increased from less than or equal to 1.5‰ to less than or equal to 1.5‰. Steps 5 and 6 are iterated continuously by comparing the relative error with the threshold until the relative error of all well points is less than the threshold of 1.5‰, at which point the process terminates. The final corrected structural map is shown below. Figure 11 As shown, the error meets the accuracy requirements, and the trend is consistent with the T0 trend, which is in line with the seismic geological law.

[0059] Since well 215H1-2 is located near a reverse fault, the structural map of the bottom surface of the Longtan Formation was created using the above method. After conventional error correction, the structural contour value at this well is 2870.6m, and after T0 trend surface correction, the structural contour value at this well is 2876.2m. Subsequent drilling revealed the bottom layer of the Longtan Formation to be 2838.76m, the core filler to be 359.86m, and the seismic reference surface to be 400m. After converting the drilling platform surface to the seismic platform surface, the drilling layer 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‰. Therefore, the T0 trend surface correction method significantly improves the structural accuracy compared to the conventional correction method and meets the error standard of less than 1.5‰ for actual drilling accuracy.

[0060] Using this method, experimental research was conducted on the bottom surface of the Longtan Formation in the Zigong Block of southern Sichuan. Through multiple iterations of the T0 trend surface structural error correction method, the problem of large errors caused by velocity reversal in reverse fault areas was eliminated. Ultimately, the accuracy of 25 wells in the whole area was reduced from 4.8‰ to less than 0.5‰, and the accuracy of subsequent drilling wells was controlled within 1.5‰, which improved the success rate of exploration and development to a certain extent.

[0061] The above-established method for structural error correction in reverse fault areas based on multiple iterations of the T0 trend surface first collects seismic and well logging data. A T0 trend surface is created using seismic stratigraphic data, and an average velocity surface is created using the velocities calibrated by well and seismic data. The two are multiplied to calculate the structural map. The values ​​of drilling data are compared with the corresponding well point data on the structural map to obtain the absolute error value. The error is then gridded according to the T0 trend surface as the error trend direction, resulting in an error surface. Finally, the structural map and the error surface are added together to correct the error. Through continuous iteration of the absolute error, and using a relative error threshold as the termination condition, the error value is minimized or even eliminated. This correction method effectively improves the accuracy of structural maps, is simple, highly operable, and has significant guiding significance for improving the success rate of exploration and development.

[0062] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions 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 method for correcting tectonic errors in reverse fault regions based on multiple iterations of the T0 trend surface, characterized in that, Includes the following steps: 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, and well stratification of the target layer; 3) Collect velocity data of the target layer after well seismic calibration; 4) Understand the seismic base level in this area; Step 2: Creating the T0 trend surface: The seismic horizon interpretation data is gridded and displayed as contour lines. This contour data is the T0 trend surface. Step 3: Creating the velocity surface: Grid the velocity data of all wells in the target layer using the T0 trend surface and display it as contour lines. This contour line data is the average velocity of the target layer. Step 4: Construction of the plot: Multiply the T0 trend surface obtained in Step 2 with the average velocity obtained in Step 3 to obtain the plot; Step 5: Error Calculation: Extract the values ​​corresponding to all well points on the construction 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. The gridded data is added to the construction map in Step 4 to obtain the corrected construction 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 defined threshold value, at which point the calculation terminates.

2. The method for correcting tectonic errors in reverse fault regions based on multiple iterations of the T0 trend surface according to claim 1, characterized in that, In step 1, the seismic horizon interpretation data is prepared in the format of x-coordinate, y-coordinate, and z-value; the fault data is for plane faults, and its format is x-coordinate, y-coordinate, and fault identifier; the well stratification data for the target layer is the vertical depth data of the well stratification; before well-seismic calibration, the seismic reference surface, well coordinates, well trajectory, and well stratification data need to be carefully checked.

3. The method for correcting tectonic errors in reverse fault regions based on multiple iterations of the T0 trend surface according to claim 1, characterized in that, In step 2, the T0 trend surface is created using the Zmap module of the LandMark software. One parameter to pay attention to during the creation process is the grid density, which is 1.2 times the interpreted density.

4. The method for correcting tectonic errors in reverse fault regions based on multiple iterations of the T0 trend surface according to claim 1, 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 method for correcting tectonic errors in reverse fault regions based on multiple iterations of the T0 trend surface according to claim 1, characterized in that, In step 4, the construction map is based on depth data with the earthquake as the reference surface.

6. The method for correcting tectonic errors in reverse fault regions based on multiple iterations of the T0 trend surface according to claim 1, characterized in that, In step 5, the error formula is: ;in Let be the error of the i-th well. For the drilling stratification of the i-th well, the unit is m; The core elevation of the i-th well is given in meters. The seismic reference surface is in meters (m). Let be the structural depth of the i-th well.

7. The method for correcting tectonic errors in reverse fault regions based on multiple iterations of the T0 trend surface according to claim 1, characterized in that, In step 7, the formula for calculating the relative error is: In the formula: k i —The relative depth error of the i-th well, expressed as a percentage; e i —The absolute error of the depth of the i-th well, in meters; h i —The seismic depth of the i-th well, in meters.

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