Method for calibrating structural plane strike based on passive source microseismic events

Abstract

The application discloses a method for calibrating the strike of a structural plane based on passive source microseismic events, comprising the following steps: S1, arranging a plurality of geophones in a monitoring area; S2, dividing the monitoring area into a grid structure; S3, extracting microseismic events with a magnitude greater than -1.5 through the geophones, classifying and counting all the extracted microseismic events, and marking the classification results of the microseismic events at the corresponding microseismic event occurrence positions; S4, counting the number of the marked microseismic event occurrence positions in each grid, and selecting a plurality of grids according to a screening condition; S5, respectively evaluating the stress concentration degrees of the selected grids; S6, selecting the grid with the highest stress concentration degree in each horizontal row of the grid structure to form a set, performing linear fitting processing, and obtaining a trend line of a concentrated area; and S7, comparing the existing strike of the structural plane in the monitoring area with the trend line of the concentrated area and making an adjustment, so that the calibration operation of the existing strike of the structural plane is realized.

Description

Technical Field

[0001] This invention relates to the field of geological exploration, and in particular to a method for calibrating the strike of tectonic surfaces based on passive source microseismic events. Background Technology

[0002] Accurate determination of the orientation of structural planes is a fundamental aspect of subsurface geological analysis, as these planes play a crucial role in oil and gas production, reservoir development, and safe extraction. Typically, the orientation of structural planes is inferred from limited data sources, such as borehole core samples or obtained through field observation and description. However, these methods are highly subjective and prone to judgment bias. Therefore, a calibration method is urgently needed to improve the accuracy of structural plane orientation.

[0003] Microseismic monitoring is becoming an important tool for monitoring hydraulic fractures and characterizing reservoirs in the oil and gas industry. Microseismic events are generated by the deformation of rock strata during hydraulic fracturing. The magnitude of microseismic events formed by hydraulic fracturing is usually between -5 and 0. The magnitude of a microseismic event reflects the stress state at that point to some extent; the larger the magnitude, the more obvious the stress concentration effect. Based on this principle, this invention uses microseismic monitoring technology to describe stress concentration areas on structural surfaces and further calibrates the existing structural surface strike to improve the accuracy of structural surface strike. Summary of the Invention

[0004] The purpose of this invention is to address the aforementioned problems by providing a low-cost method for calibrating the strike of existing structural surfaces based on passive source microseismic events, which can calibrate the strike of existing structural surfaces according to the regional concentrated stress distribution pattern.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] A method for calibrating structural strike based on passive source microseismic events includes the following steps:

[0007] S1. Arrange several detectors within the monitoring area;

[0008] S2. Divide the monitoring area evenly into several grid structures of consistent scale;

[0009] S3. Microseismic events with magnitude greater than -1.5 are extracted using a geophone. All extracted microseismic events are classified and statistically analyzed, and the classification results are marked at the corresponding microseismic event locations.

[0010] S4. Count the number of locations of marked microseismic events in each grid, and select several grids according to the filtering criteria;

[0011] S5. Evaluate the stress concentration of the selected meshes respectively;

[0012] S6. Select the grids with the highest stress concentration in each row of the grid structure to form a set, and perform linear fitting on the set to obtain the trend line of the concentration area.

[0013] S7. Compare the existing structural surface orientation of the monitoring area with the trend line of the concentrated area obtained in step S6 and make adjustments to make the existing structural surface orientation of the monitoring area consistent with the trend line of the concentrated area, thereby realizing the calibration operation of the existing structural surface orientation of the monitoring area.

[0014] Furthermore, in step S1, the detector is positioned away from the cliff and the strong magnetic field area; during installation, the three-component sensor on the detector is in full contact with the hard ground layer to ensure the coupling effect between the detector and the ground surface.

[0015] Furthermore, in step S2, when the monitoring area is divided into a grid structure, if the shortest side length of the monitoring area is not greater than 500m, the grid size is 30m; if the shortest side length of the monitoring area is greater than 500m and less than 1000m, the grid size is 50m; if the shortest side length of the monitoring area is not less than 1000m, the grid size is 100m.

[0016] Furthermore, in step S3, when classifying and statistically analyzing all extracted microseismic events, the classification and statistical analysis are performed according to the categories -1.5≤mL<-1.0, -1.0≤mL<-0.5, and mL≥-0.5, where mL is the magnitude of the microseismic event.

[0017] Furthermore, in step S4, the screening condition is: the number of locations of microseismic events marked in a single grid, Sn, and the grid scale L satisfy the formula: Sn≥L / 10.

[0018] Furthermore, in step S5, when evaluating the stress concentration of the selected mesh, the calculation formula is as follows:

[0019] F ij =n1×f1+n2×f2+n3×f3;

[0020] Among them, F ij The stress concentration of the grid is represented by f1=0.3; f2=0.5; f3=0.7; n1 is the number of microseismic events of category -1.5≤ml<-1.0 within the grid area; n2 is the number of microseismic events of category -1.0≤ml<-0.5 within the grid area; n3 is the number of microseismic events of category ml≥-0.5 within the grid area.

[0021] Furthermore, in step S6, when performing linear fitting based on the set, a planar coordinate system is established and the center point coordinates of all grids within the set are found in the planar coordinate system. The linear fitting of the center point coordinates of all grids yields the trend line of the concentrated region.

[0022] Compared with the prior art, the advantages and positive effects of this invention are:

[0023] This invention, based on data such as the magnitude and distribution of microseismic events collected by microseismic monitoring equipment, analyzes stress concentration areas within the monitoring area and obtains the trend line of these concentration areas. Furthermore, it compares and adjusts this trend line with the existing structural surface orientation in the monitoring area, ultimately achieving a calibration of the structural surface orientation. This effectively improves the internal structural development of coal mine tunneling faces, reflects the distribution pattern of concentrated stress within the monitoring area, provides a reliable basis for calibrating the structural surface orientation, and thus provides a certain level of safety assurance for coal mine roadway excavation. Attached Figure Description

[0024] 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 only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a flowchart illustrating the framework of the present invention;

[0026] Figure 2 This is a point map of microseismic events in the embodiment;

[0027] Figure 3 This is a diagram illustrating the location of microseismic event points relative to the orientation of existing structural surfaces in the embodiment.

[0028] Figure 4 This is a trend line diagram of the stress concentration area in the embodiment;

[0029] Figure 5 This is a schematic diagram of the construction surface calibration in the embodiment. Implementation

[0030] 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. Based on the embodiments of the present invention, any modifications, equivalent substitutions, improvements, etc., made by those skilled in the art to all other embodiments obtained without creative effort should be included within the protection scope of the present invention.

[0031] This invention discloses a method for calibrating the strike of structural surfaces based on passive source microseismic events. It calibrates the strike of existing structural surfaces using passive source microseismic events. Microseismic event points with relatively high energy (mL>-1.5) within the monitored area reflect the stress state of the region to some extent. This invention utilizes microseismic event points to reflect stress concentration areas within the region, adjusting the strike of structural surfaces within the region. It verifies areas with stress concentration that are not marked on structural surfaces and provides stress concentration warnings, providing a reliable basis for structural surface calibration and ensuring safety for coal mine roadway excavation.

[0032] The following specific construction examples illustrate this technical solution;

[0033] The company's mining area is located on the western side of the central section of the Taihang Mountains, in the western part of the Changzhi Basin. The area is largely covered by Quaternary loess, with the northern and western edges forming a plateau and hilly region characterized by well-developed gullies and complex topography. Only scattered bedrock outcrops are visible at the bottom of the gullies. The Jiang River flows from west to east into the Zhangze Reservoir in the central part of the mine, forming river terraces. The coal seams are buried at a depth of approximately 600m, with a thickness of 4.2-6.3m. The study area is located at the N1100 working face in the northern part of the mine, adjacent to the Wenwangshan Fault. Numerous microseismic events occurred at the N1100 working face during mining operations, providing valuable data for calibrating the strike of the structural plane.

[0034] like Figure 1 As shown, the calibration process is as follows:

[0035] (1) An NNE-trending Dongdeng syncline is developed in the N1100 working face. Taking the entire N1100 working face as the monitoring area, the overall topography and geomorphology of the N1100 working face are understood through on-site reconnaissance, and the locations of the geophones are reasonably arranged. When installing the geophones, the three-component sensors on them are in complete contact with the hard strata to ensure that the geophones have a good coupling effect with the ground surface. Time synchronization and positioning are performed for each substation. The sensitivity of the geophones is 52 volts per second / meter, and its sampling rate is 1000 SPS (1000 times / second) to obtain more accurate positioning results.

[0036] (2) The N1100 working surface is meshed and marked as G. ij (i=1,2,3…; j=1,2,3,…); The N1100 working face is 1400m long and 550m wide. The grid is divided into 308 grids at a scale of 50m each.

[0037] (3) The located microseismic events are classified into three categories according to their magnitude: -1.5≤mL<-1.0, -1.0≤mL<-0.5, and mL≥-0.5, and marked within the N1100 working surface, such as... Figure 2 , Figure 3 As shown; the statistical results are as follows: there are 338 microseismic event points with magnitudes between -1.5 and -1.0, 92 microseismic event points with magnitudes between -1.0 and -0.5, and 55 microseismic event points with magnitudes greater than -0.5, which are marked on the N1100 working face.

[0038] (4) The grid is screened. The number of microseismic event points Sn within a single grid and the grid scale L should satisfy: Sn≥50 / 10=5; the screened grid is: G 7 9 G 7 10 G 8 9 G 8 10 G 9 8 G 9 10 G 10 10 G 10 9 G 11 6 G 11 9 G 11 10 G 12 8 G 12 9 G 12 10 G 13 8 G 13 10 G 14 10 G 15 10 G 16 10 G 17 8 G 17 10 G 18 8 G 18 9 G 18 10 G 19 9 G 19 10 .

[0039] (5) The stress concentration degree F of each selected grid ij Evaluation:

[0040] F ij =n1×f1+ n2×f2+ n3×f3;

[0041] f1=0.3, f2=0.5, f3=0.7;

[0042] n1: The number of microseismic events with a magnitude category of -1.5≤ml<-1.0 within the grid area;

[0043] n2: The number of microseismic events with a magnitude category of -1.0 ≤ ml < -0.5 within the grid area;

[0044] n3: The number of microseismic events with a magnitude category of ml ≥ -0.5 within the grid area;

[0045] Calculations show that within the plane region formed by all grids, the grids with the highest stress concentration in each row are: G 7 10 G 8 9 G 9 10 G 10 10 G 11 10 G 12 10 G 13 10 G 14 10 G 15 10 G 16 10 G 17 10 G 18 9 G 19 9 Combine them into a set {G} ij (i=1,2,3…; j=1,2,3,…)}.

[0046] (6) Determine the set {G} within the grid plane. ij The coordinates of the center points of all grids (i=1,2,3…; j=1,2,3,…) are obtained, and linear fitting is performed on them to obtain the trend line of the concentrated region, as shown below. Figure 4 As shown.

[0047] (7) For example Figure 5 As shown, by comparing and analyzing the direction of the Dongdeng syncline inside the existing N1100 working face, it was found that there is a certain deviation between the direction of the Dongdeng syncline and the trend line of the stress concentration area. Therefore, it is inferred that the direction of the Dongdeng syncline should be 10-15° leftward deflection compared with the original, thus realizing the calibration operation of the direction of the Dongdeng syncline of the existing structural face.

[0048] This invention, based on data such as the magnitude and distribution of microseismic events collected by microseismic monitoring equipment, analyzes stress concentration areas within the monitoring area and obtains the trend line of these concentration areas. Furthermore, it compares and adjusts this trend line with the existing structural surface orientation in the monitoring area, ultimately achieving a calibration of the structural surface orientation. This effectively improves the internal structural development of coal mine tunneling faces, reflects the distribution pattern of concentrated stress within the monitoring area, provides a reliable basis for calibrating the structural surface orientation, and thus provides a certain level of safety assurance for coal mine roadway excavation.

Claims

1. A method for calibrating structural strike based on passive source microseismic events, characterized in that: Includes the following steps: S1. Arrange several detectors within the monitoring area; S2. Divide the monitoring area evenly into several grid structures of consistent scale; S3. Microseismic events with magnitude greater than -1.5 are extracted using a geophone. All extracted microseismic events are classified and statistically analyzed, and the classification results are marked at the corresponding microseismic event locations. S4. Count the number of locations of marked microseismic events in each grid, and select several grids according to the filtering criteria; S5. Evaluate the stress concentration of the selected meshes respectively; In step S5, when evaluating the stress concentration of the selected mesh, the calculation formula is as follows: F ij =n1×f1+n2×f2+n3×f3; Among them, F ij The stress concentration of the grid is represented by f1=0.3; f2=0.5; f3=0.7; n1 is the number of microseismic events of category -1.5≤ml<-1.0 within the grid's region; n2 is the number of microseismic events of category -1.0≤ml<-0.5 within the grid's region; n3 is the number of microseismic events of category ml≥-0.5 within the grid's region. S6. Select the grids with the highest stress concentration in each row of the grid structure to form a set, and perform linear fitting on the set to obtain the trend line of the concentration area. S7. Compare the existing structural surface orientation of the monitoring area with the trend line of the concentrated area obtained in step S6 and make adjustments to make the existing structural surface orientation of the monitoring area consistent with the trend line of the concentrated area, thereby realizing the calibration operation of the existing structural surface orientation of the monitoring area.

2. The method for calibrating structural plane strike based on passive source microseismic events as described in claim 1, characterized in that: In step S1, the detector is positioned away from the cliff and the strong magnetic field area; during installation, the three-component sensor on the detector is in full contact with the hard stratum to ensure the coupling effect between the detector and the ground surface.

3. The method for calibrating structural plane strike based on passive source microseismic events as described in claim 2, characterized in that: In step S2, when the monitoring area is divided into a grid structure, if the shortest side length of the monitoring area is no more than 500m, the grid size is 30m; if the shortest side length of the monitoring area is greater than 500m and less than 1000m, the grid size is 50m. When the shortest side length of the monitoring area is not less than 1000m, the grid size is 100m.

4. The method for calibrating structural plane strike based on passive source microseismic events as described in claim 3, characterized in that: In step S3, when classifying and statistically analyzing all extracted microseismic events, the classification and statistical analysis are performed according to the categories -1.5≤mL<-1.0, -1.0≤mL<-0.5, and mL≥-0.5, where mL is the magnitude of the microseismic event.

5. The method for calibrating structural plane strike based on passive source microseismic events as described in claim 4, characterized in that: In step S4, the screening condition is: the number of locations of microseismic events marked in a single grid, Sn, and the grid scale L satisfy the formula: Sn≥L / 10.

6. The method for calibrating structural plane strike based on passive source microseismic events as described in claim 5, characterized in that: In step S6, when performing linear fitting based on the set, a planar coordinate system is established and the center point coordinates of all grids in the set are found in the planar coordinate system. The linear fitting of the center point coordinates of all grids is then performed to obtain the trend line of the concentrated area.

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